A little help?

[Bobhook149]

Went to a service call at a store today, They said the panel was getting very hot. When we got there we agreed that it was hot and changed out the panel. It seemed as if it was hot at the main breaker but the lines were within there amperage so we figured a bad breaker. Now with the new panel it is still hot. especially the main breaker, and the wire that feeds it. But the wire is within its amperage at 50A on one leg and 60 on another. (by the way this is a sub panel)Went down stairs to the main 200A panel single phase 120v-240v and the 200A wire was warm when compared to the neutral. But as the 100A panel was within its rage at 90a on one leg and 100a on the other.

Also on further investigation we found a 20a split circuit breakers and wire to be warm, its mc. They feed 4 pepsi coolers, but when they are all running they are within there amperage. Also when we felt the mc in the ceiling it was very warm compared to the other mc wires right next to it.

So we shut the breakers to the coolers off for a 2 hour span, but the main and wire were still warm in the 100a sub.

The neutral is pretty cool and the loads seem to be balanced. A lot of coolers in this place. I don't know what we are missing.


Any help would be appreciated.

Bob

 

[raider1]

What was the temperature measured at the panel and breakers?

Chris

 

[Bobhook149]

I did not get an exact temperature on the breakers, or wire. Is it possible that it is normal?

 

[PetrosA]

...

But as the 100A panel was within its rage at 90a on one leg and 100a on the other.

...

Is this correct or did you mean to write the 200A panel had 90A and 100A?

When you say "warm" how warm exactly? Do you have some way to measure the breaker temps? If so, are they under 60?C?

 

[raider1]

I did not get an exact temperature on the breakers, or wire. Is it possible that it is normal?

60 degrees C is 140 degrees F, which would feel hot to the touch, but would be within the limits of equipment listed to operate at 60 degrees C.

Chris

 

[Bobhook149]

I would say it is definitely not over 140F. Every-once and a while we hear a buzzing coming from the panel. Can't tell if its from the main or the split circuit, but when you shut off the slit circuit the buzzing goes away. Also the red phase is warmer than the black. The temp may be within rage but under such a small load on the 100a sub wire why is it warm. Heat tends to make me nervous.

 

[jim dungar]

Do not confuse the temperature rating of conductors with the surface temperature of equipment.

Basically if you can hold your hand against a breaker it is still within normal operating temperature

Temperature rise, from an old NEMA standard for circuit breakers (AB-1, 1986):
Main circuit terminals for external connections = 45?C (113?F)
Main operating means, parts of insulating material = 60?C (140?F) above 25?C (77?) ambient.

 

[PetrosA]

I would say it is definitely not over 140F. Every-once and a while we hear a buzzing coming from the panel. Can't tell if its from the main or the split circuit, but when you shut off the slit circuit the buzzing goes away. Also the red phase is warmer than the black. The temp may be within rage but under such a small load on the 100a sub wire why is it warm. Heat tends to make me nervous.

I should have picked this up before, but is that twin feeding a three-wire or four-wire MC?

 

[Bobhook149]

3 wire mc with ground, shared neutral. But that should be okay right?

 

[Bobhook149]

But like i said, the mc for this split circuit is warm, in comparison to the other lines in the same suspended ceiling.

 

[ericsherman37]

I would say it is definitely not over 140F. Every-once and a while we hear a buzzing coming from the panel. Can't tell if its from the main or the split circuit, but when you shut off the slit circuit the buzzing goes away. Also the red phase is warmer than the black. The temp may be within rage but under such a small load on the 100a sub wire why is it warm. Heat tends to make me nervous.

I've heard that "buzzing" before and we've found that usually it winds up being a bad bus stab. Sometimes you can't visually see what's wrong with it, but for some reason, it doesn't seat properly in a breaker and causes some arcing.

We had a BR panel a few months ago with this problem and it was getting so hot you could see little wafts of vaporized breaker plastic floating around.

 

[Bobhook149]

unplugged one of the coolers. Heat seems to be dissipating.? But when it was running, it was at 9-15A max on a 20A circuit. Now why would that cause the main 100A breaker on the sub to heat up??

 

[brian john]

Did you perform a FOP on the the conductors?
Did you perform a FOP on the CB?
Did you perform an FOP across the panel to all branch CBs?

This should have been completed prior to any panel replacement IMO if you replace something and do not know why you have done a dis-service to yourself and your customer.

In addition would have taken temperature readings.
Amperage readings.

 

[ceb58]

unplugged one of the coolers. Heat seems to be dissipating.? But when it was running, it was at 9-15A max on a 20A circuit. Now why would that cause the main 100A breaker on the sub to heat up??

As far as this goes, if I understand you correctly, this twin breaker is on one phase and is using one neutral for both 20 amp breakers. If so you would be returning 18-30A on the neutral. ( if other cooler pull the same Amp.)

 

[Bobhook149]

No, they are both on separate phases so the neutral is fine. And what's a FOB?