Blinking Exit Signs

[Canton]

I have an issue where the Exit Signs on a floor in a new building are blinking when the circuit is turned off.

The branch circuit that comes from the electrical closet was ran in 10/3 MC out to the floor to power Exit Signs and Lighting. The exit signs and lights are 277 volt on (2) 20 amp circuits (multiwire branch circuit). The exit signs are A phase and the lighting is B phase.

When both branch circuits (A phase and B phase) are energized the exit signs and lighting work with no problems. If A phase is turned off the exit signs should go off. They do not, they start to blink rapidly. If I turn B phase off (lighting) and leave A phase on (Exit signs) they work with no issues.

It appears that B phase (lighting) is inducing enough voltage onto A phase (Exit Signs) to make them blink off and on rapidly......?

Some other background information: The lights and exit signs are LED's. The 10/3 MC is ran through out the entire floor feeding all the Exit Signs and Emg. Lighting like this. Total length is almost 400' from panel to last light/exit sign. It does not appear that anything is back feeding or miss wired. When B phase is energized I get 10-40 Vac on A phase (exit signs). We broke the circuit half way and in different places to see if we had any change in the blinking. The blinking occurred but it was not as bright. The more lights and the longer length of the total circuit that was included...the brighter the flashing on the exit signs....? But if I turn A phase (exit signs) back on everything works. It is only when B phase (lights) is energized and A phase (exit signs) off, does the blinking occur in the exit signs....?

Any Ideas?

 

[GoldDigger]

On the off chance that the entire energizing of the A phase wires is from capacitive coupling from the B phase in the same MC, you could try putting a 100W or so incandescent lamp temporarily in parallel on the A phase. (Make sure it can take the voltage.)
If it lights up, or if the Exit fixture blinking stops, measure the current with a clamp-on ammeter.
Another possibility besides capacitance in the wiring would be surge suppressors which are either wired between A and B or wired independently supposedly from A to ground and from B to ground but that "ground" point is actually floating.

 

[ActionDave]

I have an issue where the Exit Signs on a floor in a new building are blinking when the circuit is turned off......

When both branch circuits (A phase and B phase) are energized the exit signs and lighting work with no problems. If A phase is turned off the exit signs should go off. They do not, they start to blink rapidly. If I turn B phase off (lighting) and leave A phase on (Exit signs) they work with no issues.

It appears that B phase (lighting) is inducing enough voltage onto A phase (Exit Signs) to make them blink off and on rapidly......?

Along the same lines as GoldDigger....Turn off A phase and test for voltage with a wiggy; see if the blinking stops

 

[steve66]

Do the exit signs have battery backup?

Also, some exit signs have a fire alarm connection that makes them flash. Any chance these have that?

 

[augie47]

perhaps:
https://www.youtube.com/watch?v=pVoEp63wbNA

 

[electricalist]

What are the exit signs supposed to do when there is no power to them ? Go off or do they have a battery back up.
Is it possible the way the circuit is ran that the lighting neutral is feeding the exits ? example 1 exit to switched lighting and back out to another exit and as you add more lighting the exits get more voltage.
IF Its even possible

 

[ActionDave]

Do the exit signs have battery backup?

Also, some exit signs have a fire alarm connection that makes them flash. Any chance these have that?

What are the exit signs supposed to do when there is no power to them ? Go off or do they have a battery back up.

Doesn't matter, they don't blink when there is zero power only when the breaker that feeds them is off and the other half of the MWBC is on.

 

[electricalist]

Then that leaves only bleedover voltage from the lighting half ,,,this could mean straight lighting loads will be a problem with mwbc if there is no balance of linear and non linear ?

 

[Canton]

On the off chance that the entire energizing of the A phase wires is from capacitive coupling from the B phase in the same MC, you could try putting a 100W or so incandescent lamp temporarily in parallel on the A phase. (Make sure it can take the voltage.)
If it lights up, or if the Exit fixture blinking stops, measure the current with a clamp-on ammeter.
Another possibility besides capacitance in the wiring would be surge suppressors which are either wired between A and B or wired independently supposedly from A to ground and from B to ground but that "ground" point is actually floating.

I really do think it is capacitive coupling. I did put a wiggy up there and no movement of the solenoid. The exit lights did continue to blink though. There are no issues with both breakers being turned on. We are going to put a breaker tie between the two single pole breakers (code anyway). It just really bothers us that we can't figure it out. Thanks for the input.

 

[Canton]

What are the exit signs supposed to do when there is no power to them ? Go off or do they have a battery back up.
Is it possible the way the circuit is ran that the lighting neutral is feeding the exits ? example 1 exit to switched lighting and back out to another exit and as you add more lighting the exits get more voltage.
IF Its even possible

No, there is no battery back-up. They are on an emergency circuit (via ATS/Generator).

 

[Canton]

Do the exit signs have battery backup?

Also, some exit signs have a fire alarm connection that makes them flash. Any chance these have that?

I do believe they have a fire alarm connection. I did notice a FA and FI switch in them. I will have to look into that. Still don't know why they would flash with no battery back-up and circuit turned off. Thanks for reminding me about that.

 

[Canton]

perhaps:
https://www.youtube.com/watch?v=pVoEp63wbNA

Hey Augie, thanks for the link. The flashing is not like that though. It is more at the line voltage frequency (60 Hz) and the brightness intensifies when more lights on the other phase of the MWBC are added. If the circuit is broken into 1/4 is very little. Add another 1/4 and they get brighter and so forth when you add more..?

 

[iwire]

Stop turning the circuit off.

Problem solved.

 

[readydave8]

Stop turning the circuit off.

Problem solved.

That was funny, but would have been better with Clint avatar

 

[Canton]

Stop turning the circuit off.

Problem solved.

Thanks Iwire! I have used your advise many times in the past to solve problems....I was hoping for something.....a little more creative!!!!..:lol:

 

[electricalist]

I'm the least knowledgeable here and I do appreciate not being shunned. I'm gonna read up on what GoldDigger said, but is there a short answer how 0v on the wiggy is enough to make the exits blink.?

 

[ActionDave]

I'm the least knowledgeable here and I do appreciate not being shunned. I'm gonna read up on what GoldDigger said, but is there a short answer how 0v on the wiggy is enough to make the exits blink.?

A digital meter draws a tiny, tiny bit of current so it will read capacitance/charges that build up on circuit conductors as voltage. A solenoid tester, aka wiggy, draws some juice through its coil to pull that plunger down to the level of 120V or 240V or 277V.....it needs real electrons from the power plant to do that not stray, homeless ones hitching a ride on the circuit conductors and insulation.

 

[electricalist]

Can I assume this will be common in long runs where conductors are together?
Recently I was a job and there were conductor abandon with no wire nuts. I put my non contact tester on them and it lit up. So I checked with my digital meter and it was point something,,,like 3 . There were other energized conductors there also. It was 359-400' run. Same thing?

 

[GoldDigger]

Can I assume this will be common in long runs where conductors are together?
Recently I was a job and there were conductor abandon with no wire nuts. I put my non contact tester on them and it lit up. So I checked with my digital meter and it was point something,,,like 3 . There were other energized conductors there also. It was 359-400' run. Same thing?

I would not say that it was necessarily the same thing. It is the same as what we currently suspect is the problem with the lighting circuit.

But to me the fact that the lights continue to flicker while the Wiggy is across the same circuit strongly suggests to me that the problem is something more than just capacitive coupling. The Wiggy should be a low enough impedance load that the light flickering really should stop if there is only wire to wire capacitive coupling involved.
BTW, we do not know whether your digital meter is one which has a high impedance input or one which has deliberately designed a low impedance voltage input to avoid the phantom voltage problem. If your meter reads .3 something, I suspect that it does have a low impedance input. The input impedance of the non contact tester is even higher than a typical digital meter with high impedance input.

 

[electricalist]

Thanks GoldDigger I will re up on what you are talking about ,,its 30 here feels like 20 and rainy icy snowy, Im trapped inside.

As for the exits Im interested in whats going on. Problem solving is my favorite part about electrical work.I ll bet a dollar you know the answer already.