# Voltage Fluctuating



## Ontario (Sep 9, 2013)

I got a call to replace two floodlights from metal halide to LED lights. I thought "this should be easy, it's just plug and play".

I got to the site and tested the two existing metal halide floods. They worked perfectly. Good.

I removed them and put in two LED floodlights only to test them and find out they were strobing. "I've seen this before. It's almost always a voltage problem. Must be the autotransformer".

I replaced the auto transformers (347V to 120V) and tested it again. Same deal. I left the power on to test the circuit out. This is what I found out: the voltage fluctuates from 347V to 120V and back again. I thought it was a neutral problem but following the neutral back to the panel, everything seemed to be alright.

The only anomaly I had not tested is the splice from where the wire exits the building and goes underground to the floodlights located on the ground. I can't access those splices because someone locked the Jbox and there is no safe way to get it open (nobody has the key either). My gut tells me the problem lies there but I am hoping not or I'll have to shut down half the factory to cut the damn thing open and replace it. Not worth it for two lights.

Could there be any other explanation for this? Perhaps a damaged wire somewhere along?

The customer told me I must have done something as the metal halides worked perfectly before. I explained that the metal halide lights probably worked because of the capacitor inside them. They are better suited to withstand fluctuating voltages like that.


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## HAL9000 (Feb 28, 2016)

I had a similar problem recently, LED lights on the NL circuit were strobing badly, I never tested the voltage I traced the wires back and it was a faulty neutral splice in my case, but mine was a very easy location to access


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## telsa (May 22, 2015)

I'll hazard a wild guess.

LEDs are driven by electronics -- that needs a sweet neutral -- not so much for the power side of the equation -- but for its internal logic.

Hence, bad make-up on a neutral -- or a marginally undersized neutral -- can play havoc with its 'brain.'

You can cheat ( test) by bonding the neutral to the grounding conductor... and if the problem evaporates -- you have your proof -- the problem IS the neutral.

You don't need to get into the magic box to dope out an impaired neutral return.

It IS cheating, but driving a ground rod and bonding it to the neutral and grounding conductors as a parallel path -- for such a trivial load -- will suffice in a pinch.

One can rationalize this cure -- because it's embedded in the ground -- and the power level involved is trivial for two LED fixtures.

This may end up being your only practical solution.

Don't tell anyone about your sin. :no:


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## Big John (May 23, 2010)

Somethings hinky: No fixture is gonna happily tolerate a 290% voltage swing.

I would've temped in a big resistive load (like a couple 100W bulbs) just to see what it did to the circuit voltage.

But I agree a very weak neutral on the autotransformer would make sense: With the N side open it simply becomes a big coil of wire energized at 347V and that is what your 120V tap would see.

Why it strobes, I can't explain.


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## Big John (May 23, 2010)

telsa said:


> ...You don't need to get into the magic box to dope out an impaired neutral return.
> 
> It IS cheating, but driving a ground rod and bonding it to the neutral and grounding conductors as a parallel path -- for such a trivial load -- will suffice in a pinch.
> 
> One can rationalize this cure -- because it's embedded in the ground -- and the power level involved is trivial for two LED fixtures...


 Are we posting electrical advice we learned in the plumbing aisle at Home Depot?

That's a terrible suggestion.


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## PlugsAndLights (Jan 19, 2016)

Big John said:


> Are we posting electrical advice we learned in the plumbing aisle at Home Depot?
> 
> That's a terrible suggestion.


OK, part of telsa's suggestion may have been questionable, but fair is fair
and telsa also had the best suggestion on this thread, so far:
"You can cheat ( test) by bonding the neutral to the grounding conductor... 
and if the problem evaporates -- you have your proof -- the problem 
IS the neutral." 
P&L


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## Big John (May 23, 2010)

PlugsAndLights said:


> ...Telsa also had the best suggestion on this thread, so far:
> "You can cheat ( test) by bonding the neutral to the grounding conductor...
> and if the problem evaporates -- you have your proof -- the problem
> IS the neutral."


"And that's how we found out there was also a compromised equipment ground when everything we were touching suddenly got energized at 347V...."

All he has to do to prove his lighting neutral is connect a voltmeter between it and EGC. If it's open, it will be at line potential. If it's closed, it will stay near ground potential. Much safer.


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## Ontario (Sep 9, 2013)

PlugsAndLights said:


> telsa also had the best suggestion on this thread, so far:
> "You can cheat ( test) by bonding the neutral to the grounding conductor...
> and if the problem evaporates -- you have your proof -- the problem
> IS the neutral."
> P&L


Tried that today and here's the thing: I did that with the other light disconnected and it gave me a solid 347. After hooking up the other light, it begins fluctuating. I thought it must be something up in that vicinity.

There is a PVC Jbox near those lights and I thought I'd measure volts to ground from there. Fluctuating. Disconnected the lights, and it was solid. Must be the line running to the lights then, right? Maybe it's all hooked up wrong? Nope. Everything seemed to be in check.

There are two sets of neutrals coming in for some reason, both of which provide the same result.

I believe someone hooked up the neutral from the 347V panel to a neutral from a 120V panel somewhere inside the facility. That's the only thing I can think of. 

I may be wrong because this is the first time anything like this has ever happened. I hope I haven't overlooked something. Who knows.


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## Big John (May 23, 2010)

You replaced the tranny so you know where the circuit originates. Hook a test load up right there and see if you've got proper voltage. 

If you don't, follow your transformer feeder. If you do, follow your lighting circuit.


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## emtnut (Mar 1, 2015)

.... Deleted ... It's late


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## telsa (May 22, 2015)

Big John said:


> "And that's how we found out there was also a compromised equipment ground when everything we were touching suddenly got energized at 347V...."
> 
> All he has to do to prove his lighting neutral is connect a voltmeter between it and EGC. If it's open, it will be at line potential. If it's closed, it will stay near ground potential. Much safer.


This technique fails in practice -- when the issue is too much impedance on the neutral -- via shear length -- via poor make-up.

Temping -- for test purposes -- will expose -- absolutely -- whether the neutral is at issue.

As for undersized neutrals on underground (site) runs -- I've run into them time and time, again.

It's a RARE j-man that ever considers the length of a run as a critical factor.

LASTLY, it's as common as dust for fellas to foul up make-up -- when doing fighting runs. For many guys leave their leads so short that they have to lay down on their bellies to wire up their conductors.

AND there's a tendency for fellas to perform indifferent water proofing. (dipping)

What baffles the service trooper -- grand assumption that everything was perfect and squared away -- there are no marginal elements because the customer says so.


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## Big John (May 23, 2010)

telsa said:


> This technique fails in practice -- when the issue is too much impedance on the neutral -- via shear length -- via poor make-up.


Too much neutral impedance is literally what that voltage test is checking for. It's a lot safer and faster than cobbling your equipment ground into a temp neutral.


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## telsa (May 22, 2015)

Big John said:


> Too much neutral impedance is literally what that voltage test is checking for. It's a lot safer and faster than cobbling your equipment ground into a temp neutral.


A high impedance DMM will NOT spot the impedance problem.

It will read that everything is A-okay.

Been there, done that; 

been there, done that.

The chances that our OP is using a low impedance meter is scant. 

He would've brought that up.

It's from the school of hard knocks I speak.

If bootlegging to the grounding conductor does not instantly clean up the problem -- it's VERY safe to say that the malady is not on the neutral. 

Boy that saves an immense amount of time.

J-men practically NEVER show up on this -- or any other -- forum because they have trouble figuring out a messed up hot conductor.

Everyone is prepared to dope them out.

It's faults on return conductors that have the boys tearing their hair out, time and time, again.

&&&&&&

The most baffling situation is per the OP: everything looked fine... then a fixture was swapped... and now it's not fine at all.

Needless to say, no j-man really questions his own make-up.

But, it's EASY to do on site runs.

Yet, countless times, that was the issue - right from the start.

&&&&&

LED drivers depend upon tiny switching power supplies to generate their VDC.

These circuits depend upon CLEAN grounded conductors -- or their logic starts to float all over -- in rhythm with 120 Hz.

ANY time one sees strobing at 120 Hz -- that's a TELL.


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## Big John (May 23, 2010)

telsa said:


> A high impedance DMM will NOT spot the impedance problem....


 Sure it will: You aren't depending on the DMM itself to adequately load the circuit and stress the connections.

The lights that are already on the circuit, which are apparently what are causing the voltage to fluctuate, will do that. You're simply recording the voltage as it fluctuates.


Turn on problematic lights
Current should be flowing in hot and neutral
Connect DMM between neutral and EGC
Watch DMM for neutral voltage drop due to high impedance
Adding extra lights will create more voltage drop and make reading more obvious.


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## JoeAPinkley (Apr 3, 2016)

A voltage fluctuation is a dip or spike in the flow of electricity to your home. Fluctuations of more than six volts may cause your lights to dim or brighten.


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