Some green wire size thoughts

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petersonra

Senior Member
Location
Northern illinois
Occupation
Semi-retired engineer
Suppose the following loadbank.

Outdoor equipment enclosure.

Two power feeds into enclosure.

One feed is 480V/3ph, maybe 10A. Comes in with #14 green wire to a disconnect switch that ultimately feeds a small transformer, and a couple small motors. This is just a feeder from a panelboard inside.

GEC size would be #8 cause that is the smallest on the chart and my little SDS xfmr is only 500VA.

The other feed is configurable depending on their needs. It could be 6 seperate 210A/230V single phase feeds. Or 2 210A/230V/400V 3 phase feeds. or potentially a single phase 1300A/230V feed. I am thinking worst case the green wire that comes in with them has to be 350MCM cause they might well put an OCPD in excess of 1600A on it, and the next size up is 2000A in table 250-95.

I am thinking we have (6) phase conductors 210A each, so after derating we are looking at 300MCM.

(6) neutral conductors at 300 MCM

(1) green wire at 350MCM.

How will I ever explain this to the installing electricians?
 
Re: Some green wire size thoughts

What?s to explain? Every circuit needs a GEC or EGC (as appropriate), and these are sized in accordance with the properties of the circuit. If you choose to install two widely different types of equipment in the same box, they will need widely different green wires.
 
Re: Some green wire size thoughts

I'm not sure I totally understand the full question, but a feeder with 2000A overcurrent protection takes one 250kcmil copper equipment grounding conductor, not 350.
 
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