mstrlucky74
Senior Member
- Location
- NJ
I know I asked this a while ago but I can't find it. Even though there are 2 phase conductors this is technically considered one circuit, correct? If so why again? Thanks.
208v circuit count
- Thread starter mstrlucky74
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- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
If it is wired so that there is only one way to connect a load or loads ir is one circuit.
If all three phase wires and the neutral were present it would either still be one circuit or one MWBC, depending on whether there was a provision for single phase line-line or line-neutral loads as well as three phase loads to be connected.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
If there is a neutral involved it would be a multiwire branch circuit-- one reference you may think about is 225.30 last sentence. Also under definitions for branch circuit, multiwire
mstrlucky74
Senior Member
- Location
- NJ
Uf ah... Complicated. Spec says no more than three circuits in a raceway.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
I would say that if there is one (possibly multipole) OCPD it is one circuit.
But for the purpose of that spec, they might want to consider three switch legs off one branch to be three circuits. Needs clarification.
mstrlucky74
Senior Member
- Location
- NJ
Thanks Gold.Technically a 208 v circuit would be one circuit though, right? Clarification as to why is what I am trying to understand.
More likely, the designer (who probably just copies & pastes the same spec from job to job) needs an education.
- Location
- Massachusetts
Yes.
jeremysterling
Senior Member
- Location
- Austin, TX
Or, as Dennis brought up, in 225.30 you could have nine OCPD's and three handle-ties and that is three circuits. I would pull three boats per on mstrlucky's job.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
I can only guess why the specs contain that particular restriction, but it is clearly not an issue of conduit fill, or conductor ampacity. My SWAG is that they just either wanted to keep the wiring from being too hard to trace or they did not want to see too many eggs in one basket in case of damage.
Do the specs also require dedicated neutrals or are shared neutrals allowed?
mstrlucky74
Senior Member
- Location
- NJ
decicated.
my question is why exactly would a 208v circuit with 2 ungrounded conductors, a neutral and a ground be considered one circuit? I want to be able to explain? Sorry guys for dragging this out:dunce:
Read pages 28 and 29 of this document for some basic information on a single phase wye circuit.
Roger
kwired
Electron manager
- Location
- NE Nebraska
It is one circuit with two current carrying conductors. If is supplies 120 and 208 volt loads then it is one circuit with three current carrying conductors.
If all three phases are involved - it is still one circuit and it is either a three or four wire circuit depending if the neutral is used.
If designer intends it to mean anything different then they really need to specify what they mean.
If all three phases are involved - it is still one circuit and it is either a three or four wire circuit depending if the neutral is used.
If designer intends it to mean anything different then they really need to specify what they mean.
JDBrown
Senior Member
- Location
- California
- Occupation
- Electrical Engineer
If dedicated neutrals are required, wouldn't you need 2 ungrounded conductors, 2 neutrals and a ground? In that case, I think we would have to call it 2 circuits, not 1 MWBC.
My understanding is that it's only a MWBC if the neutral is shared, because separating the neutrals prevents the neutral currents from the 2 (or 3) phases from cancelling each other. Separate neutrals = separate circuits.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The argument gets somewhat circular, but I would say that if you have only line to line loads and no neutral required, except fir controls, you have one circuit.
If you have two independent line to neutral loads then you must have two neutrals and you have two circuits. But if I were installing that I would also use independent Cbs.
It would be the same as a dryer or range circuit and is a single circuit. The physics of how current is flowing into and out of the load(s) then back to the source through all of the circuits associated conductors is what makes it a single circuit.
Roger
mstrlucky74
Senior Member
- Location
- NJ
kwired
Electron manager
- Location
- NE Nebraska
If the load is strictly 208, you do not need any neutral.
If you are feeding 2-120 volt loads, nothing prohibits using two neutrals, but it isn't required by code either. You will have 4 current carrying conductors instead of 3 in the raceway though when it comes to ampacity adjustments, on a 208/120 system. For a 120/240 system you only have 2 current carrying conductors for the purpose of ampacity adjustment if you use one common neutral in this install.
- Location
- Massachusetts
Mrlucky, a circuit has nothing to do with the number of poles the breaker has.
Here is one definition of an electrical circuit.
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