Upsizing Nuetral to feed LED lighting panel
- Thread starter Cableman
- Start date
- Status
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
If the major portion of the load is non-linear than it is often speced to have a larger neutral. I am not certain but I believe I have heard some people say the specs call for a #10 wire in the branch circuits to LED lighting. Of course, it all depends on the load for each circuits. For instance, if the load is 10 amps per circuit than there may not be a need to upsize the neutral. The same may be true for the feeder-- if you have a 100 amp feeder and the load is 60 amps or so then I don't believe you would need to upsize.
I am not sure what the actual calculation would be to determine this-- I am sure someone here knows
I am not sure what the actual calculation would be to determine this-- I am sure someone here knows
- Location
- Massachusetts
There is no NEC requirement to do so for either feeders or branch circuits.
As Dennis mentioned it may be specified by the designer but I have very strong doubts it is ever really needed.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
I am very very skeptical that oversize neutrals for MWBC's serving modern electronic ballasts are ever necessary.
Take an example.....
An LED grow light fixture is rated at 650 Watts @ 277 VAC.
650/277 = 2.34 Amps.
Now I have a 25 Amp breaker in a single position of a 480/277 3 phase MBP.
I am wanting to make a MWBC for as many fixtures as I can pack in to save copper and work.
Run #12 wires in a metal conduit.
How many fixtures and all on a single neutral are allowed????????
I say 25/2.34 = 10.68 so 10 fixtures.
That means I can run one #12 hot daisy chained to the 10 fixtures and a single #12 neutral daisy chain as a return.
Anybody see a problem with this??????? Is this what the code says?????
- Occupation
- Licensed Electrician
You are limited to 20A on 12AWG in this application.
- Occupation
- Licensed Electrician
I have never used an oversized neutral. The closest I have come is splicing my 12AWG onto the 10AWG neutrals that come in pre-wired office furniture partitions.
Is that because a MWBC is derated due to many fixtures????
In that case I can have 20/2.34 = 8.54 or 8 fixtures on a 20A breaker???? The hot and neutral are #12. Correct???
Only 1 neutral wire returning back to panel???
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Did similar recently. In your case, stick with 20Amp as that is what #12 gives you and likely you will have 15/20 amp plugs and receps. I assume these will be continuous so you cant exceed 16 amps. 16/2.34=6 fixtures per circuit. Use a MWBC (dont forget the three pole breaker), three hots and a neutral, all #12. That is 6 fixtures per circuit so a total of 18 lights per MWBC. With the same number of lights on each phase, you will have a neutral current of 0. Due to harmonics in the electronic ballasts, you will likely have a little neutral current. When I measured it, for 16 amps per phase all balanced, I had 3 amps on the neutral. YMMV based on the topology and quality of the ballast. The oversized neutral thing comes from the the theoretical max neutral current from the 3x harmonics which add up on the neutral which is 1.732 times the phase current (someone can correct me if I didnt get that part quite right). I think in practice it would have to be an atrociously horrible ballast to get anywhere near that.
MiElectrician
Member
- Location
- mi
310.15b5c says you have to count the neutral as a current carrying conductor, so only to boats in a pipe
EMAN3406
New member
- Location
- BELLEVILLE ILLINIOS
:happysad:
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Perhaps you could elaborate?
- Status