I want to extend a feeder from building A to building B. Building A has a 600/347V Y 3 phase service. I want to bring 600V 3 wire to the second building and feed a 600V- 120/208V transformer and establish a neutral at the new service. I do not need 347V there. Is a neutral required in the feeder?
Where a service, feeder, or branch circuit requires a neutral conductor, it shall be installed (a)in all seperately enclosed switches and circuit breakers; (b)in all centres of distribution associated with the circuit; (c)with all connections to the neutral being made in the enclosures and centres;and (d)ins such a manner that any neutral conductor may be disconnected without disconnecting any other neutral conductor.
10-210 Conductor to be grounded
(1) For alternating-current wiring systems, the conductor to be grounded shall be as follows: (a)single-phase, 2 wire-the identified conductor; (b)single phase, 3-wire-the identified neutral conductor; (c)multi-phase systems having one wire common to all phases - the identified neutral conductor; (d)multi-phase systems having one phase grounded-the identified conductor; (e)multi-phase systemsin which one phase is used as in Item (b)-the identified conductor.
(2)In any multi-phase system in which one phase is used as a single-phase 3-wire system, only one phase shall be grounded.
Hope that helps. Check your local code that is in effect. - This one is from the new 20th edition - 2006.
Re: do I need a neutral conductor?#102537 05/27/0601:22 AM05/27/0601:22 AM
In my case, as I read it, a neutral conductor need only be installed if required which in this case it isn't. I see no reason it would be required, and a bonding conductor would suffice to limit any faults.
"Where a service, feeder, or branch circuit requires a neutral conductor, it shall be installed"
Re: do I need a neutral conductor?#102538 05/30/0609:45 AM05/30/0609:45 AM
I will have to agree that you would not need a neutral... You would need 3 hots and a bond thats it, UNLESS you plan on having 347V lighting... You would bond X0of the transformer to ground, effectively "grounding" the secondary... You would not connect the neutral of the feeder (if you had one) to XO as its a "groundED" conductor, not the "groundING" conductor....
Re: do I need a neutral conductor?#102540 06/09/0612:02 PM06/09/0612:02 PM
Yes you absolutely do have to bring a neutral to the next building regardless of the need for it there.
10-204(2) is the rule you want. The clue here is the 347 volts makes the system derived from a grounded system and you need a neutral or more accurately a grounded circuit conductor for your overcurrent protection
Re: do I need a neutral conductor?#102541 06/09/0604:27 PM06/09/0604:27 PM
i think if you look at appendix B you will understand the connections better. page 373 of the 20th edition. see where it says source (line side)? imagine that a transformer has been installed along the vertical dotted line at the right side of source between source and service/distribution. on the service/secondary side the neutral is still connected to the transformer XO and from the XO there is a groundING conductor connected back to the main service groundING conductor. thus there is an effective connection to ground thru the ground electrode at the main. Mikesh i think you might be mistaken about the neutral being needed. if the application is to supply 120/208v to building B all you need is the three phases to transform from 600 down to 208. a connection to the XO derives the 120v. the XO is connected to the system ground thus creating the 120v required. if there is a need for 347v in building B yes a neutral will need to extended from building A.