277v increase to 344v

[Nelson electric]

I am looking for help in a LED highbay retro.
I swapped out 21 out of 22 400 watt metal hyliade fixtures with 21 JEBL 80CRI LED highbay. (We are waiting for the 22nd one to be delivered.) The lights are divided into 3 circuits coming from a 3-pole lighting contactor, controlled by a set of 3-way toggle switches. All fixtures are 277 volts, measuring 278 - 279 volts neutral to hot leg. When the switch was turned on all 21 fixtures went out, with blinking strobe-like as they went out.
The switch was turned off and disconnected the last 2 fixtures and turned the switch back on and was reading 344 volts neutral to hot leg. Which, the 344 volts fried the capacitor inside the fixtures.
All other new JEBL fixtures on 2 other 3-pole lighting contactors were on at the same time, being fed from same panel, with no interruption or apparent voltage spike due to they did not burn out at the same time.
This isolated the 3-pole circuit from the others, from the lighting contactor to the fixtures.
All 3 circuits are sharing the same neutral. (30 year old installation).
There was one 400 watt fixture left on the 3-pole circuit.
Is this a neutral issue?
How else could there be an increase from 277 volts to 344 volts?
Thank you four your help in trying to understand the issue.

 

[texie]

I am looking for help in a LED highbay retro.
I swapped out 21 out of 22 400 watt metal hyliade fixtures with 21 JEBL 80CRI LED highbay. (We are waiting for the 22nd one to be delivered.) The lights are divided into 3 circuits coming from a 3-pole lighting contactor, controlled by a set of 3-way toggle switches. All fixtures are 277 volts, measuring 278 - 279 volts neutral to hot leg. When the switch was turned on all 21 fixtures went out, with blinking strobe-like as they went out.
The switch was turned off and disconnected the last 2 fixtures and turned the switch back on and was reading 344 volts neutral to hot leg. Which, the 344 volts fried the capacitor inside the fixtures.
All other new JEBL fixtures on 2 other 3-pole lighting contactors were on at the same time, being fed from same panel, with no interruption or apparent voltage spike due to they did not burn out at the same time.
This isolated the 3-pole circuit from the others, from the lighting contactor to the fixtures.
All 3 circuits are sharing the same neutral. (30 year old installation).
There was one 400 watt fixture left on the 3-pole circuit.
Is this a neutral issue?
How else could there be an increase from 277 volts to 344 volts?
Thank you four your help in trying to understand the issue.

Sounds like an expensive open neutral to me.

 

[Nelson electric]

Sounds like an expensive open neutral to me.

I don't think it was an open neutral for the 2 that were installed was not ast the beginning of the circuitry. If it was at the first one in the neutral line then I would think it to be the open neutral.
Could it be a bad neutral wire?

 

[augie47]

Are you sure your supply in 480/277 ?? Could it possibly be a 480 ungrounded supply ?

 

[kwired]

Are you sure your supply in 480/277 ?? Could it possibly be a 480 ungrounded supply ?

Could even be 600/347 volt system, his mentioned 344 is about right on for that.

Did anybody ever look at what tap the existing metal halides were connected to or confirm actual operating voltage?

Ungrounded 480 supply or even 480 volt corner ground, if balanced would balance out near 277 and may have never given any noticable issues if all neutrals are tied together but otherwise floating from everything else.

 

[Nelson electric]

Could even be 600/347 volt system, his mentioned 344 is about right on for that.

Did anybody ever look at what tap the existing metal halides were connected to or confirm actual operating voltage?

Ungrounded 480 supply or even 480 volt corner ground, if balanced would balance out near 277 and may have never given any noticable issues if all neutrals are tied together but otherwise floating from everything else.

The system is 277/480 volt. There is one 277/480 distribution panel fed from the main service, with a neutral. All other loads does bout have a neutral.
I checked resistance between neutral and ground at the main service and I got 28 ohms, and when I put my amp probe on that neutral (distribution panel with lighting load) I read 15 amps. The neutral bar is not is not bonded to ground at distribution point. However, it is bonded on the line side of neutral disconnect link at the main 2500 amp breaker, at which point I get .1 ohms between ground and neutral. Could the link be bad?
Should the neutral be bonded at the distribution side of the switch gear? Which is the same neutral bar throughout the gear? Just with the disconnect link between the bar?

 

[kwired]

The system is 277/480 volt. There is one 277/480 distribution panel fed from the main service, with a neutral. All other loads does bout have a neutral.
I checked resistance between neutral and ground at the main service and I got 28 ohms, and when I put my amp probe on that neutral (distribution panel with lighting load) I read 15 amps. The neutral bar is not is not bonded to ground at distribution point. However, it is bonded on the line side of neutral disconnect link at the main 2500 amp breaker, at which point I get .1 ohms between ground and neutral. Could the link be bad?
Should the neutral be bonded at the distribution side of the switch gear? Which is the same neutral bar throughout the gear? Just with the disconnect link between the bar?

What you described in OP was apparently balanced neutral load or at least very close to balanced, then you disconnected some loads and threw balance off, so neutral was going to carry some current.

I'd say you do have a neutral issue.

I checked resistance between neutral and ground at the main service and I got 28 ohms,

May be pushing it a little with this suggestion, but I think that is about right amount of resistance for high impedance ground resistor. If the lights are the only 277 volt load and were always operated in a balanced condition, they may have gotten away with little or no troubles before on something that wasn't set up for use with 277 volt loads.

 

[winnie]

May be pushing it a little with this suggestion, but I think that is about right amount of resistance for high impedance ground resistor. If the lights are the only 277 volt load and were always operated in a balanced condition, they may have gotten away with little or no troubles before on something that wasn't set up for use with 277 volt loads.

The neutral in a HRG system is an electrically good neutral, in terms of being at a stable voltage relative to the line conductors. It is not code compliant to use that neutral, but if this were an HRG system I wouldn't expect the HRG aspect to cause a change in line-neutral voltage.

-Jon

 

[kwired]

The neutral in a HRG system is an electrically good neutral, in terms of being at a stable voltage relative to the line conductors. It is not code compliant to use that neutral, but if this were an HRG system I wouldn't expect the HRG aspect to cause a change in line-neutral voltage.

-Jon

I was getting at the possibility of a failed attempt at properly installing a HRG system could be what has happened.

 

[winnie]

I was getting at the possibility of a failed attempt at properly installing a HRG system could be what has happened.

Ahh, perhaps on the one failed circuit the neutral current is passing through the resistance...

 

[kwired]

Ahh, perhaps on the one failed circuit the neutral current is passing through the resistance...

I was thinking more of current is normally balanced so there is normally little or no neutral current, once they intentionally disconnected a couple luminaires they threw that balance off and now the imbalance is trying to return through the resistance.

OP did say there was originally 22 MH luminaires. That would balance out at 7 per phase with one extra - that may not be enough imbalance to cause immediately noticeable issues for those magnetic ballast luminaires, but could be bigger issue with the LED drivers they converted to.

 

[winnie]

Okay, as the OP described there is a main panel with 0.1 ohm neutral to ground, and then a downstream panel where they measured 28 ohms. Now this measurement could be corrupt in a number of ways, but that sounds to me like a direct measurement of a neutral problem.

However there are multiple circuits from this panel, and only one showed problems, suggesting that the problem is downstream of the panel (in the individual circuit(s) neutral) .

As others have said, balanced loading on a shared neutral circuit can function fine even with a bad neutral, it is the imbalance that causes symptoms. Something else that can cause problems on a shared neutral circuit with a bad neutral is harmonic loading, because 3rd (and other triplen) harmonics always _add_ on the neutral in a 3 phase system.

-Jon

 

[kwired]

Okay, as the OP described there is a main panel with 0.1 ohm neutral to ground, and then a downstream panel where they measured 28 ohms. Now this measurement could be corrupt in a number of ways, but that sounds to me like a direct measurement of a neutral problem.

However there are multiple circuits from this panel, and only one showed problems, suggesting that the problem is downstream of the panel (in the individual circuit(s) neutral) .

As others have said, balanced loading on a shared neutral circuit can function fine even with a bad neutral, it is the imbalance that causes symptoms. Something else that can cause problems on a shared neutral circuit with a bad neutral is harmonic loading, because 3rd (and other triplen) harmonics always _add_ on the neutral in a 3 phase system.

-Jon

My understanding was the lighting that was replaced was the only 277 volt loads present, was switched by a 3 pole contactor, so probably was balanced other than the 22nd fixture. A bad neutral may not even been something obvious with the magnetic ballasts on the old fixtures, though it maybe did contribute to shorter life out of some of them but over longer periods that it wasn't obvious.

Then they changed out 21 of 22 (one wasn't there for whatever reason yet). They might have been balanced and it worked fine, but then they unhooked a couple for some reason and that unbalance maybe couldn't be tolerated by the electronic drivers.

Neutral may have been bad before ever taking original fixtures out of service but nobody ever noticed any troubles.