US2159423A - Protector for electric circuits - Google Patents

Description

May 23, 1939. H. TA BussMANN A 2,159,423

PROTECTOR FOR ELECTRIC CIRCUITS Filed OCL. 5, 1936 2 Sheets-Sheet l t /////////`)//,/////////////////////////f/,//////////////A W3? gl t IN VEN TOR. /sN/w 7.' ussMn/v/v ATTORNEY May 23, 1939 H. T. BUSSMANN PROTECTOR FOR ELECTRIC CIRCUITS Filed 0G13. 5, 1936 2 Sheets-Sheet 2 INVENTOR. HENRY 7." ,B1/ss MAN/v BY K W ZM A TTORNE Y.

Patented May 23, 1939 UNITED STATES PATENT OFFICE 32 Claims.

My invention relates to electrical protective devices adapted to be included in an electric circuit and to blow and interrupt the circuit when the current therein exceeds a certain value for a certain length of time.

An object of my invention is to provide such a device having long blowing times at overloads which could be maintained for relatively long periods of time without resulting in injury to the circuit wiring or to any energy translating device forming apart of the circuit. 'Another object of my invention is to provide such a device having the above characteristics, but also capable of blowing almost instantaneously on such higher overloads as short circuits.

Another object of my invention is to provide` lsuch a device capable of being enclosed in a fuse casing of standard size for its rating and, when so enclosed, of meeting the short circuit operating requirements as set forth in the Underwriters Laboratories Standard for Enclosed Fuses.

A still further object of my invention is to provide such a protective device in a design equally vapplicable to high and to small current ratings.

To these and-other ends my invention consists in the novel features and combinations of parts to be hereinafter described and claimed.

In the drawings,

Figure 1 is a view in longitudinal section through a cartridge type of protector embodying my invention,

Fig. 2 is an enlarged fragmentary view, in perspective, of a part of the structure embodying my invention,

Fig. 3 is a view in longitudinal section of a modified form of d evice embodying my invention,

Fig. 4 is a top plan view of a fuse strip such as may be used in the device shown in Fig. 3,

Fig. 5 is a view in longitudinal section through another form of protector embodying my invention,

Fig. 6 is a top plan view thereof with the window and closure member removed,

IFig. '1 is a longitudinal sectional View through another form of protector embodying my invention, and

Fig. 8 is a longitudinal sectional view through a still further modification of protector embodying my invention.

Referring to Fig. 1 of thef drawings, I have there illustrated a cartridge type protector 2l comprising a casing 23 of electric-insulating material and of the usual cartridge fuse form havng'ferrule terminals 25 and 21 thereon at the respective ends. These conducting ferrules may be secured by having the inner ends thereof crimped or rolled inwardly as indicated at 29 or in any other suitable manner.

'Ihe ferrule 21 has rigidly secured to the inside thereof a relatively heavy metallic heat-conducting and heat-storing member 33 in order that it may store a relatively large amount of heat or. may conduct heat away from other parts of the `protector operatively associated therewith and to be hereinafter described in detail. The inner end of member 33 may be provided with a slot 35 for a purpose to be hereinafter described.

A fuse link 31 has one end 39 thereof held in electrical engagement with the member 33 and in Figs. 1 and 2 I have shown this electrical engagement as being maintained by a relatively small mass of heat softenable material such as low melting point solder 4l. I have shown the fuse link 31 as being made of a single strip, extending over and beyond the slot 35 and held in electrical engagement with the member 33 adjacent to the inner end of the slot. The outermost end portion 39 of the fuse link may be bent slightly angularly relatively to the rest of the link in order to provide an anchorage for one end of a biasing or opening means 43 in the shape of a helical spring, the other end of which is anchored to a small portion 45 of a disc 41 which may be made of electric-insulating material, and is held at the end of the relatively massive member 33 by an offset portion I5 on the link .31. The fuse link extends through a suitable opening in the disc l1. I do not desire, however, to be -restricted to the particular details of the inner end portion of the relatively massive member 33 and the anchoring of one end ofthe biasing means 43, but have illustrated these only to show one form of such devices which I may utilize.

The disc I1 divides the interior of the cartridge 'casing 23 into two parts,- one part, a chamber 5l, being usually smaller than the other part on the other side of the disc and containing the heavy member 33, an end portion of the link 31, the small mass of heat softenable material Il and the spring means 43. The other part of the interior of the casing contains the major portion of the fuse link 31 and more particularly that part thereof which is adapted to fuse at a predetermined temperature when subjected to heavy overloads, including short circuits.

Ihat end of the heavy member 33 engaging the contact terminal 21 is attached thereto by soldering, riveting or by any other method which will maintain them in good electric and heat conducting relation with each other. The other end of the fuse link is secured to the contact terminal 25 in any manner which will maintain them in electrical connection under all operating conditions of the protector.

Referring now to Fig. 3 of the drawings, I have there illustrated a cartridge type protector 53 including a cartridge casing 55 having ferrules 51 thereon at the respective ends and being provided with knife blade terminals 59 and 6|, respectively. A fuse strip 63, which has a fusing portion B5 therein at substantially the middle of its length, has one end secured in electrical engagement with the inner end of knife blade 5.9 as by a mass 61 of ordinary solder or it may be riveted or otherwise permanently secured thereto. The other end of the fuse link 63 has y a short longitudinal slot therein .to provide two hard solder, riveting or any other suitable manner.

The end portion 1| may be suitably arranged to permit of securing thereto one end of an operating means 11, here shown as a helical spring, the other end of which is secured to a disc 19, which is at the inner end of the contact terminal 6| and divides the casing 55 into two chambers. One of these chambers contains the inner end of contact terminal 59, the major portion of the link including the fusing portion 65 and an arc quenching filler 8 I, while the other chamber contains the end portions 1| and 13 of the link, the heat softenable material 15, the opening means 11 and the inner end of contact terminal 6|.

Referring now to Fig. 4 of the drawings, I have there illustrated a fuse link 83 which is provided with a pair of fusing portions 85 near the respective ends thereof. One end is divided by a longitudinal slot into two end portions 81 and 89 corresponding to the respective end portions 1| and 13 of fuse link 63 in Fig. 3.

Referring now to Figs. 5 and 6 of the drawings, I have there illustrated a protector of the plug fuse type |01 including a body |09 which may be made of electric-insulating material, such as porcelain, and which has a central contact terminal I|| and a screw shell contact terminal ||3 thereon. A fuse link 5 which may be of any suitable kind has one end held in electrical engagement with the central contact in any suitable manner, as by ordinary solder ||1.

The other end of the fuse link ||5 is held 'in electrical engagement with a relatively massive heat-conducting member 9 which, as shown, may be vof substantially L-shape, by a small mass |2| of heat-softenable material, such as a low melting point solder. 'Ihe other end of member ||9 is electrically connected to the screw shell terminal in any suitable manner as by a mass |23 of solder which may have a relatively high melting point as compared to 12|.

That end 'of link l I5 which is held in electrical contactI with member H9 lhas secured thereto one end of a biasing or opening means |25 which, as shown in Figs. 5 and 6 of the drawings, is a helical spring, the other end of which is hooked arcanes around a metal bar |21 held by the upper end of the porcelain member |09.

Referring now to Fig. 7 of the drawings, I have there illustrated a modification of the device shown in Figs. 5 and 6, the principal difference being that the central contact terminal |33 in the body |09 may be made relatively heavier than the center contact shown in Fig. 5 either by enlarging the outer dimensions thereof or by reducing the size of an opening |35 therein, this opening |35 being adapted to receive one end of the link |31 and a small mass |39 of heat softenable material. A spring |4| of the same general type as was hereinbefore described in connection with the device shown in Fig. 5 of the drawings has one end operatively connected to that end of the link which is in electrical engagement with Contact terminal 33, while the other end of the link |31 is electrically connected to a screw shell contact I3 in any suitable manner as by a mass |42 of solder which has a relatively higher m'eltingtemperature than that of the holding means |39.

Referring now to Fig. 8 of the drawings, I have there illustrated a still further modification embodying, in addition to the other elements already hereinbefore described as to body and terminals, a fuse link |43 having one end thereof in electrical engagement with a center contact and being held therein by any suitable means as by solder |45 of relatively high melting point, while the other end thereof is held in electrical engagement with a relatively heavy heat conducting member I41, by a small mass of heat softenable material |53, such as low melting point solder. Instead of using a helical spring to break the electrical contact between one end of the link |43 and the massive heat conducting member |41, I may use a leaf spring |49, one end of which may be embedded in a small recess |5| in the body |09, while the movable end thereof interts with the other end of the link |43 so that when permitted to do so by softening of the small mass of heat-softenable material |53 normally holding the end of the fuse link in contact with member |41, this electric conducting engagement may be broken.

The operation of the device shown in Fig. 1 is as follows: If a current be passed through the protector, heat will be generated in the fuse link I and the other parts of the device l'traversed by the current but the other parts are so heavy and of such good conducting material that the fuse link is the main source of heat in theV protector. Moreover it is the only element therein purposely designed to serve as a source of heat. Accordingly whenever in the specification and claims the link is referred to as being substantially the sole source of heat in the protector, it is to be interpreted as having the above meaning. Part of this heat will cause a rise of temperature of the link and part will be conducted to the terminals, causing a rise in temperature of the terminals and intermediate parts including the heat softenable material.

When the protector is traversed by heavy overload currents some portion of the link may reacn fusing temperature and the link may blow in which case the protector acts as a fuse. This fusing portion may or may not differ in area of cross section or in material or in any other manner from the remaining parts of the link; in those links where it does not differ the fusing portion will be substantially midway between the ends of the link. Opening of the circuit by the protector operating as a fuse will occur on short circuit and on all currents in excess of a predetermined value.

The heat softenable material which I use is one which loses its holding power at a tempera.- ture below the fusing temperature of the link and when the protector carries currents within a certain range below the above mentioned value, suificient heat may be conducted to the heat softenable material to cause it to lose its holding power before any portion of the link has reached fusing temperature. When this happens, the biasing or opening means becomes operative to open the circuit in the protector by breaking the electrical connection normally maintained by the heat softenable material by moving an end portion of the link laterally, the protector therefor providing a thermally controlled mechanicallyoperable circuit interrupter which may open the circuit through the protector under certain operating conditions. Currents of still lower range of values will be carried by the protector without opening the circuit.

The heat softenable material is shown as being in good heat conducting relation with both the link and one' contact terminal, so that it can readily receive heat from the link and so that the length of time required for it to reach a temperature at which it loses its holding power may be increased by heat conducted from it to the terminal, the amount of heat conducted away from the heat softenable material being increased by the relatively heavy mass of material interposed between the contact terminal.

It will thus be seen that the fuse link used in my device has a current carrying capacity greater than the current carrying capacity of the protector as a whole and on very heavy overloads the device will open the circuit almost instantaneously, while on lower overloads a long time' lag is obtained, which time lag may be varied through a considerable range of magnitude by varying the heat conduction between the heat softenable material and the contact terminal. In other words the operation of the opening means is controlled by the holding means and that of the holding means is controlled by the link, the control by the link being modified by the amount of heat conduction provided for between the holding Imeans and one terminal.

The operation of the modifications shown in the other figures of the drawings is the same as for the device of Fig. l although minor variations are shown. In Fig. 3 of the drawings the heat absorbing mass as a separate member between the heat softenable material and the terminal is omitted, the inwardly extending end of the terminal, lengthened if desired, serving as the equivaient thereof, and an end portion of the link is shown as bridging the circuit interrupter. In this modication the opening oi' the circuit interrupter does not interrupt the total current through the protector but only that portion thereof flowing through the interrupter. After the interrupter has` operated the total current flows through the bridging portion of the link which portion fuses almost instantaneously and .thus opens the circuit through the interrupter. In order that this bridging portion of the link may operate in this manner, it is made of such cross sectional area that its`current carrying capacity will be small enough to cause fusing thereof on J any current which will cause opening of the circuit interrupter.

the heat softenable material and The obiect of this bridging member is to prevent destructive arcing at the interrupter contacts and to cause the final break to take place in an arc quenching filler, such as shown in Fig.

3, which may be desirable when the protectors are of relatively high rating.

It may be noted that the method of connecting the opening means is` such that it carries substantially no current and that the fusing portion of the link is substantially free from stress caused by the opening means.

While the drawings show preferred forms of protectors embodying my invention, I do not desire to be limited to these particular combinations or embodiments. For example, I have referred to and shown in the drawings, a small mass of heat softenable material normally holding a portion of the fuse link in electric connection with one terminal as a low melting point solder, but this may be any electric conducting or non-conducting material which is capable of holding the cooperating contact members of the circuit interrupter in electrical connection at temperatures up to a certain value and which loses its holding power when heated to, a temperature above said predetermined value. For purposes of convenience this material is referred to in the specification and the claims as a heat softenable materia This expression is to be interpreted as covering any material capable of maintaining said electrical connection at all temperatures below a predetermined value and rendered incapable of maintaining such electrical connection when heated to a temperature above said predetermined value, irrespective of whether the loss of holding power results from softening or from any other physical change accompanying an increase in its temperature.

I have shown the biasing or opening means as a helical spring in some figures and as a leaf spring in another figure, but desire it to be understood that I may use any suitable means capable of being operatively combined with the other parts of the device and effective to open the interrupter as described when the holding means 'has lost its holding power.

While I have shown a heavy heat conducting member for conducting heat from the heat sof. tenable member, in Fig. 1 of the drawings, and have shown the heat softenable material directly associated with a knife blade terminal in Fig. 3 of the' drawings, I may omit the heavy member from Fig. 1, or use its equivalent in Fig. 3 by making the inner portion of the contact terminal of Fig. 3 longer, the use or omission of this member and its size, if used, being dependent on the time lag desired.

An arc quenching filler may be used or not, but where it is used the enclosure is dividedinto two chambers by a disc to keep the filler away from the interrupter opening means.

' I do not desire to be limited to the forms of fuse links shown in the drawings, but may use any form of fuse link and may make it .of any material suited for the purpose. I may, if I nnd it desirable or necessary to get the relatively long time lag desired, use fuse links made of metals having higher melting points than ordinarily Aused in fuses. If such metals as copper, silver are not possible in a protector embodying my d aisance invention, as the circuit will be opened by the circuit interrupter, as hereinbefore described, before such unsafe temperatures can be reached.

The fusible member bridging the circuit interrupter in Fig. 3 may be used in the device shown in'Fig. l, or it may be omitted from the devicev shown in Fig. 3. This member is shown in the drawings as an integral part of the fuse link, but it would be within the spirit and scope of my invention to make it a separate member electrically connected to the link and bridging the circuit interrupter if I so desire.

All of the devices illustrated and described in "the specification embody the same inventive coneffective to move the portion of the link to open circuit position when the holding means has been heated by the link to a temperature at which it loses its holding power. Provision is also made in all of these devices` to conduct heat away from the holding means to thereby increase the time lag at overloads where the opening of the circuit is contingent on the opening of the circuit interrupter.

The fact that the fusing portion of the fuse link is substantially free from stress caused by the interrupter operating means, is an important element in my invention. It prevents injury and strain on the fusing portion and permits of obtaining closer and more uniform rating of similar' fuses in mass production and the use of a weaker interrupter opening means. This use of a weaker `interrupter opening means precludes the occurrence of fatigue in the holding means with consequent changes in the operating characteristics of the protector.

The fuses in my invention are designed for the protection of light and power circuits and while there are some similarities between the fuses built under my invention and some of the fuses called telegraph and telephone fuses, there is an immense difference between them. The telegraph and telephone fuses are designed for small currents and are a distinct type of fuse wholly outside the eld of general industrial use. Most of them are so designed that if a fuse link heavy enough to carry current values such as must be carried by fuses used in industrial service were to.be used, the springs would have to be so heavy that it would be impossible to enclose the protector element includingy such a spring in a casing of standard size for fuses of its rating. Most of the devices of this general kind known to me and using a spring have the spring connected in series circuit with the link with'consequent possibility of annealing the spring when subjected to heavy overloads and thereby rendering the device inoperative unless a spring so large as to be prohibitive because of its size is used. A heavy spring, if used, would subject a part of the link and the heat softenable material to such stress as to render diilicult, or impossible, exact rating of the protector and maintenance of initial rating during the life of the device. Again many suchvdevices known to me have electrical contacts depending for their maintenance' on spring tension and not soldered or otherwise permanently connected and a construction of this kind makes for uncertain operation at all times and more especially if the device remains in circuit for a relatively long time without opening and the abutting surfaces become more or less oxidized or corroded as is usually the case.

Bymy invention I am enabled to produce a commercially operative protective device of a size and external dimensions in conformity with present standard requirements forenclosed fuses and of such design and construction that it can be accurately rated and that it will maintain such rating throughout its entire time of being connected in an electric circuit which it is to protect.

A protector embodying my invention will have much greater time lags on ordinary overloads than fuses heretofore used, while at the same time remaining capable of substantially instantaneously interrupting a circuit under short circuit conditions.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that other modifications thereof are possible. My invention therefore is not to be restricted except insofar as is necessitated by the prior art and by the scope of the appended claims.

I claim as my invention: l

l. A protector for electric circuits comprising contact'terminals, a fuse link electrically connected to the lterminals and adapted to fuse at a predetermined temperature and a thermallycontrolled mechanically operable circuit interrupter, a portion of said fuse link constituting a movable contact member of said interrupter, a small mass of heat softenable material positioned relative to said portion of the link and the cooperating terminal to normally hold them in electrical connection with each other to provide a path of low thermal reluctance for the transfer of heat therebetween, said mass being adapted to lose its holding power at a temperature below said predetermined temperature and means for opening the circuit interrupter when said mass of material has lost its holding power, the link being substantially the sole source of heat in the protector, the link having a fusing portion substantially free from stress caused by the interrupter operating means.

2. A protector for electric circuits comprising contact terminals, a fuse link electrically connected to the terminals, a small mass of heat softenable material in contact with a portion only of said link and in good heat conducting relation with one of said terminals to maintain said electrical connectionat all temperatures up to a predetermined value, said mass being adapted to be heated by heat conducted to it from the link and to have the length of time required for it to be heated to said predetermined temperature to be increased by conduction of heat from it to said terminal and means for breaking said electrical connection normally maintained by said heat softenable material when the heat softenable material has been heated to a predetermined temperature,'said connection breaking means being substantially free from current iiow therethrough, said fuse link being substantiallyA the sole source of heat in the protector, the link having a fusing portion substantially free from stress caused by the connection breaking means. 3. A protector for electric circuits comprising contact terminals, a fuse link electrically connected to the terminals, a small mass of heatsoitenable material in contact with a portion only of said link and in good heat conducting relation with one of said terminals to maintain said electrical connection at all temperatures up to apredetermined value, said mass being adapted to be heated by heat conducted to it from the link', and means to move said portion of the link to break said electrical connection normally maintained by said heat softenable material when it has been heated to said predetermined temperature, the link being substantially the sole source of heat in the protector and having a fusing portion substantially free from stress caused by the connection breakingfmeans.

A4. A protector for electric circuits comprising contact terminals, a fuse link electrically connected to the terminals, a small mass of heatsoitenable material normally maintaining the electrical connection of the link to one terminal, said mass being in good heat conducting relation with said one terminal, and means to cause substantially lateral movement of a portion of the link to break said electrical connection normally maintained by said heat-softenable material when the same has been heated to a predetermined temperature, lsaid fuse link being adapted to fuse at a predetermined current and constituting substantially the sole means to heat said mass to said predetermined temperature when the link is traversed by currents of lower value than said predetermined value, the link having a fusing portion substantially free from stress caused by the connection breaking means.

5. A unitary protector for electric circuits comprising a fuse link, electrically conducting means comprising a terminal contact face vand a support for the link in permanently fixed low resistance thermal relation, thermallyreleasable means adapted to hold a portion of tlie link in electrical connection with said support, a member having a terminal contact face, ilxed means for connecting another portion of the fuse link to said member, means adapted to move a portion oi the fuse link substantially transversely to open the circuit when the holding means becomes releasable, said fuse link being substantially the sole source of heatfor the holding means.

6. A protector for electric circuits comprising a casing, contact terminala a fuse link electrically connected to the terminals, a mass of heat softenable materialvv normally maintaining the electrical connection of the link to one terminal Awhen the temperature of the heat softenable ma- Apredetermined temperature, the link being substantially the sole source of heat for the heatsoftenable material, the link having a fusing por- -tion substantially free from stress caused by the biasing means.A

7. A protector for electric circuits comprising a casing, contact terminals, means substantially enclosing in the casing electrically connecting said terminals with each other including a fuse link, a thermally-controlled-mechanically-operable circuit interrupter and a relatively heavy mass of good heat conducting material directly engaging one terminal, fthe circuit interrupter including a portion of said fuse link, said mass of good heat conducting material, a small mass of heat softenable material in contact with said portion of the link and with the relatively heavy mass of good heat conducting material, and normally holding the interrupter in' closed circuit the holding means becomes rel position and means for opening the circuit interrupter, said means being substantially free from current ilow therethrough, said heat conducting .member remaining stationary during opening oi the interrupter, the fuse link being substantially the sole source of heat in the protector.

8. A unitary protector for electric circuits comprising a fuse link, means comprising a terminal contact face and a support for the link permanently ilxed in low electrical resistance relation, thermally releasable means adapted to hold a portion of the link in electrical connection with said support, a member having a terminal contact face, xed means for connecting another portion of the fuse link to said member, means adapted to move a portion of the fuse link substantially transversely to open the circuit when able, said fuse link being substantially the sol source of heat for the holding means.

9. A protector for electric circuits comprising contact terminals, a fuse link electrically connected to the terminals, said link being effective to open a circuit therethrough by fusing on some portion thereof when carrying a current in excess of a predetermined value, a small mass of heat softenable material in engagement with both said link and one of said terminals for normally maintaining the electrical connection of the link and said one terminal, said link being substantially the sole source of heat in the protector and causing heating of the mass of heatsoftenable material and a reduction oi' its holding power on the passage through the link for a relatively long period of time of a current too small to fuse the link and means to move a portion of the link to break said electrical connection normally maintained by said heat-soltenable material when the holding power of the mass of heat softenable material has been reduced below' a predetermined value.

10. A protector i'or electric circuits comprising contact terminals, a relatively heavy good electric and heat-conducting member engaging one terminal, a fuse link electrically connected to said good heat-conducting member and eilective to open a circuit therethrough by fusing in some portion thereof when carrying a current in excess oi a predetermined value, a small mass of heat softenable material engaging both the heavy heat conducting member and the fuse link to normally maintain the electrical connection therebetween, the link being substantially'the sole source oi' heat in the protector and causing heating of the mass of heat softenable material and a reduction of its holding power on the passage through the link for a relatively long period of time of a current too small to fuse the link, and means to break said electrical connection between said link and said relatively heavy heat conducting member when the holding power of the mass of heatsoftenable material has been reduced below a predetermined value, the link having a fusing portion substantially free from stress caused by the connection breaking means.

1l. A protector for electric circuits comprising a casing, contact terminals and means substantially enclosed in the casing electrically connecting said terminals with each other, said means including a fuse link constituting substantially theV sole source of heat in the protector and a thermally-controlled-mechanically-operable circuit interrupter, a portion of said fuse link constituting a movable contact member of said interrupter, a small mass of heat softenable material holding said link in closed circuit position and being in good heat conducting relation with one of said terminals, said mass being adapted to be heated by the link and to lose the holding power when heated to a predetermined degree and means substantially free from current flow therethrough, effective to move said portion of the link to open circuit position when the heat softenable material has lost its holding power.

12. A protector for electric circuits comprising a casing, contact terminals and means substantially enclosed in the casing electrically connecting said terminals with each other, said means including a thermally-controlled-mechanicallyoperable circuit interrupter adapted to operate at current values within a predetermined range oi magnitude, and a fuse link adapted to fuse in some portion thereof at currents in excess of said predetermined range of magnitude, said interrupter including a portion of said fuse link, a small mass'of heat softenable material in contact with a portion only of said link and in good heat conducting relation with one of said terminals normally holding the interrupter in closed circuit position and means to move said portion of the link to open the circuit interrupter on softening of the heat softenable material to a certain degree, said link being substantially the sole source of heat for the heat softenable material, the link having a fusing portion substantially free from stress caused by the circuit interrupter opening means.

13. A protector for electric circuits comprising Contact terminals, a fuse link electrically connected to the terminals, and a thermally-controlled-mechanically-operable circuit interrupter including a portion of said fuse link and means normally holding the interrupter in closed circuit position, said holding means being in good heat conducting relation with one of said terminals, means for opening the circuit interrupter, the holding means being controlled by the fuse link and the action of the opening means being controlled by the holding means and a relatively heavy mass of heat absorbing material in contact with the holding means to modify the control of the holding means by said fuse link, the fuse link being substantially the sole source of heat on the protector, and having a fusing portion substantially free from stress caused by the opening I means, said mass of heat absorbing material remaining stationary during opening of the circuit interrupter.

14. A protector for electric circuits comprising contact terminals, arelatively heavy good Aelectric and heat conducting member engaging one terminal, a, fuse link adapted to fuse at a predetermined temperature, and having a portion engaging said relatively heavy good heat conducting member, a small mass of heat softenable material in intimate contact with said relatively'heavy heat vconducting member and the link normally holding said parts in electrical engagement with each other and adapted to be heated and to lose its holding power at a temperature ,below that at which fusion of the link occurs, the link being substantially the sole source of heat for the heat softenable material, the length of time required for the heat-softenable material to reach a given temperature being increased by the conduction of heat therefrom by the relatively heavy member, means effective to move said portion of the link to open circuit position on softening of the heat softenable material to a certain degree, the link having a fusing portion substantially free amarres from stress caused by the link-moving means.

15. A device as set forth in claim 4 and including a cartridge casing having a disc therein dividing the interior thereof into two parts, one part containing an arc quenching ller and the major portion of the fuse link including the fusing portion thereof and the other part containing an end portion of the link and the circuit interrupter, including the small mass of heat softenable material and the connection-breaking means.

16. A device as set forth in claim 4 and including a cartridge casing having a disc therein dividing the interior thereof into two parts, one part containing an arc quenching filler and the major portion of the fuse link including the fusing portion thereof, the other part containing an end portion of the link and the circuit interrupter,

the circuit interrupter including said end portion of the link, the interrupter operating means being a relatively light spring having one end engaging said end portion of the link and its other end connected to a part of the protector structure.

17. A device as set forth in claim 10 and including a cartridge casing having a disc therein dividing the interior thereof into twov parts, one part containing an arc quenching filler and the major portion of the fuse link including the fusing portion thereof, the other part containing the heat conducting member, an end portion of the link, the small mass of heat softenable material and the connection breaking means.

18. A device as set forth in claim 1 and including a cartridge casing having a disc of electric insulating material therein dividing the interior thereof into two parts, one part containing the fusing portion of the link and an arc quenching filler, the other part containing the circuit interrupter.

19. A protector for electric circuits comprising contact terminals, a fuse link having a portion adapted to fuse at a predetermined temperature and in direct contact with one of said terminals, a small mass of heat softenable material in intimate heat transferring relation with said link and its contacting terminal to normally hold said link in electrical engagement with said terminal and adapted to be heated and to lose its holding power at a temperature below that at which fusion of the link occursy-the link being substantially the sole source of heat for the heat softenable material, the length of time required to'raise the temperature of the heat softenable material being increased by the conduction of heat therefrom by the cooperating terminal, andmeans effective to move said link to interrupt the circuit in the protector on softening of the heat softenable material to a certain degree.

20. A protector for electric circuits comprising a fuse link and a mechanically operable circuit interrupter, a portion of said link constituting a contact member of the interrupter, said inter- 'rupter including also means in contact with said normally holding an end portion of said link in electrical contact with said terminal, a heat conducting path of low resistance between the heat softenable material and the terminal remaining in fixed position during operation of the protector, and means engaging said end portion of the link to cause substantially transverse movement thereof to open the circuit in the protector when the holding means has lost its holding power.

22. A protector for electric circuits comprising a fuse link, a thermally controlled mechanically operable circuit interrupter adapted to open when heated above a predetermined temperature and a member bridging the circuit interrupter and adapted to open the circuit in the protector by fusing after the interrupter has opened, said member being adapted to fuse at any current which will open said interrupter.

23. A protector for electric circuits comprising a fuse link, a thermally-controlled-mechanicallyoperable circuit interrupter including a small mass of heat fsoftenable material normally holding the interrupter in closed position and adapted to lose its holding power when heated to a predetermined temperature, said interrupter being adapted to open when said mass has been heated to said predetermined temperature and a member bridging the circuit interrupter and adapted to open the circuit in the protector by fusing after the interrupter has opened.

24. A protector for electric circuits comprising a fuse link, a thermally controlled mechanically operable circuit interrupter adapted to open when heated above a predetermined temperature and means including a portion of the fuse link bridging the circuit interrupter and adapted to open the circuit in the protector by fusing after the interrupter has opened, said portion of the link being adapted to fuse at any current value at which the interrupter will open.

25. A protector for electric circuits comprising a fuse link adapted to fuse when traversed by currents in excess of a predetermined value and having a portion adapted to fuse when traversed by currents below said predetermined value and means including a thermally controlled mechanically operable circuit interrupter to cause a predetermined time delay in the fusing of said portion of the link, said portion of the link fusing only after the interrupter has opened and being adapted to fuse at any current value at which the interrupter will open.

26. A protector for electric circuits comprising a fuse link adapted to open the circuitby fusing in relatively short times when the protector 'is traversed by currents in excess of a predetermined value, a thermally-controlled-mechanically-operable circuit interrupter adapted to open in longer times when the protector is traversed by currents of less than said predetermined value but greater than a second lower predetermined value and means including a portion of said fuse link adapted to open the circuit by fusing after opening of the interrupter, at any current through the protector which will open said interrupter.

27. A protector for electric circuits comprising a casing, contact terminals and means electrically connecting said terminals in the casing, said means including a fuse link and a thermally-controlledemechanically-operable circuit interrupter, said interrupter comprising an end portion of the link constituting a'movable contact member thereof, a small mass of heat softenable material in good heat conducting relation with both said end portion of the link and one of said terminals, holding said end portion of the link in closed circuit position and adapted to lose its holding power when heated to a predetermined temperature and operating means acting on said end portion of the link and adapted to move it to open circuit position when the holding means has lost its holding power and a second end portion of the link normally bridging the interrupter and adapted to open the circuit in the protector after the opening of the interrupter.

28. A protector forelectric circuits comprising a casing, contact terminals and means electrically connecting said terminals in the casing, said means including a fuse link and a thermally-controlled-mechanically-operable circuit interrupter, said interrupter comprising an end portion of the link constituting a movable contact member thereof, a small mass of heat softenable material in good heat conducting relation with both said end portion of the link and one of said terminals, holding said end portion of the link in closed circuit position and adapted to lose its holding power when heated to a predetermined temperature and operating means engaging said end portion of the link and adapted to move it in a direction substantially laterally of the link to open circuit position whenv the holding means has lost its holding power and a second end portion of the link normally bridging the interrupter and adapted to open the circuit in the protector after the opening of the interrupter.

29. A protector for electric circuits comprising a casing, contact terminals, means substantially enclosed in the casing electrically connecting said terminals with each other, said means including a fuse link, a thermally-controlled-mechanically-operable circuit interrupter and a member bridging the circuit interrupter and adapted to open the circuit in the protector by fusing after the interrupter has opened and an arc-quenching ller in the casing surrounding the fusing portions of said fuse link and bridging member.

30. A protector for electric circuits comprising a casing, contact terminals, means substantially enclosed in the casing electrically connecting said terminals with each other including a fuse link, a thermally-controlled-mechanically-operable circuit interrupter and a relatively heavy mass of good heat conducting material comprising an inwardly extending portion of one of said terminals, the circuit interrupter including a portion of said fuse link, said mass of good heat conducting material, a small mass of heat softenable material in contact with said portion of the link and with the relatively heavy terminal mass of good heat conducting material, and normally holding the interrupter in closed circuit position and means for opening the circuit interrupter, said means being substantially free from current flow therethrough, said heat conducting member remaining stationary during opening of the interrupter. the fuse link being substantially the f sole source of heat in the protector.

31. A protector for electric circuits comprising a fuse link adapted to fuse and open the circuit on currents in excess of a. predetermined value, a thermally. controlled mechanically operable circuit interrupter adapted to open on currents of lower value and a member bridging the circuit interrupter adapted to remain unfused on currents in excess of said predetermined value and to open the circuit by fusing on currents below u aimeras said predetermined value after the interrupter has opened, said member being adapted to fuse on any currentl which will open the interrupter. 32. A protector for electric circuits comprising i a fuse link adapted to fuse on currents above a predetermined value anni having a portion adapted to remain unfused on said currents

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