I looked at a condo today and all the branch circuit neutrals were burnt and corroded on the neutral bar in the condos panel. The feeder wires were 2/0 aluminum with a undersized neutral. I do not know the size of the neutral because the writing was worn off. My guess is that the feeder neutral was #4 aluminum but i could be wrong. The neutrals and grounds were isolated like it suppose to be for a feeder sub panel. The main service was 1000 amps and the breaker feeding the condo panel was a 150 amp breaker. i could not find anything wrong with the condos panel that would cause the neutrals to burn. All connections were tight. De ox was used on the aluminum feeders. My concern is why the neutrals are burnt. Is this simply from corrosion? I do not see any signs of water inside the panel like stains. There was quite a bit of dust and cob webs. What concerns me is every neutral was burnt on the neutral bar. I suggested changing the panel but am worried that something bigger could be going on here. Also are the feeder wire sizes even correct for 150 amps? if i am reading the NEC correctly it should be at least 3/0 for 150 amps when using aluminum. Any info would be greatly appreciated.
Branch neutrals are all burnt on neutral bar
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Did you check other panels in the condo?
What was the current on the branch circuit neutrals
What was the current on the neutral feeder
Did you do a sequence measurement on the feeder (amp-clamp reading all phase and neutral conductor simultaneously)
What was the current on the neutral ground bond at the main service
Did you take any pictures.
Often loose connections will weld shut like they were tight, but at some point were not.
What was the current on the branch circuit neutrals
What was the current on the neutral feeder
Did you do a sequence measurement on the feeder (amp-clamp reading all phase and neutral conductor simultaneously)
What was the current on the neutral ground bond at the main service
Did you take any pictures.
Often loose connections will weld shut like they were tight, but at some point were not.
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If you look at the neutral in the panel, you are only seeing one end of the connection. Try investigating the other end of that conductor. Downsizing feeder neutrals for liner loads is (has been) supported in the NEC. Also the rules for aluminum SER cables has changed during the last three code cycles, so what is now required is not the same as was in years gone by.
I wanted to check the other condos but we would have had to give 24 hr notice to the tenants to check them according to washington state law
Im not sure a amp clamp reading would help when all the appliances had been removed. The only load would have been a few incandescent lights that were on
I didn't go into the main service. Too dangerous. There was a bond from ground rods i could see going into the main disconnect. Also the building was built in 1978 if that helps for code reasons.
i don't have pictures my new i phone crapped out when i pulled it out to take pics.
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Are some neutrals feeding more than one ungrounded conductor? If so and both hot's are on the same leg of the panel they could be sending more current thru the neutrals than they are safely designed to handle.
There are some 12-3 cables. There are some cables that have 2 ungrounded conductors that are sharing a neutral. Common for the time the building was built. However there are also 14-2 and 12-2 cables that are burnt and corroded as well. I checked to make sure that the cables with 2 ungrounded conductors sharing the neutral are on opposite phases. Ive seen this happen in other condos and it burnt out a wire nut for a neutral. This however is not the case.
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Not that I want to argue about the code book. It is just that I have amp checked so many feeder neutrals in so many engineered panels that are running lots of lights and carrying lots of load- most of em had less than 20 amps on the neutral which usually was a full size as the feeder hots. Just sayin. We be overkil dem neutrals on engineered balanced panels because the code book say's so, but it is largely a waste of copper and insulation. I like it though, because it makes me richer to put in big wire. Kinda like prescribing satin drugs instead of broccoli.
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I don't have any kind of explanation, kind of a hunch that someone did something goofy when they terminated those, maybe someone came by later and tightened them without bothering to clean things up. It would be interesting to put infrared to it and see how it heats up with different loads.
I am assuming you replaced the bar and reterminated the wires, did you do some tests to see if it's drawing more than it should, or if it's heating up with various loads on the system?
I am assuming you replaced the bar and reterminated the wires, did you do some tests to see if it's drawing more than it should, or if it's heating up with various loads on the system?
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Additionally, pigtail the branch ckt neutrals to copper with purple ideal wire nuts or Alumicons then terminate to neutral bar.
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I was assuming the Al was just the feeders, if the branch circuit wiring is Al as well then that needs attention!
I think I might trust a dual rated Al / Cu bar rather than pigtailing in the panel?
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I wouldn't, but, I've seen enough AL wiring from the 1970s that that's why I prefer pigtailing.
We land AL on neutral bars for high current loads all the time, it's rated for it. I would prefer that to adding an extra splice with a wirenut or any other type of connector.
A neutral bar is a "lug" for all intents and purposes and never had an issue with AL conductors like wrap-around screw terminals did.
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If it's getting ALL the wires it suggests to me that it must be something that's common to all of them:
POCO transformer lug;
service neutral conductor,
service / feeder connections;
feeder neutral conductor,
feeder neutral connection,
neutral bar
There's only one of these that I can see high resistance scorching the wires:
the neutral bar itself.
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It seems like it would be preferred to terminate aluminum wires to an aluminum neutral bar anyway - otherwise you're dealing with dis-similar metals
That was my thought too. That someone had re tightened the neutrals or possibly the corrosion had welded them tight when they became loose. The panel is old and i wont be able to replace the neutral bar. Therefor a panel change will have to happen. My concern is that this may happen again if it is something else like a service neutral problem.
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