Grover's Service Grounded Neutral Conductor size is figured by bouncing around Chapter 2, referencing several Articles in Chapter 2, and finally landing at Section 220.61(A).
Here is the path to 220.61(A):
Beginning in Article 230 - Services, seek out Part II. Overhead Service-Drop Conductors, then slide down to Section 230.23 Size and Rating.
At the end of Section 230.23 is Subsection 230.23(C) Grounded Conductors.
This Subsection directs the user to the reference for the _MINIMUM_
Grounded Conductor size."The Grounded Conductor shall not be less than the Minimum Size as required by Section 250.24(C)"
So off to Article 250 we go!
*** BTW, Section 230.31(C) for Underground Service-Lateral Conductors references 250.24(C) for Minimum Size Grounded Conductor. ***
Arriving at 250.24, we stroll down to 250.24(C) "Grounded Conductor Brought to Service Equipment", and follow it's pathway to Subsection 250.24(C)(1) "Rating and Sizing", which dictates:
"This conductor shall be routed with the phase conductors and shall not be smaller than the required grounding electrode conductor specified in Table 250.66, but shall not be required to be larger than the largest ungrounded service-entrance phase conductor.
In addition, for service-entrance phase conductors larger than 1100 kcmil copper or 1750 kcmil aluminum, the grounded
conductor shall not be smaller than 12-1/2 percent of the area of the largest service-entrance phase conductor.
The grounded conductor of a 3-phase, 3-wire delta service shall have an ampacity not less than that of the ungrounded
(Personal Note/Comment to the last paragraph: The Grounded conductor on a Grounded 3 Phase 3 Wire Delta Service will be the "Corner" of the Triangle - or simply one of the Three Phases.
Reduction in Conductor size is not an option, as this Grounded Conductor is not a "Balanced Common Neutral")
With that whole Delta-Thing in the Rear-View Mirror, we now drive our Golf Cart over to Section 250.66 "Size Of Alternating-Current Grounding Electrode Conductor.", at which point, we volunteer for a Breath-ilizer test!
It seems we may be Drunk!!! Why are we at 250.66, which deals with Grounding Electrode System Conductor sizing!!! We are trying to size the System's Balanced Neutral Grounded Conductor! The two are worlds apart!
Breath-ilizer Test says we are 100% Sober, so we hop back in our Golf Cart and follow the path of 250.66, running into Table 250.66.
Grover's Ungrounded Service Entrance Conductors are specified as 500 MCM Copper.
Per Table 250.66, the Minimum size GEC applied to 500 MCM Cu. Ungrounded Conductors is either:
- 1/0 Copper,
- 3/0 Aluminum.
So now we know the _SMALLEST_ size our Service Grounded Conductor may be - 1/0 Cu. or 3/0 Al.
For uniformity, let's choose the 1/0 Cu., since the Ungrounded Conductors are Copper.
OK, jump back in the Golf Cart, and drive directly to Article 220 - Branch Circuit, Feeder, and Service Calculations.
Make a left turn at Section 220.61, then toss out the Anchor - as this is the end of the Trek!!!
Section 220.61 "Feeder or Service Neutral Load" contains the Subsections "(A), (B), and (C)", which regard the calculation of the Balanced Grounded Neutral Conductor.
*** Note: Since the System has been referenced as "120/240V 1 Phase 3 Wire", the Grounded Conductor will be derived from a Center-Tap on a Single 240V Secondary Winding - therefore making this a "Balancing Noodle" type of System Grounded Conductor (carries the unbalanced Load from L-N / N-L, and L-N-L connected circuitry).
This would qualify it for "Permitted reductions" called out in Subsection (B)
IF THE SYSTEM IS DERIVED FROM A 208Y/120V 3 PHASE 4 WIRE NETWORK... The above does not apply, and the Grounded Conductor is considered "Non-Balancing" (maybe a Circus reject...???).
More on this in another long-winded thread...
So, the shortcut method would be to drive the Golf Cart directly into Article 220, and hoist Anchor at 220.61.
Hope you enjoyed the Trip!!!