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Not long ago, I was asked to investigate the source of corrosion in the electrical service panels for a couple living in Northern Minnesota, whose home was built in 2001. A general service panel (far right in the lead image) and two controlled-load panels (electric in-floor heating cables supplying heat to both the garage and home; left panels in photo) showed signs of severe moisture damage. The original service panels, which were installed when the house was built, were replaced in 2022. Deterioration of the replacements in less than one year has warranted a third set of electrical panels.
Because it’s not uncommon to find corrosion in electrical panel boxes, I thought I’d share my findings here. It might help others troubleshoot the cause/s when they see it. The following is a copy of the report I sent the homeowners.
Using building diagnostics
The service panels are in the garage on a common wall shared with the conditioned living space. The panels are installed inside a 2×6 wall cavity with what appears to be 2 in. of extruded polystyrene (XPS) insulation between the back of the panel and the drywall of the conditioned space.
The garage has an in-floor heating system, which hasn’t been operating since March 2022; two small electric space heaters were conditioning the space when I was called in. There is a floor drain, and at the time of my first visit, a dehumidifier was going. (Mechanical dehumidification began after damage to the new service panels was noticed.) The homeowners indicated they have seen garage humidity levels as high as 70%. The temperature inside the garage is typically 50°F.
The photos below show the corrosion and rust in the panels after one year:
I installed three sets of SensorPush HT.w temperature and humidity monitors around the house and…
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11 Comments
Randy,
It's very common, but do you think it's a good idea in most climates to locate the panel in a garage, no matter how diligently it is done?
There are several reasons I think locating it in the garages is a good idea, none of which have to do with climate.
1. Future work doesn't interrupt the living conditions.
2. When the electrician leaves you can clean up after him with a push broom.
3. It's a potentially short run for high current draw items (generator inlets and car chargers)
The cons, independent of climate to me are
1. Increased total wire usage
2. Stepping through a messy garage in the dark, trying to get to the breaker box
3. Reluctance to 'check on it' every now and then to see if anything is amiss
Throw the climate aspect in, and I can see why it would be a good idea to locate it in the interior of the home in zones 5+.
Kyle,
Around here it is also usually not air-sealed adequately, and often shares a wall with the conditioned house.
For me the ideal setup would have the panel and all communications boxes mounted on an interior wall of a centrally located mechanical room, fed from the conditioned crawlspace below, and with good access to the trussed roof above. The panel would be mounted in a large stud bay, surrounded by a full-height removable plexiglass panel, allowing both easy access, and a view of the perfectly laid out cables behind.
I'd never considered the plexiglass, but that could count as industrial art! Mine might look a bit more ... abstract.
I like that idea very much.
I might not go as far as the plexiglass. But I'm thinking of those nice old ironing boards that folded up into a stud bay and had a frame and panel door front. Something like that in a convenient but inconspicuous place inside the house would make a lot of sense.
Speak of the devil - I just installed one of those ironing boards last week. Was great to be able to send the big awkward one that leaned against the wall in our small laundry room to the thrift store.
"Speak of the devil - I just installed one of those ironing boards last week."
Nice! I should be including them in my work. I need to find out who still makes them.
Won't the problem move from the electrical panels to the HRV?
That must be mostly due to the salt in the air judging from the severity of the corrosion.
I doubt that the salt is becoming airborne after drying on the floor. The pictures show what look to me like standard corrosion. I don't see salt salt crystals. I'd bet that the condensation is enough to do that and your theories re broken floor heater is valid.
This is puzzling. Given that it's generally slightly warmer than the garage, garage air coming into the panel shouldn't condense. It might actually be the reverse--it might be that basement or house air, which is warmer and has a higher dew point is coming into the panel and condensing there.
I'm not sure about the salt--is the minute amount of salt that becomes vapor when salt water evaporates enough to cause a problem? Certainly most is left behind but if we can smell it, there must be some in the air.
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