Sub HVAC 50A trips & takes main with it

[2TWOBEARS]

Triple socket Main Service. Original problem=Old red colored 125A main breaker (old Murray's?) apparently became loose? @ both bus bars...arced and destroyed both bus bars, one worse than other. I pulled bus bars and cut out bad sections, welded in new aluminum. Old (Murray?) red breaker no longer available. Installed new 125A that Murray said was a replacement, fit (New Murray) fits loosely, not at bus contacts but @ opposite side of breaker:-?. Everything ok for couple months or so. Soon as Grandma turns on AC, 50A in her sub pops and so does main. I Told her leave breaker in off position until summer and will get it fixed. What do you think is going on???? Obviously there is a short in the compressor circuit. But why is it popping the main at same time? The feed from main to apartment sub is aluminum...Ashamed to admit that during the replacement of said main breaker (in The Rain!) & bus bars that I did not check to see if Neutral connection was still tight!! Would a loose neutral at the main act this way? At the time I repaired the bus bars I operated all the stoves burners for 10 min, no main trip. Sincerely,
Stumped"

 

[eljefetaco]

I don't think you will get much feed back in this section. (continuing ed). Try posting in NEC forum. That being said I would check the Interuppting rating on the breaker. I would bet the main is lower than the branch circuit. Thus the main will trip before the branch circuit will.

 

[don_resqcapt19]

First, I don't see any way that you would be permitted to weld in new aluminum parts to the bus. You need to replace the panel..or the bus assembly if you can find one.
As far as the tripping, this is not uncommon if they are clearing a short circuit or ground fault. The instantaneous trip curves for breakers in this size range tend to overlap. If there is enough fault current, either or both breakers may trip.

 

[brian john]

First, I don't see any way that you would be permitted to weld in new aluminum parts to the bus. You need to replace the panel..or the bus assembly if you can find one.
As far as the tripping, this is not uncommon if they are clearing a short circuit or ground fault. The instantaneous trip curves for breakers in this size range tend to overlap. If there is enough fault current, either or both breakers may trip.

Or inrush from the HVAC.

You can buy used components online for the distribution equipment and re-build it.

 

[nate roach]

I pulled bus bars and cut out bad sections, welded in new aluminum


You need to replace the whole panel, not just try to modify/"fix" the bus bars, and Im petty sure said bus bars are not just aluminum, but a zinc/aluminum alloy, but dont quote me on that:roll:.

 

[e57]

WELDED IN NEW WHAT? To repair an obvious short-circuit damaged panel component...

Pretty sure making or repairing buss bars on your own is a listing violation - and generally a bad idea... While the expense of panel replacement may be a little much to stuff down grannies throat - the liability of doing such hoaky repairs should horrify most... Most - would remove the connections to the equipment or shut off the main - explain the dangers, and leave grannie with an estimated repair/replacement cost to consider.

 

[Cavie]

What do you think is going on????[/COLOR] Obviously there is a short in the compressor circuit. But why is it popping the main at same time? "

Can you say Murray?? Remove your illegle hack work and replace the panel.

 

[electricmanscott]

The old red Murrays are notorious for frying. Replace the panel.