I replaced main breaker about a year ago and at that time saw that it had been arcing and the contacts on the box were black and pitted. Last weekend lost power several times for a few seconds. After checking the breaker box (no breakers tripped), I heard the main breaker arcing when dryer was running. I decided to replace the whole breaker box, but after doing so, I ran the dryer again and still heard occasional arcing after putting in new box with new main breaker. Is there anything I can do to stop the arcing of the main breaker when the dryer runs and is this a common problem?

Have you had this problem checked by a qualified electrician?

I need to understand this a little better.

Your dryer, is a 240 Vac 30 or 40 Amp dryer on it's own circuit?

The dryer is always on when the main breaker arcs and sparks, correct?

What is going on at the breaker for the dryer? Is it hot to the touch? If you shut the dryer breaker off, does the Main breaker continue to arc and spark?

Have you removed the dryer breaker to verify that the 2 load positions have not fused together?

Also, turn the main breaker OFF on the panelboard and verify that both HOT bus bars are OFF (0 Vac) and then make sure that the busbars are tight instead of loose,

Other than that, get a licensed electrician in to go over the branch circuit from thee panelboard to the receptacle.

The dryer is a 30 amp 240 V on a dedicated line with double 30 amp breaker at the box. Let me clarify when I say it's arcing. It's not sparking and I cannot see it arcing but I can hear it. It sounds like a fly buzzing off and on when it's dying on the floor. From the looks of the old main breaker and contacts on the bus bars it had been doing it for a long time. The dryer breaker is not hot to the touch. When it is shut off the arcing (buzzing) at the main breaker stops. How do I tell if the dryer breakers are fused together? Will it look melted together?

Are you using the same breaker for the dryer that you had in the old panel?

Yes. Should I change it? That will be my next move.

Deffinately change the Breaker, Once you have burnt and/or corroded contacts(Arching) you need to replace both connections(Breaker and Breaker Buss(what breaker plugs onto)), or the one you didn't change will take out the new one. Damage would be visible.

It was the main breaker that was and is still arcing and I did change out both the main breaker and the breaker bus. I didn't notice anything that looked out of the ordinary with the dryer breaker when I took it out of the old panel and put it in the new one, but I'm going to replace it anyway and see if that helps.

I would change the dryer breaker. Can't provide any logic as to why a the dryer breaker would cause buzzing in main but not expensive and easy enough to do.