Removed the cover from a home circuit breaker panel (in the basement) in preparation for doing some rewiring and discovered that one or more squirrels had left a 'gift' inside the panel (see the photo below).

I have never removed the cover of the panel before this, and so I have no way of knowing how long this stuff has been accumulating.

I doubt that the pests actually got inside the box, rather I suspect that it's more likely that they made their deposits through one or more incompletely-stuffed knockouts on the top of the panel (but I will have to take a closer look tomorrow to see whether there may be some other access point that I've overlooked). At first glance, I don't see anything that looks like bite marks on any of the insulation.

I'm not concerned about PPE for the electrical side of things - I have plenty of experience in that regard - I'll shut off the main breaker, keep my arms and other body parts clear, not wear any jewelry, and will not otherwise do anything stupid electrically-speaking inside the panel.

What I'm less sure of is hazards associated with the rodent debris. Is the discoloration on the wires (most easily seen on the white 'neutral' wires) likely to be from squirrel urine or feces? I'm not sure what either of those would look like on the wiring, but I don't particularly want to come into direct contact with it so I'm thinking of wearing thick nitrile gloves while cleaning out the debris. I also don't know whether the stuff may be corrosive, or if it is, how best to neutralize it or clean it off.

I'd imagine that some kind of respiratory protection would also be good while removing the debris - I have some N99 masks, for example, but I'm unsure of whether or not those may be suitable for such a task. Who knows what kind of pathogens may be lurking - but with the pandemic panic that's going on it may be hard to get my hands on anything better than that right now (I think that I have a 3M respirator mask somewhere, but don't know the type of filter or its suitability - it's at least several years old, too, and so if there may be an expiration date, no doubt it has long since passed).

I should be able to tape up some plastic around the panel and then shove most of the debris into a plastic trash bag that I can then close up. I'm not sure whether following up with something like a paint brush to get out remaining dirt or dust is a good idea. I'm also not sure whether using a shop vac is a good idea, or whether that will possibly end up spraying particles of rodent feces that might get past the vac filter around the basement through the vacuum's exhaust port. Not sure if it's necessary, but I could probably wear a tyvek coverall when cleaning the debris out of the panel.

I've done some reading about the topic online, but I'd like to supplement that with suggestions based on practical experience if anyone here has some to share...

Just clean it out and dont electrocute yourself.

Turn power off from the street side

Shop vacuum

Done

You are so lucky you did not have a fire.

Could you clean that up and take pictures of the neutral bar and the contacts on the breakers where your wires connect?

A couple of those wires look kind of bad but it’s super hard to tell what’s mess and what might be burnt wire.

ETA: turn off the main 100amp breaker, and don’t touch the contacts on it at all. Wear leather gloves and nitrile underneath if it makes you feel better. I would definitely do a respirator too.

A couple of those wires look chewed.

If you feel really sketched out, call your power co and ask for a service shut off for the day.


Another edit: sorry, I’m used to speaking about this kind of stuff to apprentices, so I’m assuming a few things i shouldn’t be.

If you turn that main off, check both sides of the bus with a meter before touching anything. There is most likely some exposed copper ready to bite you thanks to the little assholes that lived in there. The wires coming out of the area by the meter will remain hot, do not touch anything up in that area unless you get a power company shut off.


Try a gentle degreaser like simple green, use more elbow grease than cleaning product.

Thanks for the suggestions - it looks like my initial inference that the debris was left by a squirrel may have been incorrect, and that instead the acorns may have been added to the pile by mice (along with the fiberglass insulation and who knows what else). I understand that mice can squeeze through fairly small holes, and so will have to look for candidates. I'm wondering whether spray foam insulation may be used to seal up holes that lead into power panels, or whether there may be some other material that may be more appropriate for use in or around a power panel.

I will take appropriate precautions and remove the debris, and then take a closer look to see if there's any evidence of chewed insulation.

There is a similarly-sized subpanel just to the left of this one, and so I will be removing the cover from that panel as well, to see what other delights may be in store for me...

After removing the debris and a once-over with some Simple Green I haven't seen any evidence of chewed wiring. The wires that had the 'charred' look were actually just encrusted with crud, which came off when scrubbed with the tip of a foam paint brush:




Remarkably, the adjacent subpanel was almost pristine:




Mouse traps have been deployed.

Thanks again for the suggestions.

It is hard to tell for certain from the photo (and the panel has already been closed up, so I can't do an immediate visual check) - but the appearance of those two spots is consistent with the appearance of other areas that were heavily crud-encrusted before cleaning (I did not apply the Simple Green that high up inside the panel).

A chew mark on that particular cable would not be a major concern in and of itself, because it is the neutral conductor from the service entrance meter (although if it were verified as a chew mark, it would indicate that a much more detailed inspection of the rest of the wiring would be in order).

I intend to remove the cover again when I apply sealant to the knockout holes that are not fully blocked (in order to prevent overspray) and will take another look then - I picked up a can of the 'Great Stuff' foam sealant that has a supposedly pest-resistant bittering additive https://www.amazon.com/GREAT-STUFF-Pestblock-Insulating-Sealant/dp/B007TUF0FY

How about the grey clay stuff for sealing through the wall entries.  

Mice don’t seem to eat that stuff.