Possible to fit 225a 3ph feeder in 2" EMT with aluminum??

[Dennis Alwon]

So why does the NEC require the neutral in a feeder to be at least as large as the minimum required EGC, but doesn't impose this requirement on branch circuits?

Cheers, Wayne

I asked the same thing and I think I wrote a proposal years ago but it got shot down.

 

[kwired]

I asked the same thing and I think I wrote a proposal years ago but it got shot down.

Do you think my example where the only neutral load is a few VA contactor coil needs to be 8AWG minimum? If anything I would ask why do we need a minimum on feeders?

 

[winnie]

EGC for 225A is #4 Cu or #2 Al...of course the EMT could serve as the EGC

Simpull compact stranded aluminium THHN 300 kCmil has an OD of 706 mil:
http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet327

Simpull _copper_ THHN 4 AWG has an OD of 318 mil:
http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet276

2" EMT has an ID of 2070 mil

3x 300kCmil Al + 2x 4 AWG Cu gives a fill of 39.6%

This gives you a 230A ampacity for the hots, an 85A ampacity for the neutral, and a wire EGC, by mixing copper and aluminium.

3x 300kCmil Al + 1x 2AWG Al gives a fill of 37.9% but then you use the EMT as your ground.

3x 250kCmil Al + 2x 2 AWG Al gives a fill of 36.2% but then you need to play tricks at both terminations to use the 90C ampacity.

As always, check the calculations yourself.

-Jon

 

[jap]

I did not look at wire sizes, but the only one way I see to use the 90C rating instead of the normal 75C is this set up.

Does anybody ever actually do this?

JAP>

 

[electrofelon]

EGC for 225A is #4 Cu or #2 Al...of course the EMT could serve as the EGC

Simpull compact stranded aluminium THHN 300 kCmil has an OD of 706 mil:
http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet327

Simpull _copper_ THHN 4 AWG has an OD of 318 mil:
http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet276

2" EMT has an ID of 2070 mil

3x 300kCmil Al + 2x 4 AWG Cu gives a fill of 39.6%

This gives you a 230A ampacity for the hots, an 85A ampacity for the neutral, and a wire EGC, by mixing copper and aluminium.

3x 300kCmil Al + 1x 2AWG Al gives a fill of 37.9% but then you use the EMT as your ground.

3x 250kCmil Al + 2x 2 AWG Al gives a fill of 36.2% but then you need to play tricks at both terminations to use the 90C ampacity.

As always, check the calculations yourself.

-Jon

Nice analysis :thumbsup: