Compact fluorescents and continuity

[chris kennedy]

I have a 20,000sq/ft building where all the lighting is compact fluorescent. I leave the panel with A,B,C and one neutral. During a neutral fault test, I find continuity between the neutral and EGC. So we pull the neutrals off the buss and show no current on the EGC as we energize each circuit one by one.

So I get a new uninstalled fixture and test, no continuity, lamp it and still no continuity.

How could this happen?

 

[buddhakii]

Did you read continuity with the neutral disconnected from the buss? If so I would say you have a couple neutrals of different circuits tied together. With the neutral disconnected did the lights still come on? If this is a mwbc I wouldn't turn circuits on with the neutral disconnected as you can do a lot of damage.

 

[iaov]

Dead short continuity or high resistence continuity?? I've seen some wierd things with flour.ixtures before.

 

[benaround]

Reading thru the wye connected transformer ? Really need to know exactly how you did

the test.

 

[ohm]

Did you read continuity with the neutral disconnected from the buss? If so I would say you have a couple neutrals of different circuits tied together. With the neutral disconnected did the lights still come on? If this is a mwbc I wouldn't turn circuits on with the neutral disconnected as you can do a lot of damage.

Bingo!.......

 

[iwire]

If this is a mwbc I wouldn't turn circuits on with the neutral disconnected as you can do a lot of damage.

Chris is well aware of basic wiring procedures. :smile:

 

[mxslick]

So we pull the neutrals off the buss and show no current on the EGC as we energize each circuit one by one.

Bob, I too was about to chime in on energizing MWBC with lifted neutrals until I re-read a few times and noticed the phrase in bold.

 

[chris kennedy]

I don't know if this would make a difference but the battery in the DMM I used died today. Tomorrow I will be back in the panel and will also test with a Fluke T+ and the DMM. BTW, the DMM is an Ideal 61-774. I'll let you know.

 

[buddhakii]

Chris is well aware of basic wiring procedures. :smile:

I would've thought so, but no matter how familiar someone is with anything doesn't mean we forget things. I missed the one by one part too.

 

[chris kennedy]

I would've thought so, but no matter how familiar someone is with anything doesn't mean we forget things. I missed the one by one part too.

I agree and it doesn't hurt to state the obvious. Keep them coming.

 

[cowboyjwc]

If you are simply trying to see if the neutral is clear, don't use a real sensitive meter. We were doing the same test once and found out it was reading between our fingers. I would just use one of the cheap,flashlight types.

Also anytime we do one of these tests and someone blames the transformer or lights it still usually ends up being a pinched wire or something silly like that.

 

[benaround]

No new Exit or EMG fixtures on these circuits ? Occupancy sensors ?

Your test was in the circuit downstream of the panel, is that right? From load side neutral

to EGC.

 

[ohm]

No new Exit or EMG fixtures on these circuits ? Occupancy sensors ?

Your test was in the circuit downstream of the panel, is that right? From load side neutral

to EGC.

The user doesn't have something like an old 3 wire dryer or range that connects one hot leg to ground/neutral to derive 120V for a timer or lamp does it?

 

[chris kennedy]

If you are simply trying to see if the neutral is clear, don't use a real sensitive meter.

Trying this morning with different meters.

Also anytime we do one of these tests and someone blames the transformer or lights it still usually ends up being a pinched wire or something silly like that.

If this was the case, then with the grounded conductor lifted from the buss and the circuits energized one and only one at a time, I would have had current on the EGC and the lights would operate.

No new Exit or EMG fixtures on these circuits ? Occupancy sensors ?

Your test was in the circuit downstream of the panel, is that right? From load side neutral

to EGC.

Correct, and of the 40 or so lighting circuits, only 3 or 4 have no new LED type exit/emergency lights on them.

The user doesn't have something like an old 3 wire dryer or range that connects one hot leg to ground/neutral to derive 120V for a timer or lamp does it?

No, brand new building.

 

[mxslick]

Based on all the info and answers so far, the only thing I can think of is this:

The leakage resistance from neutral to ECG in EACH fixture is of a very high value, but put enough of them together on any given circuit and the resistance drops enough to be readable.

The ultimate question I have is this: if AFCI's aren't involved, and the circuits function properly, why the fuss?

Another approach to take:

With the neutrals properly attached to the bus, power up the fixtures and lift the EGC's and see if there is appreciable voltage built up with a wiggy in parallel with a DMM, or leave the EGC's attached and see if there is current flow.

 

[cowboyjwc]

The ultimate question I have is this: if AFCI's aren't involved, and the circuits function properly, why the fuss?

If it's a system that requires a GFCI, you want to make sure that it's clear so that you don't get any nuciance tripping. That is actually one of the test's they do when they test the GFCI and will usually note if all of the circuits are not connected when they do the test.

Now of course I'm assuming that the lighting is 277 and that the service is rated at 1000 amps or more.

 

[chris kennedy]

If it's a system that requires a GFCI, you want to make sure that it's clear so that you don't get any nuciance tripping. That is actually one of the test's they do when they test the GFCI and will usually note if all of the circuits are not connected when they do the test.

Now of course I'm assuming that the lighting is 277 and that the service is rated at 1000 amps or more.

800A 208Y/120. But I'm in the habit of doing this test due to the number of GFI protected services we have done in recent years. Unfortunately it was a circus today and I didn't have a chance to get back into the panel. Poco power comes tomorrow, so I doubt I can test until Friday.

 

[cowboyjwc]

800A 208Y/120. But I'm in the habit of doing this test due to the number of GFI protected services we have done in recent years. Unfortunately it was a circus today and I didn't have a chance to get back into the panel. Poco power comes tomorrow, so I doubt I can test until Friday.

Not a bad habit to get into and it's not like it's hard to do. I usually just have them pull the neutral disconnect link and check there.

 

[chris kennedy]

Not a bad habit to get into and it's not like it's hard to do. I usually just have them pull the neutral disconnect link and check there.

From an inspectors point of view.:smile: For the installer, it's much quicker to go to each panel and while the panels are not energized, take all the grounded conductors off the buss, check each one for continuity to ground. Quickly identifies the circuits in question. Thats how I found this on the same job.

With multiple panels, simply removing the bonding jumper may tell you you have a problem, but where to look? It's like pulling wire, work your way from the furthest point to the source.

 

[cowboyjwc]

You are correct, my way will tell you, you have a problem, you can then pull the grounded conductors and isolate which panel and then you are still going to have to do it your way to isolate the circuit.