15KV CU to AL

[mstrlucky74]

Have 15kv setup here. Have a 600A 15kv ATS feeding a 1200A switch/substation. It’s being fed with (1) 4” & 3 #4/0. Again this is all “15kv” and happen prior to the substation stepping it down to 277/480. Question is they would like a deduct to go to AL feeders and I’m trying to figure which size up I would need. Never done this for 15kv. Thanks.

 

[Julius Right]

In my opinion 3 feeders of 3*350 kmil Al conductor will be suitable [NEC Table 310.60(C)(78) det.2]
The overall diameter of 15 kV 350 kmil approx. 1.41".

 

[drktmplr12]

Have 15kv setup here. Have a 600A 15kv ATS feeding a 1200A switch/substation. It’s being fed with (1) 4” & 3 #4/0. Again this is all “15kv” and happen prior to the substation stepping it down to 277/480. Question is they would like a deduct to go to AL feeders and I’m trying to figure which size up I would need. Never done this for 15kv. Thanks.

there's information missing.

what ampacity are you targeting?
You listed #4/0 but this is feeding a 600A ATS and then a 1200A switch. there's nothing indicating how many amps are required of the system. we don't know how the #4/0 was selected so we can't suggest a aluminum equivalent.

is the conduit in air or underground?

Three-conductor cable or individual conductors?

 

[mstrlucky74]

there's information missing.

what ampacity are you targeting?
You listed #4/0 but this is feeding a 600A ATS and then a 1200A switch. there's nothing indicating how many amps are required of the system. we don't know how the #4/0 was selected so we can't suggest a aluminum equivalent.

is the conduit in air or underground?

Three-conductor cable or individual conductors?

Underground and single conductors?

 

[drktmplr12]

Underground and single conductors?

how many amps are required?

 

[mstrlucky74]

how many amps are required?

Actual load? IDK. Jut going off the ATS size and switch size.

 

[Julius Right]

Because I like riddles, in my opinion it is about 1000 kVA 15/0.48 kV transformer 1200 A 480 V
and 38.5 A 15 kV. According to NEC art.450 Table 450.3(A) the 15 kV 6*38.5=231 A and this matches the cable section of 4/0 copper 240 A. What is “600 A” it is hard to assume.

 

[drktmplr12]

Actual load? IDK. Jut going off the ATS size and switch size.

The conductors need to be sized per the transformer they are serving.

Assuming underground duct with 3 single conductors, MV-90, Table 310.60(C)(77) lists #4/0 provides 295 A for 5001-35,000 Volts.

To achieve the same ampacity with aluminum, you would need to refer to Table 310.60(C)(78) which lists 350 kcmil, MV-90 provides 305 A for the same voltage levels.

Careful because there are some rules in 310.60.