Melted Leg

[laketime]

Went to a customers house who had an issue with a major short in their furnace that was repaired by a "furnace guy". He repaired what ever was wrong with the furnace but in the major short one leg on the 100amp breaker that fed the furnace had burned the buss in the panel. The homeowner replaced the breaker which in turn started to melt on that same leg. They cleaned the buss and installed another breaker. That one last about 10 minutes before it melted. I was thinking it was the spot that burned on the buss causing a gap where the breaker pushes in. That gap was causing the breaker to overheat and melt at that point. I did do an amp probe reading as the unit was running and it was drawing about 50amps/leg. What do you guys think?

 

[petersonra]

I suspect that there is some issue with something in the breaker box causing a short there, since the over current is not at the furnace end.

I am sort of surprised the breaker is not tripping if there is enough current to cause visible charring or melting.

Might be best just to replace the box and the breakers and be done with it. spending a lot fo time figuring out what is wrong will cost more in your time than the new box and breakers will.

In fact, you may never figure out with any certainty just what went wrong.

Step 1, IMO, is to replace the most likely problem.

 

[growler]

I was thinking it was the spot that burned on the buss causing a gap where the breaker pushes in. That gap was causing the breaker to overheat and melt at that point. I did do an amp probe reading as the unit was running and it was drawing about 50amps/leg. What do you guys think?

Sounds like that section is arced out. You can't always clean a bus because sometimes it's just to carbonized and pitted. Do whatever is necessary which is probably a panel replacement.

 

[laketime]

Sounds like that section is arced out. You can't always clean a bus because sometimes it's just to carbonized and pitted. Do whatever is necessary which is probably a panel replacement.

Yes that is what I figured as well. I install a new panel/breakers yesterday.

 

[jmellc]

You did right.

 

[Cow]

If it's only one burnt buss stab, I'll move the breaker off the stab into another spot, even if I have to twin something else up. I don't think I've ever tried to clean a buss stab up to reuse it, I always abandon them.

 

[brian john]

Perform an FOP determine WHY, ALWAY find out why.

Then as noted relocate the CB if it is a bus issue or replace. But in my opinion you should always know why.

We should strive to be more than a parts replacer, anyone can replace parts, if you know the cause of the issue you are working on, you can give proper answers and make the RIGHT repair.

 

[laketime]

Perform an FOP determine WHY, ALWAY find out why.

Then as noted relocate the CB if it is a bus issue or replace. But in my opinion you should always know why.

We should strive to be more than a parts replacer, anyone can replace parts, if you know the cause of the issue you are working on, you can give proper answers and make the RIGHT repair.

The original burn marks (as told to me by the owner as was told to him by the "furnace guy":roll were from a direct phase/phase short. The buss was then scarred. I replaced the panel because it was about 30 years old and the thing was doubled up already. I always try to figure out what went wrong but when you are the 4th man in (owner, 1st furnace guy, 2nd furnace guy, me) it can be tough to figure out what happened.