3-phase, 4-wire WYE system 4

[MayorMagna01]

In a 3-phase, 4-wire wye system, such as 208Y/120V system, the neutral conductor is often ground by the utility on the transformer side. It is also a common practice to size and install a grounded conductor from the service entrance connecting transformer's neutral to Main Panel's Neutral Bus Bar to Grounding Electrode.

However, a grounded conductor (on this specific system) is very useful if I have Line-Neutral Loads (120V loads). But what if ALL of my loads are either 208V 3-phase or 208V 1-phase (Line-Line) distributed across each phase..

1. Do I still need to install a grounded conductor (GC)? If so, why?​

2. For North Americans, if I will not going to install GC on this specific scenario, what are my NEC violations?
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3. With respect to sizing GC on this specific scenario, is Table 250.102(C)(1) the correct table to use?
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Your expert opinion will greatly help my young mind to understand better this kind of situations.

Thank you.

 

[jraef]

I think it might be important to stop using "Grounded Conductor" (GC), because it seems to be getting confused with Grounding Conductor. So lets call the Grounded Conductor "Neutral" to keep it clear.

If ALL of the loads are Phase to Phase, and NONE of them need a Neutral, you are not required to run a Neutral wire. In Motor Control Centers for example, we often do NOT have a Neutral Bus Bar, because for motor loads, it is unnecessary. If the MCC is a Service Entrance point, there must be a Neutral Landing Point of some sort, but there is no need for that to go anywhere beyond the Service Entrance compartment. If the Service Entrance to a site is in Switchgear somewhere else, then we often have only the three phase conductors running out to an MCC, no Neutral whatsoever. Perfectly legit.

However, you ALWAYS need to run an EGC, (Equipment Grounding Conductor), a.k.a. "Ground Wire" (although in some cases, the raceway CAN serve as the EGC, but I don't want to sidetrack this discussion further).

Whether or not the Neutral is bonded at the utility pole or the Service Entrance, or both places, is also a separate issue involving the particulars of the installation.


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