Message Board Thread - "hot spot??? please advice"

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hot spot??? please advice Manuel 10/24/2004
hi guys ,,

i recently found this main breaker.
i noted that upper center bolt was hotter that sides bolts. i take different angles thermograms to eliminate the reflex posibility.

this breaker is 850 amp loaded and balanced.

what you think guys?..

thanks an regards
Re:hot spot??? please advice Carl M 10/24/2004
I'd like to see some information on those images like the spot temperatures, reference temperatures (from the other line terminals and/or the load terminal)and a current readings of each phase.


Carl M
Re:hot spot??? please advice Carl M 10/24/2004
...I was assuming that this (the top) is the line side. Are we looking at the line or load side of the CB?

Carl M
Re:hot spot??? please advice IRJay 10/25/2004
Oveall it appears as a heated conection but the heat does not appear to originate at the bolted part. Spot temps and comparisons will not be accurate due to the material emissivity. I would do further investigation and view the entire breaker for other patterns. Verify that the amperages are actually balanced also. Consider the possibility of harmonic current which will not appear on a traditional ampere meter.
Re:hot spot??? please advice Carl M 10/26/2004
Measured temperatures may not be accurate but will give us an idea of relative temperature comparisons. A difference of a couple of degrees can look quite dramatic depending on the span setting. A breaker under substatial load is expected to have a temperature above ambient and the middle terminal is often a little warmer.

Carl M
Re:hot spot??? please advice pktsgt 10/26/2004
Hey Guys,

I have found that the lug may be loose in the breaker on some of the bigger circuit breakers. This comes with the age of the breaker. It is difficult to tell from any image taken and the temp. are usually very small.

By being an electrician along with a thermographer I can do other checks to see if it is loose. I have changed some of these breakers out and some I have let go and monitor them to make sure that the internal part of the breaker does not get worst. It all depends on what that breaker is connected to.
Re:hot spot??? please advice Dan. M 11/4/2004
I agree with Carl on getting reference temps and spot temps. The B phase of a breaker may be slightly warmer (by no more than a few degrees)than the A and C phase because of the fact that it is "sandwiched " in the middle.
Re:hot spot??? please advice Peter T. 11/4/2004
As one of the previous posters said, the heating appears to be from within the breaker. From experience, the center phase on an evenly loaded breaker will NOT be hotter than the outer phases. I would suspect that the center phase contacts either have poor contact pressure / wipe, or are pitted / damaged. A contact resistance test would be the quick and easy way to check. If the results are more than about 10% higher than the other phases, on a molded case breaker like this it would probably be best to replace it. Usually there is not much that can be done in the field to improve the condition, although sometimes for poor pressure/wipe, just exercising the breaker mechanically about 6-8 times can help. Measure contact resistance before and after.
Re:hot spot??? please advice Coen T Service Netherlands 11/4/2004
Do not forget that due to the lower emissivity of the bold and in combination with the sandwich effect as already posted above, that the second phase wil look hotter. If you gave every phase a measuringpoint with it's own emissivity and reflected temperature, things would look different.

regards from Holland
Re:hot spot??? please advice Edd Hindmarsh 12/3/2004
I agree with Peter T, I have found similar problems, generally on heavily loaded circuit breakers, I always recommend that the whole phase be checked out including the internal contacts and connections
Re:hot spot??? please advice Dave 1/6/2005
Looks like a faulty breaker to me as the heat appears to be comming from within the breaker. I would suspect internal contacts, etc.
Re:hot spot??? please advice Link 1/6/2005
With limited infomration (picture only), it appears to be an internal problem withing the breaker. Although unlikely in this case as many 3 phase applications, harmonics can attribute to excessive degradation/increased impeadance resulting in heat build up.

It has become increasingly obvious to me that many thermographers are so wrapped up in 'heat transfer' that they forget to concidor all possible electrical causes such as properties of the load.

If the Breaker checks our, perhaps a power quality anaylisys is in order.
Re:hot spot??? please advice PKS 1/9/2005
I also agree with Mr. Peter.T. This type temp. may be due to the improper contact/spring tension of the breaker contact point (inside portion). Total breaker should be physically inspected.
Re:hot spot??? please advice Carl M 1/10/2005
Lots of good ideas posted.
However, an IR image without a scale or spot temperatures is almost imposible to read. The scale could be 70º-85º, and in this case we would not be concerned if the load was 700Amps we wouldn't be concerned at all.

I have scanned a few 800 Amp breakers that were removed and repaired and/or replaced. The customer did determine and report the root cause of a couple of them (loose trip unit fasteners, loose internal bus connector fastener. Both factory installation QC problems)

But in this case, I'd say more information is needed.

Re:hot spot??? please advice Manuel 1/10/2005
hi guys
thanks for all the comments around the images.

due the request of some of you about the temperature scale i'd have attached.

sorry to forgot to include since begining.

with best regards.

roberto cruz

Re:hot spot??? please advice Carl M 1/17/2005
It appears to me that there may be some heating of the center phase, perhaps within the circuit breaker, especially if the current load is even across the three phases. If the equipment is critial and shutdown of this panel would create a problem then I would look into getting a replacement breaker and installing it asap. If a replacement breaker is locally available and there would be little effect on the the owner's business if the breaker failed,then I may decide to continue to monitor it.
We have used breaker repair facilities that will send you a re-conditioned breaker and you can send back your breaker for credit after it is swapped out.

By the way, the breaker in my image failed two weeks after a shutdown and replacement oportunity. The cost of this decision was significant.

Carl M.

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