400 amp service conductors

[augie47]

We have a difference of opinions amongst inspectors and am interested in your input.

We have a pre-fab commercial building, pre-wire with minimum lighting and receptacles and a 400 amp MB single phase service panel.

No drawings, no load calculations available. Owner is unsure about future occupancy, possibly laundry equipment,.

Contractor has installed a 400 amp meter socket, PVC to panel and a RMC riser for overhead service.
His plan is to parallel AL service conductors in the one riser.

What is the minimum size phase and neutral conductors that wold be acceptable ??

 

[electrofelon]

250 AL with next size up rule gets you to 400.
300 for full 400.

 

[electrofelon]

Minimum grounded conductor size: Single 1/0 for the 250s, or 3/0 for the 300s

 

[Dennis Alwon]

250 AL with next size up rule gets you to 400.
300 for full 400.

Did you deduct for 6 wires in a pipe

 

[infinity]

Did you deduct for 6 wires in a pipe

Yes he did. 230 amps * 2 * 80% = 368 amps.

Minimum grounded conductor size: Single 1/0 for the 250s, or 3/0 for the 300s

For a building with an unknown future occupancy I would never use the code minimum sized neutral.

 

[Dennis Alwon]

Yes he did. 230 amps * 2 * 80% = 368 amps.

I didn't check it as I was running out the door for a sec but it seemed low. ty

 

[electrofelon]

For a building with an unknown future occupancy I would never use the code minimum sized neutral.

Augie asked, im just the messenger

 

[augie47]

Minimum grounded conductor size: Single 1/0 for the 250s, or 3/0 for the 300s

Based on 220.61 and no calculations,, I felt like it would need the be 4/0

 

[electrofelon]

Based on 220.61 and no calculations,, I felt like it would need the be 4/0

Well if there are no load calculations, theoretically you can't allow anything can you? I mean I understand not allowing say the next size up rule or a neutral reduction without calcs is common, but the code says nothing about when skipping calcs is more acceptable than other times

 

[kwired]

kind of unwritten rule but many places allow reduction of neutral by one or two conductor sizes with no need to show any calculations for most circumstances with feeders or service conductors.

Many multiplexed conductor assemblies like URD come that way as well.