Breaker overheating

[Kary]

This note relates to a thread from 2003 discussing an overheating of a breaker switch. That thread never came up with a definitive answer so I am writing with what I found.

I had an overheating breaker problem on an air conditiioner compressor circuit (220 single phase) where a 40 amp breaker would heat up and trip after the unit was running for about 1/2 hour. Measuring the current on the circuit indicated 14 to 15 amps - the breaker is rated at 40 amps. The breaker was too hot to touch when it tripped.

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!

 

[zog]

Now the breaker runs cold and it doesn't trip.

Fixed.

Great forum!

Breakers are supposed to trip when an overcurrent condition occurs, the breaker may have been damaged from the excessive heating. I would not call anything "fixed" until you have tested the breaker to ensure it trips per the OEM time current curves.

 

[charlietuna]

Good job ---breaker's trip set point are effected by heat not by overcurrent conditions. Good job ! Talk your customer into replacing aluminum conductor to copper !

 

[zog]

Good job ---breaker's trip set point are effected by heat not by overcurrent conditions.

Huh? A breaker trips as a function of current over time. Not heat. show me a trip curve that has heat on it?

http://www.geindustrial.com/publibrary/checkout/GES-6239A?TNR=Time Current Curves|GES-6239A|generic

 

[brian john]

A simple investigation tool is using your multimeter and measuring voltage drop across the CB, from the load side conductor to the breaker bus.

 

[don_resqcapt19]

Huh? A breaker trips as a function of current over time. Not heat. show me a trip curve that has heat on it?

http://www.geindustrial.com/publibrary/checkout/GES-6239A?TNR=Time Current Curves|GES-6239A|generic

While you are correct that current causes the trip, it does that indirectly in the case of standard thermal/magnetic trip breakers. The current makes the heat that in turn unlatches the trip device. Heat from a poor connection or high ambient temperatures has an effect on the trip time. Remember we are talking about small breakers here, not the big ones that you work on.

 

[Volta]

Huh? A breaker trips as a function of current over time. Not heat. show me a trip curve that has heat on it?

http://www.geindustrial.com/publibrary/checkout/GES-6239A?TNR=Time Current Curves|GES-6239A|generic

Obsolete link.

 

[Smart $]

Obsolete link.

Incomplete link.

Try this one...

http://www.geindustrial.com/publibrary/checkout/Time Current Curves|GES-6239A|generic

 

[iwire]

From the link

Curves show enclosure-compensated circuit
breaker in open air, 40?C ambient, wired with
conductors of corresponding rating, no prior
load. For all other ambients, use rating shift
index at top of sheet.

 

[charlietuna]

Circuit breakers are ambient compensated designed to a point -- when a breaker has a connection problem--- bus connection--internal contact connection --or load wire connection it effects the trip setpoint. Ambient compensation is the temp. it operates in--IE = room temp !

 

[zog]

Circuit breakers are ambient compensated designed to a point -- when a breaker has a connection problem--- bus connection--internal contact connection --or load wire connection it effects the trip setpoint. Ambient compensation is the temp. it operates in--IE = room temp !

I know how a breaker works, but you said overcurrent conditions does not effect the breakers trip point, which is incorrect. That is what I quoted when I replied to your post.

 

[don_resqcapt19]

I know how a breaker works, but you said overcurrent conditions does not effect the breakers trip point, which is incorrect. That is what I quoted when I replied to your post.

Then your response did not really say what you intended it to say.

Huh? A breaker trips as a function of current over time. Not heat. show me a trip curve that has heat on it?

I also believe that the post you responded to is correct. The overcurrent condition does not change the breakers trip point.

 

[zog]

I also believe that the post you responded to is correct. The overcurrent condition does not change the breakers trip point.

So you don't think the amount of current determines how fast the breaker trips? Ugh, I give up.

 

[don_resqcapt19]

So you don't think the amount of current determines how fast the breaker trips? Ugh, I give up.

That is not what I said and is not what I thing the other poster said. I think he was saying that the amount of overcurrent does not change the trip curve, but that the ambient temperature does change the trip curve (moves it to the right or left).

 

[iwire]

So you don't think the amount of current determines how fast the breaker trips?

Zog where did you get the idea that anyone here is saying current has nothing to do with it?

Do you really think that you are the only one that knows how breakers work? :roll: Don of all people? :roll:

The ambient temperature will change the trip curve, the link you posted even mentions that. So something like a loose connection to the breaker can raise the breakers temperature and cause it to trip sooner then it would with a tight connection with the same amount of current.

Or are you going to tell us temperature has nothing to do with the operation of a Thermal-magnetic breaker?

I guess you might as you already told me a standard breaker does not protect wiring against ground faults. :grin:

 

[zog]

That is not what I said and is not what I thing the other poster said. I think he was saying that the amount of overcurrent does not change the trip curve, but that the ambient temperature does change the trip curve (moves it to the right or left).

I interpreted his comment differently, but if what you said is the intent , I would agree. Nice you can discuss this without throwing jabs.

 

[zog]

Zog where did you get the idea that anyone here is saying current has nothing to do with it?

Read what I quoted again and stop changing what I am saying.

Do you really think that you are the only one that knows how breakers work? :roll: Don of all people? :roll:

And where did I say this??? Man you just never quit do you , every single post I make anywhere you are there twisting what I say, what is your problem?

The ambient temperature will change the trip curve, the link you posted even mentions that. So something like a loose connection to the breaker can raise the breakers temperature and cause it to trip sooner then it would with a tight connection with the same amount of current.

Yes, it will, and also have an effect on the trip charatersitics of the breaker after the repair is done, just becasue the breaker is cool and closed does nto mean it is working right, I just suggested it was tested (or replaced) after being that hot for that long.

Or are you going to tell us temperature has nothing to do with the operation of a Thermal-magnetic breaker?

No

I guess you might as you already told me a standard breaker does not protect wiring against ground faults. :grin:

Well that is not what I said, what I said is correct and I stand by my statements, But here you are again twisting my words trying again to make me look stupid. I am really getting tired of your antics.

 

[LarryFine]

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?

 

[Volta]

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?

Bravo! Bravo!

 

[iwire]

Read what I quoted again and stop changing what I am saying.

I quoted your words, if I changed the meaning others will see that. I do not think I did.

And where did I say this???

From your quotes it was how it came across to me, I could be wrong.

Man you just never quit do you , every single post I make anywhere you are there twisting what I say, what is your problem?

What is my problem?

I guess the problem is I never got the memo that your posts where not to be questioned.

I fogot it is God, Zog and electricity in that order. :roll:

Well that is not what I said, what I said is correct and I stand by my statements, But here you are again twisting my words trying again to make me look stupid.

Trying to make you look stupid? I doubt that is possible.

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 am really getting tired of your antics.

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