Romex and rodents

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Electrician, semi-retired
I normally worked in a municipality where romex is not permitted, except in a certain few exceptions.
Now I am working upstate where it is allowed.

I don't like romex because when I was about 18, rats chewed up all the wiring in our garage and we
had to rewire with EMT. I have avoided it as much as possible since then.

Even where romex is allowed, I will choose to use MC cable. I was talking to a local EC about this
and he said although he agreed, people didn't want to pay for MC. He said he has seen some
rodent damage but not occurring often.

Have you guys seen rodent damage happen to romex ?
 
Occasionally, and when I see it they usually have boxes stacked so high and garbage around to attract rats. Unless you let them get out of controle then I can see an issue . I would assume a normal homeowner would get them under control
 
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They love chewing on data and phone cables! Replaced miles of it over the years in floor duct in grocery stores. From what I hear soybeans are used in the production of the insulation, and that’s why they like to eat it. The only places I’ve seen them eat romex, is where it goes through a hole, and they make more room to go through.
 
I just replaced my garage wiring with EMT because of mouse damage...

A number of years ago I was called to a radio station to investigate a tower light failure. The coax feeding the AM tower and tower light wiring traveled through a 200' wooden trough 3' above the ground, held up by wooden poles. Rotten, full of wasps, etc. The tower light breaker had tripped, so I started removing the cover of the trough.

This rado station is in the middle of farm country, and farmers did the wiring. Random lengths of NM (without ground), twisted and taped splices, covered in mouse pee, just nasty. About halfway down the trough, the white jacket disappeared. All you saw was two bare copper wires for about 50 feet or so. The wires touched at some point, tripping the breaker. I made a quick repair with some UF that was lying around, and worked to get that mess properly placed underground, where it has been trouble-free for years.
 
I see it from time to time. Last one I remember was in the hung ceiling of a commercial building supplying the lay-ins. I didn't know if the NM predated the prohibition of NM in hung ceilings or it was some jackleg's work. But squirrels had gotten into the space through holes in the concrete block wall where the roof support beams were placed. All that was left was copper in many places. For some reason none of it shorted out.

-Hal
 
A bit off topic, but I had a problem with mice and my 2017 Ford Escape. They would get into the engine compartment and chew on the wiring. Since then I noticed that Ford has issued a TSB saying that they changed the formulation of the insulation on the wire they now use because the old stuff actually attracted mice. Lets see what happens with my 2020.

-Hal
 
hillbilly1 said:
They love chewing on data and phone cables! Replaced miles of it over the years in floor duct in grocery stores. From what I hear soybeans are used in the production of the insulation, and that’s why they like to eat it. The only places I’ve seen them eat romex, is where it goes through a hole, and they make more room to go through.
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Is that what's happening when you see it chewed where it's coming out of the top plate? They're making room? I've seen that several times and was never really sure of what was going on.
 
Marshmo said:
Is that what's happening when you see it chewed where it's coming out of the top plate? They're making room? I've seen that several times and was never really sure of what was going on.
Click to expand...

Maybe you can use that to determine that it is a mouse problem. But I can tell you that squirrels don't stop at where it comes out of a hole.

-Hal
 
grich said:
I just replaced my garage wiring with EMT because of mouse damage...

A number of years ago I was called to a radio station to investigate a tower light failure. The coax feeding the AM tower and tower light wiring traveled through a 200' wooden trough 3' above the ground, held up by wooden poles. Rotten, full of wasps, etc. The tower light breaker had tripped, so I started removing the cover of the trough.

This rado station is in the middle of farm country, and farmers did the wiring. Random lengths of NM (without ground), twisted and taped splices, covered in mouse pee, just nasty. About halfway down the trough, the white jacket disappeared. All you saw was two bare copper wires for about 50 feet or so. The wires touched at some point, tripping the breaker. I made a quick repair with some UF that was lying around, and worked to get that mess properly placed underground, where it has been trouble-free for years.
Click to expand...
In SF Bay Area the initial BART data cable network used cable whose jacket was irresistible to gophers. It all had to be replaced.
The other big problem was an unreliable train detection system whenever a train was stationary coupled with software that cleared another train into block when the current occupant of the block disappeared from the middle.
 
Did a service change on a house surrounded by almond & other nut orchards, the rats had stripped all the insulation off the NM cable, where it went through the top plate into the old fusible panel, because of the orchards & a walnut tree on the property that is said to be the largest of it's variety in California, they have a good food source. BTW, that tree is huge.
 
Only call I've had specifically was about a foot of 14-3 NM in a crawl space, laying on a sill plate. Simple 2-box repair.
 
I wired a totally gutted lake house a couple of years ago. In the basement, I used a chase that was for the duct work. It was going to be covered when finished. One day the HVAC guy told me he found some skint wire. I looked and found some NM with the sheath ripped. At first I thought maybe it got hung on something when pulling it but I didn't remember having any difficulty pulling it. I repaired it and moved on.

Next day he showed me some more, so I thought maybe I had a bad roll of 14-2. So I replaced it and looked around and didn't see any more. A few days later I was shown more, this time it was 12-2 so I know it wasn't a bad roll of wire. This cable not only had the sheath missing but also bare copper showing for several inches.
Then it hit me.............. The builders told me the place was covered in rats/mice when they started demoing walls and wiring. The place had sat empty for years and the mice had taken over.

These nasty critters were actually eating the wire as fast as I could install it. I had the builders put out poison and traps and leave the ceiling and walls open where the damage was so I could check it after a few days. Finally there was no more damage that I could see. So I guess the poison took care of them.

ETA: I read that mice/rats have to keep chewing on things to wear their teeth down as they are constantly growing. I still say that NM must taste like peanut butter to them!
 
It's kind of incredible to me that in some cases, having bare wires didn't even trip the breaker, or worse.
 
I see gnawed wires periodically

most was sensor wires in attics of pig barns, got a lot of work replacing and repairing. then the farmer got more consistent with poison and profit stream dried up
 
Rodents like the rubber pieces for bedding, soft & warm.

If they can get to it, they will 'eat' it.

I once has a squirrel taking the foam from a patio table chair cushion and lining the hole in tree for self, well, a little fire foam took care of the squirrel's living room.
 
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