Rodents in the cable tray

[69gp]

Thought I would put this out there for others. Had a 2.5 meg inverter go down on a ground fault. Went to the site to start looking for the fault and found a small grass area roughly 8" x 18" under a cable tray burnt. A few minutes later full blown fire in the cable tray with about a 2' section missing. Believed to be caused by rodents chewing on the string wiring that then shorted out and melted through the feeders causing a dead short in 2 400 amp CB. Cable tray has covers that will be removed to expose the wiring so that hopefully hawks and owls will take care of the probleum once repairs are made.
Arrow indicated where the fault is located above in the cable tray.
5 minutes later.

 

[ggunn]

Any crispy critters?

 

[ptonsparky]

Any crispy critters?

MIce, I found, but never ever a gopher.

 

[texie]

Gonna be a costly fix for sure.

 

[69gp]

Any crispy critters?

No its so hot that nothing is left. This from another incident. Check out the deep galvinized Unistrut.

 

[69gp]

MIce, I found, but never ever a gopher.

Mice and rabbits is what we have found

 

[Zee]

Any arc fault protection or ground fault protection?

 

[shortcircuit2]

It may be less of an issue with open top tray as a replacement. The birds will keep the varmints out of the tray then.

 

[69gp]

Any arc fault protection or ground fault protection?

There is ground fault protection. The inverter did trip offline. This event happended between the modules and the combiner boxes. So there is no protection that you can have that will stop the arcing unless you can open the MC connectors at the strrings, cover the modules or wait until the sun goes down and then disconncet the strings. Opening the strings during an event like this draws a huge arc as you have 27 modules in a string.

 

[Fred B]

I've seen rodent damage before but this is probably the ultimate meltdown. AL trays assumed? How did the cascade event finally extinguish?

 

[ggunn]

Mice and rabbits is what we have found

We have found lizards in MDPs pretty often with their dessicated bodies bridging the service conductor lugs, and a snake one time.

 

[ruxton.stanislaw]

Jeez, if air tight, perhaps these types of trays could be filled with something like chrysanthemum/onion/rosemarry/elderberry infused mineral oil or something else that the rats will avoid like the plague. I suppose something to consider is how that would impact the temperature of the conductors. It wouldn't be fun to deal with, but it's better than the entire thing being annihilated.

 

[Fred B]

Jeez, if air tight, perhaps these types of trays could be filled with something like chrysanthemum/onion/rosemarry/elderberry infused mineral oil or something else that the rats will avoid like the plague. I suppose something to consider is how that would impact the temperature of the conductors. It wouldn't be fun to deal with, but it's better than the entire thing being annihilated.

Would like to see something like that incorporated into the NM plastic sheath, seen alot of that chewed up. Interesting thing and not sure if it is real or not but it seems they don't like the K&T as much as the NM. Job on right now and K&T running along side of some NM and the NM is all chewed up but the K&T - not a knick.

 

[PaulMmn]

Would sprinkling hot pepper sauce among the wires before closing up be useful as a deterrent?

 

[ptonsparky]

Bear spray only works if sprayed in there faces. They like the taste of it otherwise. IDK if that's relatable to rodents or not.

 

[ruxton.stanislaw]

Would like to see something like that incorporated into the NM plastic sheath, seen alot of that chewed up. Interesting thing and not sure if it is real or not but it seems they don't like the K&T as much as the NM. Job on right now and K&T running along side of some NM and the NM is all chewed up but the K&T - not a knick.

This reminds me of the few years when car manufacturers started incorporating soya bean into their automotive wiring insulation -- I'm not sure why, to be eco-friendly or reduce costs?. It caused a lot of issues with the rats targeting those vehicles specifically because they can find or smell the soy.

 

[Zee]

There is ground fault protection. The inverter did trip offline. This event happended between the modules and the combiner boxes. So there is no protection that you can have that will stop the arcing unless you can open the MC connectors at the strrings, cover the modules or wait until the sun goes down and then disconncet the strings. Opening the strings during an event like this draws a huge arc as you have 27 modules in a string.

oh wow. makes sense.

 

[jaggedben]

Seems like string level arc-fault detection devices at the modules could be worth something.

 

[Zee]

Could this happen on an older residential system with DC strings and no MLPE?
Inverters from around 2000-2010 had no AFCI.

Are these parallel arcs? I.e., the DC positives and negatives of each string are short circuiting?

What would prevent such a disaster? It is one thing in a field and another on a wood house.

 

[Buck Parrish]

Would sprinkling hot pepper sauce among the wires before closing up be useful as a deterrent?

I have used liquid tape smeared in areas I thought rodents might enter. It has a chemical smell, it is sticky and UL approoved to be on wires.