US1120212A - Protective device for electric circuits. - Google Patents

Description

A. v. A. McHARG. I PROTECTIVE DEVICE FOR ELECTRIC CIRCUITS. APPLICATION FILED NOV. 28,1918.

1,120,212. Patented Dec. 8, 1914.

UNITED STATES PATENT OFFICE.

ARTHUR v. A. McHARG, or NEW YoRK, N. Y., ASSIGNOR TO THOMAS E. MURRAY, or NEW YORK, N. Y.

Specification of Letters Patent.

Patented Dec. 8, 1914.

. Application filed November 28, 1913. Serial No. 803,521.

To all whom it may concern:

Be it lmown that I, ARTHUR V. A. Mo- HARG, a citizen of the United States, residing at New York, in the county of New York and State of New York, have invented a certain new and useful Improvement in Protective Devices for Electric Circuits, of which the following is a specification.

The invention is a protective device for electric circuits. It embodies a novel principle, namely, interrupting an electric circuit by destroying by heat electrically generated in said circuit, a body of destructible material, by means of which body terminals of said circuit are held in contact, and thereby permitting said terminals to separate and break said circuit. This principle may be embodied in many different forms of ap paratus. I herein illustrate one practical and eflicient form wherein a movable switch member normally retracted by a spring is held in circuit closing position against the resiliency of said spring by means of a fuse or stop of material destructible by heat, whlch stop is then in contact with a con- (luctor mounted on said switch member and in circuit. Upon the development of an overload current on the circuit, said conduo-tor becomes heated and in turn heats and so destroys the stop. The switch member then being released is retracted to open circuit by the spring. In this way, the circuit is protected from the efl'ects'of said overload current by a fuse or body of destructible material which is not in the circuit.

In the accompanying drawingsFigure 1 is a longitudinal section of my protective device on the line w, m of Fig. 2. Fig. 2 is a horizontal section on the line 3 y of Fig. 1. Fig. 3 is an elevation of the bridge-carrying extremity of the switch lever. Fig. 4 is a Ifnodified form of the destructible stop or ise.

Similar numbers of reference indicate like parts.

1 is a base of insulating material, 2 is a switch lever also of insulating material. Upon the upper side of said lever is a metal plate 3, integral with which are lateral side ieces 4 which are bent over and receive the liody of the switch lever between them. The lever is supported on a shaft 5 of insulating material journaled in plates 6. secured to the base 1, with which plates the side pieces 4. make contact. On the under side of lever 1 near the end thereof is a stirrup-shaped plate 7. When the lever is in circuit-closing position, as shown in Fig. 1, the plate 7 enters between the arms of a contact clip 8 secured to base 1. Extending outwardly fr om the end of lever 2 is a bridge conductor 2 in loop form. One end of said conductor is 1n electrical contact with plate 3. The

' other end is in electrical contact with the front edges of plate 7, said end being widsued to extend across said edges and being secured in place by the screw 10 entering lever 2, as shown in Fig. 3.

11 is a standard having a threaded recess in its upper end to receive the head of screw 12, which enters base 1. Between the shank of screw 12 and standard 11 is a clearance so that said standard may freely turn on said shank. The recess in standard 11 is interiorly threaded to receive the screw plug 13 which is on the end of an insulating rod 14. Rod 14 has a flange l5 and at its upper end a head 16 by which it can be rotai ed. The standard 11 supports a toothed disk 17 of fusible metal or other material destructible by heat, which disk has a central opening to receive the plug 13, so that when the plug is in place, the disk is clamped between the flange 15 and the top of standard 11.

On the switch lever 2 is an upwardly extending arm 18, to which is attached one end of the helical retracting spring 19, the other end of said spring being secured to base 1. Circuit wires 21, 20 are respectively connected to plates 6 and clip 8. A boxshaped cover 22 is provided having an opening for the passage of the head 16 and a slot in one of its walls and extending to the edge thereof for the admission of shaft 5. This slot is closed when the cover is in place by a plate 23 secured on the base 1 and provided on its upper edge with a semicircular recess receiving shaft 5. A handle 25 is secured on the end of shaft 5 which projects outside of the cover.

The operation is as follows: The cover being preferably removed, the screw plug 13 is Withdrawn from the standard 11, the disk 17 is put in place on said standard, and the plug 13 is reinserted to clamp the disk 17 firmly between the standard and flange 15. The lever 2 is then brought into circuit closing position, the bridge 9 passing through one of the spaces between the projections on the disk. The lever being retained in thisv position by the operator, the head 16 is rotated until one of said projections '24 comes directly above the bridge 9. The lever is then released, but is held from rising under the pull of spring 19 by the projection 2% with which the bridge 9 becomes held'in contact. The bridge 9 is to be so proportioned as that it will conduct a predetermined normal current without becoming hot enough to fuse or destroy the holding projection, but to become heated to a sufficient degree to destroy said projection upon the occurrence of any selected overload current. To this end, it may be made of higher resistance than the rest of the circuit. The destruction of said holding projection then releases lever 2 which is immediately thrown up, as indicated in dotted lines, Fig. '1, out of clip 8 by the action of spring 19, thus "breaking the .circuit and so protecting any devicestherein included from the eifects of said increased current.

In order to reset the apparatus, the disk 17 is rotated by head 16 until another projection on said disk comes into position toengage bridge 9, and obviously the resetting may be repeated as many times as there are projections on said disk. When all of said projections have in turn been destroyed, a

new disk is to be substituted.

wires comes directly over the bridge 9, and

acts as a stop to prevent retraction of the lever. by spring 19. This wire on the occurrence of an overload current becomes fused, releasing the lever, as alreadydescribed.

ll claim:

1. A fixed circuit terminal, a'movable circuit terminal cooperating therewith, resilient retracting means. for said movable teral,'a plurality of devices for holding ma am said movable terminal in predetermined position with reference to said fixed terminal against the resiliency of said retracting means, means for moving said devices successively into engagement with said movable terminal, and means for heating said devices to destroy the same to release said movable terminal 2. A fixed circuit terminal, a movable circuit terminal 'cocperating therewith, resilicut retracting means for said movable terminal, a plurality of stops for holding said movable terminal in predetermined position with reference to said fixed terminal against the resiliency of said retracting means, means for moving said stops successively into engagement with said movable terminal, and means controlled by an overload current on said circuit for destroying said stops.

3. A movable switch member divided into two mutually insulated sections, resilient retracting means therefor, a bridge of conducting material of higher resistance than said sections and connecting said sections, and means in contact with said bridge for holding said memberin circuit closing position against the resiliency of said spring; the said holding means, upon the heating of said bridge by current on said circuit, being destructible to release said movable member to open said switch.

4. A movable switch member divided into two mutually insulated sections, resilient retracting .means therefor, a bridge of conducting material of higher resistance than said sections: connecting .said sections and projecting front-mid switch member, and a stop in contact with said bridge for holding said member in circuit closing position against theresiliency of said spring; the said.stop, uponthe heating of saidbridge by current on said circuit, being fusible to release said movable member to open said switch.

In testimony whereof I have afixed my signature in presence of two witnesses.

T3HUR V. A. Moi ii Witnesses:

' Gnnrnunn T. PORTER,

YT. McGr.

Images