Receptacles sharing a neutral

Joethemechanic · Apr 6, 2023

ptonsparky said:
You have two GFCI breakers feeding each split duplex receptacle?

Guessing installed before the common tie requirement.

I would imagine so. I bought the building in 2015 and it was like that when I bought it

Jpflex · Apr 6, 2023

roger said:
As ptonsparky said, it only lowers the current on the neutral, it does not change the circuit capacity.

View attachment 2564759

This is obvious in a 4 wire multi-wire conductor cable 2 hots, 1 neutral (shared) 1 ground. Unbalance current travels on neutral but

What about two separate branch circuits with 2 sets of non metallic cable 3 wire each, supplying line to neutral loads with each leg on a different phase. Doesn’t the neutral carry all load current in this case?

Also can you run just one equipment ground conductor in a raceway for all circuits? Or does code favor each separate branch circuit to have its own separate equipment ground conductor ran inside EMT conduit? (Excluding using EMT as an option for EGC - boss doesn’t want this option). ?

Jpflex · Apr 6, 2023

LarryFine said:
This will actually reduce total load on the shared neutral, as well as total losses and voltage drop.

The load-side of the GFCIs must be separate and unshared. One EGC for everything is Kosher, too.

Ok one EGC for all

ptonsparky · Apr 6, 2023

Single phase MWBC, no matter cable or conduit, the neutral caries the unbalance current. One EG is all that is required.

Jpflex · Apr 6, 2023

roger said:
How old is that wire? AFAIK all THHN has been dual rated THHN/THWN for more than thirty years I think

It must be that old lol. This is an old mine.

Jpflex · Apr 6, 2023

ptonsparky said:
Curious. How many block heaters?

At least one for each receptacle and probably close to double when using dual yokes or receptacles for more. Company just said install receptacles outside but did not specify heaters would be used, how many or the way rating of each. They typically do this by adding loads after the installation

Jpflex · Apr 6, 2023

ptonsparky said:
Single phase MWBC, no matter cable or conduit, the neutral caries the unbalance current. One EG is all that is required.

I’m not familiar with MWBC conductor but I thought all current returned on a neutral for line to neutral loads and only unbalanced car was for line to line loads.

If the former is the case then current has to travel to junction of neutral and pass through another load to get to other phase to source return?

Jpflex · Apr 6, 2023

Car = current . Phone has to stop changing words

Jpflex · Apr 6, 2023

Was I right on adding a neutral? There was no double gang breaker with tie handle for multi wire branch circuit setup with one neutral?

ptonsparky · Apr 6, 2023

Adding a neutral was not right or wrong. Better for you because of no handle ties and you don't understand MWBCs yet.
There is no neutral when you have line to line loads. 230 volt.

Look closely at Rogers post #17.

Jpflex · Apr 6, 2023

ptonsparky said:
Adding a neutral was not right or wrong.
There is no neutral when you have line to line loads. 230 volt.

Just 120 volt line to neutral loads here but whether current travels entirely from line to neutral or part neutral and part other phase is not clear to me for line to neutral loads

ptonsparky · Apr 6, 2023

Jpflex said:
Just 120 volt line to neutral loads here but whether current travels entirely from line to neutral or part neutral and part other phase is not clear to me for line to neutral loads

Do you have two neutrals serving your house?
The SE is a multi wire circuit.
Get your amp clamps out. Borrow a couple if you need to. Clamp each hot and the neutral. Record the readings as you add and remove loads. The difference of the L loads should equal your neutral. It may not be exact because some may flow on the GEC.

Jpflex · Apr 6, 2023

ptonsparky said:
Do you have two neutrals serving your house?
The SE is a multi wire circuit.
Get your amp clamps out. Borrow a couple if you need to. Clamp each hot and the neutral. Record the readings as you add and remove loads. The difference of the L loads should equal your neutral. It may not be exact because some may flow on the GEC.

Yes I was planning on doing this as soon as I get free time. But why does NEC code 200.4 disallow sharing a neutral although service has one LARGER neutral?

Joethemechanic · Apr 6, 2023

Forgive me if I am thinking wrong, it's been a long day, but adding a neutral lengthens the circuit and as a result adds more I2R heating to the conduit/raceway or whatever

ptonsparky · Apr 6, 2023

Joethemechanic said:
Forgive me if I am thinking wrong, it's been a long day, but adding a neutral lengthens the circuit and as a result adds more I2R heating to the conduit/raceway or whatever

It does, but typically not an issue for reasonably length of circuits.

synchro · Apr 6, 2023

The OP

Jpflex said:
If the former is the case then current has to travel to junction of neutral and pass through another load to get to other phase to source return?

Jpflex said:
It must be that old lol. This is an old mine.

We've been assuming that this is a 120/240V single phase system, instead of a 120/208V system. Is this correct?

In a 120/208V system, the line currents would only partially cancel in the neutral even when there are equal loads on the two phases (because they are 120° apart instead of 180°). But it would still be OK to have a MWBC with the common neutral having the same ampacity as the two line conductors. The neutral would count as a current carrying conductor. however.
A few examples:
16A on L1 and 16A on L2 would have 16A in the neutral conductor.
16A on L1 and 8A on L2 would have 0.866 x 16A = 13.85 in the neutral.
16A on L1 and 0A on L2 would, of course, have 16A in the neutral.

Joethemechanic · Apr 7, 2023

ptonsparky said:
It does, but typically not an issue for reasonably length of circuits.

I agree, I just like MWBCs and will use any argument for them

Jpflex · Apr 7, 2023

synchro said:
The OP

We've been assuming that this is a 120/240V single phase system, instead of a 120/208V system. Is this correct?

In a 120/208V system, the line currents would only partially cancel in the neutral even when there are equal loads on the two phases (because they are 120° apart instead of 180°). But it would still be OK to have a MWBC with the common neutral having the same ampacity as the two line conductors. The neutral would count as a current carrying conductor. however.
A few examples:
16A on L1 and 16A on L2 would have 16A in the neutral conductor.
16A on L1 and 8A on L2 would have 0.866 x 16A = 13.85 in the neutral.
16A on L1 and 0A on L2 would, of course, have 16A in the neutral.

I’m thinking this is a standard split phase 120/240 single phase transformer source which also common to feeding the premises house wiring on site.

ptonsparky · Apr 7, 2023

Your Data
NEUTRAL LOAD	1PH	3PH WYE
	=ABS(B4-B5)	=SQRT(D7-E7)
L1 AMP (1PH)	5		=(B4)^2	=B4*B5
L2 AMP (1PH)	10		=(B5)^2	=B5*B6
L3 AMP	20		=(B6)^2	=B6*B4
			=SUM(D46)	=SUM(E4:E6)

Simple spread sheet for neutral calculations. Enter your data in the non formula area (5,10,20)
That smiley face is supposed to be '

'
Good Lord!! Colon D

wwhitney · Apr 7, 2023

ptonsparky said:
Good Lord!! Colon D

Adding an unnecessary space will defeat the emoticon conversion, so : D. Not sure if there's another way to do it.

Cheers, Wayne

Receptacles sharing a neutral

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