One or three neutrals?
- Thread starter Highlow
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winnie
Senior Member
- Location
- Springfield, MA, USA
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- Electric motor research
The NEC permits 'multi wire branch circuits', where the neutral is shared between several 'hot' conductors.
If you have a balanced three phase supply, then you can run three hot conductors with your standard size neutral.
Note however that the shared neutral must be in the same cable assembly as the hot conductors; you couldn't have the shared neutral in one MC cable, and the hots in another; you would need a single MC cable with one neutral and the three hots. You could have 3 hots and 1 neutral in conduit to a junction box, and then split out the neutrals to separate MC cables.
Your device boxes would need to be sized for all of the spliced conductors, and the breakers would need handle ties (under 2008 code). There are other rules about multi-wire branch circuits as well.
-Jon
If you have a balanced three phase supply, then you can run three hot conductors with your standard size neutral.
Note however that the shared neutral must be in the same cable assembly as the hot conductors; you couldn't have the shared neutral in one MC cable, and the hots in another; you would need a single MC cable with one neutral and the three hots. You could have 3 hots and 1 neutral in conduit to a junction box, and then split out the neutrals to separate MC cables.
Your device boxes would need to be sized for all of the spliced conductors, and the breakers would need handle ties (under 2008 code). There are other rules about multi-wire branch circuits as well.
-Jon
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
To Jon's answer I will add emphasis to the statement that you do not need to oversize the one neutral that is shared with the three hot conductors. Indeed the neutral will most often be carrying less current than the hot conductors. In fact, unless there is a significant harmonic load present, the highest current that the neutral could be carrying is the same as the highest current on one of the hots, and that only happens when another of the hots has no current whatsoever.Highlow said:
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
The three-hot-wires statements presume a 3-phase power source, and assuring no two hots are on the same phase.
If the source is 1-phase, you can use two hots w/ one neutral in a 3-wire circuit, and a separate 2-wire circuit.
Often, in either case, we might run two separate 3-wire circuits and have a spare home-run for a future addition.
If the source is 1-phase, you can use two hots w/ one neutral in a 3-wire circuit, and a separate 2-wire circuit.
Often, in either case, we might run two separate 3-wire circuits and have a spare home-run for a future addition.
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