Circuit Breaker too cold

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mgtack

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I have a client that ordered a IR study of his panels. The IR company told him a few of the breakers are too cold relative to the other breakers. They amp'd out the breakers, confirmed they were under a moderate load as were the others that were at a warmer temperature. The IR tech suggested the breakers need to be replaced because they are not as warm as the other breakers. The panels and breakers in question are all in the same warehouse, with relatively the same temperature. Has anyone ever heard of a breaker running too cold?
 
Me, no. Did they break down their analysis according to the amount of load on each breaker so that you could compare the temperature of a breaker with a small load to the same size breaker with a larger load?
 
I know that square d qo breakers have an operating temperature of 40 degrees celsius, but i dont know what kind of a deadband from that temperature there is before there is an issue. Perhaps someone else will know. Its stamped on the side of them too. Not sure what type you have but id check.
 
MasonF said:
I know that square d qo breakers have an operating temperature of 40 degrees celsius, but i dont know what kind of a deadband from that temperature there is before there is an issue. Perhaps someone else will know. Its stamped on the side of them too. Not sure what type you have but id check.
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The 40°C value is the ambient temperature used during their calibration. It has no significance in an IR scan.
 
mgtack said:
Has anyone ever heard of a breaker running too cold?
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Wow.
This is the first time that I've heard of someone saying low contact resistance is bad and therefore the device should be replaced.🤔

Is their concern the breaker may not follow its time current curve when it needs to protect the conductors?
 
Would like to see a pic of the scan.
The breaker temp should be at least ambient of the room. Needing replaced due to being to cool is a new one to me.
Ask for a copy of his written report. It will show a pic of the scan with data and his comments, or should.
The ones that had a moderate higher temp may be from being next to, across or above one that is under a higher load that could be considered continues loaded etc. There is several factors to consider related to the information provided.
What if it's a recptical circuit with no load on it.
Definitely look a little closer at the report.
 
One thing to note is that the power dissipated by a bimetallic element in a breaker will be proportional to the square of the current going through it. Therefore its temperature rise above ambient will (at least initially) also be proportional to the square of the current. The bottom line is that the temperature of such breakers will be quite sensitive to the amount of current running through them. And so a more careful look into the actual currents as Infinity mentioned would be needed before making any conclusions.

Also, if the same amount current is going through two breakers that have different current ratings, then the breaker with a higher rating would be expected to get less hot (because of the lower resistance of its bimetallic element).

Like Jim, I've never heard of the problem mentioned by the OP. Given that, the likelihood of multiple breakers having such an issue seems extremely unlikely.
 
jim dungar said:
Wow.
This is the first time that I've heard of someone saying low contact resistance is bad and therefore the device should be replaced.🤔

Is their concern the breaker may not follow its time current curve when it needs to protect the conductors?
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That is what the IR guy is insinuating.
jim dungar said:
Wow.
This is the first time that I've heard of someone saying low contact resistance is bad and therefore the device should be replaced.🤔

Is their concern the breaker may not follow its time current curve when it needs to protect the conductors?
Click to expand...
synchro said:
One thing to note is that the power dissipated by a bimetallic element in a breaker will be proportional to the square of the current going through it. Therefore its temperature rise above ambient will (at least initially) also be proportional to the square of the current. The bottom line is that the temperature of such breakers will be quite sensitive to the amount of current running through them. And so a more careful look into the actual currents as Infinity mentioned would be needed before making any conclusions.

Also, if the same amount current is going through two breakers that have different current ratings, then the breaker with a higher rating would be expected to get less hot (because of the lower resistance of its bimetallic element).

Like Jim, I've never heard of the problem mentioned by the OP. Given that, the likelihood of multiple breakers having such an issue seems extremely unlikely.
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The point about current ratings seems to be the most logical. Thank you. I would have been much more skeptical if the IR company was situated to profit from replacement but they strictly do IR. Just wanted another opinion and appreciate the thoughts.
 
I have never heard of this. I can theorize that it is plausible as follows:

The breaker has a trip element which functions by heating up proportional to the square of the current, and then tripping based on temperature. So a breaker that is cooler than expected indicates that something is up. Perhaps current is bypassing the trip element or the breaker was manufactured with the wrong trip element, or some other fault.

The question to ask the IR company is 'what temperature is _expected_ for this breaker, how did they determine the expected temperature, and what is the measured temperature of the breaker?'

IMHO 'cooler than surrounding breakers' doesn't indicate a problem. But if they have sufficient information to say 'based on the model of the breaker, the measured current through the breaker, and the ambient temperature, our predictive model says that the breaker should be at 80° but it is only at 50°' (NB: I just pulled those numbers out of a random orifice) then that is plausibly actionable info.

-Jon
 
winnie said:
I have never heard of this. I can theorize that it is plausible as follows:

The breaker has a trip element which functions by heating up proportional to the square of the current, and then tripping based on temperature. So a breaker that is cooler than expected indicates that something is up. Perhaps current is bypassing the trip element or the breaker was manufactured with the wrong trip element, or some other fault.

The question to ask the IR company is 'what temperature is _expected_ for this breaker, how did they determine the expected temperature, and what is the measured temperature of the breaker?'

IMHO 'cooler than surrounding breakers' doesn't indicate a problem. But if they have sufficient information to say 'based on the model of the breaker, the measured current through the breaker, and the ambient temperature, our predictive model says that the breaker should be at 80° but it is only at 50°' (NB: I just pulled those numbers out of a random orifice) then that is plausibly actionable info.

-Jon
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This mostly sums up what my thoughts were but probably better written than what I was likely to post.

One other thing I had on my mind is possible counterfeit breaker, maybe has no thermal trip element of any kind or at least not what it is supposed to have.

Even a switch unit only installed in a panel with a lot of loading likely sees some rise above ambient though, heat will be conducted through the bus and into other installed devices, I see this in heavily loaded panelboards even the light loaded breakers still operate warmer than if they were in a lightly loaded panel.
 
mgtack said:
I have a client that ordered a IR study of his panels. The IR company told him a few of the breakers are too cold relative to the other breakers. They amp'd out the breakers, confirmed they were under a moderate load as were the others that were at a warmer temperature. The IR tech suggested the breakers need to be replaced because they are not as warm as the other breakers. The panels and breakers in question are all in the same warehouse, with relatively the same temperature. Has anyone ever heard of a breaker running too cold?
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When breakers are “too cold”, meaning the ambient temperature is under -5deg C, (23F) it CAN affect the trip curve. This might be the concept behind his statement, but has ZERO to do with a low IR scan reading. He is over reaching…
 
kwired said:
One other thing I had on my mind is possible counterfeit breaker, maybe has no thermal trip element of any kind or at least not what it is supposed to have.
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Oooh, good thought. I have seen pics on line of a cheap Chinese knock off breaker that when opened up, is just a switch and wire, no thermal or magnetic sensing elements at all!
 
ptonsparky said:
Refer to post #4.
Ambient refers to the area surrounding an object. Not the object itself.
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How close to the object? The closer you get the warmer the "ambient" becomes. In a box, what exactly is "ambient" if the devices themselves are heating the enclosure?
 
I think bottom line is, whatever the OCPD operational specs are, are the specs for normal operations. Just because someone IR's it and sees some hot and others not as hot ("cold"), that data is only anecdotal. Specs are specs.

Now, one might have a theory, if two same OCPD's are passing same amps and one is colder than the other, you might then question why? The answer might be placement, better airflow, or Johnny ate at McD's that day, not sure, but you could ask why.
 
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