office space was moved to a new building. 120/208 3ph. The area used to be a smoking room and non smoking rm, vending and locker room. It will be turned into office space with computers and fax,copiers etc. I traced all the circuits -120v-and #12 thhn was ran in 1/2 emt to these areas from the panel. one black,one red, one blue and one white and green. Three circuits sharing that one neutral. I want to run more neutrals. I'm unable to pull any #12 in the 1/2 EMT. Can I run a dozen neutrals alone in a 3/4 pipe down to the area and branch of with MC as neutral only to these shared neutral boxes. I've heard of grouped parallel conducters creating inductance and poles catching fire. Should I pull a #8 down and share of that. There will not be any load more than a few amps unless a space heater or so is plugged in. Please help. Thanx
Sharing neutrals
- Thread starter zaptd
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No. 300.3(B).
Buck Parrish
Senior Member
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- NC & IN
That wouldn't be prudent. Just wouldn't do it.
What is your great concern, if it's harmonics?
Perhaps you could pull the #12 neutral out and replace it with a #10 .
What is your great concern, if it's harmonics?
Perhaps you could pull the #12 neutral out and replace it with a #10 .
Buck Parrish
Senior Member
- Location
- NC & IN
Some office's have started designing the neutrals bigger then the line.
Increase it to a #10 and you will be fine.
Or don't allow space heaters.
Or since you we're thinking of running all those neutrals in one pipe. Pull some circuit pairs instead . Neutrals and hots. Add some dedicated circuits for heaters, copiers , etc.
You must identify which neutral goes with which circuit.
Increase it to a #10 and you will be fine.
Or don't allow space heaters.
Or since you we're thinking of running all those neutrals in one pipe. Pull some circuit pairs instead . Neutrals and hots. Add some dedicated circuits for heaters, copiers , etc.
You must identify which neutral goes with which circuit.
- Location
- Massachusetts
If each of the three hots is on a different phase there is no reason at all to add neutrals, the single neutral will never be overloaded.
- Location
- Massachusetts
The jury is still out on if that is really needed.
Space heaters are linear loads, they will not cause any overload on the neural.
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- Massachusetts
What you have there is a multiwire branch circuit, the neutral only carries the imbalanced current from the other three. It is a very effcent way to design circuits. less voltage drop and fewer current carrying conductors.
There is a draw back to multiwire branch circuit and that is if the shared neutral opens with the circuits running some equipment may receive over or under voltage this part is harder to explain, someone may post a diagram about it.
Consider this, if you looked at the service supplying this building how many hots would be sharing the neutral?
That's the definition of the neutral.... it only carries the difference between the loads when they are on seperate phases.
3-phase wye formula is
Buck Parrish
Senior Member
- Location
- NC & IN
That's the definition of the neutral.... it only carries the difference between the loads when they are on seperate phases.
3-phase wye formula is
I was going to say that, you beat me to it...
Jim W in Tampa
Senior Member
- Location
- Tampa Florida
Just run some more circuits if the problem is heaters. The number 12 neutral should be fine. If after doing pipe fill calcs there is room to replace the 12 with 10 then fine but your not likely to need it.
- Location
- Massachusetts
Why would it need to be 10?
- Location
- Massachusetts
My avatar pic actually shows it pretty well, the really squiggly lines are current and you can see how little current there is on the neutral compared to the hots.
(The neutral is "D")
(The neutral is "D")
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Jim W in Tampa
Senior Member
- Location
- Tampa Florida
Bob ,i said it not likely to help.
As i am sure you have noticed many power poles now have upsized neutrals. Harmonics is the only reason and probably never be needed but can't hurt to up size.
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