Corrosion inside electrical outlet box. What should I do?


So we repainted our family room. It is in the the “basement,” but technically most of this room is at ground level. I was changing the outlets and light switches to white instead of the cream color that were there when we moved in (the house was built in 1961, we have owned it for one year).

I was down to my last outlet, one that we had never used before. When I checked it with my multimeter to see if I had the correct breaker off, the multimeter read 2.4 volts. Once I had the correct breaker off (now reads 0 volts), I opened up the outlet and saw some corrosion on the wires and box itself.

One of my problems is that I do not know when this water damage happened. It could have been from a long time ago and the previous owner fixed the leak but didn’t know the outlet was damaged. Or it could be from something right now (nothing appeared to be wet, but it might only get a few drops when it rains).

There are no water pipes in this area of the house and all the way above it to the roof. The outlet is on an exterior wall, but there are no issues or signs of a leak on the outside of the house (brick and concrete).

  1. Is there any way to tell if this is a current leak or a past one? I don’t really want to rip the wall apart trying to figure this out. I don’t have the knowledge to repair it, and I would prefer to not have a bill for hundreds of dollars for a problem that doesn’t exist anymore.

  2. If the leak is not a problem anymore, is there any reason I can’t continue to use the electrical box? It appears to just be surface rust, no reason to think it will collapse. I assume I can just clip off the ends of the copper wires and continue on?

Clean out the box, re-strip the wires, and replace the outlet. Take a picture of the empty box after you’ve cleaned it out. In six months, pull the outlet and see if anything has changed.

I’m guessing that there is fiberglass insulation directly touching the concrete wall with no vapor barrier and the fiberglass gets wet from condensation. If that’s the case, the fix is to open up the walls and insulate them properly.

It’s hard to tell because it’s kind of blury, but if the wiring is the type that has a seperate ground wire and the box is in good mechanical shape I’d just make sure to run a grounding wire from the outlet (which is a good idea anyway) rather than relying on the metal box.

You should also make sure that the outlet is either a GFCI outlet or is protected by another GFCI outlet (“protected” by being downstream from a GFCI outlet).

no need to clip the wires, sandpaper to shiny metal.

such damage can occur from a damp environment. if it is damp enough to rust the box it will also rot wood and cause other problems. if the room is used for people functions then you need to keep it dryer.

if the box is mounted from the front then i would remove it and replace it. this will allow you to see the condition of the electrical cable and some of the wall behind and near the box.

for the box to be effective you would like it all shiny metal. you would want the bare grounding wire to attach to both to the box (as it is) and to the receptacle.

pushing the wire in the back is not a good method to wire switches and receptacles; around the screw is better.

very good on checking voltage before touching. a safe move.

have these served by a GFCI outlet as the first in a string, read the instructions if unfamiliar.

Is this outlet at the same level as the other outlet you worked on? That drywall looks undamaged and fairly new. Perhaps there was a flood and for some reason they didn’t get around to replacing one outlet. You should be able to get a humidity/moisture level meter and test the area around the outlets and see if there is a problem in that area.

Also, any signs of animal urine on the face plate you removed?

Good suggestion.


There is a ground wire to the box. I will need to clean that up. I always run a ground directly to the outlet also.

How hard is that? Just changing to a GFCI breaker and outlet?

It is mounted from the side, so I can’t easily take it out and look around.

No signs of urine. I have worked on others on the same level. There are no other signs of flooding, but I suppose it could be possible. I don’t know how old the dry wall is, but we just painted it, so it looks decent.

I have thought about a humidity meter, but I am not sure how to use it. If it gave me a number (XX%), I wouldn’t know if that was good or bad. I don’t think the moisture is overwhelming, because there is not THAT much corrosion, and I assume these have been in there a while.

yes, it’s simple: just replace the outlet with one of those with a built-in GFCI circuit, or replace the breaker back in the box with a GFCI breaker. (But not both – having 2 separate GFCI’s in a circuit will lead to spurious false-alarm breakings – not dangerous, just annoying).

A GFCI outlet is cheaper, but protects only this one outlet, and any wired downstream from it. (Ifg you do this, please remember to put those little “protected by GFCI” stickers on the downstream outlets – it will save lots of frustration for someone in the future (possibly even you) trying to figure out why this outlet won’t work even though the breaker is on and the wiring looks intact. A GFCI breaker protects all outlets on this circuit, and is cheaper than several GFCI outlets.

Also, don’t be concerned about the 2.4volt reading from before. Most multimeters don’t accurately read AC wiring voltages when unloaded. Even your newly replaced outlet will likely not show the proper 120 Volts on a multimeter. Don’t worry about that.

I understand how a multimeter can read too high of a voltage, but how will it read too low?

It was my assumption that it tested low because the contacts between the wires and outlet were corroded (green). I tested the wires after they were removed and they tested ~120V.