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Joined: Mar 2002
Posts: 86
S
Member
I was working at a Best Buy here in Chandler, AZ, and was told to pull in the homerun wire to feed a Water Heater and an outlet only.

The building has 3-phase power. Circuit 24 is for the outlet and Circuit 25 is for the 120V Water Heater.

How many neutrals would you pull for circuit 24 & 25?

They are both 20-amp circuits and the water heater is rated at 1.7 KW.

The homerun wire is approximatly 150' away and I pulled #10 stranded copper thhn copper wire.

I pulled one neutral because circuit 24 is C-phase and Circuit 25 is A-phase.

I was told that I did it wrong. I should have pulled in two neutrals. Only consecutive groups can share neutrals. For Example: 2,4,6 ; 8,10,12 ; 1,3,5 ; 5,7,9

I stood up for my work and refused to aknowlege that I did something wrong.

Tev

Joined: Aug 2001
Posts: 545
A
Member
One neutral should be fine.
I live in Chandler :-)
Al D


The Golden Rule - "The man with the gold makes the rule"
Joined: Mar 2002
Posts: 86
S
Member
Thanks Aldav,

I just wanted to confirm that I was not missing something in the code book.

Joined: Dec 2003
Posts: 886
H
Member
...Only consecutive groups can share neutrals. For Example: 2,4,6 ; 8,10,12 ; 1,3,5 ; 5,7,9

Remind him that this is 3 phase NOT single phase.

Joined: Jan 2003
Posts: 4,391
I
Moderator
No requirement to use consecutive breakers.

Just keep it on separate phases.

You are only using two hots of the 3 phase, this neutral will be a current carrying conductor when figuring for derating.


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Oct 2000
Posts: 5,392
S
Member
straightedge...
the only possible reason i can conjure would be if the 'outlet' were required to be afci protected.

other than that, people who tell you that something is 'wrong' are obligated to substaintiate thier claims

~S~

Joined: Mar 2002
Posts: 86
S
Member
Thanks guys

Joined: Apr 2002
Posts: 2,527
B
Moderator
It's OK to do—just realize a couple of things.

For the neutral serving two phases derived from a wye system, for 20-amp 120-volt loads on different phases, there will be a full 20 amps in the neutral—making it a current-carrying conductor...one of three.

Regardless of phase selection, if for whatever reason two grounded-circuit conductors are used in the same cable or raceway with two ungrounded conductors, you now have four current-carrying conductors.

Joined: Sep 2003
Posts: 650
W
Member
I concur that running two _different phase_ hots and 1 neutral is to code. However IMHO it is slightly less safe, and it is possible that the _customer_ has requirements that exceed code and prohibit this particular installation.

If this documentation were provided ahead of time, and you missed it, then your installation was not correct, not because it didn't meet code, but because it didn't meet the customer's requirements. If they tell you this after the fact, then their specification was not correct; you put something in that meets code, and the customer wants something that exceeds code, but expected you to be a mind reader.

How is this installation slightly less safe? If the neutral opens then you will see a full 208V on the 120V receptacle. Is this a bad installation? IMHO it is fine. Multiwire branch circuits are a well accepted practise, are good enough for the NEC and are good enough for me [Linked Image]

-Jon


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