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Thread: strange occurance

  1. #1
    Licensed Electrician andrew79's Avatar
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    Default strange occurance

    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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    Moderator & Master Plumber hj's Avatar
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    What do you mean by "the grid live and not live"? Are you saying the grid is energized? If so, then it definitely unsafe. If you mean it was energized before connecting the ground to "drain" the power, then that is also unsafe, because if the ground is lost it will become live again. Ceiling grids are usually only incidentally grounded by contact with other metal objects if they are grounded. An induced current is seldom strong enough to "tag" someone.

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    Licensed Electrician andrew79's Avatar
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    two things to note though are that in theory anyways if there was a short once the ground was connected it should have tripped the breaker. The other is that i'm working off the same pricipal as electronic musical equipment. I know that in house that have no ground you can get shocked off them when you touch them. I'm assuming that's what's happening here with the electronic ballasts. I'm not sure if he got a full jolt or just thought he did. I'd rather not recreate the scenario to find out.

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    DIY Member Lightwave's Avatar
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    Quote Originally Posted by andrew79 View Post
    two things to note though are that in theory anyways if there was a short once the ground was connected it should have tripped the breaker.
    Not if the cieling grid has only a high resistance connection to a hot wire.

    You should temporarily install a GFCI breaker on this circuit and go looking for whatever connection is making the grid live. The GFCI will not reset unless the problem is fixed.

    Leaving things as-is is a bad idea as you could have both a fire and electrocution hazard.

  5. #5

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    The ceiling grid should never have power running through it regardless whether the fixtures are grounded or not. I would remove the ground and put a multimeter between the ground and the grid and make sure it reads 0. If it does the odds of you finding what caused it are low. It could have been a nicked hot touching the casing of the light fixture and it may have blown itself clear when you connected the ground. As long as everything is grounded now and the multimeter test turns up nothing you should be ok.

    I worked with a guy that got himself in the middle of a ceiling grid that had 277 volts running through it. It wasn't pretty.

    -rick

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    Licensed Electrician andrew79's Avatar
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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"
    Last edited by andrew79; 03-25-2010 at 03:38 PM. Reason: mre info

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    Retired Defense Industry Engineer jadnashua's Avatar
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    It's not surprising there's no current flowing in the grid...somebody that complete the circuit would do that. It only takes milliamps to electrocute someone.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Licensed Electrician andrew79's Avatar
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    s'ok...got it figured out...thanks for the help guys and or gals

  9. #9

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    And you're not going to tell us what it was?

    Obviously there was power going to "ground" somewhere and when the ground was disconnected it traveled thru the grid instead.

    Open neutral plus neutral/ground connection somewhere?

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    Licensed Electrician andrew79's Avatar
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    oddly enough after contacting the manufacturer and a few trade friends of mine and putting our head together we found out that the ground absolutely has to be connected for this type of ballast. They've had this problem with the equipment before and what essentially happens is that with the grid ungrounded the whole things sort of acts like a transformer with the grid being the secondary and the field the ballasts produce being the primary. According to the manufacturer the induced voltage with no ground can ctually almost get up to the 120v that your starting with but won't carry enough current to even register on a meter. Makes sense in theory...back to my original assesment...anytime your dealing with electronics a ground is a necessity for proper working conditions.

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