US1809673A - Electrical protective device - Google Patents

Description

June 9,1931.

H. E. BUTLER 1,809,673

ELECTRICAL PROTECTIVE DEVICE Filed May 21, 1930 figl.

--L mmma His Attorney Patented June 9, 1931 UNITED STATES PATENT OFFICE HENRY E. BUTLER, OF SCOTIA,'NEW YORK, ASSIGNOR '10 GENERAL ELECTRIC GOM- IPANY, A CORPORATION OF NEW YORK Application filed May 21, 1930. Serial No. 454,499.

My invention relates to protective devices used in electrical circuits to prevent excessive flow of current therethrough.

In electrical circuits where a plurality of,

burns out, the condition is met with that when a lamp burns out and its cut-out operates, the resistance of the circuit is lowered by an amount equal to that of the lamp filament burned out, which results in an increase in the amount of current flowing through the circuit, the effect of which is to cause the remaining lamps to burn' outmuch sooner. This is particularly true in the small series lamp circuits used for Christmas tree lightmg.

One object of my invention is to provide for use in connection with a string of lamps connected in series, the lamps being provided with cut-outs, an automatic current limiting device which, when a lamp burns out, operates to insert in the series circuit a resistance of a value such as to limit by the desired amount the current which will flow in the circuit. The resistance may be of a value substantially equal to the resistance of the lamp filament in which case the remaining lamps will burn with their normal brightness, 01 the resistance may be somewhat greater than the resistance of the filament, for example, 10% greater, in which case the remaining lamps in a series circuit will be 5 dimmed somewhat, thus indicating that there is a lamp in the string which has burned out.

A further object of my invention is to provide an automatic current limiting device which is simple in structure, effective in operation, easy to manufacture, and which may be used in place of the plug cap disposed at the terminal end of a string of series connected lamps. For a consideration of what I believe to be novel and my invention attention is directed o: the following description and the claims pended thereto. p the accompanyingdrawings showing il'];us'trative embodiments of my invention, {and in which the same numerals refer to the ends are threaded inwardly through persimilar parts in the several views, Fig. 1 is a diagrammatic illustration of a series lamp circuit with a device embodying my invention connected therein; Fig. 2 is a longitudinal view in section of a device shovving'one embodiment of my invention, and Fig. 3 is a longitudinal view in section showing a modified embodiment thereof. I

In Fig. 1 of the drawings, 28 indicates a number of incandescent electric lamps connected in series, each lamp being provided with a cut-out 29 which, in case the filament of a lamp burns out, operates due to the increased voltage to which the lamp is then subjectedto closeashuntcircuit around the lamp. Any suitable lamp structure embodying a cut-out may be used. The cut-out indicated in the present instance may comprise a wire coated with oxide, for example, a copper wire coated with copper oxide, and connected '10 across the leading-in wires of the lamp, Normally, the oxide acts as an insulator but, in case the lamp is subjected to increased voltage such as occurs in case a filament burns out, the oxide breaks down thus forming a shunt circuit across the leading-in wires of the lamp. It will be understood that the type of lamp and cut-out shown is only illustrative but my invention may be carried out in connection with any type of lamp provided with a cut-out.

Referring to Fig. 2, 4.- represents a cylindrical casing molded or formed out of a suitable insulating material, and having the left end closed by an integral end piece 5. The right end is closed by a disc'6 which fits snugly within the end of the casing.

A helical groove 3 is cut or formed around the outside of casing 4 intermediate its ends. A length of resistance wire 7 having a known resistance, for example, a resistance equal to or of an order about ten percent greater than the resistance of one of the lamps forming the circuit is wound in the helical groove 6 and forations which pierce the casing at the ends of the helical gro0ve.

Contacts 8 adapted to be inserted into a standard plug or service outlet extend outwardly through spaced apertures in the end 5.

The upper contact is provided by an inner lug 9 which acts as a shoulder to abut against the inner face of end 5. The lower contact is the continuation of a horizontal metal strip 10 which has an upwardly projecting offset 11 forming a shoulder, which abuts against the inner face of end 5. The contacts are held rigidly in place by having rings 12 forced over the outer end of each contact and inwardly until they abut against the outer face of end 5, where by frictionally gripping the outer surface of the contacts 8 they prevent any axial movements thereof. The strip 10 is bent transversely upwards at its right end to form a flange 13 against which the disc 6 abuts and where it is held in place by a terminal screw 17 passing through a perforation' therein, the head abutting against the outer face of the disc and the end of the shank being threaded into a tapped hole through the flange 13.

In order to have a series cutout or contact member sensitive to small increases in current, such as would be caused by the burning out of one of the lamps, a thin metal thermostat 14 is soldered or braced to the lug 9. The thermostat extends from the lug downward to about the axis of the casing 4 where it is bent transversely and extends axially toward the right for the greater length of the inner casing, where it makes contact with spring 14. The thermostat is of such cross section that when the current flowing through it exceeds a predetermined amount, it is adapted to bend upward, breaking the electri cal contact between it and spring 15. Spring 15 is attached to the upper inner face of disc 6 by a nut 17 which is threaded on a terminal screw 16 which passes through the aligned perforations in the disc 6 and in the upper end of spring 15, the head of the screw abut ting against the outer face of disc 6. Spring 15 extends downward along the inner face of disc 6 to a point in axial alignment with thermostat 14 where it is bent transversely inward.

The end of thermostat 14 is curved slightly upward, while the end of spring 15 is curved slightly downward, thereby facilitating the assembling of the protective device.

The series cut-out must be sov arranged that the electrical circuit will not be broken when the thermostatic cut-out opens. To effect this end, and at the same time limit the current within the lamp circuit and thus protect the lamps still burning, the left end of resistance wire 7 is soldered to the lug 9 while the right end is soldered to the nut 17, thus connecting the resistance wire in parallel with the thermostat in such a mannerthat when the thermostat bends upward due to the heating caused by the flow of'excessivecurrent therethrough opening the electrical current through it, the resistance 7 will be in series with the lamps.

To provide a dependable means for keeping the series cut-out open when a lamp has burned out, or after the series cut-out has operated, a small armature 18 having an end flange 19, which is soldered to the top of thermostat 14, extends upwardly and out through a radial hold in the casing 4. A small ring magnet 20 surrounds the armature 18 and is securely held within an inner enlarged portion of the aperture through which the armature projects. A second flange 21 is attached to the armature 18 at a point just below the lower face of ring magnet 20, and at a distance where magnetic attraction is a little less than that sufficient to pull armature 18 and the flange 21 upward against the tention of the thermostat.

One of the terminals 22 of a string of series connected lamps is connected to the terminal screw 16 while the other is connected to-the terminal screw 17 preferably by looping the ends around the shanks of the screws before they are tightened into place, although other securing means may be used. The terminal wires 22 pass out through a small aperture in the end of a bell shaped cover 23 which has an inner left end diameter adapting it to fit tightly over the recessed end portion of ms ing 4 where its left end abuts against an annular shoulder 24 at the inner end of the recessed section, thereby making a smooth continuous outer surface at the point of juncture. The cover is held in this position by friction, thus making the terminals and series cut-out accessible when installing or repairing.

Fig. 3 shows a cut-out similar to that above described with the exception that the thermostat 14 (Fig. 2) is replaced by a spring 25 comprising two metallic sections held in spaced relation by a piece-of insulating material 26 to which the adjacent ends are riveted. The electrical circuit through the spring is completed through a coil or solenoid 27 which surrounds the armature 18. The field strength of solenoid 27, when the normal amount of current is flowing through it, is not suflicient to create a magnetic attraction between flange 21 and magnet 20 which is strong enough to bend spring 25 upward, but a small increase of current, such as would result from the burning out of a lamp will increase this magnetic attraction sufliciently to overcome the tension of the spring 25 and pull it upwardsufliciently for the flange 21 to make contact with the fixed magnet 20, which is then strong enough magnetically to attract the flange with a force greater than the tension of the spring pulling downward.

The' operation of the series cut-out is as follows: When one of the lamps 28 (Fig. 1)

burns out, the instantaneous potential rise {resulting therefrom breaks down the resistance barrier in the cut-out 29 which is disposed between the terminals of the lamp burning out and which completes a circuit by-passing the burnt out lamp filament. Due

to the fact that the resistance of the circuit is now reduced by an amount equal to the resistance of the burnt out filament, an increase 5 of current proportional to this'decrease flows through thermostat 14 causing it to bend upward which brings flange 21 into contact with the ring magnet 20 which is stron enough magneticallyto hold the flange an thermostat in this position. When thermostat 14 moves'upward it breaks contact with spring 15 thus putting the resistance wire 7 in series with the lamp circuit, which -pro ortionally reduces the amount of current owing through the remaining lamps. When a new lamp is substituted in place of the one burned out, armature 18 is ressed downward to again complete the circuit through the thermostat 14 and spring 15. a

The cut-out shown in Fig. 3 works in the same manner with the exception that the upward bending of spring 25 is due to the increased magnetic attraction created by the increased flow of current through the solenoid 27.

While I have shown, illustrated and described certain embodiments of my invention, it will be understood that it is not limited to the exact details shown, but is capable of modification and variation within the spirit of the invention and within the scope of the appended claims.

What I claim' as new and desire to secure byLetters Patent of the United States, is:

1. In combination, a string of incandescent lamps connected in series, a cut-out connected across the filament terminals of each lamp, a resistance, and means actuated by the increase in current caused by the burning out of any one of said lamps and the .operation of its cut-out, to efiect the insertion of said resistance into the series circuit.

2. In combination, a string of incandescent lamps connected in series, a cut-out connected across the filament terminals of each-lamp, a resistance, and a thermostatic contact member actuated by the increase in current caused by the burning out of any one of said lam s and the operation of its cut-out, to effect t einsertion of said resistance into the series circuit. I

3. The combination with a string of incandescent lamps connected in series, and a cut one of said terminals contacts carried by the body and normally iorming a shunt circuit around said resistance, and current actuated means for separating said contacts.

5. A wiring device comprising a body having a pair of plug terminals, a resistance carried by' the body, and means carried by the body for eifecting automatically the insertion of said resistance in series with one of said terminals when the current flowin through the terminals exceeds a predetermined high value.

In witness whereof, I have hereto set my hand this 20th day of Ma 1930.

HENR BUTLER.

out connected across the filament terminals of I each lamp, of a combined \plug terminal and resistanceconnected to said string of lamps, said resistance being normally disconnected from-the series circuit, and means actuated by the increase in current caused by. the burning out of any one of said lamps and the operation of its cut-out for efiecting the insertion of said resistance into the series circuit.

i -A wiring device comprising a body having a pair of plug terminals, a resistanc'ecara5 ried by the body and connected in serieswith

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