Breaker overheating

[iwire]

How's that?

Seems good to me.

 

[zog]

If you think I twisted your words than tell me again about how a standard breaker will or will not protect about ground faults without trying to make me or anyone else look stupid.

I explained it pretty clearly already.

Well I guess we are even as I have been tired of your condescending attitude with everyone for a long time.

Talk about the pot calling the kettle black.

 

[zog]

How about a simple explanation: The trip mechanism will trip when it reaches a certain temperature.

Current and externally-supplied heat both contribute to the mechanism reaching that temperature.

The greater the externally-supplied heat, the less current needed to reach the tripping temperature.

Ambient temperatures and heat from poor connections both contribute to externally-supplied heat.

How's that?

That is all correct. Now here is the issue and the reason I regrettably posted to this thread. Sustained heating, from something such as a high resistance connection can permantly change the charteristics of the bimetallic strip in the thermal element, the metals, as all metals do, have thermal memory, and will tend to retian thier shapes. This will cause the trip charteristics of a thermal breaker to change following a condition as the OP described. That is why I suggested testing the breaker, or replacing it, before saying everything was fixed.

 

[Volta]

... as all metals do, have thermal memory, and will tend to retian thier shapes. This will cause the trip charteristics of a thermal breaker to change following a condition as the OP described. That is why I suggested testing the breaker, or replacing it, before saying everything was fixed.

That's reasonable.

 

[busman]

That is all correct. Now here is the issue and the reason I regrettably posted to this thread. Sustained heating, from something such as a high resistance connection can permantly change the charteristics of the bimetallic strip in the thermal element, the metals, as all metals do, have thermal memory, and will tend to retian thier shapes. This will cause the trip charteristics of a thermal breaker to change following a condition as the OP described. That is why I suggested testing the breaker, or replacing it, before saying everything was fixed.

I can't find a reference to a condition of "thermal memory" referring to a "permanently change the characteristics" of a metal in a circuit breaker. The references I can find are all similar to this one, that describe the fact that the temperature of the bi-metallic strip does not instantly reset itself after a change in conditions. We've all seen this when the first breaker trip on overload takes minutes. You reset it immediately and it trips again in seconds because the strip is still hot. I doubt that the situation the OP described would cause any permanent damage to the CB. The heat at the terminal caused it to trip at a lower setting, but I don't see any evidence that the heat was sudden enough to cause damage to the CB element.

There is no doubt that heat can change the properties of metals, but if a CB gradually reaches it's tripping temperature (not current), it should not be damaged. Just one man's opinion.

Thermal Memory
Because the thermal product relies on heat as its reference point for tripping and so if the Bi-Metal strip is cold then before it can start to work it must be warmed up, slowing down it's response time. The amount of deviation that the Bi-Metal strip moves is directly proportional to the % of heat (over current, ambient temperature and parasite heating) it is measuring. The hotter it gets the more the deviation. Now should the thermal circuit breaker trip due to a large over current situation, before it can be re-set time must be allowed for the Bi-Metal strip to cool down permitting the tripping mechanism re-engage so the circuit breaker can now be re-energised. This is just the situation you don't want in a field combat scenario when your communications equipment trips out.
Unlike the thermal-magnetic circuit breaker the HY-MAG circuit beaker has no warm up period to slow down its response to overload and no cool down (thermal memory) period after overload event, allowing it to be reset immediately. It is, simply put, much more reliable and much more efficient!

 

[ceb58]

That is all correct. Now here is the issue and the reason I regrettably posted to this thread. Sustained heating, from something such as a high resistance connection can permantly change the charteristics of the bimetallic strip in the thermal element, the metals, as all metals do, have thermal memory, and will tend to retian thier shapes. This will cause the trip charteristics of a thermal breaker to change following a condition as the OP described. That is why I suggested testing the breaker, or replacing it, before saying everything was fixed.

I will agree that over time the repeated heating will change/damage the breaker. Personaly I would not have done as the OP as far as cleaning and such for the breaker. A 40 dp is not worth the risk and is not worth the time and expence of haveing it tested. Install a new one, charge for it and be on your way.

 

[mxslick]

<snip>
The problem was due to a bad connection in one of the screw terminals. The conductor material is aluminum (Copper would be better) and cleaning up the wire ends and the screw terminals did the trick. I also made sure the screws were really tight. Now the breaker runs cold and it doesn't trip.

Fixed.

Great forum!

I will agree that over time the repeated heating will change/damage the breaker. Personaly I would not have done as the OP as far as cleaning and such for the breaker. A 40 dp is not worth the risk and is not worth the time and expence of haveing it tested. Install a new one, charge for it and be on your way.

I agree with ceb58..for the record though I think the reason zog got so passionate about this was what the OP did (see bold) as opposed to replacing the breaker.

If there was a heat wave and someone sick or elderly involved, I would have done as the OP did as a temporary repair. Otherwise I would have made a run to the supply house and replaced the breaker. Seems like in terms of real cost (time and labor involved in cleaning up the terminals), it would be more cost-effective to replace the breaker.