ECN Forum Forums Code Related Discussion NEC & other Code issues Neutral required?

I understand why Yoopersup is concerned with this setup.
It appears as if there is no _Direct Bond_ between the Metallic Enclosures on the Separately Derived System (SDS), and the Star point of the Transformer Array.

If this is accurate, then the SDS is an Ungrounded 480V 3 Phase 3 Wire; instead of being a Delta Configuration, it is a Wye Configuration.

As long as there is a local Grounding Electrode System bonded to the Metallic Enclosures on the SDS, the System is safe and conforms to NEC Article 250.

HOWEVER...

If the Star Point is tapped, with a 4th Conductor brought down from the Wye Network to the first Disconnect... AND this Conductor is usable for a "Dual Voltage SDS" (480Y/277V 3 Ph. 4 Wire), then the tap from the Star Point shall be a Grounded Conductor for the SDS, requiring all the Bonding and similar stuff.
This Grounded Conductor would need to be brought to the first "Supply Point"

Other Possible Grounding Options:

A: Star Point Ground Bonded At Pole...

The SDS might be Ground Bonded at the Pole, via a Grounding Electrode Conductor (GEC) directly Bonded to the Star Point at the Secondary.
Same GEC is also bonded to metallic enclosures on the SDS.

B: Corner Grounded SDS...

One of the Three Phase Lines may be Grounded either at the Pole, or at the first Disconnect / Supply Point.

C: Impedance Grounded System...

Either via an introduced Impedance between Grounding Electrode System (GES) and the Star Point of the Transformer Network (proper),

or;

No Physical Connection between the GES and the Star Point of the Pole Mounted Transformers - AKA Impedance of the Dirt. (not preferred, but have seen several of these!)

FYI: The "Star Point" is the common termination of all Three Secondary "X2" leads, from all Three Transformers.


The Yellow Common Connection on the Secondary side of this Drawing is the "Star Point". It is where the Common Grounded "Neutral" Conductor is derived for the 4 Wire Wye.

* BTW Yoopersup: Are the Transformers for this System connected as shown in the above drawing...,

or;

like one of the configurations found on the following pages:

3 Phase 3 Wire Wye

3 Phase 3 Wire Closed Delta

(click on the blue underlined text to jump to that page).

-- Scott