Shock from suspended ceiling grid

[splam]

I know this is not a garage question but thought I would get some advice. Today I was doing some work above my basement suspended ceiling and got a small shock when I was drilling some holes. I thought it may have come from the electric drill but that is not the case. I put a meter on the metal grid and a water pipe and I have about 25v ac. My lights are set up in with two switches each turning on 4 coffer's that have 4 t8 lamps. If I shut off either switch it drops to 12v ac. Anyone have any ideas how to fix this issue?

 

[LXCam]

You obviously have a ground fault. If you turn off both does the voltage go away completely?. Also your lights are not properly grounded as if they were it would dissipate the differential voltage or if a direct short open the breaker..

 

[wyliesdiesels]

Sounds like u have a high resistance connection to the grid. And since either the grid isnt grounded or the resistance is high enough, the breaker wont trip.

Try bonding the grid with a piece of wire to that grounded water line.

Also, are u using a true RMS meter?

 

[splam]

If I turn both switches off the voltage is gone. The lights are wired to duplex's that are switched. I will double check the grounds in the fixtures. I was using and old Simpson analog meter. I do not think the lights are on a GFI just the receptacles in the basement.

 

[yyc_ranger_4x4]

Double check all your lights and be sure the bond (ground) wire is connected properly at every light, and switches....and all the way back to the panel.

We see this a lot with new apprentices who miss a connection when doing lights on concrete ceilings with PVC conduits....

 

[Mustang51js]

Check to make sure all the bulbs are in the sockets and not half in and out,you can also disconnect one light at a time and test to see if it's certain fixures

 

[MBfreak]

Whatever you may find, fix it. Probably a worn thru cable penetration or loads of semiconductive dirt in a junction box.
Please, add a GFCI unit to your installation. 25 VAC is enough to make your muscles contract. If you are on a ladder, you might take a dive.
Ola

 

[splam]

Well I spent some time trying to isolate the issue tonight. After trying several things including checking each light and one junction box that the feed wire ran through I believe I found the issue. When I got back to the switch box that had the feed from the panel into it I checked with an ohm meter and found a fairly high resistance from ground to neutral. I checked the ground and neutral connections in the panel for this circuit and everything was tight. I did a lot of wiggling of wires and now have an open on the ground. My panel is recessed in drywall so I can not trace the wire from where it leaves the box to find where it is broken or damaged. In my switch box there are three switches, two that turn on my two banks of fluorescent's and one three way switch for the stairway leading to the basement. The three way ground wire was just tied to the ground terminal on the tree way switch. I tied that ground to the grounds going to the two banks of fluorescent's and now there is 0 volts AC on the ceiling grid. I will cut the drywall and feed a new supply to the light switch since I am concerned that the hot and neutral could also be damaged.
Thanks for your input and help.

 

[Norcal]

Are the fluorescent lights attached to the grid, and are they properly grounded? Years ago did quite a bit of work in a office building where none of the fixtures were grounded, if you touched a gas line & the T-bar, you got a tingle, it came from leakage from the ballasts, when the building was constructed in 1979 if the idiots had done the work correct, it would have been OK. The building was built as cheap as they could & the inspectors never caught they used plastic boxes & the metal flex feeding the fixtures had no grounding conductor, if they had only used metal boxes.....

 

[splam]

The metal lights sit in the ceiling grid and my thought is with a high resistance to ground the grid was energized with any bleed through from the lights. Once I gave the circuit a new ground the potential was no longer on the grid but to ground where it should be.

 

[Milton Shaw]

Flourescent light fixtures must be grounded. Glad you found the problem. The lights will light a lot faster if the fixture is grounded. There is some leakage through the ballast but also the bulb must be next to a ground to operate properly from what I have seen.