CA2070469A1 - Molded case circuit breaker load terminal assembly - Google Patents

Abstract

MOLDED CASE CIRCUIT BREAKER
LOAD TERMINAL ASSEMBLY

ABSTRACT OF THE DISCLOSURE
A molded case circuit breaker of the type employing a thermal-magnetic trip unit to interrupt circuit current utilizes a flexible electrical braid conductor to connect between the thermal-magnetic trip unit and the movable contact arm. The braid connects to the bimetal within the trip unit by means of an angular metal conductor. The terminal lug connects to the opposite end of the bimetal by means of the load strap. The an-gular metal conductor and the load strap are stamped to form protrusions which assist in welding to the bimetal. The load terminal lug is provided with a collar to facilitate welding to the load strap.

Description

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MOLDED CASE CIRCUIT BREAKER
LOAD TERMINAL ASSEMBLY

BACKGROUND OF THE INVENTION
U.S. Patent 4,513,268 entitled ~Automated Q-Line Circuit Breaker" describes a molded case residential circuit breaker employing a thermal-magnetic trip unit to aut~omatically sense over-current circuit conditions and to automatically interrupt circuit current accord~
ingly. The thermal magnetic trip unit electrically connects with the movable contact arm by mean~ of a braid conductor to pr~vide movable ele ::trical connec-tion. The bimetal within the thermal-magnetic trip unit is composed of a number of layers of different metals which complicates the welded connec~ions between the bimetal and the load strap as well as between the bimetal and the braid conductor.
A~ter the load terminal lug i5 welded or brazed to the load strap, the opening throug~ the lug must be re~tapped to remove the molten flux and metal material from the threads. The re-tapping operation deters from high speed automated assembly of the circuit breaker components.

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Accordingly, one purpose of th~ inv~ntion is to fa~
cilitate welding or brazing of the circuit breaker bimetal to the load strap and braid conductor. Another purpose of the invention is to eliminate the re-tapping of the load terminal lug after attachment to the load terminal strap.

SUM~ARY OF THE INVENTION
Both the circuit breaker load terminal strap and the bimetal connector are punched to form protrusions which assist in the welding or brazing of the load s~rap and the bimetal connector to the c:ircuit breaker bimetal.
The circuit breaker threaded load terminal lug is formed with a collar to prevent the welding or brazing material from contaminating the threads during the welding or brazing pr~cess.

: BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a front view o~ a molded case circuit in-terrupter according to the prior art with the cover re-moved to display the circu.it breaker operating compo-nents Figure 2 is a side perspective view of the circuit breaker bimetal~ load terminal assembly and braid conduc-tor prior to attachment o~ the bimetal in accordance with the invention; and Figure 3 i5 a side perspective view of the bimetal, load terminal assembly and braid conductor of Fi~ure 2 after attachment.

DESCRIPTION OF THE PREFERRED EMBODIMENT
A molded case circuit breaker 10 i5 depicted in Figure 1 and consists of a plastic base 11 which incorpo-rates a load terminal lug 12 at one end of the case and a line terminal lug 13 at an opposite end for connection within an electrical power distribution circuit. As de-scribed within the aforementioned U.SO Patent 4,513,2~8, an operating mechanism 14 including the pivotally-mounted cradle operator 15 terminating in a cradle hook 16 at one end and in a cradle pivot 19 within a journal recess 41 at an opposite end is used to automatically interrupt circuit cu~rent. The circuit current can be manually in- :
terrupted by means of the handle operator 17 that inter-acts with the operating mechanism by means o~ the operat-ing crad~e tab 18. The operating spring 20 becomes over-centered when the h~ndle operator is moved ~etween "ON" and ~FF~ positions. The thermal-magnetic trip unit 21 which ca~tains the magnetic core 22 and pivotally-mounted armature 23 interrupts circuit current .20 under intense ~hort circuit overcurrent conditions~ The compre~sion spring 24 adjusts the sensitivity of the armature 23 to provide calihration ~unction. The latch 25 is a slotted opening in the armature which receives the cradle hook 16 under quiescent current operating conditions to re~train the operating mechanism from interrupting the circuit current. The bimetal ~7 interrupts the circuit current upon so-called "long time"
and "short time" overcurrent conditions by flexing in response to predetermined overcurrent conditions for , :, -3~

predetermined periods of time and rotates the armature 23 by contacting the core 22 which interacts with the armature by means of the hook projection ~8. The rotation of the armature 23 removes the latch 25 from the cradle hook 16 and allows the movable contact arm 29 which carries the movable contact 30 at one end to sepa-rate from the fixed contact 3~ which is attached to the fixed contact arm 31. The cradle operator 15 rotates about the cradle pivot 19 which is located within the journal recess 41 formed within the circuit breaker case as described earlier. As further described with the aforementioned U.S. Patent 4,5:L3,268, electrical connection is maintained between the movable contact arm 29 and the bimetal 27 by means of a flexible braid conductor 33.
The attachment between the load strap 26, braid con-ductor 33 and movable contact arm 29 is best seen by re-ferring now to the arrangement depicted in Figure 2. The load terminal lug 12 is shaped such that a collar 40 up-standing from the lug sits within the thru-hole 39 formed within the offset bottom part 38 of the load strap. A
thin washer or disc 41 of braze or Elux material i5 posi-tioned around the collar 40 to facilitate welding or brazing the load lug ~o the load strap. It is noted that the provision of the collar within the thru-hole effec-tively prevents any of the flux or molten metals from flowing into tha inner threaded portion 12A of the load terminal lug, To facilitate welding or brazing the load strap to the bimetal strip ~7, a pair of protrusions 37A

- 5 - 41PR-6~90 are punch-formed on ~he ends of ~he top part 37 of the load strap~ During the welding or brazing operation, the protrusions penetrate through the surface layers of the bimetal 27 under pressure exerted during the welding or brazing process and promote the transfèr of heat between the bimetal and the load strap resulting in a good elec-trical and mechanical connection between the bimetal and the load strap. In a similar manner, the angled connec-tor 34 to which the end 33A of the braid conductor 33 is welded, is punched to form a protrusion 34A which affectively penetrate~ the surface of the bimetal during the welding or brazing attachment of the angled connector to the bimetal. The opposite end of the braided conducto~ is fitted with a strain relief spring 36 before baing welded or braided to the end of the movable co~tact arm 29.
The bimetal 27 is shown attached to both the braid conduc~or 33 and load strap 26 in Figure 3. The interior : threads 12A of the load lug 12 are free of any flux or metal ma~erial and the top par~ 3~ of the load strap is fixedly secured to the top part of the bimetal. The angulated conductor 34 at one end of the braid conductor is fixedly secured to the bottom of the bimetal and, the opposite end of the braid conductor i~ fixedly secured to the movable contact arm 29 to ensure a good electrical and mechanical connection.
Means have been describe~ herein for effective weld-ing or brazing a circuit breaker bimetal to the immedi-ately adjacent circuit breaker components and for wel~ing .
, -- 6 -- 41PR-6~90 or brazing the circ:uit breaker load lug to the load strap .

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Claims (11)

1. An improved circuit breaker bimetal connection and load lug connection of the type consisting of a thermal-magnetic trip unit interconnected between a load strap and a flexible braid conductor wherein the improvement comprises:

said load strap having first and second ends, said first end having a first protrusion formed therein facilitating welding or brazing said first end to said bimetal.

2. The improved bimetal connection of claim 1 wherein said second end includes means defining an aperture and a threaded load terminal lug is attached to said second end subjacent said aperture, said lug including a collar projecting from a top surface thereof.

3. The circuit breaker of claim 1 including an angulated connector attaching said braid conductor to said bimetal.

4. The circuit breaker of claim 3 wherein said angulated connector includes a second protrusion formed therein facilitating welding or brazing said angulated connector to said bimetal.

5. The circuit breaker of claim 2 wherein said collar extends partially within said aperture.

6. The circuit breaker of claim 5 including a disc of braze or flux material interposed between said lug and said second end.

7. The circuit breaker of claim 6 wherein said disc is positioned on said collar.

8. A method of attaching a circuit breaker bimetal to a flexible metal braid conductor comprising the steps of:

providing a flexible metal braid conductor and a planar bimetal strip;
welding or brazing said braid conductor to one end of a shaped metal conductor;
forming a protrusion on an opposite end of said shaped conductor;
positioning said protrusion against one end of said bimetal strip; and welding or brazing said opposite end of said shaped conductor to said bimetal strip.

9. A method of attaching a circuit breaker line terminal lug to a load terminal strap comprising the steps of:

providing a metal lug having an internally-threaded aperture extending therethrough and a load strap having a through-hole at one end:
forming a collar on said lug concentric with said aperture;
positioning said collar within said aperture; and welding or brazing said lug to said strap.

10. The method of claim 9 including the step of inserting a disc of flux material around said collar prior to inserting said collar within said aperture.

11. The invention as defined in any of the preceding claims including any further features of novelty disclosed.