Are rodents the cause of most electrical fires?

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electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
Occupation
Electrician
I'm starting to believe this more and more. I see tons of rodent damage to ramen. One in particular I saw a month ago was a very close call. It was a kitchen counter outlet not working. Looked under the sink and there was some holes in the paneling, saw a wire and gave it a tug and it pulled right out, chewed right through. I could smell the mouse nest. That end was pretty clean but punched another hole in the paneling to see the other end and it was like a foot of blackened carbonized stuff that sparkled and crinkled when I wiggled it. My house and shop are getting MC or EMT.
 
electrofelon said:
I'm starting to believe this more and more. I see tons of rodent damage to ramen. One in particular I saw a month ago was a very close call. It was a kitchen counter outlet not working. Looked under the sink and there was some holes in the paneling, saw a wire and gave it a tug and it pulled right out, chewed right through. I could smell the mouse nest. That end was pretty clean but punched another hole in the paneling to see the other end and it was like a foot of blackened carbonized stuff that sparkled and crinkled when I wiggled it. My house and shop are getting MC or EMT.
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But you have got rodent proof building code in your country.
Not implemented code provisions?
 
electrofelon said:
Maybe, but I always figured those issues would be in a box with limited likelihood of something catching fire
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Over time dust/lint or insects and what they may leave behind helps increase likelihood of spreading.

As far as dwellings - I guess I haven't been in enough that are so bad the rodents are a huge problem. Not that there aren't any at all around here, I just lucky enough I guess to not get too involved with many of them. I will say I see many cases of space heaters and other similar loads on extension cords, even undersized extension cords. Cords under a rug across a doorway or other walk way, only outlet in the living room or at least the one area with all the electrical items that has the TV, the electric fireplace, or in summer a window AC, and everything else they use in that room in a power strip or even cascade of power strips, and on top of that is on 14 AWG branch circuit protected by a 30 amp plug fuse that they replace every so often because it blows.

Now if you have rodent problems they probably add more to this with combustible nesting materials more so than because they chewed insulation off conductors. I seen them bare conductors that are just fine as long as they never get disturbed they won't short out. If they do short out they are taking OCPD with them, so as long as any sparks don't ignite anything they still aren't as big of a problem as an overheating connection. JMO.
 
Sahib said:
But you have got rodent proof building code in your country.
Not implemented code provisions?
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New buildings usually isn't the problem areas.

Doesn't have to be 100+ years old either, there are 20-30 year old buildings that were pretty rodent proof when new but have not been maintained and no longer are very rodent proof.

Long time ago we had a farm house we wired new. Someone we also did work pretty often on the farm for. He complained about mice in his attached garage (of the new house) often. Me and my boss were talking about how you drove by that place and at least one door on the garage was almost always open, wonder how the mice were getting in?
 
As far as how do they chew off insulation and not get electrocuted, I think their teeth must be good insulators.

Keep in mind they normally are not eating this insulation but rather gathering it to use as nesting material.

I've encountered up to 277 to ground underground conductors many times that was rodent damaged and never that I recall seen a dead rodent at the damaged area. Also seen many electrical enclosures that maybe had an open KO and they get inside and chew off a lot of insulation. Seldom ever find dead rodent in those situations either. Most the time I have found a dead rodent was when their feet came across different areas of potential. Found them laying on line side terminals of fused switches or motor contactors or similar more than most anywhere else when I have found a dead one.
 
electrofelon said:
No we do not have rodent proof building codes.
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No emphasis is put on rodent proofing but most the designs and codes naturally do make the buildings rodent proof to for the most part as is when first constructed. Failure to maintain the as new conditions eventually lead to possible rodent entry. Failed seal on a door is a place to start. Even if the rodent can't get through the initial opening, they may end up chewing the rest of the way through.
 
I’ve seen a lot of rodent damage to wires in both residential and commercial (floor duct mainly) usually the wire in romex maintains enough clearance to prevent any arcing. I’ve even seen mouse carcasses across lugs of 480 volt panels.
I was upgrading the wiring on a house my old boss bought for his son. I was in the attic when I moved a piece of foil wrapped flex duct out of the way. Seconds later, smoke started billowing off the duct. Yanked the duct loose and threw it down the attic access hole. Someone had made a splice in a box on the rafter, and did not insulate it. All three wires were sticking up out of the box! Could have been a good electrocution hazard too!
 
electrofelon said:
There are a zillion jurisdictions here in the us, what I meant is there is no general or widely adopted rules or practices specifically about rodent proofing
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But appendix F Rodent proofing is present in the building code (IBC/IRC) adopted by the states. Please check.
 
The international building code (IBC) is in use or adopted in 50 states, the District of Columbia, the U.S. Virgin Islands, Guam and the Northern Marianas Islands.
 
Sahib said:
But appendix F Rodent proofing is present in the building code (IBC/IRC) adopted by the states. Please check.
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Ok maybe it is, the point is rodent proofing is in practice pretty much impossible in many buildings, no matter how elaborate the codes are. In 25 years in the trades, I actually can't think of a single instance of builders or code officials concerned with or talking about rodent proofing.
 
I think the worst I have ever seen was one time in a commercial building where the lay-ins in the dropped ceiling were wired with Romex along with every thing else which ran through the ceiling. Building was concrete block which had deteriorated enough to see the outside through holes when I stuck my head up into the space. Apparently squirrels had been there and there wasn't much left of any of the Romex sheaths. How it didn't short I don't know. I wasn't there for that so I just put the tile back in place and later mentioned it to the owner. He later sold the building to another sucker.

-Hal
 
Sahib said:
The international building code (IBC) is in use or adopted in 50 states, the District of Columbia, the U.S. Virgin Islands, Guam and the Northern Marianas Islands.
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Adoption has nothing to do with the real world installation and inspection practices in many areas.
 
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