common neutral

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quiluis

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I like to know if there is a note in the Nec that said:
"A common neutral is a single neutral conductor used as neutral for more than set of feeder conductors. It must have current-carrying capacity equal in the sum of hte neutral of the neutral conductor capacities if an individual neutral conductor were used with each feeder set. A common Neutral may be used only with feeders. It may never be used with branch circuits. A single neutral of a multiwire branch circuit is not a common neutral, it is a neutral of only a single circuit even though the circuit may consist of 3 or 4 wires. A feeder common neutral is used with more than one feeder circuit"
My question is if this is true, that means that in a 3 phase system where you have a 42 circuit panel with 42 single breaker for various branch circuits than you need 42 neutral conductor as well??
I usually use a common neutral for the 3 circuit making sure that they are in different phase meaning one of each A, B, C phase an never have 2 in a common neutral from the same phase.
I will appreciated your comments and help thanks
 
roger

roger

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Location
Fl
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Retired Electrician
Re: common neutral

Read the following articles to put the myths and or beliefs you have stated to rest.

Start with the definition Branch Circuit, Multiwire in article 100 then proceed to 210.4, 225.7, and 310.15(B)(4), take special notice of the explanation of Neutral Conductor in 310.15(B)(4)

Roger
 
infinity

infinity

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Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Re: common neutral

My question is if this is true, that means that in a 3 phase system where you have a 42 circuit panel with 42 single breaker for various branch circuits than you need 42 neutral conductor as well??
Click to expand...
What would branch circuit conductors have to do with the feeders mentioned in your question?
 
davedottcom

davedottcom

Senior Member
Re: common neutral

Hello quiluis. I see you are a new member (# 24016). Hmmm, do you know another new member... paulkner member #23976? He had a very similar situation just yesterday. He used 2 different threads to try to get someone to say that sharing neutrals between 2 circuits on the same phase is ok.
Both threads were closed by the moderator!

paulkner's thread (1 of 2)

:p

Dave
 
growler

growler

Senior Member
Location
Atlanta,GA
Re: common neutral

I have a funny story along these lines. Several years ago I went to correct some problems at a restaurant. The contractors were still there and I thought this unusual. It seems that had a system for correcting problems if a phase was crossed or shorted in a three phase, four wire circuit. It was called " Bucking out the panel".They would turn the breakers on and if any of the phases were crossed they would move both to the same phase. Not a lot of black, red, blue in their panels. What bothered me is the fact that they thought it strange that I had never herd of this. I tried explaining that they were going to over-load the neutrals. Could have been talking to a rock. Now every time I go to a restaurant to work I wonder if these guys had anything to do with it. That was 15 years ago and one of them is still in business. He is also one of the world's biggest Butt-heads.
 
H

hardworkingstiff

Senior Member
Location
Wilmington, NC
Re: common neutral

growler,

You're not in Norfolk VA. going behind a guy named Mal are you?

I had the same issue there. The guy just couldn't understand why you couldn't put the two hots sharing one neutral on the same phase. I finally just gave up trying to explain it.
 
T

tx2step

Senior Member
Location
North Texas, DFW area
Re: common neutral

Originally posted by georgestolz:
Mr. Practice? I've heard of him somewhere.... :p
Click to expand...
George -- as usual, you are a hoot! That was too funny!
roflolk.gif
 
iwire

iwire

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Staff member
Location
Massachusetts
Re: common neutral

I had the same issue there. The guy just couldn't understand why you couldn't put the two hots sharing one neutral on the same phase.
Click to expand...
Actually you are allowed (or not prohibited :D
 
roger

roger

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Staff member
Location
Fl
Occupation
Retired Electrician
Re: common neutral

Hardworker, read article 225.7

Roger
 
T

tx2step

Senior Member
Location
North Texas, DFW area
Re: common neutral

Bob & Roger -- Well... I learn a lot of new stuff on this site every day -- this being a good example.

How do you guys remember all of this stuff? What's your secret?

I didn't know that you could do this with outdoor lighting. I don't remember noticing that in 225.7 before.

Now... Would one of you explain why I would want to do it that way? What's a real-world example of when it would be a good idea to do this?
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
Re: common neutral

Originally posted by tx2step:
I didn't know that you could do this with outdoor lighting. I don't remember noticing that in 225.7 before.

Now... Would one of you explain why I would want to do it that way? What's a real-world example of when it would be a good idea to do this?
Click to expand...
First a question for you.

Who says it is prohibited indoors? :D

As for your question I have tried to figure a way that using one neutral would be a benefit but I have not found one. :p

Box sizes and wire terminations seem to kill any upside.
 
H

hardworkingstiff

Senior Member
Location
Wilmington, NC
Re: common neutral

Originally posted by hardworkingstiff:
growler,

You're not in Norfolk VA. going behind a guy named Mal are you?

I had the same issue there. The guy just couldn't understand why you couldn't put the two hots sharing one neutral on the same phase. I finally just gave up trying to explain it.
Click to expand...
For you Roger,

"The guy just couldn't understand why you couldn't put the two hots sharing one (same AWG sized) neutral on the same phase. "

Thanks for the correction Roger.
 
T

tx2step

Senior Member
Location
North Texas, DFW area
Re: common neutral

Originally posted by iwire:
Who says it is prohibited indoors? :(

Oh wait... "I" say it's prohibited, cause I never thought of doing it that way before, which must mean it's a bad idea? Right? Plus I can't think of any reason I'd want to do it that way? And I'm the King, right? So there! ;) I wonder where I can get that done?

My RAM tends to reset to zero every night (not to mention that it also seems to become more "random" as time goes along). :eek: And, I think I have a 256K limit, when I really need at least 2 gig!
Click to expand...
 
roger

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
Re: common neutral

Tx, I think Bob's just plain smart. Myself on the otherhand, I've just got you buffaloed. :D :D :D

Roger
 
T

tx2step

Senior Member
Location
North Texas, DFW area
Re: common neutral

Roger -- you and Bob, along with a number of other guys on this site, are just too doggone smart. It's not natural. I think you must have some kind of enhancement thing going on -- I just want to find out where I can get it done, too. Come on, you can tell me. I'll stay quiet about it.

Sometimes you guys make me feel like a 25W bulb during a California brown-out. :D I've got to start washing my feet more often, though.
 
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