US2386094A

US2386094A - Protector for electric circuits

Info

Publication number: US2386094A
Application number: US487418A
Authority: US
Inventors: Manfred F Duerkob
Original assignee: McGraw Electric Co
Current assignee: McGraw Electric Co
Priority date: 1943-05-15
Filing date: 1943-05-15
Publication date: 1945-10-02
Anticipated expiration: 1962-10-02

Description

Patented Oct. 2, "45

PROTECTOR FOR ILIUI'RIO CIRCUITS Manfredl.nlerknb,st-Lollil,hlo.,alimrto McGraw Electric Company, Ilsin,

ration of Delaware memo- Application May 15, 1948, Serial No. 487,418

52 Claims. ((1 ZOO-123) This invention relates to improvements in protectors for electric circuits. More particularly the invention relates to improvements in enclosed protectors for electric circuits that comprise a fuse link and a thermal cut-out.

It is an object of the present invention to provide an improved enclosed protector for electric circuits that comprises a fuse link and a thermal cut-out.

Protectors for electric circuits that comprise a fuse link and a thermal cut-out are desirable because they will open the circuit before overloads can cause injury to the circuit, but will not open the circuit needlessly. Such protectors have the quick opening of the fuse link on heavy overloads as well as the desirable time lag of the thermal cut-out on lighter overloads. When, in this description, the word "circuit is used, it does not refer to the wiring along but refers also to any electrical devices that may be a part of the circuit protected by these protectors.

Protectors that have a fuse link and a thermal cut-out all have the same fundamental P p and object, but their form and structure may differ considerably. The difference in form and structure may be due to space limitations as well as to considerations of performance and function. Space limitations in protectors that are used in fuse clips. already installed and in use. are standardized; and often present an almost insurmountable obstacle to the making of an enclosed protector for electric circuits that comprises a fuse link and a thermal cut-out. Not only must the protector include an additional means to aive the desired time lag, but it must be small enough to fitinto an enclosure intended for a fuse link only, and such enclosure is often quite small.

The problem of making enclosed protectors for automotive, aircraft and radio work is particularly difficult, because such protectors must be operable in cylindrical cartridges that may have outside dimensions as small as one and one quarter inches in length and one quarter of an inch in diameter. Accordingly, the dimensions of such protectors must r 2 very very small; and when it is remembered that those protectors are used to protect power circuits; and. in the case of radio work, circuits up to two hundred and fifty volts. it is obvious how difficult it is to make such protectors. In fact, the making of a Mr that prises a fuse link and a thermal cut-out and is small enough to fit into such an enclosure. has been heretofore regarded as impossible. The present invention makes pouible such a protector byusingaminimumnumberofpartsandbymakin: several of the parts movable. It is therefore an object of the present invention to provide a protector for electric circuits, that is operable in small enclosures, by usina a limited number of parts and by making several of the parts movable.

Protectors for electric circuits that are intended for automotive and aircraft work may be. and usually are, subjected to considerable vibration. Where this is the case, the protector must be constructed to withstand considerable vibration or it will have a relatively short effective life. The present invention provides a long lived protector for electric circuits by resiliently spacing some of the parts of the protector away from the inner surfaces of the enclosure. such an monument is desirable because it absorbs the vibration imparted to the enclosure and minimizes the vibrating done by these parts of the protector. It is, therefore, an object of the present invention to provide an enclosed protector for electric circuits wherein some of the parts are resiliently spaced away from the inner surfaces of the enclosure.

In the fuses heretofore used in automotive, aircraft and radio work, the fuse links have been initially spaced away from the inner surfaces of the enclosure to insure uniformity of operation of the protector. This initial spacing is often incapable of preventing subsequent contact between the link and the inner surfaces of the enclosure, and particularLv is this true where the fuse link is quite long and subjected to considerable heat. In such cases, the link may expand sufficiently to cause a portion thereof to touch the inner surface of the enclosure, and this touching will disturb the performance and operation of the protector. The present invention obviates such touching and thereby insures a uniform performance for the protector. by maintaining some tension in the link and thereby holding the link near the diametric center of the enclosure. This tension is preferably not very heavy but is sumcient to keep the fuse link from sagging minst the inner surfaces of the enclosure. It is, therefore, an object of the present invention to provide an enclosed protector for electric circuits in which tension is used to prevent contact between the fuse link and the inner surfaces of the enclosure.

In protectors for electric circuits that have a fuse link and a thermal cut-out, a solder may be provided that loses its holding power when heated to a predetermined temperature. This solder preferably is spaced am from the terminals of the enclosure by a plurality of heat seneratin: elements. These elements largely retard the flow of heat between the solder and the terminals, and

thereby minimize the tendency of varying temperatures of the terminals to ail'ect the temperature of the solder. It is therefore an obiect of the present invention to separate the solder from the terminals, of the enclosure by a plurality of heat generatin elements.

It is often desirable in protectors for electric circuits to provide a heat absorbing element that may serve as an arcing contact, because such an absorber will help extinguish any arcs that may form when the protector opens the circuit. It can do so because its relatively large mass tends to cool the arc. and such cooling tends to extinguish it. In the present invention, a heat absorbing member is used as an arcing contact and it is also movable. This not only permits cooling of the arc, it fosters drawing of the arc and thereby makes for rapid extinction of the arc. It is therefore an object of the present invention to provide an enclosed protector for electric circuits in which a heat absorbing element constitutes a movable arcing contact of the protector.

In the operation of the present invention, a portion of the protector is moved to open the circuit. Because of space limitations, it is necessary that this movement be longitudinal of the enclosure to provide a long arcing gap and a consequent rapid extinction of the arc. It is therefore an object of the present invention to provide an enclosed protector for electric circuits in which the moving part moves longitudinally of the enclosure to open the circuit.

Other objects and advantages of the invention will become apparent from an examination of the drawing and accompanying description.

In the drawing and accompanying description, a preferred embodiment of the invention is shown and described, but it is to be understood that the drawing and accompanying description do not limit the invention and the invention will be defined by the appended. claims.

In the drawing.

Fig. 1 is a partial cross-sectional plan view of the protector embodying the invention,

Fig. 2 is a partial cross-sectional elevational view of the protector shown in Fig. l, and

Fig. 3 is a cross sectional view of modified end for the movable member 20.

Referring to the drawing in detail, an enclosure for a protector for electric circuits can be seen to consist of a cylindrical tube l and end caps l2 and i4. The tube i8 may be made of any suitable material and may be of any suitable size. In the very small sizes, for which the present invention is particularly useful, the tube '18 may be made of glass, but it may also be made of any other suitable material. Glass is particularly desirable because it enables the user to determine quickly whether or not the protector has opened the circuit. The end caps I2 and I4 may be made in any desired size and are of metal and serve as con acts between the protector and the circuit to be protected. In such a case, these end caps co .stitute the contact terminals of the protector.

Positioned within the enclosure, and secured in good electrical and thermal conducting relation with end cap I 2 by relatively high melting point alloy i6, is a fusible heat generating element i 8. This element 18 may, on overloads in the short circuit range, generate suillcient heat to fuse and thereby open the circuit. On overloads below the short circuit range, the element i8 will generate much less heat and will tend to retard heat flow from heat softenable material 22 to end cap i2, rather than to add heat to 22. Element I8 is shown in the drawing as a conductor in the form of a loop with its closed end extending into the enclosure ID. The closed end of element i 8 is held in electrical contact with a member 20 by heat softenable material 22. This material ordinarily will be a low melting point solder or alloy, but any holding material that loses its holding power when heated to a predetermined temperature may be used. The member 28 may be made from any suitable material and of any suitable size, but is preferably made relatively large and is preferably made of metal.

A heat generating element 24 is wound on and supported by member 20 and is connected to the enlarged end of member 20 at the point 24; At this point the end of the element 24 extends through an opening in member 20 and is held there by being bent over, and also by the fusible alloy 22. This element 24 is connected at its other end to end cap H by relatively high melting point alloy IT. The wire 24 is. insulated from member 28 except at the point indicated by the numeral 28; and at that point there is good thermal and electrical contact between 24 and 28. Attached to one end of member 28 is a washer 28 that is made of insulating material. This washer may be attached to the member 20 by any suitable means but preferably is attached by inserting member 28 through a hole in the washer and then enlarging the end of member 20. A spring 30 is shown, in the drawing, which has three different diameters. The smallest diameter is smaller than the external dimensions of the washer 28, the middle diameter is larger than the external dimensions of the washer 28 but slightly smaller than the internal diameter of tube 10, and the third diameter is larger than the internal diameter of tube to, but smaller than the internal diameter of end cap l4. The washer28 is desirable because it insulates spring 30 from the heat absorbing member 20 which may become quite warm. Furthermore, the washer 28 frees spring In from current flow therethrough, and thereby obviates impairment of the resilient properties of the spring due to any electrical heating thereof.

The end of the wire 24 that extends beyond washer 28 and is connected to end cap l4 must be relatively flexible because it must collapse when the circuit is opened by movement of mem ber 28. Such an arrangement is entirely feasible because a relatively small wire can be used. The use of the end of wire 24 in place of a lead in wire is desirable because it keeps down the number of parts and connections needed. Furthermore, the end of wire 24, between washer 28 and end cap I4, may also fuse on overloads in the short circuit range. The wire 24 is not primarily intended to fuse on overloads in the short circuit range and it is so dimensioned that it will not fuse until after the fuse link I 8 has fused. Should the wire 24 fuse after the fusing of element l8, no harm will result and in fact an unusually quick extinction of the arc may be had because of the formation of two arcing gaps in series.

The wire 24 is wound on and supported by the exterior surface of the member 28 and can thus radiate considerable heat into the atmosphere in the enclosure. This radiation is quite desirable because it delays the heating of member 28, and therefore the heating of solder 22, by heater 24. Such a delay is desirable because it gives more time lag to the protector and thus prevents needless opening of the circuit. This radiation.

does not halt the heating of solder 22 and where the overload is prolonged unduly, the heater 24 wi l cause the solder 22 to soften and permit the protector to open the circuit.

The drawing shows the fuse link It with two legs and a closed end. This kind of link is quite desirable because it can be held rather easily by the heat softenable material 22 since the closed end enable the material 22 to get a positive hold on the link. In large size protectors, there is sumcient area of contact between the solder and the end of a straight link to assure a permanent hold; but in the small sizes for which this protector is well adapted the diameter, and therefore the area, of the link is quite small. Accordingly, it has been found desirable to provide the loop to guarantee a firm connection between the solder 22 and the link II.

The provision or two legs for the link is also desirable because it permits the link to burn quite readily when the circuit is opened on overloads, and such burning rapidly increases the gap and quickly extinguishes the arc. The mass of each leg of the link is considerably less than the mass of an ordinary link of the same current carrying capacity, and the legs of element l8 can therefore burn back much more readily. In the present invention the two legs of the fuse link are further useful in affording support to the end of member 2|. This support is particularly useful against movement in the plane of the two legs of the link but it is also useful against movement in other planes. This construction of the link i| cooperates with the construction of spring 30 to resiliently space element 20 away from the inner surface of tube i0. Such an arrangement is highly desirable in reducing the vibration imparted to the member 20 when the enclosure is subjected to vibration.

In automotive and aircraft work. protectors are often subjected to very considerable vibration. If the parts were rigidly secured to the enclosure, the vibration imparted to the enclosure would immediately be imparted to the parts of the protector without diminution. Such vibration might have serious results if it caused premature and accidental opening of the protector. The arrangement shown in the drawing is very helpin] in reducing the amount of vibration imparted to certain parts of the protector, because much of the vibration imparted to the enclosure will be absorbed by the tensioned link i8 and by spring 2| and only a very little of it will be imparted to member 2| and solder 22. This insures that the life of the protector will not be shortened by injuries caused by vibration.

This arrangementof parts is also helpful because it thermally insulates link ll, heater wire 24 and heat absorber 2| from the tube l0. Spring 2| places link i2 and member 2| under tension and keeps H and 2| from sag i g to such an extent that they contact the inner surfaces of tube II. This is particularly desirable in the case of link i| because it will be heated and will expand. Such expansion cannot cause the link to sag against the enclosure because the spring will absorb the expansion and hold the link away from the enclosure. Spring 3| is additionally enabled to space member 2| away from the inner surfaces of tube l|. because the middle diameter of the spring is preferably dimensioned so it is only slightly less than the inner diameter of the tube. As a result the small diameter of the spring, and the washer 2| and the end of member 2| supported by the mall diameter of the spring, are prevented from moving from the dis-metric center of the tube I I.

The wire 24 is insulated from member 2| except at the point 2|. The drawing shows the wire covered with insulation, and in practice a cotton covered wire has been found to be very aw tory. However it is possible to use other kinds of insulation on the wire 24, and it is also possible to coat the external surface of member 2| with insulating material. The insulation that is used will electrically insulate the turns of the coil of wire 24 from each other and from member 2|, but it must not prevent substantial heat flow from wire 24 to member 2|. Where cotton covered or enameled wire is used to insulate heater 24, the member 2| will absorb heat from the cotton or enamel insulation. This heat will be conducted to solder 22 and before the temperature of the insulation gets dangerously high. the solder will soften and permit the member 2| to move and open the circuit.

In the preferred construction shown in the drawing, member 2| has a relatively large end to which fuse link I2 is soldered. This large end is not so large that it will not pass through the smallest diameter of spring 3|, but it is preferably large enough to absorb an appreciable amount 01' the heat generated in the protector and thereby delay the heating of solder 22. Such a large end is also desirable because it will be one of the arcing contacts of the protector and will readily absorb heat from the are generated when the protector opens. The large end of member 20 is further desirable because it can carry a considerable quantity of heat softenable material. Such a quantity of material not only appreciably increases the time lag but also helps cool arcs that may form when the circuit is opened. If desired, the end of member 24 can be formed in a cup-like shape to hold even more heat softenable material. Such a construction is shown in Fig. 3, and the additional amount of heat softenable material held in the cup-like end will provide even more time lag for the protector.

Member 2| and the portion of wire 24 supported on that member, as well as material 22, are positioned in the approximate diametric and longitudinal center of the enclosure. By this construction they are each spaced away from the enclosure and at least partially insulated from the effects of varying temperatures of the enclosure and the temperature of the clips to which the protector is secured. This arrangement is desirable because it insures a uniform rating for the protector.

The positioning of members 2| and 24 in the longitudinal center of the enclosure is desirable for another reason. In fuses that are enclosed in glass tubes, it is sometimes dimcult to determine visually whether or not the fuse is intact. This is largely due t the fact that the fuse wires are generally quite small and is partially due to the fact that the e .d caps cover up a portion of the tube. with the arrangement shown in the drawing, these problems are not present because the members 2| and 24 constitute a thick mass that can be seen quite readily because it is large and it moves an appreciable distance when the circuit is opened. Such movement is an excellent index of the condition of the protector, and facilitates ready detection of protectors that have operated to open the circuit.

The movement of the member 2| is not only useful in indicating the condition of the protector, but is useful inbreaking the are. Whether the circuit opens by fusion of element i8 or fusion of solder 22, the member 20 will move. As it does so, it draws out any arc that may form until the arc breaks. This is done quickly and helps extinguish the arc.

Under ordinary conditions when the circuit is carrying a normal load, current will flow through end cap l2, through element i8, through a, short portion of member 20 into element 24, and cut end cap 14. Element l8 and element 24 will generate some heat but will not cause solder 22 to lose its holding power or cause element l8 to fuse. As a result, the protector will carry such a load indefinitely.

If an overload occurs that is below the short circuit range but is so heavy that it would injure the circuit if prolonged unduly, the device will operate to open the circuit. Upon the occurrence of this type of overload, the element 24 will generate more heat than it does under normal loads. The heat generated in element 24 will be conducted to solder 22 through the wire itself and also through member 20. This flow of heat to solder 22 is not rapid because it takes time for the heat from the coil to heat the member 20 and the wire 24 that forms the coil. As a result there is an appreciable length of time that must elapse before the heating of wire 24 can cause the solder to lose its holding power.

The heating of wire 24 is primarily intended to raise the temperature of solder 22 to the point at which it loses its holding power, but the heating also acts to retard heat flow between solder 22 and end cap l4. In the absence of heater 24, differences between the temperature of solderi22 and end cap i4 would cause heat to flow between them. Such heat flow would vary in response to temperature conditions of the end cap i4 and might be completely independent of the overload in the circuit. This would be objectionable because it would cause undesirable variations in the performance of the protector.

In much the same fashion, fuse link l8 retards and much of its heat is absorbed and dissipated by end cap l2. As a result, it is the heat from element l8 instead of the heat from solder 22 that .is absorbed and dissipated by end cap I2. This arrangement minimizes variations in the temperature of solder 22 in response to changes in the temperature of end cap l2.

When, under the heating effect of wire 24, the heat softenable material 22 loses its holding power the member 20 will be moved away from link l8 by spring 30 and will open the circuit. In the event an arc forms between the ends of i8 and 20, it will be extinguished rather readily by continued movement of member 20, the cooling action of the large end of member 20, and the buming back of element IS. The burning back of element is is rapid because the use of two legs permits the mass of each leg to be small and permits the legs to be consumed quite readily.

When however, an overload in the short circuit range occurs, the element It will become hot enough to cause one or both of its legs to fuse almost instantly. In the event only one leg of element It fuses initially, the current will all flow assaoes through the other leg and will be great enough to cause an immediate fusion of that leg. Where such fusions occur, the arc will be extinguished rather rapidly because the member 20 will quickly 5 be moved away from the end of the element i8 by the spring 30 in the manner explained above.

In the case described above where the overload causes the thermal cut-out to open the circuit, the overload must continue for a predetermined length of time. Where the overload is of short duration only, the temperatures in the thermal cut-out will not be high enough to cause it to open the circuit, and this is desirable because it prevents needless blowing of the protector.

This is well illustrated by the following table that is a. comparison between the time lag of a simple fuse link and a protector of the same rating. The fuse link and the protector were each rated at one half of an ampere and were tested at one hundred and thirty-five, one hundred and fifty, two hundred, three hundred, four hundred, five hundred, six hundred, seven hundred, eight hundred, and nine hundred per cent loads. No entries are made for the fuse link above two hundred per cent load because the opening times above that load were so short they could not be measured with a stop-watch.

I In these (uses the link was touching the inner surface of the glass enclosure and that touching was materially disturbing the opening time of the fuse.

The attainment of the above results is made possible by the use of the construction shown 4,5 in the drawing. In this construction, a fuse link I! may be selected that will give the desired action on overloads in the short circuit range; and when this has been done, the length and character of the wire 24 is adjusted to give the desired action on overloads below the short circuit range. By proper selection and dimensioning of the wire 24, it is possible to obtain the exact rating desired. It is desirable to rely on the wire 24 rather than fuse link l8 for the determination of the rating, because the wire is much longer and a good portion of it is spaced a considerable distance from the end caps. The sizeable length of Wire 24 is advantageous because a variation in the length of a long con- 0 ductor is not as noticeable as an equal variation in the length of a short conductor such as fuse link l8.

Ti 2 length of wire 24 may be varied to change the time lag and rating of the protector, but 'ther is a minimum length that must be pre served. For example, the developed length of the wire must be longer than the overall length by a distance not less than six times the diameter of the wire 24, and in most cases will be considerably longer. With such a construction the overall length of the heater may be said to be substantially smaller than its developed length.

In the preferred form shown in the drawin the heater 24 is coiled aroimd the movable memher 20, but it need not be formed as a coil. In-

stead it may be bent into various shapes and conflsurations such as crimps. crinkles, kinks, loops or other developable forms. In all cases. however, the developed length must be longer than the overall length by a distance not less than six times the diameter of the wire in the heater. 1'

The spacing of ,the coiled portion of wire 24 from the end cap. I: and I4 reduces the eilect that the end caps might have on the rating or the protector. Therefore. the use of the portion of wire 24, between washer 2! and end cap I4, and the fuse ink II to space the coiled portion or wire 24 away from the end caps is helpful in providing a uniform performance of the protector. Such uniformity would not be possible if i'use link It we rethe element that was used to determine the rating of the protector, because it is quite short and is intimately connected with the much more massive end cap 12. The relatively massive end cap I! will have quite an effect on the temperature of link I8 and if the temperature of link il determined the rating or the protector, the temperature of end cap I! would materially aifect the rating of the protector. By avoiding such an occurrence, the present invention makes possible a better and more dependable protector.

In almost all cases, the temperature of theprotector will be less than that of the fuse link it replaces. This is the result of the use of relatively low melting point solder that melts considerably below the temperature at which a fuse link fuses. In a simple iuse the temperature must reach the fusing point of the link before the circuit can be opened, whereas in the protector shown in the drawing the overall temperature cannot rise above the melting point of the solder 22.

The protector shown in the drawing is presently being used in certain ampere ratings to protect circuits up to two hundred and fifty volts. when such circuits are opened, there can be considerable arcing but the protector shown in the drawing operates faultlessly despite the arcing. This is remarkable because the outside dimensions some of the enclosures in which the protector is used are only one quarter of an inch by one and one quarter inches.

While this invention is particularly desirable for use in very small enclosures, it is not necessarily restricted to such enclosures. The many desirable features of this invention may be used equally as well on devices to be inserted in larger enclosures.

The invention makes it possible to position a protector in very small enclosures by using a small number of parts ahdmaking some of the parts movable. Furthermore several of the parts periorm dual functions. For instance in the protector shown in the drawing, the member 20 functions as a heat absorber, an arcing contact and a movable support for the heater 2. The link it serves as a iuse link, serves as an arcing contact and serves as a support for the end of member 2|. The spring II also has a dual function in that it serves to move member 20 longitudinally of the enclosure to open the circuit and it also serves to resiliently space member 20, wire 24 and element It away from the inner surfaces of the tube "I. This interaction of parts is desirable because it obviates the necessity of making each of the parts self-supporting, permits the parts to be made quite small, and eliminates the necessity of having supporting parts that might keep the protector from being positioned and operated in a small enclosure.

The protector shown in the drawing can be assembled quite easily. One end of wire :4 is inserted in hole 20 in one end of member 2| and bent over and the wire is wound onto member 2|. The other end of member 20 is inserted in a hole in washer 2| and planished to prevent its withdrawal. The end of link it, the end of member 2| and the end of wire 24 are then secured together by heat softenable material. Spring 30 is then slipped over the link II and member 20 until its small diameter engages washer 2|. The assembly is then dropped into tube II and tensioned by pulling the free ends of link it. The end caps are then put on and soldered to elements II and 24 and the free ends of ll are out on. This simplified procedure is due in some measure to the use of the three di-' ameter spring 80. Such a spring is desirable because it obviates the use of a pin or solder to secure it to the end cap I 4. The use of such a pin or solder makes assembly more expensive and diflicult because the use 0! a pin means the making and handling of a separate part and the use of the solder is difficult because some spring materials are not soldered easily.

Whereas a preferred embodiment oi the invention has been shown and described in the drawing and accompanying description, it is obvious to those skilled in the art that various changes in the form of the invention may be made that do not aitect the scope of the invention.

What I claim is:

1. A protector for electric circuits that comprises contact terminals, a movable member, heat softenable material, a resilient member and a plurality of heat generating elements, at least one of which is fusible on predetermined overload of the protector, another of said heat gen erating elements being arranged so the major portion thereof is supported on and coextensive with said movable member and a minor portion thereof extends from said movable member to one of said contact terminals and is permanently secured thereto, said heat softenable material normally maintaining an electrical conducting relation between said heat generating elements and being arranged to permit an interruption of said relation by said resilient member when heated to a predetermined temperature.

2. A protector for electric circuits that comprises contact terminals, a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, another 0! said heat generating elements having a developable major portion positioned relatively remote from said terminals and being arranged so heat flow between said terminals and said major portion is retarded by heat in a minor portion of said other heat generating element that extends between said major portion and one of said terminals and also by heat in said fusible heat generating element, heat softenable material that is positioned between and arranged to hold said heat generating elements in electrical conducting relation, and a resilient member arranged to move said major portion and interrupt said relation when said heat softenable material loses its holding power.

3. A protector for electric circuits that comprises contact terminals, heat softenable material spaced from said terminals, a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit,

another of said heat generating elements having a portion thereof in the form of a coil that is arranged to add heat to said heat softenable material, and a second portion thereof extending from said coil portion to one of said ter. minals, and a resilient member, said fusible heat generating element and said second portion being arranged to generate heat and thus retard heat flow between said coil portion and said terminals,

'said resilient member being arranged to move said coil portion of said other heat generating element away from said fusible heat generating element when said heat softenable material has lost its holding power.

4. A protector for electric circuits that comprises contact terminals, a plurality of heat generating elements. at least one of which is adapted to fuse and thereby open the circuit, heat softenable material normally connecting said heat generatin elements, a movable member and a resilient member, another of said heat generating elements having a portion thereof that is coextensive with a portion of said movable member, said coextensive portions being fixedly spaced apart by a non-conductor of electricity, said resilient member being arranged to move said movable member and break said connection when said heat softenable material has lost its holding power.

5. A protector for electric circuits that comprises an enclosure, contact terminals, a plurality of heat generating elements permanently secured to said terminals, at least one of said elements being adapted to fuse and thereby open the-circuit. heat softenable material and a resilient member, said heat softenable material normally maintaining an electrical conducting relation between said heat generating elements, said resilient member being arranged to be substantially free from current flow therethrough and to cooperate with said fusible heat generating element to space another of said heat generating elements from the inner surface of said enclosure.

6. A protector for electric circuits that comprises an enclosure, contact terminals, a movable member, a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, a resilient member, another of said heat generating elements having a portion thereof supported on and coextensive with a portion of the exterior surface of said movable member, and means normally holding said heat generating elements in electrical conducting relation, said resilient member and said fusible heat generating element cooperating to space said other heat generating element away from the inner surface of said enclosure, whereby contact between said other element and said enclosure is prevented and uniform rating of the protector is insured, said resilient member being arranged to move said movable member when said holding means has lost its holding power.

7. A protector for electric circuits that comprises an enclosure, contact terminals, a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, a movable member. a resilient member, and means normally holding said terminals in electrical conducting relation, said resilient member being arranged to cooperate with said movable member and said fusible heat generating element to space another heat generating element from the inner surface of said enclosure without subjecting t". major portion of said other heat generating element to tension and being arranged to move said movable member when said holding means has lost its holding power.

8. A protector for electric circuits that comprises contact terminals, a transparent enclosure, a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, another of which has a developable portion, heat softenable material, a movable member that is positioned in said enclosure and supports said developable portion, said movable member and said developable portion constituting a mass thicker than said fusible heat generating element, and a resilient member, said resilient member being arranged to move said movable member to open circuit position whenever said fusible heat generating element fuses or said heat softenable material loses its holding power. said transparent enclosure permitting the position of the thick mass to indicate the condition of the protector.

9. A protector for electric circuits comprising contact terminals, a plurality of heat generating elements, at least one of said heat generating elements being adapted to fuse and thereby open the circuit on predetermined overload of the protector, a movable member, heat softenable material adjacent one end of said movable member normally contacting each of said heat generatin elements whereby said heat generating elements are held in thermal and electrical lation, and a resilient member biasing said movable member for movement whenever said heat softenable material loses its holding power or said fusible heat generating element fuses.

10. A protector for electric circuits comprising a plurality of heat generating elements, at least one of said heat generating elements being adapted to fuse and thereby open the circuit on predetermined overload of the protector, a movable mem ber constructed and arranged to support and carry a portion of another of said heat generating elements, heat softenable material on said movable member normally contacting each of said heat generating elements to hold them in thermal and electrical conducting relation, and a resilient member biasing said movable member and said portion of said other heat generating element for movement away from said fusible heat generating element to open the circuit whenever said heat softenable material loses its holding power.

11. A protector for electric circuits that comprises a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, another of said heat generating elements having a portion whose overall length is substantially smaller than its developed length, heat softenable material normally holding said head generating elements in electrical conducting relation, and a resilient member that is operable to move said portion of said other heat generating element and interrupt said electrical conducting relation whenever said heat softenable material loses its holding power.

12. A protector for electric circuits that comprises contact terminals, a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, another of said heat generating elements having a developable portion whose overall length is substantially smaller than its developed length and having a second portion extending from said developable portion to one of said terminals, heat softenable conducting rematerial normally holding said heat generating elements in electrical conducting relation, and a resilient member that is operable to move said developable portion of said element and interrupt said electrical conducting relation whenever said heat softenable material loses its holding power, said fusible heat generating element and said second portion of said other heat generating element being arranged to generate heat and thus retard heat flow between said developable portion and said terminals.

13. A protector for electric circuits that comprises an enclosure, contact terminals, a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit. heat softenable material normally holding said heat generating elements in electrical conducting relation, and a resilient member that is operable to move a portion of another of said heat generating elements and to interrupt said electrical conducting relation whenever said heat softenable material loses its holding power, said resilient member being arranged to resiliently space said fusible heat generating element, heat softenable material and other heat generating element away from the inner surface of said enclosure.

14. A protector for electric circuits that comprises a contact terminal, a heat generating element that is permanently secured to said terminal and has a portion whose overall length is substantially smaller than its developed length, heat softenable material, a member associated and movable with said portion of said heat generating element that is arranged to absorb an appreciable portion of the heat generated in the protector, and

a resilient member that is operable to move said portion of said heat generating element and said movable member to open the circuit whenever said heat softenable material has been heated to a predetermined tem rature.

15. A protector for electric circuits that comprises a heat generating element having a portion whose overall length is substantially smaller than its developed length, heat softenable material, a normally stationary member arranged to absorb an appreciable portion of the heat generated in said protector and to be moved whenever the protector operates to open the circuit, and a resilient member that is operable to move said normally stationary member whenever the protector opens the circuit.

16. A protector for electric circuits that comprises an enclosure, contact terminals, a fusible heat generating element, heat softenable material, a movable heat absorbing member having outside dimensions appreciably smaller than the inner dimensions of said enclosure, and a resilient member substantially free from current flow therethrough that is arranged to exert a tension in said movable member and in said heat generating element longitudinally of said enclosure whereby said movable member will remain resiliently spaced away from the inner surface of s id enclosure regardless of any expansion of said fusible heat generating element and will be moved to open circuit position when said heat softenable material has been heated to a predetermined temperature, said fusible heat genrating element remaining in substantially fixed position when said movable member is moved.

1?. A protector for electric circuits comprisin a plurality of heat generating elements, at least one of said heat generating elements bein adapted to fuse and thereby open the circuit on predetermined overload of the protector, a movable member. heat softenable material in direct contact with a portion of said movable member and a portion of each of said heat generating elements that normally maintains said elements in current conducting relation, another of said heat generating elements being arranged to heat said material directly by thermal conduction at said contact and indirectly by heating said movable member, and a resilient member arranged to move said movable member and a portion of said other heat generating element out of electrical connection with said fusible heat generating element to open the circuit whenever said heat softenable material loses its holding power.

18. A protector for electric circuits comprising contact terminals, a plurality of heat generating elements, at least one of said heat generating elements being adapted to fuse and thereby open the circuit on predetermined overload of the protector, a movable member, another of said heat generating elements having the major portion thereof coextensive with a portion of said movable member whereby said movable member can absorb an appreciable portion of the heat generated by said other heat generating element and can conduct said absorbed heat to one end of the movable member, heat softenable material adjacent said end of said movable member normally contacting each of said heat generating elements and thereby holding them in thermal and electrical conducting relation, and a resilient member biasing said movable member for movement to break said relation and thereby open the circuit when-said heat softenable material has lost its holding power.

19. A protector for electric circuits comprising a plurality of heat generating elements, at least one of said heat generating elements being adapted to fuse and thereby open the circuit on predetermined overload of the protector, a movable member constructed and arranged to carry another of said heat generating elements, a resilient member biasing said movable member to open circuit position, and heat softenable material that normally directly contacts each of said heat generating elements and is arranged to be heated on certain overloads of the protector to permit said movable member to move to open circuit position.

20. A protector for electric circuits comprising a plurality of heat generating elements, at least one of said' heat generating elements being adapted to fuse and thereby open the circuit on predetermined overload of the protector, a movable member and another of said heat generating elements that are arranged for concurrent movement, a portion of said other heat generating element being coextensive with but spaced from a portion of said movable member by a nonconductor of electricity, heat softenable material normally connecting said other heat generating element and said movable member with said fusible heat generating element, and a resilient member biasing said movable member and said other heat generating element for movement away mom said fusible heat generating element to break said connection and thereby open the circuit when said heat softenable material has lost its holding power.

21. A protector for electric circuits that comprises a plurality of heat generating elements at least one of which is adapted to fuse and thereby open the circuit on predetermined overload of the protector, a movable member, another of said heat generating elements having the major portion thereof coextensive with a portion of said movable member and being supported on and carried by said movable member, said other heat generating element being arranged so at least a portion thereof will flex upon movement of said movable member, heat softenable material normally maintaining said heat generating elements in electrical conducting relation, and a resilient member biasing said movable member and said major portion of said other heat generating element for movement to open circuit position when said heat softenable material loses its holding power.

22. A protector for electric circuits that comprises a plurality of heat generating elements, one of said elements being relatively short and being adapted to fuse on predetermined overloads of the protector, a plurality of contact terminals that are each massive relative to said fusible heat generating element, another of said heat generating elements being flexible and being relatively long, said fusible heat generating element being positioned adjacent to and in good electrical and thermal connection with one of said contact terminals whereby the major portion of the heat generated by said fusible heat generating element is absorbed by said terminal, heat softenable material normally maintaining said heat generating elements in electrical conducting relation, said elements being arranged so heating of said material at certain overloads is mainly due to the heating of said other heat generating element, and resilient means arranged to movesaid other heat generating element whenever the protector opens the circuit.

23. A protector for electric circuits that comprises an enclosure, contact terminals, a movable member, heat softenable material, a resilient member and a plurality of heat generating elements, at least one of which is adapted to fuse, another of said heat generating elements being arranged so the major portion thereof is supported on and coextensive with a portion of said movable member, said resilient member and said fusible heat generating element cooperating to space said heat softenable material and said major portion of said other heat generating element away from the inner surface of said enclosure, said heat softenable material normally maintaining said fusible heat generating element and said other heat generating element in electrical conducting relation and being arranged, when heated to a predetermined temperature, to permit an interruption of said relation by movement of said other heat generating element away from said fusible heat generating element.

24. A protector for electric circuits comprising a movable member, heat softenable material, and a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, another of said heat generating elements being arranged so the major portion thereof is supported on and coextensive with said movable member, said movable member being constructed and arranged to aborb an appreciable portion of the heat generated in the protector. heat softenable material adjacent one end of said movable member normally contacting each of said seat generating elements to maintain them in electrical conducting relation and being arranged to permit movement of the movable member and consequent opening of the circuit when heated to a predetermined temperature.

25. A protector for electric circuits that comprises an enclosure, contact terminals, heat softenable material, a movable member, a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, and a resilient member, said heat softenable material being positioned adjacent one end of said movable member and normally contacting each of said heat generating elements and thereby maintaining them in thermal and electrical conducting relation, said resilient member and said fusible heat generating element cooperating to space said heat softenable material, movable member and another of said heat generating elements away from the inner surface of said enclosure. said resilient member biasing said movable member for movement whenever said heat softenable material loses its holding power or said fuse link fuses.

26. A protector for electric circuits that comprises an enclosure, contact terminals, a movable member, heat softenable material, a resilient member and a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, another of said heat generating elements being arranged so the major portion thereof is supported on and coextensive with said movable member, said heat softenable material being positioned adjacent one end of said movable member and normally contacting each of said heat generating elements and thereby maintaining them in thermal and electrical conducting relation, said resilient member blasing said movable member for movement to open circuit position whenever said heat softenable material loses its holding power, said resilient member and said fusible heat generating element cooperating to resiliently space said heat softenable material and said movable member away from the inner surface of said enclosure.

27. A protector for electric circuits that comprises heat softenable material, a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, another of said heat generating elements having a portion whose overall length is substantially smaller than its developed length, a movable member arranged so said portion of said heat generating element is supported on and coextensive with said movable member, said heat softenable material normally maintaining said heat generating elements in electrical conducting relation, said resilient member being operable to move said portion of said element and said movable member to interrupt said relation whenever said heat softenable material loses its holding power.

28. A protector for electric circuits that comprises an enclosure, contact terminals, heat softenable material, a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, a movable member and a resilient member, said resilient member cooperating with said fusible heat generating element to resiliently space said heat softenable material and said movable member away from the inner surface of said enclosure, another of said heat generating elements having a portion whose overall length is substantially smaller than its developed length, said movable member and said portion of said heat generating element being arranged so said portion is free from stress due to said resilient member and being normally held in closed circuit position by said heat softenable material and being arranged to be moved to open circuit position by said resilient member whenever said heat softenable material loses its holding power.

29. A protector for electric circuits comprising a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, another of said heat generating elements having a portion whos overall length is substantially smaller than its developed length, a movable member constructed and arranged to support said portion of said heat generating element and to absorb an appreciable portion of the heat generated in the protector, heat softenable material adjacent one end of said movable member normally contacting each of said heat generating elements and thereby maintaining them in thermal and electrical conducting relation, said resilient member biasing said movable member and said portion of said heat generating element for movement out of electrical contact with said fusible heat generating element to open the circuit whenever said heat softenable material loses its holding power.

30. A protector for electric circuits comprising a movable member, heat softenable material, a resilient member, and a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, another of said heat generating elements having a portion whose overall length is substantially smaller than its developed length, said movable member being constructed and arranged to be coextensive with and to support said portion of said heat generating element and to absorb an appreciable amount of the heat generated in the protector, said heat softenable material normally contacting each of said heat generating elements and thereby maintaining them in thermal and electrical conducting relation, said resilient member being operable to move said portion of said heat generating element and said movable member whenever said heat softenable material loses its holding power.

31. A protector for electric circuits that comprise an enclosure, contact terminals, a plurality a: heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, heat softenable material, a movable member havmg outside dimensions appreciably smaller than the inner dimensions of said enclosure, and a resilient member that is normally arranged to exert a tension in said movable member and said fusible heat generating element longitudinal of said enclosure without subjecting another of said heat generating elements to tension, whereby said movable member and said heat softenable material will remain resiliently spaced away from the inner surfaces of said enclosure regardless of any expansion of said fusible heat generating element, said other heat generating element being arranged so the major portion thereof is supported on and is coextensive with a portion of said movable member.

32. A protector for electric circuits that comprises an enclosure. contact terminals, heat sof tenable material, a movable member, a plurality of heat generating elements normally held in electrical conducting relation by said heat softenable material and at least one of whi'h is adapted to fuse and thereby open the circuit, and a, resiilent member, said movable member having outside dimensions appreciably smaller than the inner dimensions of said enclosure, said resilient member being substantially free from current flow therethrough and arranged to exert a tension on said movable member and on said fusible heat generating element longitudinally of said enclosure whereby said movable member and said heat softenable material will remain resiliently spaced away from the inner surface of said enclosure regardless of any expansion of said fusible heat generating element, said fusible heat generating element being arranged to remain in substantially fixed position when said movable memberismoved.

33. A protector for electric circuits comprising an enclosure, contact terminals, a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, a movable member and a resilient member, said movable member being constructed and arranged to absorb an appreciable portion of the heat generated in the protector, said heat softenable material being positioned adjacent one end of said movable member and normally contacting each of said heat generating elements and thereby maintaining them in thermal and electrical conducting relation, said resilient member being arranged to exert a tension in said movable member and in said fusible heat generating element longitudinally of said enclosure whereby said movable member and said heat softenable material will remain resiliently spaced away from the inner surfaces of said enclosure regardles of any expansion of said fusible heat generating element, said resilient member biasing said movable member for movement away from said fusible heat generating element to open the circuit whenever said heat softenable material loses its holding power.

34. A protector for electric circuits that comprises an enclosure, contact terminals, a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, heat softenable material, a movable member and a resilient member, another of said heat generating elements having a portion whose overall length is substantially smaller than its developed length, said movable member having outside dimensions appreciably smaller than the inner dimensions of said enclosure and being arranged to carry said portion of said heat generating element, heat softenable material normally contacting each of said heat generating elements and thereby maintaining them in thermal and electrical conducting relation, said resilient member being arranged to exert a tension in said movable member and said fusible heat generating element longitudinal of said enclosure whereby said movable member and said heat softenable material will remain resiliently spaced away from the inner surface of said enclosure regardless of any expansion of said fusible heat generating element and whereby said movable member will be moved away from said fusible heat generating element when said heat softenable material is heated to a predetermined temperature.

35. A protector for electric circuits that comprises an enclosure, contact terminals, a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, heat softenable material, a movable member and a resilient member, another of said heat generating elements being arranged so the major portion thereof is supported on and coextensive with a portion of said movable member, said movable member having outside dimensions appreciably smaller than the inner dimensions of said enclosure and being arranged to absorb an appreciable portion of the-heat generated in the protector, said heat softenable material being adjacent one end of said movable member and normally contacting each of said heat generating elements and thereby maintaining them in thermal and electrical conducting relation, said resilient member being arranged to exert a tension in said movable member and said fusible heat generating element longitudinally of said enclosure and to move said movable member whenever the protector opens the circuit.

36. A protector for electric circuits that comprises an enclosure; contact terminals. a plurality of heat generating elements. at least one of which is adapted to fuse and thereby open the circuit, heat softenable material, a movable member and a resilient member, another of said eat generating elements having a portion whose overall length is substantially smaller than its developed length. said movable member having outside dimensions a preciably smaller than the inner dimensions of said enclosure and being arranged to support said orti n of said heat generating element and to absorb an appreciable portion of the heat generated in said protector. said heat softenable material normally ma ntaining an electrical conducting relation between said heat generatin elements. said resilient member being arranged to exert a tension in said movable member and said fusible heat generating element longitu inally of said enclosure and to move said movable member and flex a second portion of said other heat generating element.

37. A protector for electric circuits that comprises contact terminals, a movable member, a resilient member and a plurality of heat generating elements. at least one of which is ada ted to fuse and thereby open the circuit. heat softenable material normally connecting said heat generating elements. another of said heat generating elements being arranged so the major portion thereof is sup orted on and coextensive with a portion of said movable member and a minor portion thereof extends from said movable member to one of said contact terminals and is permanently secured thereto, said resilient member being operable to move said major portion of said other heat generating element away from said fusible heat generating element and to open the circuit when said heat softenable material has been heated to a predetermined temperature.

38. A protector for electric circuits that comprises a movable member, heat softenable material, and an electrical conductor, said conductor being arranged so the major portion thereof is supported on and coextensive with a portion of said movable member, and means operable to move said movable member whenever the protector opens the circuit.

39. A protector for electric circuits that comprises a contact terminal, heat softenable material, a heat generating element that is permanently secured to said terminal and has a portion thereof in the form of a coil that is arranged to add heat to said heat softenable material, and a resil ent member, said resilient member being arranged to move said coil portion of said heat gener' ting element toward said terminal when said heat softenable material has lost its holding power.

40. A protector for electric circuits comprising a plurality of heat generating elements, at least one of which is adapted to fuse and thereby open the circuit, a resilient member and heat softenable material, another of said heat generating elements having a developable portion arranged to be moved by said resilient member to open circuit position when said heat softenable material reaches a predetermined tempermining in substantially fixed position when said portion is moved, said developable portion and said heat softenable material and said fusible heat generating element being arranged so heating of said heat softenable material at certain overloads is mainly due to heat from said developable portion.

41. In a protector for electric circuits, an enclosure, a movable member and a coiled resilient member, said resilient member having at least one external dimension closely approximating one interior dimension of said enclosure, said resilient member being arranged to support at least one end of said movable member, said dimensioning of said resilient member being arranged to resiliently space said end of said movable member away from the inner surfaces of said enclosure.

42. A protector for electric circuits that comprises a heat generating element, heat softenable material, a resilient member, and a movable member, said heat generating element having a portion spaced away from said movable member by a non-conductor of electricity, said portion of said heat generating element being supported on and coextensive with a portion of said movable member, said non-conductor of electricity being in contact with said portion of said heating element and with said portion of movable member, said movable member being arranged to absorb heat from said non-conductor and to conduct said heat to said heat softenable material, said resilient member being arranged to move said movable member whenever the protector opens the circuit, said heat generating element and movable member and heat softenable material being arranged so the protector will open the circuit before said non-conductor of electricity is injured by heat from said heat generating element.

43. In a protector for electric circuits, an enclosure, an end cap for said enclosure, a movable member and a helical resilient member, said end cap having an internal diameter greater than the external diameter of said enclosure, said resilient member having a plurality of diameters, one of which diameters is smaller than the internal diameter of said enclosure and another is larger than the internal diameter of the enclosure but smaller than the internal diameter of the end cap whereby said resilient member can be held in assembled relation with said enclosure by said end cap.

44. In a protector for electric circuits, an enclosure, a fusible conductor, heat softenable material and a movable member, said fusible conductor being bent to form a U and being posi tioned in said enclosure so the closed end of the U extends inwardly of said enclosure, said closed end of said fusible conductor normally engaging and being secured to said movable member by said heat softenable material, said closed end of said fusible conductor providing a good hold for said heat softenable material whereby separation of said fusible conductor and said movable member is prevented until the heat softenable material reaches a predetermined temperature.

45. In a protector for electric circuits, a heat generating element, a movable member that is arranged to be heated by said heat generating element, a resilient member and a member of insulating material arranged to thermally insulate said resilient member from said movable member.

46. A protector for electric circuits that comature, said fusible heat generating element reprises Contact terminals. a pl rali y of heat 8 erating elements, at least one of said elements being adapted to fuse on predetermined overload of the protector, heat softenable material, a movable member and a resilient member, another of said heat generating elements having 2. developable portion supported on and coextensive with a portion of said movable member, said movable member and said p01 tion of said heat generating element being spaced from said terminals, said heat softenable material normally contacting each of said heat generating elements to hold them in electrical conducting relation, said resilient member being arranged to move said portion of said heat generating element and said movable member away from said fusible heat generating element to interrupt said relation whenever said heat softenable material loses its holding power.

47. A protector for electric circuits comprising an enclosure, a plurality of heat generating elements, a movable member, heat softenable material and a resilient member, said heat generating elements having their inner ends in proximity to each other and normally secured to one end of said movable member by said heat softenable material, said resilient member biasing said movable member for circuit opening movement when said heat softenable material has been heated to a predetermined temperature.

48. A protector for electric circuits comprising a supporting member, a flexible conducting member having the major portion thereof supported on and coextensive with a portion of said supporting member, heat softenable material, and means operable to move at least one portion of one of said members to open the circuit and to flex a portion of said conducting member when said heat softenable material has been heated to a. predetermined temperature.

49. A protector for electric circuits comprising a supporting member, a iiexible conducting member having the major portion thereof supported on and coextensive with a portion of said supporting member, heat softenable material, and means operable to move one of said members and thereby open the circuit when said heat softenable material has been heated to a predetermined temperature, said flexible conducting member being substantially free from stress due to said opening means at all times when the circuit through the protector is closed.

50. A protector for electric circuits that comprises contact terminals, a heat generating element having a portion whose overall length is substantially smaller than its developed length and another portion permanently secured to one of said contact terminals, heat softenable material and a resilient member substantially free from current flow therethrough that is operable to move said portion of said heat generating element and open the circuit whenever said heat softenable material is heated to a predetermined temperature.

51. A protector for electric circuits comprising an enclosure, a plurality of heat generating elements, a movable member, heat softenable material and a resilient member, said heat generating elements having their inner ends in proximity to each other and secured to said movable member adjacent one end thereof, one of said heat generating elements being secured to said movable member by said heat soitenable material, said resilient member biasing said movable member for movement away from said one heat generating element when the heat softenable material has been heated to a predetermined temperature.

52. In a, protector for electric circuits 9. heat generating element, an enclosure, a resilient member having a relatively large portion thereof positioned in close proximity to said enclosure whereby heating of said resilient member is retarded by heat transfer between said resilient member and said enclosure.

MANFRED 1'. DUERKOB.