My main panel is 100 amps and was completely full with about 10 breakers. About 5 years ago I had an addition put on the house and the contractor said that the service would need to be upgraded (but didn't specify how). After the licensed electrician left ,I realized that he had installed a subpanel in the garage with 4ga copper wire with 8 more breakers on it and a 60 amp breaker for it in the main panel . This was all inspected by the town and approved.
I had no problems till about a month ago when the lights (only those coming from the subpanel) started dimming. ALOT(I measured a voltage drop of >15v for a few seconds). I had the local power company come . They replaced all connections to the house and wires on the poles and the neutral block in the meter pan. No signs of water in the meter pan. The main panel had signs of moisture/rust from when the house was first built 24 yrs ago and the basement was damp. The main breaker had residue of rust leaking from the switch. I replaced the main 100 amp breaker. One contact was rusted ,the other looked burned. I had to clean up the buss bars before installing the new main. The problem stopped for a short time but is back.
I haven't pulled the main breaker to inspect it but I'm wondering if my service should have been upgraded to 200amps before adding the subpanel?
Any thoughts on this would be appreciated. Thank you.

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Originally Posted by redmax

My main panel is 100 amps and was completely full with about 10 breakers. About 5 years ago I had an addition put on the house and the contractor said that the service would need to be upgraded (but didn't specify how). After the licensed electrician left ,I realized that he had installed a subpanel in the garage with 4ga copper wire with 8 more breakers on it and a 60 amp breaker for it in the main panel . This was all inspected by the town and approved.
I had no problems till about a month ago when the lights (only those coming from the subpanel) started dimming. ALOT(I measured a voltage drop of >15v for a few seconds). I had the local power company come . They replaced all connections to the house and wires on the poles and the neutral block in the meter pan. No signs of water in the meter pan. The main panel had signs of moisture/rust from when the house was first built 24 yrs ago and the basement was damp. The main breaker had residue of rust leaking from the switch. I replaced the main 100 amp breaker. One contact was rusted ,the other looked burned. I had to clean up the buss bars before installing the new main. The problem stopped for a short time but is back.
I haven't pulled the main breaker to inspect it but I'm wondering if my service should have been upgraded to 200amps before adding the subpanel?
Any thoughts on this would be appreciated. Thank you.

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I am not clear as what the garage panel has to do with the remodel. Is the garage attached? The service is an overhead I gather and has moisture issues possibley. Any water stains around the main panel which is in the basement I take it?
The dimming is due to a loose neutral connection on the ground bus if only the lights are being affected. Please indicate if the above is correct. Nm

While a loose shared neutral may cause some lights to dim, it will always cause other lights to be brighter due to higher than normal voltage.

The voltage drop can be due to high resistance of the corroded bus connection the Main breaker connects to, that you mentioned you had cleaned once before. The metal is difficult to clean properly, and sanding you may have down removes material from the contact surface that the breaker needs to come in contact with.

The panel may now need to be changed to replace the corroded bus tabs that Main breaker plugs onto. Replacing the breaker that got wet was correct, and breaker that gets wet must be replaced. I don't think you can save the bus bar now thou. And the contacts on the new breaker may be burnt also.

I don't think a larger service is the needed, if it was the Main breaker would be tripped due to overload. But if the panel needs to be changed, now may be a good time to consider replacing the entire service.

First ,let me answer NM's questions: The electrician mounted the 60 amp subpanel off the main panel in the attached garage because the addition is directly behind the garage and the main is about 60' (by routed wire length)from the subpanel. I suppose it was easier/cheaper to run the 8 circuits to the nearby subpanel in the garage than to route them to the main panel. Anyway the main panel was full.
Yes it is an overhead service ,the meter is on the outside wall of the house and the main is in the basement. When the technician from the local power company came he inspected the meter pan , the feed down to the main panel , and the main panel(even though he isn't required to) and felt that it was all sealed well and no water was getting in to the main. That's when we noticed the rust stain on the main breaker.
The rust stain looked like it was from rusty water that had come out of the main breaker (about 1/4" long stain).
I forgot to write yesterday that the first thing I had done when this dimming started to occur was to tighten all the neutral connections. I did not find anything to be loose.
I hope this explanation helps. Please let me know.

Now to answer TK: The voltage is not always low. When it gets dim it flickers quickly which is why I called the power company because it seemed like it could have been due to an outside feed line blowing in the wind with a poor connection. But it wasn't.
It seems to almost always occur when the electric garage door(which is wired off the subpanel) operates so I monitored that line with a meter and continuously opened and closed the garage door for literally 20 minutes. During that 20 minutes, the lights only dimmed once for about 5 seconds which was when I saw it drop from 120v to 104 v.
I was wondering what the buss bar was made of. It looks like aluminum but wondered if it was plated and if like you said ,I had damaged it by sanding it. But it looked like it would make such a poor connection to the new main breaker that I had to clean it up. Also ,I am noticing now that there is white fine flakes on the bottom inside the panel like corrosion of some sort. Ever seen anything like that?

Thanks again to both of you for taking the time to read and answer this.

Sure have , the white flakes is the aluminum bus bar oxidizing.

For the load you have the voltage should not be sagging down to 104 volts.

The poor contact is due to high resistance, and will be creating heat, that will erode the contact further, and damage additional parts of the panel. The problem will not get better on it's own.

Hi Redmax,

Thanks for the precise answer. One thing I wonder about now, is the feed to the subpanel, is it a 4-wire hookup with the bonding strap disconnected. The neutral must be isolated from the enclosure. As tk mentions, the white in the main panelboard bus is oxidization. Replacing those abraided aluminum bars may take more than it is worth to replace the whole main.

The rust in the main and accelerated oxide flaking is an indication that there is a high moisture sweating condition in the basement. A small baseboard heater near the panel will cut that down. (Up in the great NW we install a 500w baseboard in the fire control equipment room to stop condensation in cold weather.) I am not sure what you have but if the description here matches what you have, give it a try. Nm:)