The contractor nailed it


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Old 07-15-14, 09:28 AM
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Question The contractor nailed it

Hi all, my first post here. Sorry for the length, but I'm trying to be thorough.

I did the "finish" work on my parents' house addition, which consisted of putting in the outlets, switches and ceiling fans after the sheet rock was completed. A licensed contractor handled all the wires going back to the box.

As I was finishing out one of the four circuits, I kept getting a breaker tripping, as if on a dead short. I was sure of my work, so I began isolating the issue by removing outlets one by one and using a continuity tone on the multimeter. I finally found a nail through a wire in the attic, so I cut the wire and put in a junction box. When the breaker tripped again, I wound up taking apart the wall to find another nail through a wire. Also, toning out using the multimeter shows that there is likely a THIRD nail through a wire on this same circuit.

I can repair this particular issue by running a cable from a different outlet to bypass the third nail; however, this whole situation made me nervous about other nails through wires in other parts of the addition. The walls all have a layer of OSB on both sides which was put up by a young headstrong guy with a nail gun; the existing three nails are nails from a nail gun used to hang the OSB, and he did the rest of the OSB throughout the house as well.

I obtained a General Tools CA-10 circuit analyzer, and it appears I am several ways out of spec on another circuit. While I'm showing 0.0V bleed-through on the neutral, my voltage drop on the 20A load test is 8.6% on one outlet, 10.1% on another, and impedance checks on all the outlets in the bedroom section show 0.35 ohms or higher. It's my understanding that spec for 14 AWG wire is 8% voltage drop on a load test, and 0.15 Ohms or less on the impedance check. Is this correct?

How likely is it that I have another nail through the wire in this circuit? Is there another more likely cause? Is there another test I can run with this piece of equipment, or is there a different piece of equipment I should be using for this kind of check?

The contractor is balking at the idea that there are other nails through the wiring, even after being shown the others in the first circuit. He insists that since the breaker doesn't trip, and a nail would cause a dead short, that there is no possibility there is another nail. This may need to become a legal matter at some point, but I don't want to do anything else until I confirm whether or not something is actually wrong.

I'm also hampered in the use of an infrared thermometer due to the OSB, insulation and sheet rock; I'm not sure how accurate the readings might be, so I haven't purchased one yet.

If I confirm that there are likely more nails through the wire, I'll of course hire another electrical contractor for an independent assessment, but I'd like to be able to ask the right questions and understand the answers when the contractor arrives.

TL/DR: What's the best way of testing to see if there is a nail partially through a wire in new construction?
 
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Old 07-15-14, 12:20 PM
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Can anyone provide a link to the specs for circuit impedance and voltage drop under load for a standard, non-GFCI residential 20A circuit? I can't seem to find them in the NEC. I'm in rural TN with no local codes, so NEC is all that I have to worry about.
 
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Old 07-15-14, 12:37 PM
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And what will those specs tell you or do for you ?

When building and renovation work is done..... the proper fastening method and that includes
the type of nails are supposed to be chosen so that you don't have the problem you are having.

You will need to buy, rent or borrow a megger. This is a special meter that puts out a high voltage pulse and looks for a short.

Infrared thermometer will not help.
That CA-10 isn't going to be of much help either.

Trust me...... if you can't see or get to the wiring...... a megger is the ONLY way to test.
 
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Old 07-15-14, 12:48 PM
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Okay, it looks like Megger is a manufacturer of electrical testers and analyzers.

Is there a particular model you would recommend for this issue?
 
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Old 07-15-14, 12:58 PM
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From what you describe you do not need a megger or a tripped breaker to know their are likely more nails in your circuit.

So before you spend the cash on buying a megger (and learning how to properly use it and assure its properly calibrated), you might want to step on the toes of the contractor. It is up to him to have a licensed electrician rectify this. If the hack doesn't want to play nice, then its time to visit your lawyer.
 
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Old 07-15-14, 12:58 PM
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A megger can also be known as an insulation tester. Fluke makes some basic units that start at $500. The one I use was several thousand dollars. Not something you'll be buying for a one time use.
 
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Old 07-15-14, 01:00 PM
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Megger is a generic term for a high voltage insulation tester. You'll fall over at the cost most likely, though they do sell cheap no name brands. Not sure how good they would be. Better models start at several hundred and go up from there. Better bet might be to see about possibly renting one, or paying someone to do the testing.
 
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Old 07-15-14, 01:22 PM
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I'd love to step on the toes of the contractor (and step on a few other things as well), but I need some more ammunition to show that there is indeed a problem before I can force him to fix it. TN has arbitration through the state licensing board, but before I can take it to them, I have to show that there is indeed a problem. He's offered to run a new cable to fix the nail I haven't fixed yet, but denies there could possibly be any others. Keep in mind this would be a simple jump from the next outlet over on a different circuit, and I've already removed the OSB - a newbie electrician could do that job in 5 minutes. I'm mostly concerned with knowing whether or not there is definitely a problem, and if there is, finding proof of the problem. Then I can go to the licensing board with this info.

I would think that the impedance differential and voltage drop on the load test I'm seeing on the CA-10 would be enough to indicate there is a problem, this is why I was asking if anyone had the specs on this. If this isn't enough to indicate, though, I guess I should look for someone with a license and a Megger. Could there be another cause for the test failures on the CA-10?
 
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Old 07-15-14, 01:38 PM
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I don't know how the CA-10 works. In order to check voltage drop on a circuit it would have to apply a calibrated load. It IS going to change from receptacle to receptacle. As far as impedance.... I don't know what impedance it's referring to. Possible a measurement between ground and neutral.

These measurements won't tell you anything about a circuit that could possibly short in the future,
 
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Old 07-15-14, 01:42 PM
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Also, some backstory as to the nails...

Mom wanted OSB on all the walls under the sheet rock to provide insulation. The contractors used a nail gun, and they did such a poor job with cutting the OSB that they wound up having to angle the nails into the studs at the edges of the OSB. On top of that, they used 2 1/4" nails with the nail gun pressure up so high the nail heads went halfway through the OSB. The electrical contractor did his job correctly and stapled the wire to the center of the stud; this meant the wire was held in place when the nail hit it rather than being able to push outwards just a bit.
 
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Old 07-15-14, 01:50 PM
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The CA-10 is a Circuit Analyzer made by General Tools. The load test simulates a 12A, 15A, and 20A load to test the voltage drop. Yes, I am getting different readings from different outlets, as expected, but a couple are waaay over "the line" (which the CA-10 manual says is 8%); one outlet shows 8.6% drop at 15A, 10.1% @ 20A. Several on the same circuit are slightly over 8% (8.2, 8.5) @ 20A.

The impedance check is supposed to test for wire condition issues - if the wire is damaged (such as being partially crushed due to a staple being too tight, or a nick in the wire), it should affect the impedance. The circuit in question shows 0.32 - 0.36 Ohms of resistance (depending on outlet tested) on the Line side; the CA-10 manual says it should be no more than 0.15 Ohms.
 
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Old 07-15-14, 02:15 PM
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I don't have much to say about the electrical part of this thread, but as a carpenter, I will say that when wires are run the way they are supposed to be run, there is never any danger of nailing into them in the first place... assuming the carpenter is using common sense and isn't nailing drywall on with 16d nails.

And if wires ARE in a location where there is the chance they could be nailed into, isn't it the electrician's responsibility to use Nail Stopper plates?
 
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Old 07-15-14, 02:45 PM
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Nails

And if wires ARE in a location where there is the chance they could be nailed into, isn't it the electrician's responsibility to use Nail Stopper plates?
The NEC says there must be 1 1/4 in. of wood between the edge of the stud and the hole where a wire passes through a stud. When using 1 5/8 in nails or screws and 1/2 in drywall, all is good.

The OP is saying a nailer was used and the nails came out the side of the stud where the wire was stapled. An electrician would have no way of knowing such an unprofessional method as this would be used. See post # 10.
 
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Old 07-15-14, 03:19 PM
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Yes, Wirepuller38, you're correct. I believe the electrician can't be blamed here, as a reasonable person would never have expected some numbskull going nuts with an overpressured nail gun right down the stud where the vertical wire drops were. Don't get me wrong, I'm not happy with the electrician for other reasons (who runs the light above the sink through the GFCI?) but his wires were all ran in the center of the 2x4 studs.

The fault lies with the contractor for failing to train and/or supervise his worker. The work is obviously subpar and theoretically dangerous, but until I can prove that there is actually more damaged wire, he's going to insist that the wiring is fine (there's no dead short, right?) and refuse to rip apart the wall and reconstruct it. Of course, even if I do prove it, he might still not do the work willingly, but having the proof of wiring not meeting specs, coupled with the evidence of the nails I have already, should be enough to seek legal counsel.

Also, I re-ran the tests and received different numbers, specifically in the load simulation - the worst one that was reading 10.6% drop @20A now reads 9.4%, while a different one that read 8.8% @ 20A now reads 10.0%. There was nothing plugged in on the circuit, and all lights were off when the tests were ran.

Should I be concerned about these numbers changing, or is this normal?
 
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Old 07-15-14, 03:31 PM
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Ah, I didn't see post #10... That explains it. Sounds like the sort of thing a sheathing stapler would be used for... I know guys miss studs all the time with those staples.
 
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Old 07-15-14, 03:58 PM
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A Megger engineer emailed me back with a recommendation for the MIT200-DS. It appears to measure electrical resistance in the same way that the CA-10 does, albeit far more precisely. However, if the CA-10 numbers are already what appears to be far out of spec, would a more precise measurement offer any advantage in determining that there is a problem with the wire insulation?

Or am I reading the literature incorrectly and the Megger device measures resistance differently than the General CA-10?
 
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Old 07-15-14, 04:09 PM
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Okay, now I see what I was reading wrong. The CA-10 measures resistance of the wire, the Megger device measures resistance of the insulation.

I'm seeing some pretty cheap insulation resistance testers on ebay in the $20-$25 range. I'm pretty sure this one of those things where you get what you pay for, but since I'm only concerned about using it for one day or so, will a cheapo get me the test that I need with enough precision to be reasonably certain that I have a problem on a specific wire? I don't need to know the size of the nick, just whether or not one is there.
 
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Old 07-15-14, 04:37 PM
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Your not an electrician. So you need to hire one, let him test, form an opinion, fix if necessary and document it all.
 

Last edited by PJmax; 07-15-14 at 05:02 PM. Reason: removed unnecessary comment
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Old 07-15-14, 05:04 PM
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A cheap meter isn't going to cut it here. Without a good and proper meter you aren't going to get the answers to your questions.
 
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Old 07-15-14, 07:29 PM
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Mom wanted OSB on all the walls under the sheet rock to provide insulation.
Bad choice, OSB provides little if any insulation value.

On top of that, they used 2 1/4" nails with the nail gun pressure up so high the nail heads went halfway through the OSB.
Negligence on the part of the general contractor.
 
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Old 07-15-14, 08:11 PM
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As I said in my first post, I know that I'm going to need an electrician (I'm going to have to have some kind of report in my hand from someone with a license in order to make the contractor budge), I just need to be able to ask the right question and understand the answers. I'm in redneckville TN where the guy who did the original work (with the lights ran through the GFCI's) is the most reputable person around, and he couldn't understand what I was testing with the multimeter when I was continuity toning to show him where the third nail must be.

I'm going to have to pay someone to drive an hour or two from Memphis or Nashville, so I want to make sure it's worth it.

If you guys say that the cheapo insulation tester won't do any good, then I won't waste my money. Is there anything else I should tell the electrician, or make sure that he brings (and knows how to use)?
 
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Old 07-15-14, 08:15 PM
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Bad choice, OSB provides little if any insulation value.
Yeah, try telling my Mom that. The contractor sure wasn't going to. Also, she wanted to be able to put a nail in her wall to hang a picture or whatever she wanted ANYWHERE.

Negligence on the part of the general contractor.
Absolutely. But he's not going to admit that anything is wrong, because then he might have to fix it. Mom and Dad are so frustrated now they'd rather pay some else than deal with him anymore.
 
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Old 07-16-14, 03:27 AM
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I painted a house for an engineer [why do they always have crazy ideas] who made the builder install OSB on both sides of every load bearing wall claiming the wall wouldn't be strong enough to support the load otherwise. I did a lot of work for that builder and he was one of the better ones .... but we did joke about those walls.

The extra thickness might add a tad of R value but she will be able hang pictures anywhere

Mom and Dad are so frustrated now they'd rather pay some else than deal with him anymore.
That's understandable but they need to keep receipts/documentation in case it ever get to the point where they need to take the contractor to court to recoup what they spend to make it right.
 
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Old 07-16-14, 05:08 AM
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If you guys say that the cheapo insulation tester won't do any good, then I won't waste my money. Is there anything else I should tell the electrician, or make sure that he brings (and knows how to use)?
Unfortuneately, few electricians would know how to test or prepare a credible report that could be used in court. I believe you need an engineering firm with credentials to do the testing and prepare a proper report. With the possibility of nails being driven through the cables on every circuit, I wouldn't want to live in that home till I was assured all was right, the best insurance in the world cannot prevent a fire from starting.
 
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Old 07-16-14, 06:08 AM
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Agreed, it sure seems like a waste of time with all this testing ,when a known problem exists the best route would seem to be an engineering firm for good doc's then a lawyer.
Geo
 
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Old 07-16-14, 12:15 PM
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I think you are on the right track with the circuit analyzer, but you need to check other outlets in your house to see whether the >10% line drop is isolated to the remodel area or affects the whole house. If there is a "hot spot" where you have a compromised circuit you should be able to narrow it down to a single length of wire (i.e. from outlet to outlet or from the first outlet to the box).

I suggest running this test across your house and looking for any readings that are really abnormal. If you see a big jump then you should replace that length of wire.

Overall the impedance test is a good check too, but keep in mind that the L and N test is based on Ohms per Meter, so if your circuit is 10 feet long it shoud have an impedance less than 0.15 Ohms * ~3 Meters = 0.45 Ohms. The Ground test (Z-E) should always be less than 0.25 Ohms... Those values seem high to me, but they may be including internal impedance caused by the circuit analyzer or test cable
 
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Old 07-16-14, 01:56 PM
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mnmattmn....... a "hot spot" ? I don't see how a 10% line drop is going to be indicative of a potential short.
 
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Old 07-17-14, 02:02 PM
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Sorry, to clarify, I was using "hot spot" as a reference to an area of high impedance responsible for a significant portion of the voltage sag. This could be an area where the wire is pinched, nicked, bent at a very tight radius, poorly connected, etc... This is the type of event the OP would be searching for with an IR camera/thermometer.

Based on the OP's posts I'm assuming he's not looking for an actual short but instead for an area of compromised wire that coud start a fire.

If there is no particular spot that is responsible for a majority of the voltage drop then the voltage drop is spread across the entire circuit and the risk of fire is minimal.
 
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Old 07-17-14, 06:35 PM
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I think you are on the right track with the circuit analyzer
A good circuit analyzer will provide a lot of information, but it's all useless if this case goes to court where documentation must be presented by an expert witness with credentials.
 
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Old 07-17-14, 07:24 PM
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I'm not sure how far this will get in court (not that I'm skeptical, I just have no clue), I was just trying to advise on getting something meaningful out of the circuit analyzer and coming to a determination if the wiring is safe or not.
 
 

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