grounded conductor

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apj

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greetings fellow electricians:
My question to all of you smart people is am I required to bring a neutral to a three phase panel used for equipment only that does not require a neutral? I thought the code required a grounded conductor for a return path for shorts to trip the breaker, even if the neutral is not needed for load. I can see L-L shorts would not need it, and a ground fault would travel on the EGC back the breaker via the same path as L-L shorts (to the main disconnect bond, to the transformer, and back to the breaker). Wouldn't a grounded conductor only be needed for L-N shorts on L-N loads? I am kind of confused on this issue. :confused: Code references please and thanks in advance!
 
Re: grounded conductor

Originally posted by apj: greetings fellow electricians:
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I hope the greetings are also extended to those of us who are not electricians, such as we inginears. ;)
Originally posted by apj: Wouldn't a grounded conductor only be needed for L-N shorts on L-N loads?
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If there is no N, then there cannot be a L-N short. If there are no L-N loads, you do not need to bring an N to the panel.

I?ll let you deal separately with Don?s question. My answer presumed you were talking about a panel downstream of the main service panel.
 
Re: grounded conductor

yes, my greetings apply to all who are in this to help others, no matter what your trade. The answer to the other question is, no, this is not the main disconnect. This panel is a subpanel fed from a breaker in another panel. If this would have been the only panel fed from the transformer, then would I have to a neutral as well (for what purpose?), and would it be sized according to 250-66? Thanks.

[ November 26, 2005, 02:15 PM: Message edited by: apj ]
 
Re: grounded conductor

Originally posted by apj:
yes, my greetings apply to all who are in this to help others, no matter what your trade. The answer to the other question is, no, this is not the main disconnect. Thanks.
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Then you don't need the neut. per the NEC.
 
Re: grounded conductor

Originally posted by apj:
. . . a ground fault would travel on the EGC back [to] the breaker via the same path as L-L shorts (to the main disconnect bond, to the transformer, and back to the breaker).
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The italicized part, "a ground fault would travel on the EGC . . . to the transformer" is why the neutral must be brought at least to the main disconnect, and bonded with the EGC.

This provides a low-impedance path from the point of the fault to the transformer's grounded conductor, assuring operation of the short-circuit and/or overload protection device(s).

No, a neutral need not be run any farther to any portion of the system that does not require a connection to it. BTW, a L-to-L fault does not use the neutral or EGC pathway.
 
Re: grounded conductor

apj,
This panel is a subpanel fed from a breaker in another panel. If this would have been the only panel fed from the transformer, then would I have to a neutral as well (for what purpose?), ...
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The purpose is to provide a fault clearing path. All current must return to the source, and the grounded conductor between the utility and the service disconnect it part of this path. This is the main path for "ground fault" currents to return to the source. At the main disconnect the service grounded conductor is connected to the load side equipment grounding conductors via the main bonding jumper. Three phase loads on the load side of the service disconnect only require the ungrounded conductor and an equipment grounding conductor.
Don
 
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