[0001] This invention concerns electrical circuit breakers of the type employing a positive
make and break (PMB) bimetal. Such a PMB bimetal comprises a compensator fastened
to a U shaped armature. Example of such circuit breakers are disclosed in U.S. patents
2,585,068, 4,521,760, 4,636,766 and 4,663,606.
[0002] In the past, the compensator was always made narrower than the U shaped armature.
See, for example, column 4, lines 65-68 of 2,585,068 and column 2, lines 12-16 of
4,521,760. Such an arrangement was satisfactory when the rated ambient temperature
for the circuit breaker was not too high, say, 85
oC.
[0003] However, we have found that for a higher rated ambient temperature, say, 125
oC, the compensator should be about the same width as the U shaped armature.
[0004] In the drawing, Fig. 1 is a plan view and Fig. 2 and 3 are front and side elevational
views of one example of a circuit breaker in accordance with this invention.
[0005] As shown in Fig. 1, the circuit breaker comprises a compensator 1 fastened, such
as by welding, to a terminal 2 at one end, the other end of compensator 1 being fastened
to a U shaped armature 3. U shaped armature 3 has a shorter leg 4 and a longer leg
5. Compensator 1 is fastened to the end of shorter leg 4. There is a contact 6 at
the end of longer leg 5. Contact 6 is, during normal operation, in physical and electrical
contact with a fixed contact 7 mounted on terminal 8.
[0006] In Fig. 1, the upper surface of compensator 1 is the low expansion layer of the bimetal
and the lower surface is the high expansion metal. Thus, as the temperature of the
circuit breaker increases, the end of compensator 1 which is fastened to U shaped
armature 3 tends to move upwards, thereby increasing contact pressure between contact
6 and contact 7. For U shaped armature 3, the high expansion layer is the inner surface
of the U and the low expansion layer is the outer surface. Thus, as the temperature
of the circuit breaker increases, the contact end of U shaped armature 3 tends to
move downward, thereby decreasing contact pressure between contact 6 and contact 7.
When the circuit breaker reaches its rated opening temperature or current, the opening
pressure of U shaped armature 3 overcomes the closing pressure of compensator 1, and
contacts 6 and 7 separate, thereby opening the electrical circuit.
[0007] In one example, compensator 1 was 17 mils thick by 550 mils long by 218 mils wide.
U shaped armature 3 was 20 mils thick by 218 mils wide and had an overall length of
1121 mils. The length of longer leg 5 was about 680 mils and the length of shorter
leg 4 was about 420 mils.
[0008] Terminals 2 and 8 were embedded in and protruded through, a plastic base 9. The bottom
portions of terminals 2 and 8 can be plugged into a suitable electrical receptacle.
[0009] In operation, upon electric current overload, the circuit breaker will open and stop
current flow. The circuit breaker will then cool, the contacts will close, and current
flow will resume. Thus, this type of circuit breaker can be called a cycling circuit
breaker.
1. An electrical circuit breaker comprising: a bimetal compensator having a high expansion
layer and a low expansion layer, one end of the compensator being fastened to a first
terminal and the other end of the compensator being fastened to a U shaped bimetal
armature, the armature having a high expansion layer and a low expansion layer, the
low expansion layer being on the outer surface of the armature and the high expansion
layer being on the inner surface of the armature, the armature having a shorter leg
and a longer leg, the compensator being fastened to the armature at the end of the
shorter leg thereof, the high expansion layer of the compensator being in contact
with the low expansion layer of the armature, the longer leg of the armature having
an electrical contact fastened thereto, said electrical contact being in electrical
and physical contact, when the circuit breaker is closed, with a fixed contact mounted
on a second terminal, the width of the compensator being substantially equal to the
width of the armature.
2. The circuit breaker of claim 1 wherein the two terminals are embedded in, and protrude
through, a plastic base.
