Sharing neutrals in lighting circuits

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wavector

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Do to harmonics in lighting circuits feeding flourescent lighting, the code requires dedicated neutrals for each lighting circuit. I spoke with a company owner yesterday, and he said that with the new electronic ballasts, that we can go back to sharing neutrals for flourescent lighting as long as the lights have electronic ballasts. I disagree with him. What do you think?
 
The code never required dedicated neutrals for each lighting circuit, that is a design choice.

You may end up counting the neutral as a current carrying conductor if the major portion of the load is non-linear.
 
Wavector, there are many rumors about harmonics, this is another one.

Read 310.15)(B)(4) for what the NEC actually says concerning the neutral.

Roger
 
I knew about the counting of the neutral as a current carrying conductor when connected to nonlinear loads.

I thought that was the point of have a dedicated neutral for flourescent lighting, the fact that the resulting overcurrent was nonlinear. The fluctuation of harmonics overloaded shared neutrals in circuits that feed flourescent lighting and caused problems (i.e. heat overloaded neutrals due to nonlinear shaped overcurrent). I also thought that is why electrical manufacturers derated the neutral in some of their MC cable assemblies.
 
I don't believe anyone is saying that a dedicated neutral on fluorescent lighting is a bad idea, just not a code requirement.

Mark
 
Still unsure of what the first poster means by a "dedicated" neutral. Does he want one per breaker or one per three breakers on all three phases? There's a difference.

I generally require one neutral per "three phase grouping."
 
Ragin Cajun said:
Still unsure of what the first poster means by a "dedicated" neutral. Does he want one per breaker or one per three breakers on all three phases? There's a difference.

I generally require one neutral per "three phase grouping."
Click to expand...

A dedicated neutral, in this instance, would be one neutral dedicated to each circuit.
 
Ragin Cajun said:
Still unsure of what the first poster means by a "dedicated" neutral. Does he want one per breaker or one per three breakers on all three phases? There's a difference.

I generally require one neutral per "three phase grouping."
Click to expand...

Ragin Cajun-

Be sure to check out 210.4 Multiwire Branch Circuits. Unless you generally specify 3-pole breakers, this wouldn't be a safe practice. When you break a neutral under load, part of it goes to line voltage. It's not fun working in a large industrial space where all the lights share one neutral circuit.

JMHO.
 
DGrant041 said:
Ragin Cajun said:
Still unsure of what the first poster means by a "dedicated" neutral. Does he want one per breaker or one per three breakers on all three phases? There's a difference.

I generally require one neutral per "three phase grouping."
Click to expand...

Ragin Cajun-

Be sure to check out 210.4 Multiwire Branch Circuits. Unless you generally specify 3-pole breakers, this wouldn't be a safe practice. When you break a neutral under load, part of it goes to line voltage. It's not fun working in a large industrial space where all the lights share one neutral circuit.

JMHO.
Click to expand...

How does opening the nuetral have anything to do with what Mr. Cajun was saying? And why would you have to specify three pole breakers? (not a code requirement). You don't even need a handle tie across the phases, much less a common trip breaker.
 
I would also ask what qualified individual would be opening any splice or lifting any wire from a terminal without knowing it was underload?


Roger
 
ryan_618 said:
How does opening the nuetral have anything to do with what Mr. Cajun was saying? And why would you have to specify three pole breakers? (not a code requirement). You don't even need a handle tie across the phases, much less a common trip breaker.
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210.4 Multiwire Branch Circuits
Code: 
(A) General Branch circuits recognized by this article shall be permitted as multiwire circuits. A multiwire circuit shall be permitted to be considered as multiple circuits. All conductors shall originate from the same panelboard or similar distribution equipment.
(B) Devices or Equipment Where a multiwire branch circuit supplies more than one device or equipment on the same yoke, [b]a means shall be provided to disconnect simultaneously all ungrounded conductors supplying those devices or equipment at the point where the branch circuit originates.[/b]
(C) Line-to-Neutral Loads Multiwire branch circuits shall supply only line-to-neutral loads.
Exception No. 1: A multiwire branch circuit that supplies only one utilization equipment.
Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.

And Roger, I don't appreciate the "Unqualified Person" comment. Anyone who's worked in a industrial/manufacturing environment knows the systems are complex and documentation is nil. If one of the moderators would like to see my qualifications in order to participate, I'd be glad to submit them.
 
DGrant041 said:
ryan_618 said:
How does opening the nuetral have anything to do with what Mr. Cajun was saying? And why would you have to specify three pole breakers? (not a code requirement). You don't even need a handle tie across the phases, much less a common trip breaker.
Click to expand...

210.4 Multiwire Branch Circuits
Code: 
(A) General Branch circuits recognized by this article shall be permitted as multiwire circuits. A multiwire circuit shall be permitted to be considered as multiple circuits. All conductors shall originate from the same panelboard or similar distribution equipment.
(B) Devices or Equipment Where a multiwire branch circuit supplies more than one device or equipment on the same yoke, [b]a means shall be provided to disconnect simultaneously all ungrounded conductors supplying those devices or equipment at the point where the branch circuit originates.[/b]
(C) Line-to-Neutral Loads Multiwire branch circuits shall supply only line-to-neutral loads.
Exception No. 1: A multiwire branch circuit that supplies only one utilization equipment.
Exception No. 2: Where all ungrounded conductors of the multiwire branch circuit are opened simultaneously by the branch-circuit overcurrent device.

And Roger, I don't appreciate the "Unqualified Person" comment. Anyone who's worked in a industrial/manufacturing environment knows the systems are complex and documentation is nil. If one of the moderators would like to see my qualifications in order to participate, I'd be glad to submit them.
Click to expand...

In Rogers defense, he wasn't speaking about your qualifications. You bring up a valid point about opening a neutral in a multiwire circuit and the safety factor of using a 3 pole CB. However, as Roger stated a qualified person or electrician shouldn't be opening splices if they're unaware of danger involved. As Ryan stated your idea is not required by the NEC but can add a certain amount of safety.
 
Dgrant, my post was not directed at you but, are you saying you would just randomly start opening connections with out knowing what they are doing?

I was pointing out that qualified individuals should be qualified, now if that doesn't sit well with you I'm sorry.

The majority of my career has been in industrial, healthcare, schools, institutional, manufacturing,... environments and that changes nothing as far as not reseaching a circuit before turning on, off, or tampering with it.

As far as 210.4, what is it you are saying it requires?

Roger
 
wavector-

I'm sorry for turning your thread into my soap box. That's not fair to you as people are responding to my topic and not to your original question. It's one of those topics that gets under my skin (literally). Everyone has their own personal favorite, for example dnem's is # of receptacles per circuit. :lol:

This will be my last post to this thread. Additional posts should be to wavector's topic or start a new thread (Go ahead and call me out--I'll bite!) :)

210.4 (B)
"Devices or Equipment. Where a multiwire branch circuit supplies more than one device or equipment on the same yoke, a means shall be provided to disconnect simultaneously all ungrounded conductors supplying those devices or equipment at the point where the branch circuit originates."

In this case I'll also add a portion of the commentary from the Handbook. It's not "Law" but relevant none-the-less.

?Multiwire branch circuits can be dangerous when not all the ungrounded circuit conductors are de-energized and equipment supplied from a multiwire circuit is being serviced. Equipment and devices on a common mounting yoke or strap pose a significant risk because of the close proximity of their wiring terminals or connections. For that reason, all ungrounded conductors supplying the devices or equipment on that strap must be simultaneously disconnected to reduce the risk of shock to personnel working on equipment supplied by the multiwire branch circuit. The simultaneous disconnecting means requirement takes the guesswork out of ensuring safe conditions for maintenance."

-Dale
 
Dale brings up a good point. We should be responding to the OP. The original question was regarding the requirement for dedicated neutrals for lighting circuits containing harmonic currents. As stated, dedicated neutrals are not required. If your circuits did contain harmonics it would be a design issue as to how to keep your shared neutrals from being overloaded. One solution would be to use a separate neutral for each circuit. Another would be to use an oversized neutral for shared circuits.

As Dale pointed out a shared neutral if opened can cause significant safety and other issues. To minimize this a mutlipole CB may be used to simultaneously disconnect all circuits sharing a neutral. This is not a requirement for the lighting circuits mentioned in the OP. It is a requirement for devices sharing the same yoke as specified in 210.4(B).
 
Ragin Cajun said:
Roger,

Like you avatar. Being originally from new Orleans, I am a huge fan of the hot stuff. Have to grow my own here in upstate S.C.
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Ragin Cajun, I know what you mean, I have to grow mine also. I do enjoy growing them though. :D

Dale, as far as the answer to the question, it was given in Iwires post.

BTW, it is not uncommon for a thread to not stay on topic :lol: :lol: :lol:

In addition to the other posts, when discussing a wye system, a dedicated neutral would be (1) grounded conductor common to (3) ungrounded conductors of the same circuit.

A two wire circuit would not have a neutral, so the term "dedicated neutral" would not be technically correct. :wink:

Infinity is correct that the handle tie or three pole breaker is only required for one yoke installations.

Roger
 
A two wire circuit would not have a neutral, so the term "dedicated neutral" would not be technically correct.
Click to expand...


Roger is technically correct. If I could throw away the IEEE definition I would. :wink: I should change the word neutral to grounded conductor. This is one of those times when the incorrect terminology is understood more than the correct terminology.
 
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