Help! Furnace Breakers Melting!!!

[renosteinke]

I once saw a Square D "QO" 100-amp main breaker that had melted and charred before failing. There was also damage to the buss where the breaker attached.

In that instance, it was simply the result of age- and pushing things to the max. The breaker routinely ran for hours at 105+ amps; it fed the dryers in a laundromat. When, a few years later, a Square D rep told me that their breakers were designed for only 80% loading, that they would instantly trip at the handle rating ... I could only smile.

So, I'd power up the heaters and see what they REALLY draw - you may find your answer there. Sure, the paint didn't help- but there might be an underlying issue. If the guy is pushing his equipment, he created his own problems.

 

[K8MHZ]

How did you come up with the current measurement? 116 amps is a bit high for a 2 second trip, but the high end of the time current trip curve shows 90.

We used the bosses clamp on ammeter.

He was upstairs and I was in the basement putting breakers in an upgrade. When I flipped on one of the 15A breakers, all the lights in the basement dimmed out to nearly nothing. When I turned the breaker off, the lights came back to full brightness.

Since this was an old house, I suspected a bad connection. I figured that this would show up as a very low current. I had boss man come down and clamp the #14 conductor as I turned on the breaker. When he said "115.7", I said (almost as a reflex), 'not volts, amps'. He chuckled and said, "that IS amps".

I then clicked the breaker back off. We found a hot to neutral direct short in an outside light.

 

[K8MHZ]

Are you sure it's the CH style? Not the BR style? BR's are warmed over Westinghouse breakers and are not very quick to trip. I have never had a CH style give trouble, very small arc on a short circuit, comparable to the Square D QO style.

I used 'C-H' to mean 'Cutler-Hammer'. I don't know if it was a BR or a CH style panel, it was a few years ago.

One of our local inspectors carries around a pen knife with the end melted off it. Not just a nick, but almost a half inch of blade is gone. When the inspector was an EC, he messed up and managed to short the hot and neutral of a 15 amp C-H circuit with his knife. The breaker did not trip and the knife fused between conductors until the blade finally melted off. He was about 15 feet from the breaker panel. Again, I don't know if it was a CH or BR style.

 

[rich000]

Hi RichOOO and thank you for your reply. If I read this thread as a poster and not the author, I would completely agree with you. However, our customer is truly a cut above and I think they are primarily looking for absolute safety for their tenants at this point. I'm sure the finger pointing will come but it is down the road at this point.

As for snapping in breakers on a bussing with over spray, all I can tell you is that in new construction, there often is drywall dust etc on the bottom of a load center while breakers are being snapped in. Most likely, the guys didn't think a thing about it, rather they thought either A. drywall dust or B. will rub off as breaker snaps on. I've been doing this for over twenty years and I had no idea that overspray could cause this problem. I'm sure my crews didn't either...They WILL no though!

Thanks for your response Sir!

You are welcome.

While the overspray can cause this, CH may me doing a CYA. Ask them for their reports of contact resistance of the breakers. Also try to find out if those breakers were all from the same "batch". I have recently just had a bad "batch" of Eaton breakers that needed to be replaced. These were 225A breakers, but same principle.

Another thought that came to mind. Are these heat pumps with emergency heat strips in them? If so, are the heat strips the correct size for the breaker? I have seen where the heat strip on the outside of the unit was improperly marked. Just a thought.