Any tips for locating damaged wiring insulation?

[gatorgrabber]

I'm currently doing a full rebuild/remodel of my mid 70's era home, thanks to Hurricane Irma. I'm wondering if there's a decent way to locate any damaged wiring that may be hiding out of view in the attic or walls. I've already located a nail that was driven thru a 14/2 line in the wall behind a cabinet...nice! This, of course, set loose the semi-paranoid demons in my engineer's brain, making me wonder what other gremlins might be lurking.

I remember hearing a conversation (somewhere) where the guy was using some flavor of multimeter to find such damage. How, I'm not certain, hence this post. Any sage wisdom on how I might pull this off? Thanks!

 

[readhead]

Remove all the drywall and inspect? I think you are over thinking this.

 

[gatorgrabber]

With all due respect, I don't think I am. Remember, I've had hurricane damage to the roof. I did find another leg (the exterior lights in the soffit area) that also showed damage to the insulation on the wire. It has taken me 2yrs to rebuild my home and I'd prefer not to lose it to a damaged piece of wire.

My question then, other than a visual inspection (which I'm doing), is there a way to verify the integrity of a wiring run? I'm planning on replacing the existing breakers with AFCI units, but that just brings my panel up to current standards and isn't much of a test.

 

[pizza]

yes, he is not overthinking it imo. this is a real concern.

in the case of water damage, it's perhaps wise to pay someone to 'meg' it (high voltage measurement of the insulation resistance of your wiring runs). google 'megger' and 'insulation tester'.

here's one post to get you started https://www.electriciantalk.com/f29/megger-residential-wiring-120866/#post2189442

also, even wiring that didn't get directly exposed to water should be subject to inspection.
water can wick up through the wiring via capillary action, in some cases several feet above the original water level.

and really, imo replace anything that was underwater. don't even bother megging it.
imo, megging is more about considering whether or not you can salvage wiring runs above the water line that may or may not have wicked up water or have been otherwise compromised. talk to your town's electrical inspector! harass him and get his opinion.

 

[LOW1]

If you had significant water in the house I would rewire the place. Did your panel get wet?

 

[readhead]

The OP didn’t really provide much info. If the house was flooded then the wiring should be replaced. Now we go down an insurance rabbit hole. Next, was that nail in the wire there for forty five years or was it a recent addition? Back in the seventies we were installing cabinets with nails because deck screws weren’t on the scene yet. Back in the seventies and eighties when I was doing a lot of remodeling it was common to find wires with nails in them. That doesn’t make it okay and fortunately there are more requirements to protect wires today. There is more to this story.

 

[gatorgrabber]

Megging...that's the term I was trying to remember! I'm going to dig into the link you were kind enough to provide this afternoon. A bit more info on the damage done to the house so folks have context. I'm inland in N FL, so we didn't have any storm surge to deal with. What did happen was tree damage to the roof. With that came water flooding in thru the holes before I could get a patch on them. Fortunately, the damage was on the opposite end of the house from the breaker panel, so it didn't get wet.

The wiring damage I'm concerned about is on the corner of the house where the impact occurred. I can't easily reach areas where the roof meets the exterior block walls. So, short of tearing everything apart (overkill), I'm trying to validate the individual legs and insure I didn't miss anything. The info here has been very helpful, thanks!

BTW, the nail thru the wiring was done when the house was first built years ago. I just happened upon it when I was tearing drywall off to be replaced. From what I've seen, they didn't pay close attention to building codes around here in the 70's!

 

[AntonLargiader]

Dunno what it involves to meg it but if you're going all AFCI/GFCI anyway, they should alert you to anything that is or becomes a problem. IMO they are truly intended to catch stuff like that.

 

[Bretny]

A megger won't really tell you much that an ohm meter will on a DVOM. You won't detect a crack in the insulation with a merger.

If that nail lasted since 1970 what's to worry about now? The only thing that changed since then is you found it.

 

[MattT]

I'm planning on replacing the existing breakers with AFCI units, but that just brings my panel up to current standards and isn't much of a test.

AFCI breakers will continuously "test" your wiring. Or if you want tighter ground fault protection use dual function breakers. That said connecting 40+ year old wiring to either breaker type is opening a can of worms. Keeping each neutral isolated from ground and other neutrals didn't cause any obvious problems back then but these faults will trip *CFI breakers. Sometimes intermittently. So you'll likely be hunting down wiring faults if you go that route.

You really should just re-wire the place.

 

[gatorgrabber]

My approach to the electrical system has been to replace wiring that's damaged, upgrade legs to better suit how I use the house and replace all switches, outlets and fixtures to update the look of the home. Basically, all that remains of the original electrical system will be wiring in the walls and the service panel. When in doubt, I upgrade.

 

[Innovate1]

A megger won't really tell you much that an ohm meter will on a DVOM. You won't detect a crack in the insulation with a merger.

If that nail lasted since 1970 what's to worry about now? The only thing that changed since then is you found it.

A megger uses much higher voltage than a vom so will find marginal insulation but only to other conductors. A vom will only find direct shorts.

 

[Kevin54]

Gatorgrabber......Ask NUTTS_GT on here. He's a fireman and is up on this sort of thing. It's something you don't want to take lightly.

 

[gatorgrabber]

I'll get in touch, thanks for the suggestion. I don't take the chance of a house fire at all lightly, having been in one as a kid.

 

[NUTTSGT]

Gatorgrabber......Ask NUTTS_GT on here. He's a fireman and is up on this sort of thing. It's something you don't want to take lightly.

There's not much I can say other than to follow the advice of the guys that frequent this section of the forum. There are some very talented and knowledgeable guys in the Electrical Section.

Personally, if I had any doubt of the condition of the wiring, switches/outlets or breakers, I'd switch them out.

If you have the drywall off in a room, by all means use cable protectors that you hammer into the stud to prevent nails/screws from penetrating wires.

 

[PNWguy]

The last time I found an insulation problem was in the romex in my soffit. I flipped on the porch lights and tripped a breaker.

When I took things apart, I found a fried squirrel had chewed through the insulation overnight - and was working when I hit the switch. There was about 3 feet of uninsulated wire.

 

[nadogail]

FOLLOW THE SMOKE, that will pinpoint the damaged wiring, but you have to be very quick or the flames will destroy the evidence.

 

[Copymutt]

Please excuse my ignorance, naivety. What your going through sounds like a major pain and I sympathize. Why would you rebuild in a hurricane prone region? I get, family, kids school etc., but to me it’s like doing the same thing again and again but, expecting a different outcome.

 

[gatorgrabber]

I'm in N central FL, 60 miles from either coast. This wasn't storm surge, it was wind damage. As a native Floridian, I refuse to live within 10 miles of the coast for that very reason.

 

[wyliesdiesels]

Megging...that's the term I was trying to remember! I'm going to dig into the link you were kind enough to provide this afternoon. A bit more info on the damage done to the house so folks have context. I'm inland in N FL, so we didn't have any storm surge to deal with. What did happen was tree damage to the roof. With that came water flooding in thru the holes before I could get a patch on them. Fortunately, the damage was on the opposite end of the house from the breaker panel, so it didn't get wet.

The wiring damage I'm concerned about is on the corner of the house where the impact occurred. I can't easily reach areas where the roof meets the exterior block walls. So, short of tearing everything apart (overkill), I'm trying to validate the individual legs and insure I didn't miss anything. The info here has been very helpful, thanks!

BTW, the nail thru the wiring was done when the house was first built years ago. I just happened upon it when I was tearing drywall off to be replaced. From what I've seen, they didn't pay close attention to building codes around here in the 70's!

This is the megger I use....

https://www.amazon.com/dp/B017OVC2UI/?tag=atomicindus08-20

 

[RPH]

A megger won't really tell you much that an ohm meter will on a DVOM. You won't detect a crack in the insulation with a merger.

If that nail lasted since 1970 what's to worry about now? The only thing that changed since then is you found it.

Well my megger goes to 5 kV on Ac, one at work will do 5 kV and 6 kV dc.
I have it set up to fault at 1 mA of arc current. Hipot sand megger are capable of testing the lines. I would test at 600 vac on the home system. If you go to high high it will create the problem you are trying to avoid.