Panel bus bar melted

[Ranger86]

400A panel, 480V, 3phase (no neutral), fed from 480/277V system but neutral not brought to panel.
The panel feeds 480V, single phase infrared heaters. This is an old building, they used 3-pole breakers to feed groups of heaters, it turns out that each breaker has unbalanced phase currents (they alternate the phase connections for each heater, AB, BC, CA). There is no neutral branch circuit conductors. I am thinking that this may have caused the bus bar to over heat. The individual heaters do not need neutral, but combining multiple heaters on 3-pole breakers create unbalanced currents. The main breaker did not trip so this is probably not an overload situation. I am waiting for name plate data of the heaters to run a load calc on the panel. Do you think the unbalanced branch circuit currents can cause the panel bus bar to overheat?

 

[pete m.]

Overloading will definitely cause heat but I lean more towards one or more loose connections to the buss.

Pete

 

[Ranger86]

Overloading will definitely cause heat but I lean more towards one or more loose connections to the buss.

Pete

Actually, the original panel that was about 30-40 years old, burnt up. They thought that it failed because of it's age. Then they replaced it with a new one of same characteristics, and this one did not last long before the bus bar melted. The first panel I believe the breaker actually partially melted, on the second panel one of the bus bar phases melted.

 

[GoldDigger]

Unbalanced currents from single phase line to line loads cannot cause higher current in any phase at any point on the bus bars than the branch breakers and the main breaker will allow. It is possible that the main breaker is not meeting its specification and therefore allowing the bus to be overloaded.
I sincerely hope that when they replaced the panel they got all new breakers too. If they did not, the damaged jaws of some of the old breakers could have caused local hot spots and destroyed the new bus.
Also make sure that none of the branch breakers exceed the "per stab" rating of the panel (unlikely but check everything).

 

[jap]

We've heard everything except for the simple stuff.


What size is the size of the main,,, what is the size of the branch circuits,,, what is the amperage of the branch circuits and what is the full load on the panel?


JAP>

 

[Ranger86]

Unbalanced currents from single phase line to line loads cannot cause higher current in any phase at any point on the bus bars than the branch breakers and the main breaker will allow. It is possible that the main breaker is not meeting its specification and therefore allowing the bus to be overloaded.
I sincerely hope that when they replaced the panel they got all new breakers too. If they did not, the damaged jaws of some of the old breakers could have caused local hot spots and destroyed the new bus.
Also make sure that none of the branch breakers exceed the "per stab" rating of the panel (unlikely but check everything).

It is a new panel and new breakers.

 

[Ranger86]

We've heard everything except for the simple stuff.


What size is the size of the main,,, what is the size of the branch circuits,,, what is the amperage of the branch circuits and what is the full load on the panel?


JAP>

I am waiting for name plate ratings from the field to do a load calculation.

 

[Ranger86]

Actually, the original panel that was about 30-40 years old, burnt up. They thought that it failed because of it's age. Then they replaced it with a new one of same characteristics, and this one did not last long before the bus bar melted. The first panel I believe the breaker actually partially melted, on the second panel one of the bus bar phases melted.

I think there is a code violation here but I don't see to get a code section to back this up ....

The 3-pole breaker is feeding a group of single phase heaters. Each heater would normally fed by a 2-pole breaker (2-hots, 1-ground, no neutral). But feeding a group of heaters with a 3-pole creates an unbalanced load on the breaker. The branch circuit has no neutral conductor, and actually there is no place to connect the neutral at the heaters.

Does anybody see a problem here?

 

[jim dungar]

I think there is a code violation here but I don't see to get a code section to back this up ....

There is no 'code' violation when using only 1 or 2 poles of a 3-pole breaker.
In fact, this condition is part of the testing required by breaker standards.

 

[Ranger86]

There is no 'code' violation when using only 1 or 2 poles of a 3-pole breaker.
In fact, this condition is part of the testing required by breaker standards.

All 3-poles are used. My question is having the unbalanced (phase currents not equal) load on each breaker , and no neutral branch circuit conductor.

 

[jim dungar]

All 3-poles are used. My question is having the unbalanced (phase currents not equal) load on each breaker , and no neutral branch circuit conductor.

There is nothing wrong with having current flow through only 2 poles of a 3-pole breaker. NEMA and UL standards include this type of loading as a basic requirement for all multi-pole breakers.

 

[Ranger86]

There is nothing wrong with having current flow through only 2 poles of a 3-pole breaker. NEMA and UL standards include this type of loading as a basic requirement for all multi-pole breakers.

The 3 poles have current flow. Each pole is different current in most cases. In some cases there may be 2 poles with same current and the third pole with different.

 

[GoldDigger]

The 3 poles have current flow. Each pole is different current in most cases. In some cases there may be 2 poles with same current and the third pole with different.

Still absolutely no problem. As long as none of the three carry more current than the breaker rating.
Up to 134% might never trip the breaker and could cause slow deterioration.
But bad connections are the more common culprit.
In case the load distribution over the phases is not as designed I would amp-clamp all three lines on each breaker.

 

[Ranger86]

Thank you everyone for your comments. I am just trying to go over all opposites that could of caused this to happen. Thanks again.

 

[jap]

You have some type of odd issue going on or it wouldnt have happened to both panels.
Was it the same phase both times?


JAP>

 

[Ranger86]

You have some type of odd issue going on or it wouldnt have happened to both panels.
Was it the same phase both times?


JAP>

Yes, there is definitely something fishy going on. The main breaker partially melted on the old panel but I don't know exactly what the problem was because I was not involved on the investigation back then.

Now I am wondering if it could be a grounding problem since there is no neutral in the panel and it has unbalanced loads. That is a very old building that needs to have a major electrical upgrade done.

 

[kwired]

Grounding problem will only contribute to shock hazards should a ground fault develop if there is no neutral load.

Maybe, though I would think it would need to be somewhat an extreme case to do it, have you confirmed that conductor sizes are sufficient for the load? Both the feed to the panel and the branch circuit conductors? Or that a 200 amp panel bus is needed when only a 100 amp bus is being used or something like that?

 

[Ranger86]

Grounding problem will only contribute to shock hazards should a ground fault develop if there is no neutral load.

Maybe, though I would think it would need to be somewhat an extreme case to do it, have you confirmed that conductor sizes are sufficient for the load? Both the feed to the panel and the branch circuit conductors? Or that a 200 amp panel bus is needed when only a 100 amp bus is being used or something like that?

I am still waiting for nameplate data verification of the heaters to run a calc. The weird thing is that the main breaker did not trip if it was an over load. The feeder and branch conductors are sized for their overcurrent protection.

 

[jap]

I am still waiting for nameplate data verification of the heaters to run a calc. The weird thing is that the main breaker did not trip if it was an over load. The feeder and branch conductors are sized for their overcurrent protection.

The Load calculations arent going to tell you anything that the burnt up equipment is not already trying to tell you.

Seeing as how the same problems occurred with 2 different panels,from what you described it seems like a simple result of a Panelboard that is loaded to the max that stays that way for extended periods of time.

Panels and breakers can run for a very long time at full load without anything tripping, sometimes to the point of self distruction if they are expected to run at full tilt for long amounts of time.

Shed some load and your problems will more than likely go away.


JAP>

 

[Ranger86]

The Load calculations arent going to tell you anything that the burnt up equipment is not already trying to tell you.

Seeing as how the same problems occurred with 2 different panels,from what you described it seems like a simple result of a Panelboard that is loaded to the max that stays that way for extended periods of time.

Panels and breakers can run for a very long time at full load without anything tripping, sometimes to the point of self distruction if they are expected to run at full tilt for long amounts of time.

Shed some load and your problems will more than likely go away.


JAP>

Yep, I agree with you 100% ... Thanks.