Shared Neutrals

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qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
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Engineering
Repeate question I'm sure.
I'm installing 2 30a 120v circuits for a small Network closet in our office. It will be used for our 2 UPS's in the data rack.
My question is:
Can I run 1 #10 neutral along with my 2 #10 hots to feed the circuits or do I need 2 neutrals?
If I read it correctly I only need 1 neutral.

http://www.ecmweb.com/sites/ecmweb.com/files/uploads/2012/06/205ecmCQfig2.gif

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Yes, as long as you put it on a 2 pole breaker or use a tie bar on 2 single pole breakers. and they are on opposite phases.
But, You need to read installation manual first. MFGR. may require a private neutral for each UPS.
 
Repeate question I'm sure.
I'm installing 2 30a 120v circuits for a small Network closet in our office. It will be used for our 2 UPS's in the data rack.
My question is:
Can I run 1 #10 neutral along with my 2 #10 hots to feed the circuits or do I need 2 neutrals?
If I read it correctly I only need 1 neutral.

http://www.ecmweb.com/sites/ecmweb.com/files/uploads/2012/06/205ecmCQfig2.gif

Thanks
By NEC you can share neutrals as long as you use handle ties to "interlock" the two breakers. So the circuits need to be next to each other in the panel. If this is not possible, then you need separate neutrals.
The reason for this "as I see it, as a former service technician", If you are working on a circuit, you should have it turned off (in general for safety), If you have that circuit off, and the circuit that shares it's neutral is NOT turned off (hence the handle tie) then you can get zapped on the neutral when you take it apart, because it is still serving the other circuit.
As an estimator let me request that you ALWAYS ADD DEDICATED NEUTRALS, fatten up those estimates boys!
 

MAC702

Senior Member
Location
Clark County, NV
Can you account for the possibility of triplen harmonics with a larger, but still shared, neutral? I know I've seen it, but don't know if that was work done to Code at the time.
 

Unbridled

Senior Member
Location
Tampa, Fl
Repeate question I'm sure.
I'm installing 2 30a 120v circuits for a small Network closet in our office. It will be used for our 2 UPS's in the data rack.
My question is:
Can I run 1 #10 neutral along with my 2 #10 hots to feed the circuits or do I need 2 neutrals?
If I read it correctly I only need 1 neutral.

http://www.ecmweb.com/sites/ecmweb.com/files/uploads/2012/06/205ecmCQfig2.gif

Thanks
I concur with Ron, electronic equipment can generate harmonics on a shared neutral. Consider upsizing your neutral. NEC permits multi-wire Br. Circuits, however a designer needs to be aware of when and when not to utilize a MWBC.
 

mstrlucky74

Senior Member
Location
NJ
Repeate question I'm sure.
I'm installing 2 30a 120v circuits for a small Network closet in our office. It will be used for our 2 UPS's in the data rack.
My question is:
Can I run 1 #10 neutral along with my 2 #10 hots to feed the circuits or do I need 2 neutrals?
If I read it correctly I only need 1 neutral.

http://www.ecmweb.com/sites/ecmweb.com/files/uploads/2012/06/205ecmCQfig2.gif

Thanks
A branch circuit is a portion of a wiring system that extends beyond the final, automatic overcurrent protective device (i.e., fuse or breaker) which qualifies for use as branch-circuit protection, and terminates at the utilization device or outlet (such as a lighting fixture, motor, or heater).
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Electrician
A branch circuit is a portion of a wiring system that extends beyond the final, automatic overcurrent protective device (i.e., fuse or breaker) which qualifies for use as branch-circuit protection, and terminates at the utilization device or outlet (such as a lighting fixture, motor, or heater).
What does this have to do with the OP's question?
 

just the cowboy

Inactive, Email Never Verified
Location
newburgh,ny
Split voltage

Split voltage

One thing to remember, if you share your neutral and it opens then your voltage will divide the 240 Volts between the loads depending on their resistance. In other words magic smoke time, something you don't want.
 

Unbridled

Senior Member
Location
Tampa, Fl
Repeate question I'm sure.
I'm installing 2 30a 120v circuits for a small Network closet in our office. It will be used for our 2 UPS's in the data rack.
My question is:
Can I run 1 #10 neutral along with my 2 #10 hots to feed the circuits or do I need 2 neutrals?
If I read it correctly I only need 1 neutral.

http://www.ecmweb.com/sites/ecmweb.com/files/uploads/2012/06/205ecmCQfig2.gif

Thanks
Don't forget the current on the shared neutral of 2 phases of a 3 phase 208/120V Y system does not cancel each other. In fact the current is the sum of the current draw on each of the two phases.:thumbsup:
 
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GoldDigger

Moderator
Staff member
Don't forget the current on the shared neutral of 2 phases of a 3 phase 208/120V Y system does not cancel each other. In fact the current is the sum of the current draw on each of the two phases.:thumbsup:
Not really.
It is still the phasor (~vector) sum of the two currents. If current of magnitude I flows in both hots with identical power factor, the magnitude of the neutral current is also I, not 2I
 

Miguel Bas

New User
Location
Florida
Occupation
Project Manager
The IEEE std 80 talks about the standard for the ground system. In the integrity tests it turns out that about 20% of the Isc current returns through the branches and the rest goes to the conductor with the largest gauge (main ground), that is, the best ground (most conductive). Therefore, it will be necessary to unite the breakers with a tie bar to eliminate any possibility of return in cases of neutrals shared by 2-3 circuits. These cases are common in remodeling.
 
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