US1996720A - Electrical resistance unit for overload relays, etc. - Google Patents

Description

April 2, 1935.

B. E. GETCHELL ELECTRICAL RESISTANCE UNIT FOR OVERLOAD RELAYS, ETC

Filed Oct. 5, 1932 2 Sheets-Sheet l GET HELL INVENTOR BENJAMIN April 2, 1935. B. E. GETCHELL ELECTRICAL RESISTANCE UNIT FOR OVERLOAD RELAYS, ETC

Filed Oct. 3, 1932 2 Sheets-Sheet 2 INVENTOR BENJAMIN E.GETCHELL Patented Apr. 2, 1935 1,996,720

-UNI TED STATES PATENT OFFICE- ELECTRICAL RESISTANCE UNIT FOR OVERLOAD RELAYS, ETC.

Benjamin E. Getchcll, Plainville, Conn. assignmto The Trumbull Electric Manufacturing Compang, alainvllle, Com, a corporation of Connec on M Application October 3, 1932, Serial No. 835,913

4 Claims. (Cl. 201-63) My invention relates particularly to electrical sometimesthe entire switch must alsobe replaced. protective switching devices for apparatus of the The principal object of my invention is to procharacter described in my copending application vide a practical and efllcient automatically oper- Ser. No. 524,652, which issued as Patent 1,886,477, d means which will insure t blowing f the 5 November 8, 1932. fuse instantly in case of a short circuit on the 5 Such constructions include manually controlled line and before any harm can be done to the circuit making and breaking apparatus together switch mechanism or its correlated parts. with a thermostatically actuated device including Another object is to pr vide an auto a ca a heater or resistance element for automatically p r vice of this har r which will n 1 p ning the circuit upon overload. These devices Only protect the heater element and the switch are usually called enclosed or safety switches. p ts b will al o gr y reduce h fire hazard In installing switches of this type, it has been which is characteristic of devices of this type.

the usual practice to protect the switch from Another object is to provide a means which short circuit by means of a fuse of approximately w l h t n he n h 01 the 1 caused y E four times the rating of the heater element but it h rt circuit so as to greatly reduce its GXDIOSiVB 15 is frequently desirable to install such switches in fl'ec and destructive force. gangs of from five to fifteen with a, single fuse Another object is to provide an automatically in the circuit to protect the entire installation perated'means for accelerating the blowing of and such an installation requires a fuse of such a protective fuse so as to reduce the danger of large capacity that it will not protect the heater damage to th switch 1 other correlated DB 20 element from burning out in the event of a short Another object is to provide automatically opcircuit, Such gauging installations are permitted erated protectingmeans for the switch and its by the underwriters provided the fuse is arranged correlated parts and including an easily renewto blow an open the circuit quickly enough to able and relatively inexpensive heater unit.

prevent the are caused by the automatically op- Another object is to provide a heater unit so 25 "erated elements from damaging the switch mechdesigned as to localize or confine ionization beanism or causing a fire hazard outside of the entween its respective terminals in such a manner closing box. Usually, in the event of a short cirthat the are between the terminals will be of cuit,.the heater element will be burned out and suflicient intensity to insure the instantaneous rendered inoperative but, in some instances, the blowing f & correlated fuse but in whi h he 30 intensity and volume of the arc will be great ration and destructive force of the arc is not great enough to actually destroy the operating mechaenough to harm the switching mechanism with nism of the switch. which it is associated.

The underwriters require that such a burning I accordingly arrange the heater unit and its out must not cause sufllcient flash to ignite absupport in such a manner that, in case of a 35 sorbent cotton outside of the enclosing box. They short circuit on the line, the circuit will be dialso require that the switch, per se, shall remain verted or shunted from its normal path through operable in spite of the burning out of the heater the coils of the heater and a flash-over will occur element. between the opposed portions of the relatively In constructions of this character and with a heavy terminals of the unit and this flash-over 40 large fuse in series with the heater the resistance or are will permit substantially full short cirof the heater, as a rule, is the greatest factor of cuit conditions to pass through the fuse and blow resistance in the circuit and consequently holds it before the are between the terminals of the down the current momentarily in proportion to its heater unit assumes sufiicient magnitude to inresistance and this reduction in current to a jure the adjacent switch parts and without sufll- 45 value much below the short circuit intensity, recient flash to cause injury inside of the switch tards the blowing of the fuse and in the event box or to blow out'through any normal openings of a short circuit, the heater becomes incaninthe box or its cover. descent and ionizes the air surrounding the heater The opposed portions of the terminals of the and its terminals and a flash-over will take place heater unit are spaced apart one thirty-second of 50 which usually destroys the heater element and an inchor less for the purpose of making the sometimes burns the adjacent parts so as to renlength of the are very short and a slotted insuder the switch inoperative. Obviously, under lating plate or strip of mica or equivalent insuthese conditions, at least a new heater element lating material is interposed between the opposed must be provided after each short circuit and portions of the terminals, the purpose of the slot 55 being to definitely locate the point at which the,

arcing will occur and also to limit the width and laterally spreading tendency of the arc.

The slot or opening in the mica or insulating plate which determines the point at which arcing will occur is positioned adjacent the heavy portions of the opposed terminals and away from the relatively light and easily ionized coil of the heater.

From the foregoing, it will be clear that I have provided for a very short arc between relatively heavy metal terminals, at a definite point and within an area so restricted that the flash of the arc is kept down to the minimum and thus prevented from spreading enough to cause damage to the coil windings or other parts.

7 Fig. 1 shows one type of enclosure for a switch or relay of my invention.

Fig. 2 is a front view of the interior construction embodying my invention.

Fig. 3 is a side view and vertical section showing parts of the switch m r. .mand the thermostatic relay.

Fig. 4 is a vertical sectional view sho one of the switch units with thermostatic strip device andheater in place.

Fig. 5 is a perspective view of the removable heater unit.

Fig. 6, Fig. 7 and Fig. 8 are mthe heater unit.

Fig. 9 is an exploded pe of the heater unit.

The box it for enclosing the race may be of any suitable to.

The conducting parts are preferably mounted upon an insulating H. The station-x2 contacts i2 and is may be of suitable type and are adapted to be connected by a o at swi member id of any suitable type actuated manually by any suitable mec 71.1 a" such as a lever it: which projects outside oithe w is pivoted at 56 to a i it supported by the The movable switch members 66 are carried by a cross bar is which is no cutwardly by a spring 69. latch so is pivoted at 2! and connected by a link 82 to the lower end of the lever 23. The lever 28 is connected atits upper end by a link 2% to the cross bar is and at an intermediate portion is a pin or roller 25 which slides in an inclined slot 2&3 in the operating lever i 5. When the outer end of the lever 85 is pressed upwardly the pin 25 is forced toward the right, as viewed in 3. lhe lower end of the lever 23 being stationary at this time of course the upper end with the link 25 is pushed in y so as to bring the movable switch member id into electrical engagement with the conts it and It to close the circuit, the parts being held in this position by engagement of the pin 25 in the notch 2i.

The normal electric circuit is completed from the contact E3 to the terminal 28 the strip '29, anchor member 39 and heater coil 30. This coil is mounted on the arm 32 but insulated from it by layers of mica 33, one end oi? the coil being secured at 34 to the arm 32 and the other end of the coil being secured to the rivet 3b which also serves to anchor the l strip 29 to the insulating block 86. This insulating block 36 also carries the anchor piece 3b which is secured to it by rivet 31. The insulating block 35 is secured at one of its ends to the insulating base ill by views of r a screw 38 and the other end oi the block is seby means of screw 38' in such a manner that the block Ii and the attached heater 3| may be readfly removed as a completely assembled commercial unit. The'bi-metallic thermostatic strip 40 has one end secured to the anchor piece 4| which is secured to the base II by screw 42. The other end 01' the thermostatic strip is adapted to warp or flex with changes in temperature due to the current flowing through the coil 3|. The member. is pivoted at 44 and has an arm 45 which coacts with the pawl of the latch '20 when the parts are in their normal running position. A rod 46 extends through the members 40 and 43 and may be in the form of a screw with a nut ll so that the eil'ective length of the rod may be adjusted. A spring 48 on this rod holds the parts yieldingly in a normal running position.

In case there is a sufiicient overload the bimetallic strip 40 bends sufliciently to release the trip member 45 from the latch 20 thus permitting the mechanism of the switch to operate and open the circuit.

The parts to and 28 are separated from each other preferably by a space or gap of or an inch or less. A layer of insulation 33 is preferably interposed between the two members 30 and 28 except'at the point 50 where there is an opening or slot at of relatively small and narrow di-- mensions and, in this restricted space arcing may take place when the coils of theheater have come to a sufiicient temperature to permit ionization to break down the resistance or the air gap and start an arc. The instant this arcing takes place the load is shunted around the heater and passes between the opposed'portions of the unit te and the impulse of this are permits a surge in the circuit through the fuse which will blow and open the circuit before the arc has w sufllcient destructive force to injure the heater element, the switch or its operating parts.

This heater unit is preferably made removable so that in case it is w-gedit may be readily rep.

While these heater units are preferably y replaceable, they may-serve to are over to open the circuit in case or short circuits before being rendered inoperative or destroyed.

As previously indicated, the prime object of unit is to provide a readily removable unit which constitutes a positive means for blowing a fuse on short-circuit conditions without injury to the switch or its operating means, but obviously the means employed for limiting, c i' on and restricting the arc caused by a short circuit may be used to advantage in other similar constructions or for r purposes without departing from the spirit or scope of invention.

1. In an overlrelay an ting support, a conducting bar secured thereto and constituting one to 1 w of the relay, a second conducting bar constituting another to u .1-

of the relay in a plane substantially P rpendicular to the plane of the first bar, a resistance wire wound around one of said bars but insulated therefrom and having its opposite ends electrically connecting said bars, said bars having portions fixedly spmed approximately one thirty-second oi an inch apart from each other to permit arcing between said bars under certain circuit conditions. J

2. In an overload relay, a heater unit including an insulating block, a conducting. bar secured thereto and constituting one terminalof the relay and projecting at substantially right angles from the general plane of the block, a second conducting bar constituting another terminal of the relay secured to the block and in a plane substantially parallel to the plane of the block, a resistance wire wound around one of the bars but insulated therefrom and having the opposite ends of said wire electrically connecting said bars, said bars having portions definitely spaced apart from each other to permit arcing under predetermined circuit conditions.

3'. As an article of manufacture, a heater unit for an overload relay including an insulating support, a conducting bar securedthereto and constituting one terminal and projecting at substantially right angles from the general plane of the block, a second conducting bar constituting another terminal secured to the block, a resistance wire wound around the first mentioned bar but insulated therefrom and having the opposite' spaced apart from each other to permit arcing between said bar's under predetermined circuit conditions.

4. In an overload relay, a heater unit including an insulating support, an angular conducting bar having one arm secured thereto and constituting one terminal of the relay and having another arm projecting at an angle from the general plane of the support, a second conducting bar constituting another terminal of the relay and secured to the support and in a plane generally parallel to the plane of the support, a resistance wire wound around the projecting arm but insulated largely therefrom, the opposite ends of said wire electrically connecting said bars, said bars having portions adjacent said support spaced apart from each other at a distance just sufilcient to permit arcing under certain predetermined conditions.

BENJALUN E. GETCHELL.

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