Chasing wires for continuity

[MNMike]

Hi Guys,

Building a new 28x32 detached garage, electric is all roughed in, the roof and siding are on and it is completely insulated. Here is my problem. When the siders put on the siding they pierced an electrical run, I happen to see it when I was checking my insulation by the service panel.

How do I go about checking the wires to see if they pierced any other wires??

Going after the contractor is not an option.

Thanks for looking,

Mike

 

[dogdog]

Not sure of Ohm testing would be a good test for pierced insulation and not broken/shorted wires..... Ohm/continuity testing is good for shorts and a quick verification for broken wires.

maybe find an electrician with a megger meter? These meters are not cheap and it is specific purpose so .... not much use for everyday stuff....


you can google more of megger meters for their uses.

 

[dogdog]

A normal ohm/continuity test I normally do would be
use caution and common sense.


on a given branch circuit, unhook everything connecting to it. Verify no voltage is at the wires before begining the test.

Unhook the wires at the breaker panel and the breaker to make sure no power from the electric meter or connect to anything live, Then test for continuity between that hot-hot-neutral-ground , six unique combinations if 220V. or hot neutral ground if 110V 3 unique combo. Nothing should ring or show resistances if nothing is hooked up to that branch.

Then just tie hot-hot wires (not connected to line power) go to the other end and test for continuity it should beep only on the wires you tie together. but not the wires you didn't.

then just step through the rest of the combinations.......

But these test doesn't indicate the insulation is pierced ... and arcing or sparking from a pierced insulation of a wire inside wall is still possible when under load.... maybe... some transient condition.

 

[sberry]

Don't panic. Does it really look like there is another problem? Fix the wire and move on.

 

[RPH]

Hi-pot testing can eliminate your concerns for danger insulation. We test hifrequency transformers for shorts and leakage to a thousand volts. And these are water cooled devices. The water is in direct contact with the wires and windings. You should be able to rent one to do the job.

 

[MNMike]

Don't panic. Does it really look like there is another problem? Fix the wire and move on.

The building is insulated and before I sheet rock I'd like to make sure their isn't a problem. Maybe I'll just not worry about it, maybe it won't burn down.


Thanks DogDog, I don't have any receptacles wired yet, for that matter I haven't pulled the service line from the house.

RPH, I'll look into Hi-pot testing.

Thanks for your input.
Mike

 

[Warrenator]

You can buy inexpensive meggers now, Amazon has one for 44 bucks.


https://www.amazon.com/VICTOR-Digit...Type=all_reviews&sortBy=recent#R140WU7Q52NBP7

The megger will find any gaps in the insulation that might cause a short.

If you find a problem with a broken wire there is also a tool called a TDR (time domain reflectometer) that will tell you exactly how far away from the wire end your break in the wire is so you don't have to rip down everything. Telephone technicians use them to determine where a break in a phone line is. (I have been told it is usually bullet damage grazing the line!)

 

[ard]

How did the siders MANAGE to pierce a wire?

I've never had a concern because no wire is placed where it CAN be pierced. Did they use the wrong nails?? If you placed wires too close to the exterior sheating and used the wrong size nails, the only solution is an inspection.

What KIND of insulation? Batts? Easy.

Also, a pierce but 'no contact yet' can turn into a problem down the road....

I had a framer drive a nail into the middle of a bay when he was doing shear nailing.... 2 months later, just after the hardwood was laid, the nail that had JUST punctured the copper water pipe backed out- leading to destroyed hardwood....

 

[MNMike]

Thanks Warrenator.

Ard, yes, they used long nails when installing the siding. All the wires were run where they were supposed to, checked by the electrical inspector and the framing inspector even commented on the job.

I'll have to look into the megger,

Thx,
Mike

 

[wyliesdiesels]

You can buy inexpensive meggers now, Amazon has one for 44 bucks.

https://www.amazon.com/VICTOR-Digit...Type=all_reviews&sortBy=recent#R140WU7Q52NBP7

The megger will find any gaps in the insulation that might cause a short.

I would NOT trust a $44 megger...

If you find a problem with a broken wire there is also a tool called a TDR (time domain reflectometer) that will tell you exactly how far away from the wire end your break in the wire is so you don't have to rip down everything. Telephone technicians use them to determine where a break in a phone line is. (I have been told it is usually bullet damage grazing the line!)

TDRs arent cheap. I wanted one for my business but it will have to wait...

Thanks Warrenator.

Ard, yes, they used long nails when installing the siding. All the wires were run where they were supposed to, checked by the electrical inspector and the framing inspector even commented on the job.

I'll have to look into the megger,

Thx,
Mike

Why arent you asking the siding installers to pay to inspect and fix it? Sounds like they used the wrong length nails...

 

[zmaxmotorsports]

Start turning on breakers and see if anything trips.
One of the reasons I like to wait till after siding guys are done before wiring.

 

[MNMike]

Zmax,
I just have the wiring roughed in, no power and I am planning to put receptacles in after the sheet rock .

 

[sberry]

Tie them together and turn on. But unless there is reason to suspect a huge problem do some simple inspection and don't jump to the conclusion that the place will burn down unless you do a test no one does. No good substitute here for taking a little time and looking around to see if the same mistake has been repeated.

 

[MNMike]

fair enough, I'll just take out some insulation where I know I have runs and check them.
As with everything on this project, I am over thinking it.

Thanks All,

Mike

 

[Warrenator]

So far as "trusting" a cheap megger, it is a piece of measuring equipment. You get your wires all in front of you and hook one side of the megger to ground or to the metal building. Then test the white wire, then the black wire, then the red wire, etc, to see if any current leaks to ground. Then hook up one side of the megger to the white wire, test it against the black wire, the red wire, etc, to see if the white wire insulation leaks over to the other wires. Repeat all combinations, write down your results. You can test at 500v or 1000volts.

Worried that the cheap megger is no good and doesn't give a good result? Make yourself a control wire and nick the insulation, set it next to the bare steel of the building or next to a ground wire and see if the meter will detect the faulty wire.

If I have a new meter to measure anything I usually set up a test for the meter to see if it is accurate before I start using it. Sometimes I calibrate it against a known good meter, or weigh something with a known weight, or temperature, etc. Some thought has to go into the process.

A TDR is an expensive bit of gear, though if you're an electronics nerd you can use an oscilloscope and some other kit to fab one up. Probably well beyond the scope of finding a broken wire in a garage, just threw it in there for fun. Apologies for muddying the waters.

 

[ishiboo]

Buy one combination AFCI/GFCI and simply test all the circuits on it with a load. Won't take long and it should find 99.9% of serious issues.

 

[sberry]

I like the afci idea. But there is nothing wrong with taking a look around and if they dun it once they might do it twice. I had a few screw ups but to fix it , is it foamed in, if not dissect some and look. If you got doubts fix it now. If the ruff inspection is done would wire it up and buy some wide masking tape.
I wouldn't rely on a test if the installation was in question. If this looked like its not a fluke but is typical thru the install then it needs to be fixed.

 

[zmaxmotorsports]

Zmax,
I just have the wiring roughed in, no power and I am planning to put receptacles in after the sheet rock .

Temp it in off an extension cord.

 

[sberry]

I had a helper hit cable with a staple, I really don't cause I am too lazy but I probably did a couple that got hit over the years from a nail or screw. I remember my bud said he chased a problem down when we hook up something drunk on a weekend, showed up years later. If I really was going to megger it would have it all hooked up minus fixtures.
I havnt looked at the 44$ tool but if it is half as good as the 50$ battery tester its a deal. I agree you can verify its working. As a matter of fact I had the tester 20 yrs of perfection and something did go wrong. I am not sure but noticed it didn't seem to be working and put it on the tech bench and my Bud took a spin on it and had it fixed in about 10 minutes. Worked great since.

 

[RPH]

Ok, we use both a fluke megger for the field trips as it is light. But real in depth testing I use the hipot. Ac/dc voltage test (up to 5000 volts), I can set the amount of leakage current, arc current, time device is under test, ramp up and down. The hipot has the trust of us guys that have to work on hipower induction heating systems. The megger has passed things that the hipot fails it on. If you’re that concerned about this the rent the hipot for peace of mind.

 

[sberry]

I will ask my tech if we need one of those? 50$ isn't much.

 

[TractorJeff]

Hipot is the way to go if you are going to do it.
I'd pull insulation myself.

 

[arkieguide]

Next time, when pulling romex in walls and ceiling, put a battery bell, between hot and neutral / ground in the panel, if staple are nail enters the romex the bell goes off, saves a lot of trouble after walls are covered. Don't help you much now, but in the future, I too would ask the siding crew to help find the spot.Now if the wire is shorted are grounded, using the bell will still help, just make sure all the ends are free tie the bell in the panel if it goes off seperate the cables to find which one it is.

 

[nsula_country]

1st, Hi-Pot. 2nd, Megger. 3rd, just hook it up and try it out!

CT

 

[tonyprovo723]

Can you simply grab the romex and give a tug/ push and feel for resistance? I'm assuming you do not have it guitar string tight? Probably would not need to pull back the insulation.

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[tonyprovo723]

Another thought. What style of siding? I'm guessing the nails will be in a horizontal line and you could eliminate most of the area of concern.

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[pcmeiners]

If you know a IT/Tel cable guy, they have TD reflectometers, tells you to a fraction of a foot where wire breaks are located. Have one for CAT 5/6 wiring but used it a few times on house/ building wiring.

Time-domain reflectometer

https://en.wikipedia.org/wiki/Time-domain_reflectometry

 

[PT Doc]

How did the siders MANAGE to pierce a wire?

I've never had a concern because no wire is placed where it CAN be pierced. Did they use the wrong nails?? If you placed wires too close to the exterior sheating and used the wrong size nails, the only solution is an inspection.

What KIND of insulation? Batts? Easy.

Also, a pierce but 'no contact yet' can turn into a problem down the road....

I had a framer drive a nail into the middle of a bay when he was doing shear nailing.... 2 months later, just after the hardwood was laid, the nail that had JUST punctured the copper water pipe backed out- leading to destroyed hardwood....

Our friends were told that their ac Lindsey was pierced by the stucco company when they put up the lathe. They said it happens more than you would think. Wtf? How? Unless you are using 3 inch nails staples.

 

[OH_Varmntr]

What insulating rating do the wire(s) in question hold? 600V?

Be careful what you hipot. You may inadvertently compromise the insulation

 

[wyliesdiesels]

What insulating rating do the wire(s) in question hold? 600V?

Be careful what you hipot. You may inadvertently compromise the insulation

Newer NM-b is rated 600v

 

[OH_Varmntr]

Newer NM-b is rated 600v

Yep, but unless I missed it, he didn't say what the wiring was. I had assumed it was NM-b but you know what they say about assuming.

 

[RPH]

Specs for hipot testing.
“ Electrical strength is one of the tests outlined in the standard. It is performed after humidity treatment, abnormal tests, impact tests and heating tests. The standard requires the electrical strength of insulating materials used within the equipment is adequate. For a line voltage of 120 VAC, a basic insulation test would apply 1000 VAC or 1414 VDC to the tied together mains supply and ground. For 230 VAC, 1500 VAC would be applied or 2121 VDC. The voltage is ramped up until the test voltage is reached; the voltage is then held for 60 seconds. There should be no breakdown during the test. Insulation breakdown occurs when the current flow increases rapidly because the insulation is not restricting the current.