Shared Neutral on Florescent Lighting

[njtrombley]

Is it against NEC to share one neutral with three hots for florescent lighting? We are having a heated debate i.e. boss vs. employee. I have heard that the harmonics can add additional current to the neutral and we would be required to pull a "super" neutral or a bigger conductor for the neutral than the hots.

 

[raider1]

Welcome to the forum.

There is nothing in the NEC that prohibits installing fluorescent lighting on a multiwire branch circuit.

There could be issues with harmonic current, but that would be a design issue.

Chris

 

[sameguy]

count that neut. as a current carrier.

 

[LarryFine]

I have heard that the harmonics can add additional current to the neutral and we would be required to pull a "super" neutral or a bigger conductor for the neutral than the hots.

Keep in mind, however, if the loading is balanced, there won't be any "normal" current, so the triplen harmonics would be the only current.

 

[Ken In NJ]

I believe .. in IMHO .. that electronic ballasts do fail more on shared neutral circuits ..

We stopped doing it years ago .. and do not share them when running feeds for florescent lighting

Buts its not a code issue as far as I know

 

[ActionDave]

Ken, are you talking about T-8 or four pin G base lamps?

 

[iwire]

I believe .. in IMHO .. that electronic ballasts do fail more on shared neutral circuits ..

We stopped doing it years ago .. and do not share them when running feeds for florescent lighting

Buts its not a code issue as far as I know

That makes no sense electrically.

Every light you have, and will wire is supplied with a shared neutral.

 

[A/A Fuel GTX]

That makes no sense electrically.

Every light you have, and will wire is supplied with a shared neutral.

Bingo!........The service coming into any building is essentially a MWBC.

 

[Jim W in Tampa]

Only real down side is the 3 pole breaker. You will be killing all 3 circuits. But even that is not as bad anymore with the required disc. at each fixture. In times where money is tight i would not be wasting wire.

 

[njtrombley]

Thanks Everyone, Very Helpful

Thanks Everyone, Very Helpful

That was the first question I ever posted on this forum and it won't be my last. Thanks everyone for helping me out. I don't think my boss will believe me and will still do it his way, but as my co-worker says, "He who has the gold makes the rules." Thanks again and God Bless.

 

[480sparky]

Bingo!........The service coming into any building is essentially a MWBC.

Not really....... services are not branch circuits.

 

[Jim W in Tampa]

Not really....... services are not branch circuits.

Sure they are ,just from a very large panel LOL

 

[LarryFine]

Bingo!........The service coming into any building is essentially a MWBC.

Not really....... services are not branch circuits.

Sure they are ,just from a very large panel LOL

And they don't even have to follow the NEC tap rules.

 

[nyhockey]

Is it against NEC to share one neutral with three hots for florescent lighting? We are having a heated debate i.e. boss vs. employee. I have heard that the harmonics can add additional current to the neutral and we would be required to pull a "super" neutral or a bigger conductor for the neutral than the hots.

Whith the 2008 Code starting to be used more, we are probabaly going to share neutrals less
210.4(B) Each multiwire branch circuit shall have a means to simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates
So if you do a multiwire circuit you will have to shut 2 or 3 circuits, thats alot of lights.

 

[infinity]

Whith the 2008 Code starting to be used more, we are probabaly going to share neutrals less
210.4(B) Each multiwire branch circuit shall have a means to simultaneously disconnect all ungrounded conductors at the point where the branch circuit originates
So if you do a multiwire circuit you will have to shut 2 or 3 circuits, thats alot of lights.

The requirment for simultaneuos disconnect first appeard in the 2005 NEC for MWBC's feeding furniture partitions. This requirement was deleted in the 2007 NYC electrical code. My guess is that the new requirment for simultaneous disconnect, that appears for all MWBC's in the 2008 NEC, will also be removed from the 2010 NYC electrical code.

 

[nyhockey]

The requirment for simultaneuos disconnect first appeard in the 2005 NEC for MWBC's feeding furniture partitions. This requirement was deleted in the 2007 NYC electrical code. My guess is that the new requirment for simultaneous disconnect, that appears for all MWBC's in the 2008 NEC, will also be removed from the 2010 NYC electrical code.

As of right now it seems the City is going with the new code on this one. Way to maney workers are getting hurt when opening a neutral.

 

[infinity]

As of right now it seems the City is going with the new code on this one. Way to maney workers are getting hurt when opening a neutral.

It will be interesting to see how this one plays out. Shutting off three circuits to work on one might create some problems out in the field especially during business hours in an occupied building. In that scenario the electrician will likely perform the work with the circuits energized.

 

[nyhockey]

It will be interesting to see how this one plays out. Shutting off three circuits to work on one might create some problems out in the field especially during business hours in an occupied building. In that scenario the electrician will likely perform the work with the circuits energized.

That is why we are pushing for 2 wire branch circuits, in both a conduit system and cable

 

[Ken In NJ]

That makes no sense electrically.

Every light you have, and will wire is supplied with a shared neutral.

Really ??

So running say a 12-3 to a switch location for two different lighting circuits, would be no different then running 2 - 12-2s to get the 2 circuits ?

I'm a bit confussed here ..

 

[nyhockey]

Really ??

So running say a 12-3 to a switch location for two different lighting circuits, would be no different then running 2 - 12-2s to get the 2 circuits ?

I'm a bit confussed here ..

If you run a 12-3 with 2 circuits you can share the neutral but they need to be shut off simultaneously