# Checking Wiring Integrity



## hdavis (Feb 14, 2012)

I've smelled the old hot plastic smell with some breakers turned on. Turn them off, it goes away. No breakers tripping. I'm thinking about having my electrician go through and test the insulation integrity and resistance of all the wires, then rewire anything that shows questionable.

Does this even make sense? I want to get a feel for the alternatives before I talk with my electrician.


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## tjbnwi (Feb 24, 2009)

The electrical will megger the circuit(s). This test shows insulation leakage. 

Yes, it makes sense to have it checked. 

Tom


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## griz (Nov 26, 2009)

You sure it's not a breaker, a ballast or an over lamped fixture?


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## hdavis (Feb 14, 2012)

griz said:


> You sure it's not a breaker, a ballast or an over lamped fixture?


Positive. Breakers are in a different part of the building, all the lamps are on breakers that are shut off when it happens. There is one fixture that's an exception to that - I'll check it out to see if the ballast is going.

Needless to say, panel labeling would be helpful if there was much...


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## hdavis (Feb 14, 2012)

tjbnwi said:


> The electrical will megger the circuit(s). This test shows insulation leakage.
> 
> Yes, it makes sense to have it checked.
> 
> Tom


I plan to have both leakage and resistance checked. I know of a subdivision in Texas that had 2 houses burn after 30 years - nails through a wire. This was wired about 30 years ago, and it looks like it was all done backstab. 

I want to make sure this is absolutely safe when it's done.


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## griz (Nov 26, 2009)

hdavis said:


> Positive. Breakers are in a different part of the building, all the lamps are on breakers that are shut off when it happens. There is one fixture that's an exception to that - I'll check it out to see if the ballast is going.
> 
> Needless to say, panel labeling would be helpful if there was much...



Yea, I figured....

but it's always best to ask a question you already know the answer to...:thumbsup:


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## hdavis (Feb 14, 2012)

griz said:


> Yea, I figured....
> 
> but it's always best to ask a question you already know the answer to...:thumbsup:


No, great question, it reminded me there was one light fixture with a ballast, everything else is clean. Any where a device has to be pulled to check, it's getting a new device, so I think that fixture is going to go.:thumbsup:


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## rrk (Apr 22, 2012)

In the mean time you can use a laser temperature gun. Customer used one this week to find outlet that was getting hot. Loose wire on terminal.


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## GettingBy (Aug 19, 2010)

hdavis said:


> hot plastic smell
> insulation integrity


#14 @ 15A dissipates about a watt per foot of cable. Your insul resistance would have to be about 15 kilo-ohms to match this, instead of the normal megohms.
I wouldn't bother with a Megger test.

You could torch a Wirenut to see what this smells like, vs. an overheated backstabbed outlet vs. an overheated CB.


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## hdavis (Feb 14, 2012)

rrk said:


> In the mean time you can use a laser temperature gun. Customer used one this week to find outlet that was getting hot. Loose wire on terminal.


I already did a quickie with my thermal imager - nada, but you really have to do this early in the morning to spot anything in the walls or ceiling. I had the electrician out today, and couldn't reproduce the problem. His take was it was probably the one transformer / ballasted fixture on that circuit.


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## jaydee (Mar 20, 2014)

just curious..

how old is the building and wiring ?


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## hdavis (Feb 14, 2012)

GettingBy said:


> #14 @ 15A dissipates about a watt per foot of cable. Your insul resistance would have to be about 15 kilo-ohms to match this, instead of the normal megohms.
> I wouldn't bother with a Megger test.


That isn't really a practical view for real live installed wiring. A significant nick in the copper causes local heating, and the insulation will break down. Pinched insulation will also eventually break down. Rodents, install goof, someone put a nail or screw where they shouldn't have, there is plenty of room for problems with wire. Houses burn from this type of problem all the time.

I'm really not interested in having people's deaths on my conscience, and this is an area a little google-fu isn't going to make you an expert.


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## hdavis (Feb 14, 2012)

jaydee said:


> just curious..
> 
> how old is the building and wiring ?


Wiring in this part is ~30YO, smoke wiring ~10, building is over 100.


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## GettingBy (Aug 19, 2010)

hdavis said:


> A significant nick in the copper causes local heating, and the insulation will break down.
> 
> people's deaths


You have a link for this?

Depends if they're good guys or bad guys.


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## rrk (Apr 22, 2012)

hdavis said:


> That isn't really a practical view for real live installed wiring. A significant nick in the copper causes local heating, and the insulation will break down. Pinched insulation will also eventually break down. Rodents, install goof, someone put a nail or screw where they shouldn't have, there is plenty of room for problems with wire. Houses burn from this type of problem all the time.
> 
> I'm really not interested in having people's deaths on my conscience, and this is an area a little google-fu isn't going to make you an expert.


In the past I have traced out miles upon miles of wiring in system wiring in all sorts of institutional and multifamily residential buildings. The only way you are going to find a nicked wire is from heat if you are lucky. Your best bet is to take and ohm meter and check the line to ground or another wire in the jacket, with everything disconnected from the line. Or put a resistor on the end of the line and to ground and check it all along the way. If it is an intermittent problem which it usually is it can take a real long time.

I always wished I could have put high voltage on the line and then just look for the smoke and sparks, but my boss thought otherwise.


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## hdavis (Feb 14, 2012)

rrk said:


> In the past I have traced out miles upon miles of wiring in system wiring in all sorts of institutional and multifamily residential buildings. The only way you are going to find a nicked wire is from heat if you are lucky. Your best bet is to take and ohm meter and check the line to ground or another wire in the jacket, with everything disconnected from the line. Or put a resistor on the end of the line and to ground and check it all along the way. If it is an intermittent problem which it usually is it can take a real long time.
> 
> I always wished I could have put high voltage on the line and then just look for the smoke and sparks, but my boss thought otherwise.


I may have a solution for all this, but nobody makes one... I could make one, but there is a good chance there are patents covering most of it, so I couldn't sell it:laughing:


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## GettingBy (Aug 19, 2010)

rrk said:


> The only way you are going to find a nicked wire is from heat if you are lucky.


I doubt that even a TDR unit could find this.

The nick is a high resistance area but of almost zero length, so the total heat delivered into the insul from this should be minimal and most of the heat gets carried off by the rest of the wire.

If anybody wants to nick a wire, run 10A through it and do the touch test, go for it. 42C will never burn you, 70C will burn you quick.


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## Jeff G (Apr 5, 2010)

Hey Davis, have you, or your electrician used a circuit analyzer that will load a circuit down to 10, 15, and 20 amps and measure things such as voltage drop percentages?

I have  this one and have had excellent result in dividing the problem into smaller and smaller zones.


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## GettingBy (Aug 19, 2010)

This thing should pay for itself quickly

http://www.idealind.com/media/pdfs/products/instructions/nd-5481-4_61-164-165_instructions.pdf


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## hdavis (Feb 14, 2012)

Jeff G said:


> Hey Davis, have you, or your electrician used a circuit analyzer that will load a circuit down to 10, 15, and 20 amps and measure things such as voltage drop percentages?
> 
> I have  this one and have had excellent result in dividing the problem into smaller and smaller zones.


No, but I'm gathering good ideas, so thanks!


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