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?
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?
