Wire count

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mstrlucky74

Senior Member
Location
NJ
3phase 4w 277/480v panel. 3pole 30a breaker feeding a motor(connected load is 23.88 amps). How mn ay conductors? Obviously 3 hots...but not sure of the ground and neutral if they are both needed. Thanks.
 

Ponchik

Senior Member
Location
CA
Occupation
Electronologist
You don't need the neutral (grounded). However, there must be a effective path for the ground fault. If the wiring method is metallic then you can use that as your EGC, if not then you need to install an EGC. (equipment grounding conductor)
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I think I have it figured out :D
You are celebrating your 1 yr. anniversary of posting under this name by posting "teaser" questions today. In your 6 years of posting here, hopefully you don't have to ask if a 3 phase motor needs a neutral.:)
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Code requires neutral or handle ties, right?
Code requires handle ties if this is an MWBC with line to neutral loads, and you should use a single common trip breaker if it is only a single three phase load, in particular a motor load.

If you are driving a motor, a set of single phase breakers without common trip (or a set of fuses) would not give you single-phase protection of the motor, so that would have to be supplied elsewhere (possibly by internal overload device in the motor), whether a neutral is run to the motor or not.

Not directly related to your question, but you are only allowed to interrupt the grounded conductor (neutral in this case) if the same operation also interrupts all ungrounded conductors. That absolutely requires common trip rather than just handle ties.
 

mstrlucky74

Senior Member
Location
NJ
I think I have it figured out :D
You are celebrating your 1 yr. anniversary of posting under this name by posting "teaser" questions today. In your 6 years of posting here, hopefully you don't have to ask if a 3 phase motor needs a neutral.:)

Geez.....:p. I did not know the following



A 3-phase motor by definition would never require a neutral conductor.
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Neutral connections are only needed on single phase circuits.


A very straight forward answer to the original question, end of story.


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Why is a neutral not required?" Well, because in three phase, the phases conduct through one another and a dedicated load like a motor uses all three phases and ONLY all three phases.

That said, three phase services can and do have neutrals to furnish single phase loads.

It should be remembered that single phase is really "split phase" with the center tap of the [COLOR=blue !important][FONT=inherit !important][COLOR=blue !important][FONT=inherit !important]transformer[/FONT][/FONT][/COLOR][/COLOR] grounded and serving as the neutral except in some cases where "isolated grounds" are wanted.
 

cdslotz

Senior Member
Forget about EGC's for a minute...

A 3ph service is 277/480V......therefore a neutral is required because 277V lighting requires a neutral.
A 3ph motor is 480V....no neutral is required
A 3ph service is 120/208V.......therefore a neutral is required because recepts require a neutral
A 3ph motor is 208V 1ph or 3ph.....no neutral is required
A 1ph service is 120/240V.....a neutral is required because recepts and lights required a neutral
A 1ph A/C unit is 240V......no neutral is required

Occasionally you will see Fan Powered Boxes that require a neutral because there's a little 277V motor that needs that neutral.

Here's a hint....when you see that slash on any equipment or service rating like, 277/480, a neutral is required.
Have you not ever seed panels that are rated 480V 3ph? No neutral required because all of the loads are 480 3ph.


Seriously....did you spend any time in the field? You have been estimating for a while and you have to ask some of these questions????
 
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