Taking the cover off my electrical panel, I notice white flakes primarily on the hot bus bar just after the main breaker and under some of the individual breakers. The breakers I have removed for replacement show no problems on their conductors (they are being replaced because of circuits being replaced, I figure why not spend a few extra bucks on renewed critical safety equipment).

Are these white flakes corrosion? A home inspector did not report any sign of corrosion or moisture in the service panel, but this is subtle. That said, these white flakes are visible on the hot bus bar under the main breaker, as in this photo:

White deposits on hot bus bar under main breaker in electrical panel

Here are two more photos showing these white deposits under a breaker that was removed:

White deposits under breaker on hot bus bar in electrical panel

White deposits under breaker on hot bus bar in electrical panel

One other breaker was removed and had less but still some of these white deposits on the hot bus bar.

Is this corrosion, indicative of a moisture issue? Is this a safety hazard, or just something to prevent from getting worse? In case it is relevant - outside the house on the other side of the service panel, the electric meter box does show signs of rust and we need the utility company to come take a look at that.

For context, this is in a temperate climate far from coasts, on a house that is about 60 years old and otherwise seems well constructed and maintained. The house is basically all electric, with baseboard heaters and an air-sourced heat pump, electric stove/oven, electric water heater, and electric well pump.

  • Corrosion is not good between electrical contacts, where breaker contacts the bus bar. It causes increase in resistance, causing extra heat. Are you near salt water or smelly industrial plant?
    – crip659
    Commented May 31, 2022 at 14:02
  • @crip659 added a little more context. No salt water nearby. Heavy past industry, but lots of fresh air around here. House otherwise seems well maintained, but moisture could be coming through the meter box outside somehow.
    – cr0
    Commented May 31, 2022 at 14:34
  • So this does look like corrosion to you? Not sure what else it could be. The main breakers and other breakers do not feel warm at least, but of course I'm touching their insulated surface and not their conductors.
    – cr0
    Commented May 31, 2022 at 14:39
  • 5
    Far more important than "replace breakers because of circuits being replaced" is replace breakers that don't belong. Assuming, based on most of the breakers pictured being QP breakers, that the panel does not take BR breakers, you need to replace the BR breaker (the blue handle). Please upload a picture of the entire panel and a picture of the instruction label - usually on the inside of the door. Commented May 31, 2022 at 14:52
  • 2
    While the air now is clean and fresh, "Heavy past industry" could have been pumping chemicals into the air that may have caused these deposits years ago.
    – FreeMan
    Commented May 31, 2022 at 16:19

2 Answers 2


That looks like good old aluminum oxide.

Is aluminum oxide a problem? It can be but this looks like it is on uncoated edges, you can stop it from getting worse with a deox or noalox (oxide inhibitors).

A plastic artist brush can be used to first knock the loose stuff off then spread some noalox on the aluminum. I do this on connection points, many are nickel coated aluminum but the coating gets scratched during assembly.

As far as some rust on the box this is also not a big deal but if external I might touch it up. Rain and humidity cause both problems and it is somewhat common on external and basement panels.

Is using noalox safe to put on breaker electrical connections, yes. It’s not only safe but most manufacturers put their custom blend on the plug in part of the breaker and it is recommended for all aluminum parts.

Part of the problem may be the alien breakers made for a copper buss may not have had the oxide inhibitors and that is the root of the problem as dissimilar metals and electrical currents without an oxide inhibitor cause damage to the least noble metal, in this case the buss bar, so hopefully they are not two badly damaged

That bussbar needs a good cleaning and a thin coat of a oxide inhibitor.

It would be best to clean and protect with the main turned off, the oxide is not conductive but you are and it looks like some work is needed to clean up from the alien breakers.

This is not the power company’s problem but yours. It might be a good idea to have a pro inspect to see if the damage warrants a replacement for safety.

  • Thanks for the very clarifying answer. That makes sense of a few points. I did have the utility company out here today and they confirmed, it seems like water is creeping into the meter box because of a poor water-sealing where the utility's service line connects with the house's main line. They did not look in the panel but said it is probably aluminum oxidation from the sound of it, likely not serious if no electrical symptoms (e.g. flickering lights). We'll have a pro take a look, helpful to know these details you shared.
    – cr0
    Commented Jun 1, 2022 at 0:58

That’s not corrosion it’s a sealant applies in the factory to Semens breakers. It to prevent from tampering with that screw and is sometimes over sprayed. Not corrosion this isn’t a battery.

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