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Old 03-25-2010, 12:25 AM   #1
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new here and had a very strange thing happen today. The place where my father works is having some renovations done. A new dropped ceiling was put in and some 2 by 4 lights installed. The poor fellow doing the work got tagged off the ceiling grid so i said i'd take a look at it for them as i'm a licensed electrician. I found that there was no ground running to the lights, someone had cut it off. After reconnecting it the circuit works fine. It has me absolutely baffled as to why the grid livened up due to there not being a ground though. I checked every light and there no pinched wires....nothings crossed anywhere. Is this a property of an electronic ballast that i don't know about? I know most electronic equipment needs a ground to function normally but i've never seen anything like this happen before. I know the answer is right there but i just can't seem to wrap my head around it. Any help would be greatly appreciated.

note...i should also mention that the lights did work with both the grid live and not live.
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Old 03-25-2010, 01:52 AM   #2
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did you actually read a voltage? Did you feel it?

I know a lot of times I have had guys think they got bit but it was actually things like the tie wires poking them or a sharp corner poking them and they thought they were getting shocked.

It never hurts to ground the grid. It should be grounded simply through contact with the lights but if you don't have a ground wire to the lights or there is not good electrical contact between the light and the grid, it might not be grounded.

Anyway, can't say I have ever had a grid with an induced voltage from lights that I could feel but say I have ever installed lighting without a grounding conductor either.

The only other thing I can think of is maybe somebody hit a wire with what ever was used to attach the wall angle to the wall. I don't know what type of system (conduit, NM, whatever) was used so this may not be applicable at all.

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Old 03-25-2010, 04:07 AM   #3
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I agree with nap, I've been installing boxes with new wire not even connected to the power yet and (imagined?) I got little zaps before.
Maybe nerves reacting? Not sure, but it's nice to know it's not just me.

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Old 03-25-2010, 05:55 AM   #4
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I've had my share of 'imagined' shocks,too. I get cramps in my hand,especially when working with pliers.
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Old 03-25-2010, 07:08 AM   #5
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That's most likely what happens to me too.
Wire strippers, screwdrivers, needle-nosed pliers.... I can see that.

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Old 03-25-2010, 11:53 AM   #6
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Naw this guy is the size of a house and he's been doing work for a long time. If he says he got a jolt off it it i believe him. I didn't have a meter handy to check voltage and all they had there was a proximity tester and that could have lite up on anything from 10 to 120v most likely. I would have assumed that if there was a problem it should have tripped the breaker once i reconnected the ground. My working theory on this now that i've had some time to think about it follows the same route as old houses with no ground and musical instruments. sometimes you'll get a jolt off the instrument. Not deadly just hurts a little. Because the circuit wasn't grounded there may have been a potential difference between the ceiling grid and the earth ground which the person was touching when this happened.
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Old 03-25-2010, 11:59 AM   #7
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If it were me, just for my own peace of mind, I'd tear open the fixture(s) and make sure it/they was/were wired correctly.

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Old 03-25-2010, 12:28 PM   #8
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Quote:
Originally Posted by DangerMouse View Post
If it were me, just for my own peace of mind, I'd tear open the fixture(s) and make sure it/they was/were wired correctly.

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I have seen way too many with a wire pinched in the trough cover to dismiss this possibility.

or a tombstone wire that has come out of it's terminal and contacting the fixture body. That will impose a high voltage low current onto the metal components.



another thing I wonder about:

what type of wire or cable was used to connect the lights? If any sort of metal sheathed cable and it was connected to a grounded supply box, that would have acted as a ground.

also, what was the guy touching that was grounded when he touched the energized grid?


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I would have assumed that if there was a problem it should have tripped the breaker once i reconnected the ground.
Not necessarily true at all. If the fault connection will not sustain enough current flow to trip the breaker, it will simply leak current continuously. You need to realize to trip a breaker on the instantaneous trip function, you need to expose the breaker to many times the breaker rating.

If the connection is resistive enough, it simply adds to the load.

Grounding things will appear to have remedied the problem but in reality, it actually hides the problem. The short circuit can still be present and if that ground is ever lost again, you already have a built in problem.

I really believe you are doing your dad a disservice writing this off to induced currents.

Last edited by nap; 03-25-2010 at 12:32 PM.
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Old 03-25-2010, 12:35 PM   #9
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Quote:
Originally Posted by nap View Post
I have seen way too many with a wire pinched in the trough cover to dismiss this possibility.
Me too, even on new, 'out of the box' fixtures!
Makes ya wonder what ever happened to "quality control"?

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Old 03-25-2010, 01:53 PM   #10
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a few things i should mentioned in my first post. I did infact take all the lights apart and check them. My first assumption was indeed a pinched wire. another guy went through them all as well so they've had three sets of eyes on them now. The gentleman who got the supposed shock was standing on the ground and grabbed a bx that was laying on the grid...that's how he initially spotted it. I checked his boots and there was a nail in one of them. The ground in question was cut off at the panel from the last "electrician" that was there for some unknown reason. The wire commin out of the panel is a 12/2 romex so there wouldn't be a path for ground other than the cut wire.
what makes me think it was parhaps an induced voltage is the fact that the shock was mild enough for the guy (stupidly) to reach up and brush the bx again to make sure he felt what he felt. Either that or maybe it's a bad ballast wire which would give a scarey high votlage and not alot of current...wouldn't be the first time i've seen that one. i'm thinking about going back and recreating the scenario just so i can get an accurate meter reading off the grid when it's "live". It pains me to do so much work for free though .
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Old 03-25-2010, 05:44 PM   #11
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i've got an update...i had a thought that perhaps all the bulbs weren't seated properly so i went back through and sure enough found one that wasn't. unfortunately this didn't fix the problem. I tested the circuit with both the ground open and closed. Both instances there was zero amps running through it. With the ground connected there is zero volts...with the ground not connected there is 75volts. I'm assuming that there's a high resistance short in the one light as all the bulbs aren't working properly and i changed the ballast already so it's not that. I've told the contractor to get his guy back and fix it.
note...by testing the circuit i mean testing the ceiling grid. plus it's written right on the ballast that "ground must be connected for proper operating"
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Old 03-25-2010, 05:51 PM   #12
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says alot for working off a fiberglass ladder
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Old 03-25-2010, 05:52 PM   #13
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Wood is good too. Po)

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Old 03-25-2010, 05:52 PM   #14
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If it is a suspended ceiling, I would check to see if the nails or hooks to tie the main rails of the ceiling grid are not driven into a wire. I would also check the rail around the Perimeter for the same thing.

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Old 03-25-2010, 05:57 PM   #15
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How many times while working on those "tray lighting" fixtures in dropped ceilings have I found a cracked tombstone, still working, but allowing the wiring to touch the metal panel of the fixture? So many possibilities in your situation. I'm glad the guy just got "tagged" and not hurt. David
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