US1920031A - Electric switch - Google Patents

Description

y 1933- s. s. GREEN 1,920,031

ELECTRIC SWITCH Filed May 26, 1930 2 Sheets-Sheet l A TT'OVRNEY 5 July 25, 1933- s. s. GREEN ELECTRIC SWITCH Fi1 ed May 26, 1930 2 SheetsShe et 2 INVENTOR ATTORNEY Patented July 25, 1933 UNITED STAT it STANLEY S. GREEN, OF FAYETTE, INDIANA, ASSIGNOR T0 DUNCAN ELECTRIC MANUFACTURING COMPANY, OF LA FAYETTE, INDIANA, A CORPORATION OF ILLINOIS ELECTRIC SWITCH Application filed. May 26,

My invention relates to controllers for electric circuits and is of particular utility in connection with structures forming the subject matter of my copending application Serial N 0. 285,114, filed June 13, 1928, though my invention is not to be limited to this use. In my said copending application I have disclosed an electric circuit controller which is inclusive of a body of electric current conducting material, such as mercury,

that is normally contained in the bore or,

passage of a conduit made of insulating material. This current conducting liquid serves to electrically connect two electrodes of the associated circuits, when the device is in circuit closing position. When there is an abnormal flow of current through the device, the liquid conductor, or a sufiicient portion of it, is expelled to break the electrical connection between the electrodes and thereby open the circuit and guard the translating devices within the circuit. The liquid conductor and associated electrodes and parts thus constitute a circuit protecting switch.

My present invention has for its general object the formation of a switch structure which is simple and yet strong enough to withstand the violence which attends its operation. Another object is to provide an air tight envelope for the switch, so protected from the arcing and mechanical shocks originating within the switch as to be unaffected by them. It also aims to provide a generous flash-over distance within the switch to minimize destructive arcing. Still another object is to provide a controller having the proper time-lag characteristics upon automatic operation.

In carrying out my invention, I reenforce the conduit of insulating material with a metallic band and support which fasten it firmly in spaced interior relation to the container. I desirably provide such container in the form of two mating shells or cups of insulating material clamped together with a sealing material or cement therebetween and arranged to beimperforate to the outer air. Reenforcing and supporting means on the conduit of insulating material are desirabl 1930. Serial N0. 455,679.

confined to a zone intermediate the ends of the conduit, thereby providing greater flashover distance of the controlled current around the conduit and through the metal support thereof and such reenforcing and supporting means for the insulating conduit as well as one or more of the electrodes are given a large volume of metal and extended radiating surface to cause as small a time lag as desired in the automatic operation of the device. The arcing distance between electrodes when the circuit is broken is made ample to prevent any continuation of such arcing through the insulating conduit and all arcing is removed from the walls of the container a sutficient distance to prevent injury of such walls by the arcing. One of the electrodes is also preferably extended to provide an arc shield for the container.

The invention has other characteristics and will be more fully explained in connection with the accompanying drawings, in which Fig. 1 is a front elevation of the preferred formof circuit controller shown in normal circuit closing or on position; Fig. 2 is a side elevation of the device as it appears in Fig. 1; Fig. 3 is a front elevation partially in section, the removable front section of the enclosing casing being omitted; Fig. 4 is a view, somewhat similar to 30 Fig. 3, but showing the controller in the off position and illustrating parts in ele vation that appear in section in Fig. 3; Fig. 5 is a sectional view on line 55 of Fig. 1, but with the conduit of insulating material and its supporting structure removed so as to show the iron feed tube and its support clearly; Fig. 6 is a view similar to Fig. 5 but with the conduit of insulating material fastened in place in the housing, such conduit and its supporting structure being shown in cross section; Fig. 7 is a. sectional view on line 77 of Fig. 1 with the insulating conduit and its supporting structure removed to show more clearly the upper electrode and its support; Fig. 8 is a. view partly in section of a modified form of insulating conduit and its support; and Fig. 9 is a view partly in section of still another modification of the insulating conduit and its support.

In the forms of the invention illustrated, the casing is formed of insulating material, such as moulded bakelite or a similar moulded material having a phenolic resin base, excepting for the bolts, screws and the anchorages that are united therewith. This casing is inclusive of the front half or removable cup shaped section or shell 1 and the rear half or removable cup shaped section or shell-2. These casing sections are clamped snugly together, as by means of the metallic bolts 3 which pass through external ears 3 and 3 formed on the casing sections and into the nuts 3 The pressure exerted by said bolts is sufiicient to bring the engaging flat faces of the casing sections into intimate contact so that the easing is imperforate in this region and throughout the entire circumference of the casing which is desirably cylindrical. The mating surfaces brought together by bolts 3 should be flat and may be ground so if desired before being put together. A film of cement, such as Bakelite varnish, is desirably applied to these flat surfaces before placing them together and tightening bolts 3. The circuit controlling element is within the casing and is operable to on and off positions by suitably moving the casing which is desirably rotatively mounted upon a shaft 2 that is coaxial with the casing for this purpose. This circuit controlling element includes. as shown in the embodiment of the invention illustrated, a control tube or conduit 4 of refractory heat resisting insulating material, preferably porcelain produced by the wet process. This tube or conduit is surrounded by a reenforcing metal collar or jacket 5 that is preferably of iron and is initially of smaller internal diameter or size than the portion of the conduit it surrounds and requires expansion by heat in order that it may be tightly secured in place about conduit 4, the jacket -being allowed to cool and contract tightly upon the conduit to provide the reenforcement desired. A circular clamp 6 having ears 6 is placed over both tube 4 and jacket 5. Said ears 6' are securely fastened by a screw 7 passed therethrough into a metallic supporting rod or insert 7 that is embedded in but does not pass through casing section 2 in the process of moulding this casing section. anchored end sov as to be firmly gripped by the Bakelite and prevented from turning. Screw 7 not only tightens and fastens clamp 6 about jacket 5 and conduit 4 but it immovably secures and supports the entire assembly of conduit 4, jacket 5, and clamp 6 on the insert 7 which is of a length to support the entire assembly at a suitable distance from the walls of the container and This rod is desirably knurled at its generated within conduit 4 passes by direct conduction through the rod 7 and other metallic parts. As rod 7 is quite long and radiation within the casing from the surface of jacket 5 and clamp 6 as well as from the surface of rod 7, itself, cuts down the temperature of the metal in this rod, a destructivelyhigh temperature is never attained for that portion of it which is embedded within the bakelite.

If desired, jacket 5 may be omitted and the circular clamping band 6 used as the supporting and reenforcing member for conduit 4, but jacket 5 is preferred due to its firmer grip upon the conduit.

The bore of conduit 4 communicates with the bore of an L shaped metallic feed tube 9, preferably of iron, which fits snugly into an enlargement of the lower end of the conduit core. When in the normal circuit closing position of thecontroller, as shown in Figs. 1, 2 and 3, feed tube 9 constitutes the lower electrode of the device. Current enters this electrode from a lower metallic lead-in stud 10 about which the casing section 2 is so moulded that this stud is fixed with respect to and extends through the casing and has around it bosses 10 that effectively seal the stud in its passage through the casing wall and strengthen such casing where the stud passes therethrough. A metal clamp 11 is securely and fixedly mounted on the inner end of stud 10 by a screw 12 which passes through clamp 11 and into this stud. This clamp has ears 11 which respectively engage the legs of the L shaped feed tube 9. The stem of metallic screw 12 is positioned against the inner side of the bight of feed tube 9 to hold the tube against the clamp ears 11' and the head of this screw holds the feed tube against the body of clamp 11. This arrangement affords adequate electrical contact between the metallic stud 10 and the metallic feed tube or electrode 9.

The upper end of the bore of the conduit 4 is enlarged to form a well 13 adapted to receive the spoon shaped end 14 of the upper metallic electrode 14, which conforms to the well 13 and contacts with the mercury 15 or other liquid conductor contained in the conduit bore and the well enlargement 13 when the device is in circuit closing position. Slight clearance desirably intervenes between the w 11 of well 13 and the electrode part 14'. pper electrode 14 is positioned independently of conduit 4, being fastened in position upon a metallic lead-in stud 16 by a screw 17 threading into the inner end of this stud. Bosses 16' constituting parts of casing section 2 are securely moulded about the knurled end of stud 16 which is thus firmly mounted in the casing but does not pass therethrough.

' The lead-in studs 10 and 16 are shown with annular channels 10 and 16 in addition to the usual knurling to further secure anchorages for the studs and to provide longer, tighter and more diflicult'leakage paths for the diffusion or'leakage of air or gas there- 'along. The spoon shaped end 14 of the upper metallic electrode 14 has sufliciently full contact witht-he liquid conductor in the well 13 without substantially obstruct-' temperature might otherwise strike the casing wall forcibly with injurious effect. Said shield or barrier 14 also absorbs most of the heat contained in the liquid conductor and vapor striking it, since being a metal, it has a relatively large heat absorbing capacity that acts to condense the liquid conductor vapor and has a marked eflect in quenching any are which might arise between the electrode 14 and other parts of op posite electrical polarity in the casing. Electrode 14 is preferably made of copper or other metal of high electrical and thermal conductivity but plated with a mercuryresisting substance such as iron or nickel. The other metals exposed in the container to the action of mercury or mercury vapor may also be made out of non-ferrous metal such as copper, if such metal is coated with iron or other mercury resistant metal.

Mating projections 19 and 20 are respectively integrally moulded with the casing sections 1 and 2, and form, with contiguous portions of the casing, a funnel-shaped space 21. The receiving end of the tubular electrode or feed tube 9 may be freely received within the stem of the funnel to virtually constitute a. continuation thereof. Said funnel and the conduit 4 are so positioned with respect to the casin that, when the device is turned from on to 0d position, the mercury will be discharged from the conduits 4 and 9 and the well 13 into the surrounding space and to an extent to open the circuit at 14, the liquid conductor then falling to the then bottom of the casing as indicated at 22 in Fig. 4. When the device is turned from off to on position, the cup of funnel 21 will gather most of the liquid conductor at 22, this gathered liquid passing by gravity through the cup and stem of the funnel and into the feeding tube or hollow electrode 9 and the bore of conduit 4 and well continuation 13 of the conduit borewhereby the circuit is closed at the electrode tip 14', Figs. 1, 2 and 3. To insure closure of the circuit, I provide an excess of mercury or liquid conductor which finds lodgment in the then bottom of the casing as indicated at 22 in Fig. 3, this excess flowing from the well when the device has been fully brought to its on or circuit closing position.

I have shown no means of limiting the movement of the casing and the enclosed switch to a range between the on and off positions as such may obviously be employed and located as desired.

Current of the circuit to be controlled is supplied to the device through leads 23 and 24 which are preferably flexible to permit proper motion of the device and which are fastened to the res ective lead-in studs 10 and 16 by means of binding screws 23' and 24'.

When the device is in the on position, and the controlled circuit is closed at a lamp or other translating device, the circuit is inclusive of the flexible lead 23, lower lead in stud 10, metal feed tube clamp 11, metal feed tube and hollow lower electrode 9, the liquid conductor 15 in the bore of the conduit 4 and well 13, the upper electrode 14, the upper lead-in stud 16 and the flexible lead 24.

An interiorly threaded sealing boss 25 is preferably provided in the casing, this boss having a normally sealed bore which may be opened to aflord passage into and out of the casing when desired. Normally this casing is sealed or, in effect, imperforate throughout. A sealing screw 26 may be employed to normally close the bore of boss 25 and thereby complete the sealing of the entire casing or container from the admission of air. Except for the liquid conductor, the device is first assembled completely and the cement or varnish seal between the two mating casing halves 1 and 2 allowed to dry. During the drying process sealing screw 26 is removed, thus allowing access of outside air to the interior of the casing to facilitate the drying. Sealing screw 26 is then applied whereafter the entire device may be immersed for a short interval in a suitable sealing var- I nish in a tank under heavy pressure. This pressure drives small globules of such varnish or sealing compound into any pores in the casing that remain unfilled. The casing may then be removed from the impregnating tank, sealing screw 26 again removed and the varnish again allowed to dry, thus effectively completing the sealing up of the pores last remaining unfilled. After the final drying, the air in the casing is exhausted through the bore of sealing boss 25, whereafter nitrogen, hydrogen, or other suitable non-oxidizing gas is passed into the casing through this bore to take the place of the exhausted air. The required amount of liquid conductor is now introduced through the boss whereafter the sealing screw 26 is permanently screwed in place, sealing varnish having first been applied to its threads. My experiments have shown that a casing of bakelite thus equipped provides a seal which will so minimize the diffusion of the oxygen of the outer air into before the mercury therein is depleted by oxidation to a suflicient extent to require its renewal or interfere with the successful operation of the switch. 7

As illustrated, the metal parts such as reenforcing metal jacket 5 and circular support clamp 6 are so related asto prevent arc ing between the electrodes from occurring around the outside of insulating conduit 4 rather than through its bore. To assure this result, I make the outside'diameter of insulating conduit 4 large as compared with the diameter of its bore. In one preferred form designed for nominal 115 volt circuits, such outside diameter of insulating conduit 4 is P approximately one inch, giving nearly a one half inch radius through the conduit from any portion of the electrically alive liquid conductor to the metal of jacket 5 and clamp 6 and an even greater distance measured over the surface of the conduit. Jacket 5 and clamp 6 surround conduit 4 but are spaced from its electrode receiving ends sufficiently to insulate said jacket and clamp from both electrodes. Moreover the creepage or arcing spacing around th conduit 4 is divided into two gaps in series, one gap being at each end of such conduit, and this aggregate spacing is greater than the distance through the bore of said conduit. Because of such construction and spacing as well as the generous size of the conduit 4, undesired arcing cannot occur, even though small cracks or flaws may occur in the porcelain of the conduit 4 itself which might tend to connect either electrode by way of the liquid conductor forced into such cracks to the exterior metal reenforcement of the tube. It should also be noted that any cracks or flaws developing in the porcelain cannot enlarge due to the metal reenforcement of the conduit and consequently would be almost microscopic in cross section. Any mercury forced into any such cracks would therefor have a negligible current-carrying capacity and negligible effect on the predetermined or rated current-carrying capacity of the device. Experiments prove that the bore of conduit 4 when such conduit is fashioned of preferred material such as wet process porcelain is not marred to more than a negligible degree by the destructive action of arcing occurring upon the breaking of current at commercial distribution potentials of approximately 15, 230, or 460/volts, the length of the column of liquid conductor in the bore 10 between electrodes bein kept above a certain minimum. I have iscovered that this minimum distance above which destructive arcing does not occur within the conduit bore upon the breaking of such current either by manual or automatic operation of the device is of an inch for 115 volts and somewhat greater distances, although not proportionately greater. for the higher voltages mentioned. I attribute this action to the fact that upon the opening of the circuit the resultant arc is confined to the small cross sectional area of the conduit bore and that above the critical arcing distance the circuit volta is not suflicient, except for an exceeding y small period of time to possibly sustaln arcingaround the conduit 4. Because of the short ford a commercially acceptable limit to the.

interval of time required for the circuit controller to automatically open the circuit under predetermined standard conditions of overload. The hottest spot in the circuit controller is the liquid conductor in the bore of conduit 4, heat flowing outwardly from this spot to the outer surface of the casing and being thus conducted and radiated away. This escaping heat reaches the external surface of conduit 4 through the porcelain of the conduit and flows into and through jacket 5 and clamp 6 and into rod 7. Such heat is also radiated and conducted from the outer surface of the aforesaid parts to the gas filling the otherwise unoccupied portion of the casing interior and from thence to and through the casing to be dissipated from its exterior surface. Rod 7 also transfers heat to the casing at the point where it is moulded and held into the same. The escaping heat also flows, by way of the electrodes, into and through the lead-in studs and into and through the casing at the point where said studs are cast into the casing.

It is also radiated and conducted from the.

surface of the electrodes and lead-in studs to the gas filling of the interior of the casing, from thence to and through the casing gall to be dissipated from its exterior surace.

For a predetermined length and crosssection of bore, any increase in the total heat conductivity of the aforementioned heat paths increases the long-time current-carrying capacity of the controller because it enables heat to be conducted away fromthe bore of conduit 4 to the exterior at a greater rate without the liquid conductor in such bore exceeding its boiling or rupturing tem perature.

The long-time current-carrying capacity may be considered as the value of the maximum sustained current which the controller will carry for an indefinitely extended interval. The short-time current may be considered as the value of current required when applied to the controller, starting at room temperature, to produce an automatic interruption in a given short-time interval, usually one minute. The ratio of short-time current to long-time current may be considered as an indicator of the time-lag of the device on overload. When the ratio is large, the time lag is large and the controller is slow in opening the circuit. When the ratio is smaller, and approaches unity, the timelag is small and thecontroller is fast in opening the circuit.

In the preferred construction of my invention, upper electrode 14 has an extension or radiating fin 14 which fin, together with shield 1& radiates heat from the electrode surface to the gas in the interior of the container and increases the resultant heat conductivity for the escaping heat by way of this electrode. Such conductivity is also assisted by the large cross-section of the electrode in a direction normal to the prevalent heat flow,-a cross-section which is greatly in excess of that really needed for actual electrical conductivity in the electrode. Tt is obvious that metal support clamp 11 with its ears 11' actually'aids in procuring the desired result and may be enlarged in its size and surface area if desired for this purpose. The escaping heat which passes through the porcelain l encounters the jacket 5 and clamp 6. These latter parts have a greater heat conductivity than the insulating material of the conduit 4:. The heat is therefore, more easily conducted and radiated to the gas filling the casing interior by the relatively large surfaces of these parts. Ears ii also conduct heat rapidly to supporting rod 7 and to the casing wall. By these means, the longtime current for a predetermined length and cross section of bore is increased. Without them, it is inherently smaller. Shorttime current, however, is largely unafilected by such means.

Heat generated with short-time current flowing tends to spread out and escape to the exterior of the casing but before it can penetrate more than a small distance from where it is formed within bore of conduit 4, the circuit is interrupted. Short-time current is mainly aflected by the cross section of such bore. It is also affected by the heat storage capacity and heat conductivity of the liquid conductor in the bore itself and a zone or layer of material immediately surrounding the bore,also, to an extent, by the length of bore. It is only slightly afiected by thermal characteristics of the electrodes, in-

sulating conduit and its support and the casing at any distance from the active or hot portion of such bore. Long-time current values can, therefore, be increased or decreased by employing the means described for increasing or decreasing escape of heat from the hot spot of the controller and without substantially altering the value of the short-time current. The ratio between invention, suitably designed, it is possible to shorten this naturally excessive time lag to particular for one controller having a long time current carrying capacity in excess of forty amperes l have secured a ratio of short time capacity to long time capacity (on a one minute interval basis) of less than 1.20 in contrast to a. commercially acceptable ratio of about 1.36. The circuit-controlling element shown in Fig. 8 is slightly modified to show how the increase of heat conductivity from the bore outward may be effected. The metal ring of jacket 5 at about the midpoint out the insulating conduit 4 is enlarged in the shape of a. metal band 5' which is substantially integral with jacket 5 but which may be inserted in an annular groove left for it in the porcelain before jacket 5 is applied. This metallic band 5 extends inward toward the hot spot in bore 15 and is of almost any commercially desired value. In

tions 5 on each end of the. jacket 5 are 7 crimped down over an annular shoulder near each end of conduit at after Such jacket is applied to the conduit. The conduit 4 is thus given some longitudinal reenforcement against fracture by jacket 5 that supple-.

ments the radial reenforcement normally effected by this jacket. In the construction shown in Fig. 9 the clamping ears 6' for the support of the conduit 4 and jacket 5 are fastened directly to and made enlargements of 'acket 5 as by welding.

hanges may be made without departing from the invention.

Having thus described my invention, I claim:

1. An electric circuit controller including a casing; a conduit of heat-resisting insulation within the casing; a liquid conductor within the bore of the conduit; electrodes connectible by the liquid conductor; and metal supporting means within the casing and electrically insulated from the electrodes for fixedly supporting said insulating cons duit within the casing. v

2. The structure of claim 1 wherein the supporting means for the insulating conduit is fastened securely to a wall of the casing.

3. An electric circuit controller including a casing containing a quantity of liqud conductor; and control tube, two electrodes capable of being connected by such liquid conductor when in said control tube, one of such electrodes being bent and tubular and communicating with said control tube; a lead-in stud fastened firmly in the casing wall; and means for fastening the tubular electrode to said stud.

4. An electric circuit controller including a casing forming a chamber therewithin; electrode within the casing; a liquid conductor within the casing connecting the electrodes when desired; lead-in members for the current in the circuit to be controlled moulded into and through the casing wall, said casing being moulded of an insulating material and comprising two parts having mating surfaces; and means entirely exterior of said chamber for clamping said surfaces together.

5. An electric circuit controller including a casing; a conduit of heatresisting insulation within the casing; a liquid conductor within the bore of the conduit; electrodes within said casing connectible by said liquid conductor; and a metal shield on one electrode and opposite one end of the bore of said conduit to receive impact from hot gases expelled from the conduit to protect the electric circuit controller including a casing; a conduit of heat-resisting insulation within the casing and mainly s aoed substantially therefrom; a liquid con uctor within the bore of the conduit; electrodes connectible by said liquid conductor; and means having a greater thermal conductivity than the'thermal conductivity of the inshield wit sulating material of said conduit and so applied to the exterior of such conduit as to assist in the conduction of heat from the bore of said conduit to the exterior of the casing.

7. An electric circuit controller including a casing; a conduit of heat-resisting insulation within the casing and mainly spaced substantially therefrom; a liquid conductor within the bore of the conduit; and electrodes connectible by said liquid conductor, one of these electrodes having a heat radiatmg portion positioned out of the line of the predominating path of electrical current flow in the electrode.-

8. An electric circuit controller including a casing; a conduit of heat-resisting insulation within the casing and mainly spaced substantially therefrom; a liquid conductor within the bore of the conduit; and electrodes connectible by said liquid conductor, one of the electrodes having a portion unessential to the flow of current through this electrode, and serving to enlarge the heatconductmg capacity of this electrode for heat flowing from-the conduit bore to the exterior of the casing.

9. An electric circuit controller including a casing; a conduit of heat-resisting insulation within the casing; a liquid conductor wlthin the bore of the conduit, this bore be inclusive of a well at one end for holdmg 'quid conductor; and electrodes connectible by said liquid conductor, one of said electrodes ha a s n-sha ti that extends into well. P

10. An electric circuit controller including a cas1ng; a conduit of heat-resisting insulation within the casing; a liquid conductor within the bore of the conduit; electrodes connectible by said liquid conductor; and. an anchoring member mainly sup rtmg said conduit and carried by a wall of the casing and insulated from said electrodes.v

11. An electric circuit controller including a casing; a conduit of heat-resisting ination within the casing; a liquid conductor within the conduit bore; electrodes connectible b said liquid conductor; and a the casing and opposite one end of the conduit bore to receive impact from hot gases expelled from the conduit to protect the casing.

12. An electric circuit controller including a casing; electrodes within the casing; a liquid conductor within the casing adaptable to connect the electrodes; lead-in members for the current in the circuit to be controlled moulded into and through the casing wall, said casing being molded of an insulating material and comprising two parts having mating surfaces; a cement-like material between said mating surfaces for sealing and holding them together, and a control tube mating surfaces and one of which-parts is of moulded insulating material; and a cement-like material between said mating surfaces for sealing and permanently holding them together; said control tube having a termined maximum current without interrupting the circuit. K

14. An electric circuit controller comprising a casing movable to oil and on positions; a control tube within the casing; a liquid conductor within the casing, a feed tube for collecting liquid conductor from the casing and conveying it into the control tube as the casing is moved from off to on;

3 a supporting member for the control tube to hold it in spaced relation to a wall of the container, the bore of said control tube being inclusive of an enlarged portion at the end opposite the feed tube; and an electrode exposed to make contact with liquid conductor in said enlarged portion of the control tube bore; said electrode being so shaped and spaced within said enlarged portion as to form a passage communicating with said 40 bore and said container andproviding a free discharge port from the control tube to the container.

' 15. An electric circuit controller, comprising a casing movable to .oil and on po- 4 sitions; a control tube within the casing; a liquid conductor within the casing; a metal feed tube for collecting liquid conductor from the casing and conveying it into the control tube as the casing is moved from off to on; a supporting member for the control tube to hold it in spaced relation to a wall of the container," the bore of said control tube being enlarged into a well at the end opposite the feed tube, and an electrode dipping into the liquid conductor in said well.

16. A control tube of insulating material for a circuit controller employing liquid conductor, said tube having a bore calibrated to the magnitude of current which it is desired to control, ametal jacket surrounding a portion of said tube and metal means surrounding said tube and extending inwardly from the outside of the tube toward bore of such caliber as to carry only a prede-V its bore for the purpose of rapidly conducting heat generated within the bore to the outer surface of the tube.

17. A control tube of insulatingmaterial for a circuit controller employing liquid conductor, said tube having a bore calibrated to'the magnitude of the current which it is desired to control and metal means associated with said tube and placed in a reduced portion of the outside of said tube, said metal means serving to rapidly conduct away a portion of the heat generated within said bore.

18. A control tube of insulating material for a circuit controller employing liquid conductor, said tubehaving a bore calibrated to the magnitude of the current which it is desired to control and metal means associated with said tube and placed in a reduced portion of the outside of said tube approximately even with the center of the bore, said metal means serving to rapidly conduct away a portion of the heat generated within said bore.

19. An electric circuit controller including a casing; a conduit of heat-resisting insulation within the casing; a liquid conductor within the bore of the conduit; electrodes connectible by said liquid conductor; and a separable metallic anchoring member mainly supporting said conduit, carried by a wall of the casing and insulated from said electrodes.

20. An electric circuit controller including a conduit assembly formed mostly of heat-resisting insulating material but including a reinforcing metallic band, a liquid conductor within the bore of the conduit, electrodes connectible by the liquid; conductor, and a casing enclosing said elements and leaving around them a space for expansion of the mercury into vapor; the length of said bore between electrodes being at least seven-sixteenths of an inch and the shortest distance which would be traversed by a current such as an are between said band and one of said electrodes being approximately seven-sixteenths of an inch.

21. An electric circuit controller including a conduit assembly formed mostly of heatresisting insulating material but including a reinforcing metallic band, a liquid conductor within the bore of the conduit, electrodes connectible by the liquid conductor, and a casing enclosing said elements and leaving around them a space for expansion of the mercury into vapor; the length of said bore between electrodes being at least seven-sixteenths of an inch and the shortest total distance which a current flowing from one electrode to the other through the band would have to jump by arcing being at least seven-sixteenths of an inch.

STANLEY S. GREEN.

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