Hot spot on feeder at termination

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bigal1

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I had a GE 200 A 1 phase fused disconnect in front of a main lug only 200 A panel. Indoor on a commercial building in the Houston,TX area. Ever since A/C season has begun, the A phase conductor was getting hot on the line side at the termination, transfering the heat to the 200 A fuse and blowing the fuse. The hotter it has gotten the faster it was blowing fuses. It was an older disconnect being fed by 3/0 TW copper. Before we replaced it a thermal camera showed the conductor running 178 degrees.

We replaced the disconnect with a 200 A main breaker enclosure and new 3/0 THHN/THWN-2 copper feeders. The same thing is happening again, on the same phase and at the same termination.

When this first started happening I checked voltage, good at 120 v and only 1 volt imbalance to B phase. Checked amperage for a decent period and never saw more than 115 amps on The problem phase. Also, there,s only one A/C condensor on the panel.

Any ideas on where to look next ?

Thanks
 
bigal1 said:
I had a GE 200 A 1 phase fused disconnect in front of a main lug only 200 A panel. Indoor on a commercial building in the Houston,TX area. Ever since A/C season has begun, the A phase conductor was getting hot on the line side at the termination, transfering the heat to the 200 A fuse and blowing the fuse. The hotter it has gotten the faster it was blowing fuses. It was an older disconnect being fed by 3/0 TW copper. Before we replaced it a thermal camera showed the conductor running 178 degrees.

We replaced the disconnect with a 200 A main breaker enclosure and new 3/0 THHN/THWN-2 copper feeders. The same thing is happening again, on the same phase and at the same termination.

When this first started happening I checked voltage, good at 120 v and only 1 volt imbalance to B phase. Checked amperage for a decent period and never saw more than 115 amps on The problem phase. Also, there,s only one A/C condensor on the panel.

Any ideas on where to look next ?

Thanks
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This sounds so much like a loose wire terminal connection . Even though the amps are within limits , I do not believe that the wire terminals are tightened correctly . Possibly striped out and can never get tight enuff . Did you do the install or some one else ?




Don
 
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Is this a crimped lug connection? If you’ve replaced the disconnect and the same thing is happening. It seems the most likely place to look to me. (The common denominator)

Re-crimping won’t solve it as burning and oxidisation will have occurred inside the lug. Cutting back to undamaged/un-oxidised conductors is the only option.
 
It's sounding like that conductor is damaged somewhere under the insulation. I'd try replacing it and see what happens. It might not be a bad idea if it's been running that hot anyway since the insulation has to have been compromised at this point.
 
You probably landed a heat damaged conductor into the new lug. Once the conductor material has been heated up and loses it's temper, you never have same quality of conductor again. Always trim off heat damaged portion of conductor when such a connection has failed.

Problem now may be that you have compromised the lug on the new breaker - so if you trim the conductor now you only fix one side of the connection.
 
kwired said:
You probably landed a heat damaged conductor into the new lug. Once the conductor material has been heated up and loses it's temper, you never have same quality of conductor again. Always trim off heat damaged portion of conductor when such a connection has failed.

Problem now may be that you have compromised the lug on the new breaker - so if you trim the conductor now you only fix one side of the connection.
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He replaced all the wire Kwired, otherwise I would agree with you.

bigal1 said:
We replaced the disconnect with a 200 A main breaker enclosure and new 3/0 THHN/THWN-2 copper feeders. The same thing is happening again, on the same phase and at the same termination.
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Cow said:
He replaced all the wire Kwired, otherwise I would agree with you.
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Somehow I missed that.

Could be that line has the higher load on it, and if so it should be higher temp then the others, but it may not be so high that it is actually a problem. He did not say that it tripped the new breaker just that the same line is hotter then the others.

He did mention it had a 115 amp load on it. If that load is continuous there will be some heating that is easily detectible and at levels that can be alarming to some.

Go to a typical dwelling unit panel where there is typically limited continuous loads and all breakers are all cool, except for the air conditioner breaker when it has been a hot day, or a breaker feeding electric heating units on a really cold day. They will be warm enough that if you haven't been around them enough it concerns you - but it is normal.
 
Commercial building, 200A single phase service, it's likely high harmonics from non-linear loads like energy efficient electronic ballasts and computer power supplies, but not well balanced between the two legs.
 
iwire said:
I would be with you except for the fact the switch has already been replaced once and did not fix the problem.
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That Replacement is where I would look for a problem . I have found that the allen head screw , applying pressure to conductors at terminals , if stripped ,will never get a tight connection . A man may not tell anyone that he f...ed up the Panel or connection . One feeder wire was bare for 7" from terminal , insulation burnt off , Still had power . Installation was 6 years old . I only found it looking for why another panel was half dead ...




Don
 
Do you have any of the infrared images you could post?

if the conductor heat is uniform over the length of the conductor, it's overloading.

If it dissipates the farther you get from the switch, then there's a termination problem.

Is there any equipment at all that was common from the original to the new installation? Did you reuse the same fuses or anything?
 
iwire said:
Everyone does things differently but for me if the new part is showing the same failure as the old part I tend to look elsewhere.
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He never got back ... Probably not a bad termination but a blown AC Condenser , blowing the same leg as before ... Ha Ha . He never did say that he replaced the AC Condensor .

He led us to believe he had a bad termination , Power of suggestion .


Don
 
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donaldelectrician said:
He never got back ... Probably not a bad termination but a blown AC Condenser , blowing the same leg as before ... Ha Ha . He never did say that he replaced the AC Condensor .

He led us to believe he had a bad termination , Power of suggestion .


Don
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He also never said how hot the replacement was getting. Could just be that particular pole has more load and is warmer then the others, but is not so high that it is a problem needing immediate attention.
 
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