Conventional Fixtures Strange Electrical Fault

[LavaASU]

So this will be investigated and fixed in the near future-- but for right now this has me stumped.

We're troubleshooting a flickering circuit, we cross patch and determine it's somewhere between (inclusive of) the pigtail to the dimmer rack. While repatching to the original circuit (fumbling in the dark) we accidentally touch the hot pin of the cabling leading to the fixtures to the hot pin of the female stage pin of the bad circuit (N and G pins are not touching) and the fixtures light up.

In order of testing:

Fixture 1 plugged into Pigtail 1= works normally (other than intermittant flicker)
Fixture 1 plugged into Pigtail 2= works normally, no flicker
Fixture 2 plugged into Pigtail 1= works normally other than flicker
Fixture 1 H pin touching Pigtail 1 H pin= fixture lights up
Fixture 1 H touching Pigtail 2 H= nothing happens
Fixture 2 H touching Pigtail 1 H= nothing happens
Fixture 1 plugged into Pigtail 1 normally= fixture lights up
Fixture 1 H pin touching Pigtail 1 H= fixture lights up
Fixture 1 N pin touching Pigtail 1 N= breaker pops (pretty instantly)

I realize I listed some things multiple times, but did so to show that nothing changed during testing and definitively where the breaker tripped. There are other grounded fixtures on the pipe with these.

Up for ideas here-- I'm thinking there must be 2 faults in 2 different places. One would likely be a N-G short on the Fixture 1. However that does not explain why the breaker tripped on N-N and if this were the only problem then the fixture would light up when H was touched to pigtail 2.

We are taking precautions and most of the circuits involved are locked out at the moment. Kids this is a professional theatre with professional technicians with the experience to work on this safely-- don't mess with electricity if you aren't competent to do so.

 

[BryanKacz]

I can't speak fo the flickering, you don't mention what type of dimmers they are, but I've seen pretty good flickering from some of our smart packs here, it normally starts when someone plugs in a large load with the dimmer hot, and it ends when I replace the power cube.

As for the other issues:

The first thing I would do is take a meter to each of the pigtails, to make sure they're wired properly, that Hot is actually Hot, Neutral is actually Neutral, and Ground is Actually Ground.

Then I would take a look at those fixtures (and the cable leading to them), it sounds to me at the very least there is a neutral and ground swapped on Fixture 1.

 

[JD]

Touching one pin of a connector should not light the lamp unless the neutrals are wired in common post patch. Not sure why that would be the case if the panel is stage pin connectors. Time to take a meter to the pigtail and check continuity post patch and see what is connected to what. With the fixtures unplugged or de-lamped, you should not see any continuity between any combinations outside of the ground-ground due to frame connection (if you just removed the lamps.) With the fixtures plugged in and lamped, you will see low readings across hot-neutral on each circuit due to the cold lamps, but there should be no readings from any H/N to ground or between any fixtures.

 

[n1ist]

You have a number of problems:
Fixture 1 has neutral shorted to ground inside the fixture or whip. THis lets the batten be the return path.

Pigtail 2 has hot and neutral reversed.

Pigtail 1 has some issue. I can't figure out why the breaker is tripping if only the neutral is connected - do you have some sort of dimmer-doubling?

Note that you are dealing with some mis-wiring here, so be careful. Touching fixture 1 (especially if it gets removed from a grounded batten) can give you a shock.

Even in a properly-wired fixture, if you only connect the hot pin, the unconnected male neutral pin will be hot, and will be a shock hazard.

I would start by removing fixture 1, find the short, and fix it. I would also measure the voltages from all three socket pins on pigtail 2 to a known ground (it looks like the batten that fixture 1 is on would work here .

In any case, be careful.
/mike

 

[LavaASU]

You have a number of problems:
Fixture 1 has neutral shorted to ground inside the fixture or whip. THis lets the batten be the return path.

Pigtail 2 has hot and neutral reversed.

Pigtail 1 has some issue. I can't figure out why the breaker is tripping if only the neutral is connected - do you have some sort of dimmer-doubling?

Note that you are dealing with some mis-wiring here, so be careful. Touching fixture 1 (especially if it gets removed from a grounded batten) can give you a shock.

Even in a properly-wired fixture, if you only connect the hot pin, the unconnected male neutral pin will be hot, and will be a shock hazard.

I would start by removing fixture 1, find the short, and fix it. I would also measure the voltages from all three socket pins on pigtail 2 to a known ground (it looks like the batten that fixture 1 is on would work here .

In any case, be careful.
/mike

There is no dimmer doubling at all. The dimmers are 3 phase 120/208 Sensor racks. And if it makes a difference what I'm calling fixture 1 and fixture 2 are each a 2-fer with 2 1k units on it.

I'm wondering if there's some sort of possibility that a 2nd fixture has a N-G short and the N on the connector that tripped had less resistance than the ground through the other instruments (theres at least a dozen fixtures on the pipe in question) so the N on fixture and pigtail 1 became the N for the other fixture. What I'm not sure is if there's any way for a N overload to trip a breaker-- other than it happened. I'd think N-H flip on pigtail 1, but I don't see how the fixture could light up with only N connected.

Is there any way the pipe could be at 120? If that is the case there could be a N-G swap on the pigtail 1, and a N-G short in the fixture 1 which would make the hot pin the return for fixture 1 when only it was touched, and would make a dead short when the neutrals are touched.

Bouncing ideas around in the wee hours of the morning. Not totally sure if either of these are possible or make sense. Of course the whole thing is a bit odd.

We are being careful. Fortunately we are in a situation where the only ground nearby is the pipe, so touching a fixture on the pipe (without touching a wire as well) is not going to result in any potential. I've never been shocked by anything that we knew or thought might be live-- it's the ones that never should be live that cause problems (fresnel with a N-G swap for instance!)


Of course that said we've already established that normal electrical concepts don't apply here. Anyone want to loan me some linesman gloves/boots/tools .

 

[David Ashton]

get a portable appliance tester, test each lamp and fix it then using a long extension cable test each circuit, you may get a high earth resistance reading because of the long cable but ignore that.
Quite how "Kids this is a professional theatre with professional technicians with the experience to work on this safely-- " can be justified is beyond me.It sounds very dangerous even with 120 volts.
If you've got this level of faults test and tag the whole place, then at least you'll have a starting point in future.
If you were in Australia with that sort of problem and you were inspected, you wuld be closed until an eletrician would certify the place.

 

[icewolf08]

There is no dimmer doubling at all. The dimmers are 3 phase 120/208 Sensor racks. And if it makes a difference what I'm calling fixture 1 and fixture 2 are each a 2-fer with 2 1k units on it.

So, are saying is that you have two circuits and each has two lights in it on a 2-fer? If that is the case, then I would start by testing the fixtures and the 2-fers. I have found that usually when I have funkiness happening n a circuit with a 2-fer, it is almost always the 2-fer that is the problem. This is even more true when the 2-fers are home-made.

Bad wiring on any of the three connectors in a 2-fer could account for many of the issues you are describing.

 

[shiben]

So, are saying is that you have two circuits and each has two lights in it on a 2-fer? If that is the case, then I would start by testing the fixtures and the 2-fers. I have found that usually when I have funkiness happening n a circuit with a 2-fer, it is almost always the 2-fer that is the problem. This is even more true when the 2-fers are home-made.

Bad wiring on any of the three connectors in a 2-fer could account for many of the issues you are describing.

And twofers are always having problems in the wiring... Annoying buggers at that.

And can we edit the orriginal post to be "don't mess around with electricity ever... It tends to kill you when you do"? I feel like most of the issue here is things need to be tested a lot, my personal feeling is to pull the instruments in question and re-build them, or at least take them apart and do that whole thing.

 

[LavaASU]

And twofers are always having problems in the wiring... Annoying buggers at that.

Icewolf and Shiben, totally agreed-- these are the homemade flavor of twofers, and were metered before being used (though as I did not make them I can't speak to the quality of workmanship beyond what the meter said, but I definitely don't trust that they didn't develop a fault! I'm fully intending to kill power to everything that may be involved and meter it all for continuity or lack thereof in the appropriate places as soon as we get the time to do it safely and carefully.

David, I appreciate your concern, but we don't do PAT testing in the US (at least not that I've ever seen). We did however go through and check continuity and separation as appropriate on the cables at the beginning of the year. Lights were checked as well. Obviously faults have developed since or are in something that wasn't checked.

 

[n1ist]

As been mentioned before, don't stop testing at these two fixtures. If they have a problem, there's a chance that problems exist elsewhere. Everything needs to be tested (all fixtures, 2fers, extension cords in the facility, plus the installed wiring) by someone qualified to work on this gear. Cables must be tested not only for continuity but for pin-to-pin shorts in both ends. Fixtures must be tested for ground faults as well. All wiring must be visually inspected as moving the cables for testing can open a fault (loose strand, too much exposed copper, or metal edge with no grommet or heyco cutting through the insulation).

When troubleshooting a problem, you always need to simplify it. Testing with multiple 2-fer lights gives many more places for problems to occur than testing with a GAM Chek or three nightlight bulbs wired to a stagepin. Also, 2kw loads tend to cause a lot more damage in fault conditions than 7w ones.

If you suspect a hot batten or other grounding problem, start by plugging an extension cord into an outlet with a known good and tested ground, and use a wiggy to test between the extension cord's ground and anything you plan to touch.

Given what you have mentioned so far, the situation could be lethal, so be very careful.

/mike

 

[David Ashton]

the rationale behind using a portable appliance tester is speed and accuracy, in a few seconds you can check insulation, polarity and earth continuity and you don't need to be qualified to understand "pass" or "fail".The amount of time wasted with measuring these parameters is very wasteful.So you do do pat testing, just in a slow and inefficient way, you just don't use the terminolgy.It may be worth investing in one of the US made units and become a leader in safe practices.

 

[Dionysus]

"this is pro theatre"... Unfortunately I've seen some "professional" theatre electrics people do some pretty un-professional electrical work. Now this more exception than rule, but you never know what they've done, or the quality of work they've done.
I've seen some licensed electricians who I can't believe have licenses too.

as n1ist said you really should do a through check of everything.

And a note on ground with your battens and such and your comment on safety, you can still get quite a jolt (trust me). If there is more than one way to ground, or the way to ground has different levels of resistance you can end up getting nasty potential when a fault occurs.
Over at Control Geek there was recently a blog about some nasty stuff from some PoE cameras. Thats nasty enough.

12 volts can be just as nasty as 120..... 347v still hurts a LOT though lol.

All too often when I do fixture maintenance or go to fix circuiting, etc. I commonly find things like conductors that are stripped way too far, not properly seated, cable sheathing stripped back to far with excess wire jammed in the cordcap, conductors not stripped enough, no strain relief, pinched conductors, etc..
I agree that twofers are even more prone to failures developing (especially if not treated nicely). If there is a problem with a circuit and there's a two-fer in it, theres your problem right there.

Electricity is fun

 

[JChenault]

One test I have not seen mentioned.
I would test continuity between each of the six pins in question ( 3 per plug ) and between the batten ( or between the male pin on the twofers and the fixture housing )
Might be instructive.

 

[STEVETERRY]

get a portable appliance tester, test each lamp and fix it then using a long extension cable test each circuit, you may get a high earth resistance reading because of the long cable but ignore that.
Quite how "Kids this is a professional theatre with professional technicians with the experience to work on this safely-- " can be justified is beyond me.It sounds very dangerous even with 120 volts.
If you've got this level of faults test and tag the whole place, then at least you'll have a starting point in future.
If you were in Australia with that sort of problem and you were inspected, you wuld be closed until an eletrician would certify the place.

Hi David--

Unfortunately, one would have to go to London or Sydney to locate a certified Portable Appliance Tester in the US. We don't have the same regular testing requirements for electrical equipment, and PAT equipment is not part of the US toolbox.

So, while the tests suggested on this thread seem "home grown" they are probably appropriate for a "non-PAT" country.

Cheers

ST