US2003260A - Circuit controller - Google Patents

Description

May 28, 1935 s. s. GREEN ZGO CIRCUIT CONTROLLER Filed March 6, 1933 f l l Patented May 28, 1935 yUNITED STATES ,PirlaN'rv OFFICE aooazso omcm'r coN'aoLLEa Stanley S. Green, La Fayette, Ind., asaignor to Duncan Electric Manufacturing Company, La Fayette, Ind., a corporation of Illinois Application March s, 193s, serial No. 659,715

26 Claims.

5 therein a control tube, electrodes on oppositev sides rof the control tube, and a liquid conductor such as mercury to connect the electrodes through the control tube, the construction being such that upon an overload the mercury in the control tube is vaporized, thereby breaking the circuit. The circuit may be re-established by turning the controller to the-*olf position and back to the on position, these movements flowing the mercury back in the control tube. Circuit controllers of this type have been the subject matter of various applications made by the present inventor, the last of which was tiled May 6,

` '1931 (Serial Number 535,401), in'which the former applications are listed. The present applicationv is concerned with an improved circuit controller of this type, and includes numerous renernents.

Numerousobjects are accomplished by this invention, including the prevention of current leaks along the surface of the casing, the provision of a control tube material which is chemically stable under arcing conditions, the minimiging of arcing in the control tube, the provision of more dependable mercury feeding means, the simplification of structure and construction, and the provision of an indicator for showing whether or not the circuit breaker has lbeen blown by an overload, i. e., whether or not an overload has caused it to break the circuit which it controls. I

With these and various other objects in View, the invention may. consist of certain novel features of construction and operation, as will be more fully described andl particularly pointed 40 out in' the specification, drawing and claims appended hereto.

In the drawing, which illustrates an embodiment of the device, and wherein like reference characters are used to designate like parts,

Figure l is a perspective view of one embodiment of this invention without the indicator, and showing the controller unit slightly turned from its normal on position;

, Figure 2 is a vertical view partly in section of the structure in Figure l, showing the controller in its normal on position;

Figure 3 is a view similar to Figure' 2, but showing the controller inthe reverse position and illustrating dinerent details;

Figure 4 is a vertical transverse section substantially through the line 4-4 of Figure 2;

Figure 51s a view similar to Figure 4 but taken substantially through the line 5--5 of Figure 2; Figure 6 is a diagrammatic illustration of the connection of the indicator to the controller.

Although my invention may take many forms, only one has been chosen for illustration. In this form, the assembly comprises the base 2 and the controller 4 pivotally mounted thereon and electrically connected thereto. The structure of the mounting was fully set forth in the application Serial Number 535,401 mentioned above, and r therefore may' be described here with brevity. The main support is furnished through the support terminal 6' to which is pivoted a conductor link 1 which is rigidly secured by a screw or otherwise to a lead-instud 8. This furnishes one path of current to the controller, and the other path extends through the terminal connector I0 to which is pivoted the connector link II which is rigidly secured as by a screw to the second lead-in stud I2. It may be seen that the only pivotal connections-are between themembers 6 and l and the members I0 and II. Both of these connections include relatively large areas of sliding contact, and a firm connection may be insured in each instance by including a spring washer (not shown) on the pivot pin to press one of the sliding members against the other. The terminal supports 6 and I0 are cf course secured as by rivets to the base 2 andare provided with suitable connection screws I4 and I5 as shown, for connecting the controller in the circuit to be controlled.

The general constructionof the controller 4 includes a casing made up of a rear half I6 and the cover half I8, both preferably molded from an insulating material such as thatfknown commercially as Bakelite. These two parts are provided with telescoping ilanges 2li and are preferably sealed together as is hereinafter described. 'I'he cover member I8 may include an upstanding ring 22 which may lit an opening in a metal switch box, a handle 23, and suitable wording such as the words Oi and On" and any other data that may be desired. The rear casing half I8 has molded into it the lead-in studs and an arc by-pass stud described below, which may all haveknurled surfaces for tighter engagement of the -Bakelite".

Within the casing is a control unit which may be designated in its entirety by the numeral 24. This/imit includes the control tube 26, metallic reinforcing jacket 28, the feed tube welded thereto and the insulating coating 3.2. This control unit is supported by the mating shoulders 34 and' 35 formed on the two parts I6 and I8 respectively of the casing which engage the feed tube 3D, and also by the cradles 31 and 38 likewise formed on the two parts I6 and I8 of the casing, and which cradles engage the jacket 28 or its coating 32.

'I'he shoulders 34 and 35 are in the nature of extensive partitions and are so shaped as to'form a passage 40 which is a continuation of the feed tube 30 and which widens out at its mouth to form a funnel 42. Y

'I'he lead-in stud 8 extendsthrough the partition 34 and has secured at its end as by a screw,

Ian electrode 44, which electrode is shaped to extend into the feed tube 30, as shown best in Figvure 2.V The feed tube 30 communicates with a ing of the controller 4. When the controller is in the off position shown in Figure 3 this mercury runs tov the then bottom of the controller as shown in that figure. As the controller is rotated in a clockwise direction from the position shown in Figure 3 to the position shown in Figure 2, the mercury flows into. the funnel 42 by which it is fed into the passage 40, from which'it flows on into the feed tube 30. From the feed tube 36 the mercury is forced into and through the bore 46 of the control tube 26., For low amperage controllers the bore 46 is necessarily of extremely small diameter and oe'rs considerable resistance to the ow of mercury therethrough. For this reason, it is desirable that the passage 40 be of comparatively small diameter, as shown, so that a comparatively small amount of mercury will fill it to the top, thus providing a considerable hydrostatic head of mercury at the entrance to the bore 46, and the quantity of mercury inthe controller should be the amount necessary for this purpose, with perhaps a small reserve in excess thereof. For one form of breaker havingda rating of 10 amperes, 4the diameter of the bore should be approximately 026 inch. To start the mercury into such' a bore a head of. approximately .67 inch is required. For the sake of dependability, it is preferred that the head of mercuryprovided be twice this, or approximately one andone-third inches. Comf' mercially this head is desirably provided for all circuit breakers rated for I6 or more amperes, although a much lower head of mercury could be used dependably for circuit breakers of a higher `ampere rating. For example, a fifty ampere circuit breaker may have a. bore diameter of-approximately .098 inch and a .22 inch mercury head would be twice the 'necessary Obviously, if a circuit breaker were to be rated for less than 10 amperes, a greater head than one and one-third inches might be desired. The now of mercury can be facilitated by tapering the bore slightly, so that it is large toward the upper end, i. e., smaller at the end which the mercury enters. Once the mercury has passed entirely through the bore .46 it will continue flowing therethrough until it reaches a state of equilibrium, usually when the level in the feed tube is the same as the A umns and will therefore raise the temperature 'of' the mercury in the bore 46 until the same vaporizes. The vaporization of the mercury in the'bore will expel some of the mercury from the bore,

with the result that there will be a gap in the mercury column between the electrodes 44 and 50 so that the circuit will be broken between these electrodes. For the sake of simplicity this phenomenon will be referred to as the blowing of the controller, since it corresponds to the blowing of a fuse.v

It is desirable that the feed tube 30 extend at an angle to the bore 46 of the control tube as shown, and that it make a mercury-tight connection therewith, so that once thehbore 46 has been filled with mercury itwill be impossiblefor mercury to flowtherefrom by gravity. In other words, the

feed'tube and control tube together should comprise an inner container so shapedas to retain mercury therein indefinitely, until it is spilled out by manually turning the controller, or until itis blown out by an overload. Because of the explosive force of severe" overloads, it is necessary that the feed tube 30 be strongly Secured to the control tube 26. For these reasons, the bias butt-welding illustrated in Figure 2 is preferred. As is clear from that figure, the feed tube, which is generally curved throughout its length, is severed at its bottom end at a sharp angle. This biased end may then be butt-welded to the corresponding portion of the jacket 28 either by electricity or otherwise. The hole through the jacket 2 8 which permits the mercury to ow from the feed tube to the bore may be formed either before or after the butt-welding. It may be explained that the jacket is previously formed from a flat piece of sheet iron, as by drawing. The discharge end of the iron jacket should be thoroughly insulated to prevent arcing, for reasons described below. There are various forms of insulation that may be used, such as porcelain cement, vitreous enamel, or sleeves of bakelite or mica. It is preferred, however, that the insulation be provided by ,winding asbestos tape around the end'of the jacket in the position shown, soaking this tape in some such material as those known as bakelite lacquer or glyptal lacquer. Afterwards the unit should be thoroughly baked. Such an insulation is easier to apply than the porcelain cement or vitreous enamel and will withstand the Y temperature towhich it is subjected, since the control tube 26 insulates the jacket from the high temperatures occasionally sustained in the bore 46 of the control tube.

thanthose ordinarily encountered commercially have demonstrated the fact that it is possible for the current capacity of such `a circuit cont/roller to varysughtly withcontmued use. -A1thoughl such variations would probably never be enough to be detrimental commercially, it is obviously preferable that they 'be eliminated, or at least minimized to a point where even extraordinary commercial conditions cannot cause a substantial change. There are various causes that might contribute to variations o! current carrying capacity. One of these is a change in the purity of "the mercury and the change in the contact resistance between the mercury and the electrodes which this is likely to cause. Such` impurities may also cause slight changes in the resistance of the mercury itself. Obviously changes in electrical resistance in the controller, whether they be increases or decreases, change the amount of heat generated in the controller for a given current ow and thus vary the accuracy of rating although such effects are, as mentioned before, small and secondary' in their nature. Mercury has a very high anty for many foreign substances,vand it is therefore desirable that such substances be avoided. lAll of the metal parts which are exposed to the mercury are therefore preferably made of the purest iron that can be attained commercially. It may be mentioned that this iron is also desirable because it has a higher .electricall conductivity than other iron. 'I'he lead-in studs 8 and I2 may be made of copper or brass, since they are completely embedded in the Bakelite and therefore are not exposed to the mercury.

Another possible cause of variation in currentcarrying capacity is the enlargement of the bore 46 of the control tube. It may be explained that this bore is subjected to severe attack; first, by the hot mercury as it is being heated in the bore, and subsequently by mercury vapor after a break has occurred, and to some extent at least by arcing which takes place through such vapor at the moment of the breaking of the current, particularly when a heavy current is broken. The most severe of these attacks is the arcing. Oscillo- \graphs taken on the breaker as it opens a-heavy current, show clearly that the duration of the electric arc in the bore is very shortof the order of 1/60th of a second in most cases, or even less in others. The arc temperature is such that if long continued it would vaporize surface portions of the control tube bore and thus Wear it away by a mechanical or burning action. If such were the case, however, control tube substances having the highest using or volatilizing temperatures should exhibit the greatest resistance to such arc erosion or wear. .In my experiments I have found this by no means to be always so. Such measurements of bore erosion have been very delicate and tedious because even for hundreds of current interruptions, the amount of erosion in a given bore of a given control tube material is very small. My results indicate that diierent ceramic substances have quite different erosion-resisting properties and this resistance is moreclosely connected with its chemical composition than with its physical properties such as the boiling or Vaporization point.

At the temperature of the electric arc the chemical 'reactions between the substance of the control tube and the other substances which may be present becomes of great importance. Among the other substances which can be present in addition to the mercury are the gases enclosed in the circuit breaker chamber such as air, the metal of the electrodes and impurities. that one of such substances could act as a catalyzer or intermediary agent in some chemical action which would deteriorate the walls of the tube. To eliminate as many variables as possi- It is possible ble, experiments have been made using commercially pure iron for electrodes and with all other materials as pure as possible and with control tubes of a wide variety of different substances. The commercial names of some of these substances are herewith listed in approximately the order of their erosion-resisting property: lava, quartz, crolite #445, Pyrex glass, and sillimanite. Of the substances named, I prefer lava, as it has the greatest erosion-resisting properties; lava being the commercial name of an artificially prepared ceramic. It may have slightly diifering characteristics and appearance depending upon treatment and source of supply. The grade which I prefer, however, has a body which is composed of talc, which is a silicate of magnesia; feldspar, which is a silicate of aluminum, and a carbon binder. The body, after being formed, is kilned at approximately 2500" F., and the carbon binder burns out. Crollte #445, which is also erosionresistant, but not to the same degree as lava. also contains magnesia silicate as two-thirds of its total weight is a multiple magnesia silicate comprising silica magnesia and alumina.

Sillimanite, which, among those mentioned, gives the least desirable (although still commercially satisfactory) results, is analuminum silicate (AlzOSiOz). There are of course many other materials which may be used, but those listed are among the ones known to be satisfactory, at least if pureiron is the only metal exposed, and if pure distilled mercury is used.

Arc minimizing Since any chemical action or erosion takes place principally during arcing of the mercury, it is of course desirable that the arcing within the control tube should have as short a duration as possible. For this reason an arc shunt is provided. This shunt comprises a plug 60 molded into the casing half I6 and extending therethrough to a point close to the electrode 50 and which is connected to the lead-in stud 8 as by a coiled resistance Wire 62 which may be located inv a channel 64 provided therefor. In order to carry the current of a severe overload, this Wire should be fairly heavy and might conveniently be made of iron. When such an arc shunt is provided, however, it is necessary that it be so restricted as to be harmless and not self-sustaining. Putting a resistance 62 into the circuit is of some aid in this connection. It is preferred, however, that the arc be restricted by covering over all of the plug 60 but its end, with a shield, such as lthe fiber bushing 66. When such a ber bushl ing is used, as shown, so that the exposed ,area of the plug is kept sufticientlysmall, the resistance coil 62 may be replaced by a substantially non-resisting conductor. vIn this form a stud of .078 inch diameter, not closer to the electrode than .30 inch, has been found satisfactory up to volts. Of course these factors are all interrelated. and any arc by-pass stud arrangement that is so restricted that the arc dies quickly would be satisfactory in this respect. There may be considerable leeway beyond the dimensions given by way of example.

It may be explained that, from the standpoint of effectiveness, the shunt Willprcbably function properly as long as it is closer to the electrode 50 than is any other exposed conductor which is connected with the electrode 44. When there is severe overload liquid mercury is blown entirely out of the control tube 26 so that as long as the plug 60 is closer to the electrode 50 than the length of the bore of the control tube, the arc will take the path ofv least resistance, and

-jump between the electrode' 50 and the plug 60 rather than through the controlytube.4 'This transfers a large part of the harmful arcing during the short period when such arcing exists, outside of the control tube bore where it can do no harm. The plug 60 may be considerably shorter than that shown, and, in fact,may be shorter than the bushing 66.' --In this event, the plug would be exposed only at its end, and that at the bottom of the hole in'the bushing, so thatY the arc would-be well restricted.

It may be noted at this point thatit is -also necessary to make some provision to prevent arcing between the electrode 50 andthe metallic 'jacket 28. It is for this purpose that the ins- Prevention of the surface current leaks Although the material known "as Bakelite is admirably suited for the formation of thecasing,

it is theoretically-possible for the exposed surface of this material to become so carbonized that it will conduct current. For this reason it is preferred that there shouldbe no path between the two electrodes or other conductor connected thereto which is entirely along the Bakelite surface. It is for this reason that the ber bushing 54 is provided between the electrode 50 and the Bakelite casing. It is not necessary that this bushingbe madeof ber, as it may be made of any material which does not becomeconductive under any circumstances.' The material known commercially as lava or almost any ceramic material will also answer this purpose. If the `electrode 50 does not interlock with the well of the control tube 28 in suchmanner as to prevent the electrode from swinging outwardly to contact the peripheral wall of the casing, then' the bushing 54 should be especially shaped to prevent `such movement of `the electrode 50, or a special stop of a similar material may be provided f elsewhere. The asbestos washer 56 is used simply to provide a mercury-'tight seal so that no' mercury can get under the ber bushingf54 and complete a path from'the screw 52 to some exposed portion of the-Bakelite surface.

With v'such a construction, it is obvious that there is nocontinuous exposed Bakelite surface connecting the two electrodes, no'r connecting any conductor which is connected'with the electrode 50 to any conductor connected with the electrode 44. The possibility of the occurrence of'objectionable surface current-leaks is thereforeV completely overcome.

- v Assembly The final assembly of the parts is quite simple.

The two casing halves I6 and I8 are molded according to the standard practice for such Bake-` lite parts,the diameter being approximately 2.5

inches. However,` the inale half 'is molded originally tobe approximately .008,to .010 inch larger in diameter than the female half. In thiscondition the male half cannot-go into the female half ,without breaking'it. The parts, however, are

-theiessl it is subject ,to material shrinkage by further and complete curing. The male half of/ the casing/*is therefore cured substantially to the stabilization point by baking severalhours ata temperature inexcess of ninety to o'ne hundred degrees cen. whichvshrinks it sufficiently for it to fit within the femalev half. Some cement," such as vBakelite varnish is then applied to the mating surfaces and also the exterior of the feed tube '30, where it engages the-partition members 34,

and to the cradles 31'and 38; the female member is pressed in place, and the entire assembly is then baked suiiiciently to cure the female half ofthe casing, which, during the'curing process, shrinks down over the male half, as the male half does not shrink as much, if at all, during this ,nal curing.;Y One half of the casing may be provided Awith a sealing channel 68 which may be filled with the varnish, and which is maintained in a position to retain" the varnish during the entire operation. i As a nal operation, the metal band 10, previously flanged along one edge, is forced over the assembled controller and spun around the other edge into engagement1 with the controller,`as shown best inFigure 5. This band 10 may be made from the same iron that is used for the jacket 28since in this pureform it will be rust-resisting. Asa matter .of fact, from the standpoint of commercial practice, it is desirable to form the jacket out of that portion of the metal which is cut from the center of the band.

The controller is now ready to be mounted on the base, in accordance with the description of this ounting'alrea'dy given.

Indicator Because of the nature of this controller, there is no visible change to indicate when a controller has been blown. It follows, therefore, that if there are anumber of such controllers grouped 'together lt will not be obvious to a person un` familiar-with the circuits, which one of them may be blown out in a given instance. Although thisy often would be no handicap, since it would merely be necessary to turn the two or three suspected controllers on and then on again, yet, in some instances it may be desirable to have some means -Aan inch and sealed into a'small glass tube which contains a "luminous gas at such pressure that a glow may be obtained by small voltages, at least as low as' 100 volts, and with infinitesimal currents. f Such a glow tube 'may be connected across the terminals of the controller, .as illustrated in Figure 6, one or both of the connections between the glow tube and the controller including a resistance 18 which preferably has a value of around 100,000 ohms. This high resistance limits the current which 'can pass through the glow tube to such a small value that it is harmless to the tube as well as harmless and negligible in the circuit which is beingcontrolled. As a matter of. fact, the glowtube of theindicator described is so sensitive that with alternating current it can be .glow tube is substantially zero.

operated on the capacitance of the wires in an open circuit, so that'even though the short circuit -no longer exists, and-even though the circuit is not otherwise completed the glow tube will glow as a result of the difference of potential between the terminals Il and I5 ofthe controller when the mercury 'columrr' has been interrupted.

Unless special provision were made, such a tube would glow even when the controller was manually turned to the off position. This would ordinarily be objectionable; however, since it is preferred that the indicators glow only whenthe controller has been blown, not when it has been manually turned off. This result is accomplished according to the present vinvention by connecting the glow tube through .a contact 14 which is only.

connected with the terminal of the controller when the controller is in an on position. Thus with the circuit controller` turned even slightly away from the on position,Av as shown in Fig--A ure l, and as shownl diagrammatically in Figure 6,the contact 1I is not connected in the controlled 'circuit andthe glow tube 16 therefore would under no conditions be illuminated. However, if the controller is turned fully to the on position, the connector link il engages the contact 14 and completes the 'circuit to the glow tube 16, but as the glow tube 16 is normally connected acrossan .uninterrupted column of mer' cury, the potential across the electrodes of the On the other hand, if an overload occursso that the mercury column is broken and the circuit interrupted, the potential across the electrodes of the glow tube will be suiiicient to illuminate the same.

It is to be understood that many other rembodiments of the' invention, including some-in improved form, will vbe apparent, and in the course of time more will be devised by those skilled in the art. -It is not desired thatthis invention be limited to the details described, for its scope includes all such forms orimprovements as come within the spirit of the following claims, construedr as broadly as the priorart will permit. Especially it is to be noted that although the various novel features described herein have their greatest value when all areI used together, yet each may be used without any or with onlysome of the others.

What is claimed is:

l. A liquidvconductor current limiting circuit controller including? a control tube made of heat resisting insulation and having a current limiting bore therewithin, a casing surrounding said con,- trol tube and formingv an expansionfchamber with which said bore communicates suitably for the passage of a liquid into said bore, a pair rof electrodes, a suitable quantity of liquid conductor within said container, ,said container including tube by anoverload will be prevented from reconnecting said electrodes except upon operation 2. A liquid conductor current limiting circuit controller including: a 'control tube made o! heat resisting insulation and having a current limiting bore therewithin, a casing surrounding said control tube and forming an expansion chamber with which said bore communicates suitably for the passage of a liquid into said bore, a pair of electrodes, a suitable quantity of liquid conductor withinsaid container, said container including means for flowing said liquid conductor into said bore and into contact with said electrodes to electrically connect said electrodes lengthwise through said bore, the shape and arrangement of said container and control tube being such that liquid conductor expelledfrom said control tube by an overload will be prevented from reconnecting said electrodes except upon operation of said means; said controller being characterized by the fact ithat the casing is formed in part of a material which becomes conductive under certain conditions, andthe lead-in portions of said electrodes exposed within said casing are insulated from one' another by a material which has the quality of maintaining substantially itsfull insulating qualities in spite of its exposure vto high temperatures and to hot gases in contact with its surface. f

3. A liquid conductor current limiting circuit controller including: a control tube made of heat resisting insulation and having 'a current limiting bore therewithin, a casing surrounding said control tube and forming an expansion chamber with which said bore communicates suitably for the passage of..a liquid into said bore, a pair of electrodes, a suitable quantity of liquid conductor Within said container, said container including meansfor flowing said liquid conductor into said bore and into contact with said electrodes to electrically connect said electrodes lengthwise through saidfbore, the shape and arrangement of said container and Vcontrol tube being such that liquid conductor expelled from said control tube -by an overload will be prevented from reconnecting said electrodes except upon operation of said means; said controller being characterized by the fact that the casing is formed in part of a material which becomes conductive under certain conditions, and the portions of said electrodes exposed within said casing when not connected by said liquid conductor are insulated f rom` one another by a solid material which retains substantially its full insulating properties during control tubeand forming an expansion chamber with'which said bore communicates suitably for the passage of a liquid into said bore, a pair oi electrodes, a suitable quantity of liquid conductor within said container, said container including meansfor ilowing said liquid conductor into said bore and into contact with said electrodes to electrically connect said electrodes lengthwise through said bore` the shape and arrangement of said container and control tube being such that liquid conductor expelled from said control tube" by an overload will be prevented from reconnecting said electrodes except upon operation of said means and; means to minimize arcing in said bore when current is interrupted therein.

5. A liquid conductor current limiting circuit controller including: a control tube made of heat resisting insulation and having a current limiting bore therewithin, a vcasing surrounding said control tube and forming an expansion` chamber with which said bore communicates` suitably for the passage of a liquid into said bore,

a pair of electrodes, a suitable quantity of liquid conductor within said container, said container including means for owing said liquid conductor into said boreI and into contact with said electrodes to electrically connect said electrodes 10A lengthwise `through said bore, the shape and arrangement of said container-and control tube being such that liquid conductor expelled from said control tube by an -overload will be prevented .r from reconnecting said electrodes except upon operation of said means; and means to minimize arcing in said bore when current is interrupte therein, comprising an arc by-pass.

6. A liquid conductor current limiting circuit controller including: a control tube madeof heat resisting insulation and having a current limiting bore therewithin, a casing surrounding said control tube and forming an' expansion chamber with which said bore communicates suitably for the passage of a liquid into said bore, a pair of g electrodes, a suitable quantity of liquid conductor within said container, said container including means for flowing said liquid conductor into said bore and into contact with said electrodes to elec; trically connect said electrodes lengthwise through said bore, the shape and arrangement of said container and control tube being such that liquid conductor expelled from said control tube by an overload will be prevented from reconnecting saidl electrodes except upon operation of -said means; and means to minimize arcing in said bore when current is interrupted therein comprising an arc b y-pass electrically connected to one electrode andJ located so close to the other electrode that an arc will jump more readilyl be- 40 tween the last named electrode and said by-passf controller including: a control tube made of heat resisting insulation and having a current limiting bore therewithin, a casing surrounding said control tube and forming an expansion chamber Y with which said bore communicates suitably for the passage of a liquid intosaid bore, apair of electrodes, a suitable quantity of liquid conductor within 'said container, said container including means for owing said liquid conductor` into said bore and into contact with said electrodes to electrically connect said' electrodes lengthwise e through said bore, the shape and arrangement of said container and control tube being such that liquid conductor expelled from said control tube by an overload will be prevented from reconnecting saidrelectrodes except upon operation of said means; and means to minimize arcing in said bore when current is interrutped therein comprising an arc by-pass electrically connected to one .electrode and located so close to the other Ielectrode that an arc will jump more readily between the last named electrode and said by-pass than -between said last named electrode and the liquid conductor electrically connected to Athe other electrode, and arc restricting means oicring such resistance to the arcing to said by-puss I that the arcing is not self-sustaining.

8. A liquid conductor current limiting circuit controller including: a control tube made of heat resisting insulation and having a current limiting bore therewithin, a casing surrounding said concluding means for flowing said liquid conductor into said-bore and into contactwith said electodes to electrically` connect said electrodes lengthwise through said bore, the shape and arrangement of said container and control tube being suchthat liquid conductor expelled from said control tube vby an overload will be prevented from reconnecting said electrodesxcept upon operation of `said means; and meansto minimize arcing in said bore when current is interrupted therein comprising an arc by-pass electrically connected to one electrode and located so close to the other electrode that an arc will jump more readily between the last named electrode and said by-pass than between said last named electrode and the liquid conductor electrically connected to the other electrode, and arc restricting means oieringsuch resistance to the arcing to said by-v pass that the arcing is not self-sustaining, said means comprising insulation for covering all but a small exposed area of the part of said by-pass which would otherwise be accessible to an arc.

9. liquid conductor current limiting circuit controller including: a control tube made of heat resisting insulation and having a current limiting bore therewithin, a casing surrounding said control tube and forming an expansion chamber with which said bore communicates suitably for the passage of a liquid into said bore, a pair of electrdes, a suitable quantity of liquid conductor within said container, said container including means'for owing said liquid conductor into said bore and into' contact with said electrodes to electrically connect said electrode lengthwise through said bore, the shape and arrangement of said container and control tube being such that liquid conductor expelled from said control tube by an overload will be prevented from reconnecting said electrodes except upon operation of said means; and means to minimize arcing in said bore when current is interrupted therein comprising an arc by-pass electrically connected'to -one electrode and located so close tothe other electrode that an arc will jump more readily between the last named electrode and said by-pass'than between said lastnamed electrode and the liquid conduc-v tor electrically connected to the other electrode, and arc restricting means oiering such resistance to the arcing to said by-pass that the arcing is not self-sustaining, said arc restricting means comprising-a resistance in said by-pass.

10. A liquid conductor current hunting circuit controller including: a control tube madel of heat resisting insulation and having a current limiting bore therewithin, a casing surrounding said control tube and forming an expansion chamber with which said bore communicates suitably for the passage of a liquid into said bore, a pair of electrodes, a suitable quantity of liquid conductor within' said container, said container including means for owing said liquid conductor into said bore and into contact with said electrodes to electrically connect said electrodes lengthwise through said bore, -the shape and arrangement of said container and control tube being such that liquid conductor expelled from said control tube by an overload will be prevented from reconnecting said electrodes except upon operation of said means; and means to`minimize arcing intsaid bore when current is interrupted therein v welded to said jacket.

comprising an arc by-pass electrically connected to one electrodel and located so close to the other electrode andvsaid by-pass that an arc will jump more readily between the last named electrode and said by-pass than between said last named electrode and the liquid conductor electrically connected to the other electrode, and arc restricting means offering such resistance to the arcing to said by-pass that the arcing is not self-sustaining, said arc restricting means comprising a resistance in said by-pass and insulation for covering all but a small exposed area of the pai-t of said bypass which would otherwise be accessible to an arc. i

1l. A liquid conductor current limiting circuit controller, including: a. control unit including ,a control tube made of heat resisting insulation and having a current limiting bore therewithiri, a casing substantially surrounding said control unit and forming an expansion chamber withv which said bore communicates at both ends, a pair of electrodes, a suitable quantity of liquid conductor within said container, said controller including means for flowing said liquid conductor into said bore and into contact with said electrodes to electrically connect said electrodes lengthwise through said bore, the shape and arrangement of said container and control unit being such that liquid conductor expelled from said control tube by an overload will lbe prevented from reconnecting said electrodes except upon operation vof said means; said control unit including a metallic jacket surrounding and reinforcing said control tube, and a metallic feed tube integrally secured to said jacket and communicating with said bore. Y

l2. A liquid conductor current limiting circuit controller, including; a control unit including a control tube made of heat resisting insulation and -having a currenty limiting bore therewithim a casing substantially surrounding saidcontrol unit and forming an expansion chamber with which said bore communicates at both ends, a pair of electrodes, a suitable quantity of liquid conductor within, said container, said controller including means for iiowing said liquid ,conductor into said bore and into contact with said electrodes to electrically connect said electrodes lengthwise through said bore, the shapeI and arrangement of said container and control unit being such that liquid conductor expelled from said control tube by an overload will be prevented from reconnecting said electrodes except upon operation of said means; said control unit includ;- ing a metallic jacket surrounding and reinforcing said control tube, and a metallic feed tube' integrally secured to said jacket and communieating with said bore, said feed tube beinglbutt- 13. A liquidconductor current limiting circuit controller,'including: a control unit including a control tube made of heat resisting insulation and having a current limiting bore therewithin, a casing substantially surrounding said control unit and forming an expansion chamber with which said bore communicates at both ends, a pair of electrodes, a suitable quantityof liquid conductor within said container, said* controller includ- -ing means for flowing said liquid conductor into said bore and into-contact witlisaid electrodes to electrically connect said electrodes lengthwise,

that liquid conductor expelled from said .control tube by an overload will be prevented from reconnecting said electrodes except upon operation ,of said means; said control unit including a metallic jacket surrounding and reinforcing Asaid control tube, and a metallic feed tube integrally secured to said jacket and communicating with `said bore and extending from said jacket at an angle to said bore. c

14. A liquid conductor current limiting circuit controller, includingz a control unit including a control tube made of heat resisting insulation and having aV current limiting bore therewithin, a

casing substantially surrounding said control unit and forming an expansion chamber with which said bore communicates at both ends, a pair of elactrodeaa suitablefiquantity of liquid conductor within said/container, said controller including means for flowing said liquid conductor into said bore and into contact with said electrodes to electrically connect said electrodes lengthwise through said bore, the shape and arcontrol tube made of heat resisting insulation and having a current limiting bore therewithin, a cas'- ing substantially surrounding said control unit and forming an expansion chamber with which said bore communicates at both ends. a pair of electrodes, a suitable quantity of liquid conducf' tor Within said container, said controller including means for owing said liquid conductor into said boreH and into contact with 'said electrodes to electrically connect said electrodes lengthwise through said bore, the shape and arrangement of said container and 4control unit being such that liquid conductor expelled from said control tube by an overload will be prevented from reconnecting said electrodes except upon operation of said means; said control unit including a metalflic jacket surrounding and reinforcing said control tube, and a metallic feed tube integrally secured to said jacket and communicating with said bore, and insulation surrounding the portions of said jacket close to the electrodefon the opposite side of said control tube from said feed tube.

i 16. A liquid conductor current limiting circuit controller, including: a control unit including a control tube made of heat resisting insulation and having `a current limiting bore therewithin, a casingfsubstantially surrounding said control unit and forming an expansion chamber with which said bore communicates at both ends, a pair of electrodes, a suitable quantity of liquid conductor within said container, said controller including means for flowing Vsaid liquid conductor into said bore and into contact with-said electrodes to electrically connect said electrodes y lengthwise through said bore, the shape and arrangement of said container and control unit being such that liquid conductor expelled; from said control tube by an overload will be prevented from reconnecting vsaid electrodes except uporfi" operation ofxsaid nreans; said control unitJ including a metallic jacket surrounding and reinforcing said control tube, and a metallic feed tube integrally securedA jacket close to the electrode on the opposite side v of, said control." tube from said'feed tube, said insulation comprising a heat resisting insulating material wrapped around said jacket.

17. A liquid conductor current limiting circuit controller, including: a control unit including av control tube marie of heat resisting insulation and having a current limiting bore therewithin, a cas- -ing' substantially surrounding said control unit and forming an expansion chamber with which said bore communicates at both ends, a pair of electrodes, a suitable quantity of liquid conductor within said container, said controller including means for vilowing said liquid conductor into said bore and into contact with said electrodes to electrically connect said electrodes lengthwiseI through said bore,.the shape and arrangement of said container. and control unit being such that liquid conductor expelled from said control tube `by an overload will be prevented from reconnecting said electrodes except upon operation of said means; said control unit including a metallic jacket surrounding and reinforcing said control means, and a metallic feed tube integrally secured to said jacket and communicating with said bore, and insulation surrounding the portions of said jacket close to the electrode on the opposite side of said control tube from said feed tube, said insulation comprising a heat resisting jnsulating material wrapped around said jacket, and a heat resisting and insulating lacquer impregnating said material. Y

18. A liquid conductor current limiting circuit *controller manually operable as a switch including: a casing, a control unit, a pair -of electrodes located within said casing, said electrodes being electrically connected to controller terminals and being electrically connectible by liquid conductor in said control unit, said control unit being constructed to cause said mercury to flow therefrom and interrupt the ow of current between said electrodes both in response to an overload and in response to manual operation of said controller, and a space discharge tube connected across said controller terminals, said discharge -tube being operable at the voltage of the circuit controlled by said controller, and contact means for disconnecting said tube when said controller is manually'operated rto disconnect the electrodes therein.

19. A liquid conductor current hunting circuit controller manually -operable as a switch in cIuding: a casing, a control unit, a pair of elec-fy conductor in said control unit, said control unit being constructed to cause said mercury to ow therefrom and interrupt the ow of current between said electrodes both in response t'o an overload and in response to manual operation of said bore therewithin, va casing surrounding said con-I trol tube and forming a'n expansion chamber with which said bore` communicates suitably for the passage of a liquid into said bore, a pair of electrodes, a suitable quantity of liquid conductor within saidl container, said container including means for iiowging said liquid conductor into said bore and into contact with said electrodes to electrically connect said electrodes lengthwise through said bore, the shape and arrangement of said container and control'tube'being such that liquid conductor expelled from said control tube by an overload Will be prevented from reconnecting said electrodes except upon operation of said Y means, said controller being'chara'cterized by the fact that the control tube is formed of'a particular non-porous material and that the liquid conductor and the elements with which it comes in contact and by which it may become contaminated are substantially free of any substances which would have a chemical reaction with said particular material of which the contlIQl tube is made under the conditions oi their contact.

21. A liquid conductor current limiting circuit controller including: a control tube made of heat resisting insulation and having a current limiting bore therewitliima casing surrounding said control tube and forming an expansion chamber with .which said bore communicates suitably for the passage vof a'liquid into said bore, a pair of electrodes, a suitable quantity of liquid conductor within said container, said container including means for iiowing said liquid conductor into sai". bore and into contact with said electrodes to electrically connect said electrodes through said bore, the shape and arrangement of said container and control tube being such that liquid conductorexpelled from said control tube by an overload will be prevented from reconnecting said electrodes except' upon operation of said means; said controller being characterized by the fact that the control tube is composed chiefly of talc which. has been kilned ata temperature in excess of 1900 F.

22. A liquid conductory current limiting circuit controller-,in'cluding: a control tube made of heat resisting insulation and lhaving a current limiting bore therewithin, -a casing surrounding said control tube and forming an expansion chamber with which said bore communicates suitably for the passage of a liquid into said bore, a pair of electrodes, a suitable quantity gf liquid conduc` tor within said container, said container including means lfor owing said liquid conductor into saidbore and into contact with said electrodes to electrically connect said electrodes lengthwise through said bore; theshape and arrangement of said container and control tubel being such that liquid conductor expelled from said control tube by an overload will be prevented from reconnecting said electrodes except upon operation of said means; said controller being characterized by the fact that the control tube is formed of a ceramic substance composed principally of silicate of magnesia and silicate of aluminum.

23. A liquid conductor current -limiting circuit controller including: a control tube made of heat resisting insulation and having'a current limiting bore therewithin, a casing surrounding said control tube and forming an .expansion chamber with which said bore communicates suitably for the passage of a liquid into said bore, a pair of electrodes, a suitable quantity of liquid conductor within said container, said container lengthwise agooaseo including means for iiowing said liquid conductor into said bore and into contact with said electrodes to electrically connect said electrodes lengthwise through said bore, the'shape and arrangement of said container and control tube beof a ceramic substance composed prlncipallyof Yao silicate of magnesia and silicate of aluminum with the silicate of magnesia predominatlng in quantity.

24. A liquid conductor current limiting circuit controller including: a control tube made of heat i resisting insulation and having a current limiting liquid conductor expelled from said control tube by an overload will be prevented from reconynecting said` electrodes except upon operation of said means; said controller being characterized by the fact that said casing isformed of telescoping parts, the female portion of which is shrunk upon the male portion.

- 25. As an article of manufacture, an unnished liquidconductor current limiting circuit controller including: a control tube made Yof heat resisting insulation, and having a current limiting bore therewithin. a casing surrounding said control tube and forming an expansion chamberwith which said bore communicates suitably for the passage of a liquid into said bore, a pair of electrodes, a suitable quantity of liquid conductor within said container, said container including means for ilowing said liquid conductor into said bore and into contact with said electrodes to electrically connect said electrodes lengthwise through said bore, the shape and arrangement of said container and control tube being such that liquid conductor expelled from said control tube by an overload will be prevented from reconnecting said electrodes except upon operation of said means; said controller being characterized by the fact that the male portion is substantially fully shrunk as by baking, while the female portion is materially less completely shrunk, and of such size'that if fully shrunk. lt would be too Small t0' receive the male portion. i

26. `A liquid conductor current limiting circuit controller `manually operable as a switch including: a casing, a control unit, a pair of electrodes located within said casing, said electrodes being electrically bconnected to controller terminals and being electrically connectible by liquid conductor in said control unit, said control unit being constructed to cause said mercury to flow therefrom and interrupt the ow of current between said electrodes both in response to an overload and in response to manual operation of said controller, means .for connecting a space discharge tube across said controller terminals, and contact means for disconnecting said tube when said controller is manually yoperated to disconnect the electrodes therein.'

. STANLEY B. GREEN.

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