I was doing DIY wainscoting in my dining room, and I put a few nails in the walls to secure the panel frames.
So here's the problem - I have two wall lights on a wall. I noticed something weird when I was hammering the nails into that wall. I felt I hit something very hard (the stud??) and the nail could not go all the way in. (I used 1 1/4 inch finish nails)

After I finish that wall, I turned on the wall lights, and Boom! The lights flashed and went out, tripped the breaker. I immediately turned off the switch, and use voltage tester to test the nails on that wall. The nail that did not go all the way in shows positive readings. All other nails were fine.

I pulled out that particular nail, and went on testing the other nails again. Now the weird thing is, they weren't showing positive before but after I pulled the first nail out, 2 of them became positive. I pulled the 2 out, and re-tested. Another 2 became positive. Anyways, I ended up pulling out 5 nails in total and now all the remaining nails tested fine.

I turned on the wall lights again and now the lights are working fine!!! So what was that Boom? Can anybody tell me what happened? did I or did I not hit an electrical wire? Do I need to worry? I really don't want to call an electrician to open my drywalls coz that means I have to do a lot of work to patch the wall and re-paint and everything! Please help !!!

 

Welcome to the forums.

Technically... those nails should have not hit the power wiring. That tells us that you either have a shallow depth wall or the holes thru the studs were not drilled in the center.

When you put the nails thru the cable it created shorts between the hot wire and either the neutral or the ground. The nail created the short. When you pulled the nail out you removed the short but the area where the short occurred could be blackened and be a future problem.

Should you replace the cable..... YES.

If you have an attic above that room or a basement below it may not be that hard to run a replacement cable.

 

Thank you PJmax!! By future problems, what do you mean? Is there a fire hazard? That's what I worried about most.

Shouldn't shorts burn the light bulbs? but the light bulbs were fine.

This is a 12-year-old home so I assume they should have metal plates protecting the cables, and because I felt I hit something hard I am wondering if I could have hit the metal plate?

But if I hit a plate then why are the nails testing positive? Just puzzles!!! Is there a way I can test further without cutting the drywalls?

 

No, that isn't what a short is. A short is an increase in amperage at the contact point that trips the breaker. Of course this all happens in milliseconds. You won't know if it will cause a fire till it does. You need to open the wall and fix the cable.

 

Thank you ray2047. After googling I think I might have "nicked" the cable, since my nail hit something hard and did not penetrate all the way through, and the lights work ok (breaker did not trip) after I removed the nails.

So for peace of mind, I should probably still call an electrician in and cut the drywall to inspect right?..

 

BTW, I think the electricians usually put the drywall back on after repairing, but will they patch the drywall? I have no idea how to repair a drywall

 

The electrician may be able to run a new cable without opening the wall depending on access over or under that room.

If that was me called for that repair, I'd go to the house and first turn the circuit off and then send a tracking tone thru the wire. I'd want to know how the wire was run. It is possible that it could be fixed with two openings..... one under each sconce.

I would replace the sheetrock that was cut out but not normally do the patching.



Just a basic diagram. The red is the cable. The blue are the sconces. The green holes may be all that's needed. Actually, you know where the cable is in the wall..... your nails hit it. If there is an attic above or basement.... they may be able to run a new cable without opening the walls.

 

Typically, electricians in the U.S. don't patch drywall.

 

The good thing is, the patch doesn't have to be real pretty if you are wainscoting over it. A California patch would be fine.

 

Thank you PJmax, your diagram is really helpful, the green squares are where I put the nails in, and it's pretty close to the floor. I do have a basement below, so maybe the electrician does not have to cut the wall? But I guess cutting the wall is easier for him and will charge me less hours? lol

An electrician quoted $125 diagnosis and first hour, and $90/hr thereafter. Is that reasonable?

Also per Gunguy45, patch work should not be extremely difficult for me to do it myself? So should I take the wainscot frame off before the electrician arrives?

 

In the meantime waiting for the electrician, I'm wondering if I should continue with the rest of the wainscoting? or wait for him to fix the cable problem?...
I have maybe 1/3 of the room left.

 

That price is pretty common for residential troubleshooting work. It would save the electrician's time to have the wainscoting removed in that section before the electrician arrives. If this is an interior wall that will be covered by the wainscoting I probably wouldn't even bother patching the drywall beyond screwing the "plug" back in place.

 

Thank you ibpooks.
I am only doing picture frame wainscoting on drywall, so it will not cover the whole lower wall.

 

Since you said that you hit something hard, just for kicks, what is on the back side of the wall where the problem nail is? Is there perhaps a receptacle or switch box directly behind it? Pretty low odds, but your 1-1/4" nails should not have otherwise reached anything electrical.

 

It's not too late to change your design on wainscot. Even cheap backing will paint better than drywall and will hide damage due to running new cable.
Poplar or Maple plywood paints very well. Even Masonite with primer would be adequate.

 

I don't want to change my wainscoting design now since I am already 2/3 finished...So it's pretty difficult to hide the damage on wall?

Are there any alternative solutions such as shutting down eletricity to the two wall lights? Not using the wall lights at all. Will then be enough to keep this room safe?

 

It may be possible to just disconnect those sconces and put a blank plate on them if you have at least one other lighting source in that room. Code requires at least one switched light per room. If you were to abandon these lights the damaged wire would need to be permanently disconnected at the supply box so it won't be a fire hazard. The electrician should be able to do that pretty easily.

 

What type of tester are you using? The fact that you removed some nails and other nails got hot, leads me to believe that you used a proximity tester and not a physical touch the wires sensor. The proximity tester would pick up the live wire buried in the wall, not necessarily the nail itself. The chance of you poking a wire 5 times in a row are slim to none.

 

Thank you czizzi. I am actually using a tester with probes, I followed some online instructions, use drop line from a known outlet, and put one probe in the extension cord's ground/hot/neutral in turns, and put the other probe on the nails. The reading is positive when one probe is in the hot, and one probe on the nail.

I wonder too, why after removing a few nails, other nails became positive?...if I did poked the wire 5 times in a row, shouldn't they all be reading positive from the beginning? lol

 

Thank you so much ibpooks! That sounds like something I can pursue. I never use those sconces, and we do have a ceiling light in the dining room! I will ask my electrician if that's something he can do!

 

Personally, I'm not the electrical guru by any means, but you used an extension cord and tested your nail head off of that???? I'll let the other chime in, but that doesn't seem correct to me. Multi-meters have internal battery sources and work independent of outside electrical power sources.

 

Czizzi, She was using the extension cord as a ground reference point for measuring voltage. That is a valid test method. If you are testing a point that is hot you should get a 120v measured to any ground on the system. The extension cord provides the ground.On an analog MM the battery is only for resistance measurement. On digital MMs one battery is for the electronics and one for resistance reading. Voltage and amperage measurement rely on the voltage or amperage being measured for the reading. No battery used for those on an analog and on a digital the battery only powers the internal circuit board that drives the display and logic functions..

 

Just to add my two cents worth.... be sure to find out why your nails hit the cable. You were using the proper sized nails.

 

Thanks guys, sorry to interrupt your thread, but I learned a new trick and have better knowledge as a result.

In all the remodeling I have done, and all the nails driven, I have never hit an electrical line. It just doesn't compute that someone could have hit a line 5 times on one project. and with 1 1/4" nails at that. The drywall is 1/2", the molding is 1/2" so the finished nail only penetrated 1/4". What could possibly have been hit? It is curiosity that is killing me now. I would love for the OP to upload a picture of the offending area when the wall is opened so that the mystery can be solved.

 

Ray, I'd swear my old Fluke digital just has one 9V battery. I might have to open it and check. Probably wouldn't hurt to change the battery too, I know it's been at least 4 or 5 years since it was last changed.

 

Never take what I say as gospel. Only owned one digital and my statement was based on that.

 

as czizzi said, what could have gone wrong? I am so upset at myself now. I really do not want to cut the drywall. Electrician did not return my call as promised, gives me more time to think...

 

I can't see how you would have hit a wire. I would check all the connections in the two light boxes to make sure nothing is loose. It is possible the banging on the wall loosened a connection just enough to short it.

As for the nails being live, maybe there was an issue with your testing method that was giving you a false reading.

 

The older Simpson 265's used two sets of batteries, but they, too were for resistance at different levels, not for voltage readings.

 

is it possible that my testing method is giving me false readings? Sconces are working fine now so no loose connections.

 

Am I correct to assume that by positive you mean you are getting a 120 volt reading on your meter? If so, this would mean the nail is somehow grounded and not something I would be quite so concerned about. I assumed you have wood studs, but is it possible you have steel studs? I am just not convinced that 1 1/4" nails would hit the wiring.

 

That's what has me concerned.... there WAS at least one actual short at one time.
Do you have the nails.... where they black on the end ?

 

My one theory is that the nail that would not go all the way in actually hit a drywall nail or screw that was both "already in the wall" and "already driven deep enough to puncture a wire".

However, it does not explain the breaker only tripping once (and not continuing to trip) and hot readings on 5 nails. Unless all the banging caused to actual short of an already punctured wire.

 

We aren't 100% sure the nail was hot. That would depend on which slot the meter was plugged into in the extension cord. Normally we just use the ground pin of the extension cord method.

 

PJmax, it was the short slot the meter was plugged into in the extension cord.

When it is plugged into the ground pin of the extension cord, there is no reading.

 

the nails are not black on the end, they are still "normal", silver...but one of the nails end was bended.

steel stud? really?

casualJoe - yes I was getting a 120 volt reading on my meter. What do you mean the nail is somehow grounded and something I should not be worried about? please elaborate, sorry I have very limited knowledge of how electrical wires work lol


BTW this is the meter I used - Southwire Analog Voltage Detector

Shop Southwire Analog Voltage Detector at Lowes.com

 

If you had one end of the tester connected to the nail, and the other end connected to the ground on the extension cord, and you got no reading, then the nail was not live.

My guess is your nail hit a gyproc screw and that's why it bent.

I would still check the lights themselves to make sure all the connections are good. It is not impossible for the wire nut to come off, and for the connection to be loose, especially since many people do not twist the wires together before using the wire nut.

 

Thank you Keith Weagle. My nails were not live then!!
but why one end in the short slot of the extension cord and one end on the nail gives me 120V reading?
and how do you explain that when I switched on the sconces they suddenly went out?

After they went out, I took out the light bulbs to examine them and put them back in. Now the sconces are working fine. So no loose connections.

 

Your nail could have been grounded somehow. It could be you have metal studs in the wall, or you have a foil type vapour barrier in the wall. Either way, if you did not get a reading from the nail to ground it was not live.

You should take the fixtures right off the wall and inspect the wiring, not just the bulbs. They will usually come of quite easily with one or two screws. No need to disconnect them completely, just pull them off the box enough to see that all the wires are connected tightly, and that none of them have worked their way loose and are just barely touching. I guess another way to test it would be to turn the lights on and bang on the wall with your hand around the lights. If there is a loose connection, they should flicker or short out again.

 

got it.. so there's nothing wrong with my nails? no need to open walls? hoo-ray!!!

I will research a bit on how to take the sconces off, I tried earlier did not succeed lol