phase to neutral

[ajhill]

can someone help me with my memory. why is it that when using a neutral that it is nesesary to use it on for example A, B, and C phase and should not be used on two of like phases such as 2 A phases

 

[hurk27]

When a neutral is use for the same phase it will carry the sum of both circuits, which will exceed its capacity, when a neutral is on different phases, it Carry's the differential current, which it can only be loaded to the max of any one phase.

 

[hardworkingstiff]

You can use it for 2 circuits of the same phase, but it must be rated for the sum of those circuits.

 

[charlie b]

You can use it for 2 circuits of the same phase, but it must be rated for the sum of those circuits.

I heard a rumor to the effect that the next code edition is going to outlaw that practice. Here is the source of that rumor (look at post #1, right after "Chapter 2"):
http://forums.mikeholt.com/showthread.php?t=128423

 

[don_resqcapt19]

We can get a bit closer to the source

5-49 Log #3644 NEC-P05 Final Action: Accept in Principle
(200.8 (New) )
Submitter: Donald A. Ganiere, Ottawa, IL

Recommendation: Add new text to read as follows:
200.XX Common Neutral Conductors. Common neutral conductors shall not be used unless specifically permitted elsewhere in this code.

Substantiation: It appears that CMP 2 is attempting to prohibit the use of common neutral conductors by specifically permitting them in 215.4(A) and 225.7(B). There is no reasonable reading of the words ?shall be permitted? that can lead the code user to the conclusion that these words actually prohibit the use of common neutral conductors in other cases. The act of specifically permitting something in no way prohibits something else. Section 3.1.2 in the NEC Style Manual says that the words ?shall be permitted? are to be used to permit an alternate installation method. The words ?shall not? are required to be used to prohibit an installation method per 3.1.1 of the Style Manual. This change will make the wording in 215.4 and 225.7 comply with the style manual rules. Also the prohibition of the use of common neutrals should rest with CMP 5 as they have control of Article 200, Use and Identification of Grounded Conductors and not with CMPs 2 and 4.

Panel Meeting Action: Accept in Principle
Revise the recommendation to read:
200.4 Neutral Conductors. Neutral conductors shall not be permitted to be used for more than one multiwire branch circuit or for more than one set of ungrounded feeder conductors unless specifically permitted elsewhere in this Code.

Panel Statement: CMP-5 revised the proposal to more specifically apply to multiwire branch circuits and feeders.

Number Eligible to Vote: 16
Ballot Results: Affirmative: 16

Comment on Affirmative:
JOHNSTON, M.: Continue to accept this proposed revision as amended by the action of CMP-5. This additional section provides clarity to users about how neutral conductors should be used and coordinates with the newly defined terms neutral conductor and neutral point. Additional uses of the term common conductor are not necessary and the NEC should migrate to removal of the term as it is undefined and can cause inconsistency in enforcement.

_______________________________________________________________
5-33 Log #1987 NEC-P05 Final Action: Accept in Principle
(200.8 (New) )
Submitter: Donald A. Ganiere, Ottawa, IL

Comment on Proposal No: 5-49
Recommendation: The proposal should be accepted as submitted.

Substantiation: There are cases where multiple ungrounded conductors having no potential between them are being installed with a single oversized grounded conductor. (example: Two #12s on 20 amp breakers both installed on A phase with a #8 grounded conductor. There is no code rule that prohibits this practice in the 2008 code. The two specific provisions that use the currently undefined term of ?common neutral, only apply to multi-wire type circuits. If this proposal is accepted proposal 5-7 must also be accepted.

Panel Meeting Action: Accept in Principle
Revise the ROP draft text to read as follows:
200.4 Neutral Conductors. Neutral conductors shall not be used for more than one branch circuit, multiwire branch circuit, or for more than one set of ungrounded feeder conductors unless specifically permitted elsewhere in this Code.

Panel Statement: The revised text clarifies that the restriction on use of the neutral in more than one branch circuit is prescriptive and not permissive. The panel concludes these changes resolve the issues raised by the submitter.

Number Eligible to Vote: 16
Ballot Results: Affirmative: 16

 

[hardworkingstiff]

I heard a rumor to the effect that the next code edition is going to outlaw that practice. Here is the source of that rumor (look at post #1, right after "Chapter 2"):
http://forums.mikeholt.com/showthread.php?t=128423

Thank you.

We can get a bit closer to the source

And, thank you.

 

[brother]

hmmm, interesting change. Actually, I know im going to be singled out and probably picked on and bad mouthed.

But I think they should leave this alone. As someone said, as long as the neutral is sized properly, it can handle the same phase of the ungrounded conductors. Takes away the reason for 'training' to be an electrician. Just like the 'requirement' of having the multiwire branch circuits having to be a handle tie/multipole breaker. Proper training will prevent people from doing this stuff.

 

[kwired]

hmmm, interesting change. Actually, I know im going to be singled out and probably picked on and bad mouthed.

But I think they should leave this alone. As someone said, as long as the neutral is sized properly, it can handle the same phase of the ungrounded conductors. Takes away the reason for 'training' to be an electrician. Just like the 'requirement' of having the multiwire branch circuits having to be a handle tie/multipole breaker. Proper training will prevent people from doing this stuff.

Has to some degree always been my opinion. Let the people that don't know what they are doing open a neutral and destroy some equipment. You can explain to them what happened and they still won't get it many times. More reason for them to realize that they are not electricians. I love it when someone tries to utilize a wild leg for 120 volts also. You would think there may be a reason why almost every third space has no breaker on it - ah they saved spaces for me to use:grin:

 

[jumper]

I love it when someone tries to utilize a wild leg for 120 volts also. You would think there may be a reason why almost every third space has no breaker on it - ah they saved spaces for me to use:grin:

Aw man, I only did that once and it was 8 years ago.:grin:
My first encounter with a high leg delta. Smoked a copier.

 

[hurk27]

Aw man, I only did that once and it was 8 years ago.:grin:
My first encounter with a high leg delta. Smoked a copier.

yea mine was a 120v diesel fuel pump, for a truck garage, in 1978, never forgot it, probably never will.:grin:

Just part of learning I guess

 

[technoid52]

yea mine was a 120v diesel fuel pump, for a truck garage, in 1978, never forgot it, probably never will.:grin:

Just part of learning I guess

You guys brought back a bad memory to me also. I was wiring in circuits for very expensive telemetering equip. Someone befor me had placed breakers in all the high leg spots to fill in the knock-out slots. I thought they were future spares for the job. So me being young and mindless at that time, hooked them all in. Turned on the juice and walked away. I Burned out all of it. Got Hell for it, almost suspended from work, and never forgot the lesson.

 

[dbuckley]

hmmm, interesting change. Actually, I know im going to be singled out and probably picked on and bad mouthed.

But I think they should leave this alone. As someone said, as long as the neutral is sized properly, it can handle the same phase of the ungrounded conductors.

In that case they can badmouth me too.

This is lunacy.

If you cant determine a minimum size for a neutral for the circuits using it (irrespective of if the phases are 180 or 120 apart) then you shouldn't be doing the job, or you should select another circuit configuration.

Note that "determine a minimum size" does not require heavy maths for three phase neutral currents; you just need a big enough neutral that it in practice cant be overloaded, which is addition and ampacity table lookup.

 

[hurk27]

In that case they can badmouth me too.

This is lunacy.

If you cant determine a minimum size for a neutral for the circuits using it (irrespective of if the phases are 180 or 120 apart) then you shouldn't be doing the job, or you should select another circuit configuration.

Note that "determine a minimum size" does not require heavy maths for three phase neutral currents; you just need a big enough neutral that it in practice cant be overloaded, which is addition and ampacity table lookup.

the OP was asking about using a neutral on the same phase, which is even easier, just add the breaker handles and size the neutral from that.:roll: