Main breaker incident - should I be concerned?

Cooktop kept blowing 50A breaker. Heard sizzling in breaker box.

1. Removed breaker box cover
2. Found cooktop negative wire sparking at connecting point of 50A breaker and screw completely backed out. (Appeared it was installed this way.)
3. Turned off main breaker and Tightened screw on 50A breaker to secure connection.
4. Left 50A breaker off to keep circuit isolated in case there was a problem with the cooktop itself.
5. While main power was off, Checked all other breaker/wire connections for tightness. No other problems.
6. Turned main breaker on. Experienced One Loud pop with sparks at the main breaker. It appeared they came from around the switch itself and maybe from the top of the breaker. Main power to house came on without delay, no further problems. No other breakers tripped. All appears normal. Main breaker is cool to the touch.
7. Turned on 50A breaker and cooktop. No arcing/sizzling.
8. Replaced panel cover.
8. Turned off main breaker, then back on. Operated normally. Did this one more time, no issues.

In summary - I did not move any wires, just tightened the 50A breaker connection and left it off. Yet, when I turned on the main breaker back on, sparks flew. It did this only once and all now appears normal. (We have used this house in the past as a second home, so have turned the main breaker off and on when we were going to be away for long periods. Have never experienced anything like this before.

My concern is two-fold.
First - the obvious "what caused it?"
Second - is the "tripping" feature of the breaker possibly fused now and I'm getting power straight from the meter box to the other sub breakers. I wouldn't think that would be possible, and if the breaker was bad, all power would be off.

Thoughts anyone?

 

No negative wires on an AC system. From your description that was one of your two "hot" wires (ungrounded conductor/240 leg).

Best to turn off the branch circuit breakers first so you don't have a load when it connects. What happened could have been arcing from a heavy load. Pulling the breakers and checking for pitting on the bus bars plus making sure it is tightly seated isn't really a DIY job. You should probably have an electrician check it out.

If the breaker cuts off all power it is probably still good. No way in the field to really test if its trip function is working correctly. Best to have electrician evaluate it or just replace it. It can fail in either the on or off position.

Your original problem with the stove breaker was probably just a loose connection either never properly tightened or loosened by vibration and/or thermal expansion and contraction.

 

You have a problem. What happened is anything but normal. Can you post information on the panel such as manufacturer's name, amperage and approximate age. Can you post pictures of the panel with the cover/door removed? There may be a problem on the line side of the main breaker which wouldn't necessarily trip it. There is no protection ahead of the main breaker so anything that goes to ground will burn the fault open; that may be what happened. What you don't want is the burning to catch your house on fire. Electrical problems don't fix themselves.

 

If your 50a breaker for the range is burned at the lug, where the wire connects, then it may need to be replaced.

At your main... it sounds like the main wiring coming into the main breaker may be loose. That would require an electrician to check as the meter may need to be pulled.

Don't try to check the incoming wiring to the breaker as it can not be shut off at the panel.

 

Cutler Hammer panel was installed in 1998. Photos attached of main breaker connections and main lines running to breaker.

 

Guys, what am I looking at here. Is it just a trick of light?

 

I am thinking heat, too, Ray. If these conductors are copper, disregard, but if they are aluminum, there's no NOALOX on them, and there could be corrosion.

 

Looking at the second picture down, it appears to be copper poking out of the other sige of that lug on the right.

 

Good eyes, droo. Couldn't tell from the others.

 

The wires are copper.
The discoloration on the insulation is from the flashlight I was using to illuminate the panel.

Thanks for the responses. Will get someone to check the main breaker Monday. My wife reminded me that when we flipped the main before, we had all the other breakers off ( as ray suggested). This time I just didn't think to do it. Hopefully it was just a temp overload, but will have it checked out nonetheless.

Super forum here. I appreciate your time. On an aside, I did notice a large number of ladybugs and other insects in the panel. All leftovers from the winter and dead. There were some on top of the main breaker and had covered the one of the two narrow openings on the top of it. I wonder if they could have been part of the cause.

 

The picture that Ray posted is just the nylon jacket of the THHN wire wrinkling. Not an issue.

The cooktop issue for sure was a bad connection.

The main issue could have been a combination of heavy start up load at one time

 

I agree, I do see something though. The left lug appears to a slightly different color than the right one. Is that right or is that because of the lighting. Looking closely at the right lug I thought I saw just a small bit of copper wire sticking through, not an issue. Looking at the left lug closely, it not only appears to be a slightly different color, maybe from overheatring, but I think I see corrosion on the wire at the top of the lug. If you have an electrician coming, have him inspect it closely.

 

Joe - the left lug is in the shadow of the box, while the right lug is getting the full illumination of the light.

Cooktop is working fine now, with all burners on high and a 50A breaker that is no longer sizzling or even getting warm.

Will have the main breaker checked on Monday. As stated before the right lug has good pass through of the wiring. I can't tell on the left lug though.