600v CU to Al

[mstrlucky74]

OK a 600v feeder questions. If I have (1) set 3-1/2” EMT w/ 3#600 # 1 #2( for 420 amps) and want to go to aluminum I’m thinking I need 3 sets of 3/0 and the appropriate conduit size. Southwire does offer 1000kcmil which is good for 445amps but that doesn’t make sense. THanks.

 

[JFletcher]

What ampacity do you need? And what doesn't make sense about 1000 MCM in aluminum

 

[petersonra]

I think he is saying he has 420A worth of conductor per phase plus an EGC, or maybe a neutral.

3X 3/0 AL would give him 465 A of ampacity but I think he would need more than one conduit.

Unless it is a very short pull, I can't imagine a 1000 kcm conductor making much sense either.

(3) 1/0 Copper might make more sense. that would be nine CCC in a conduit. would give you 357 A worth of ampacity. that might be enough depending on his actual load.

 

[infinity]

Forget that they even make any conductor above 750 kcmil and go from there. How long is the run?

 

[mstrlucky74]

Forget that they even make any conductor above 750 kcmil and go from there. How long is the run?

Run is 225'

 

[mstrlucky74]

I think he is saying he has 420A worth of conductor per phase plus an EGC, or maybe a neutral.

3X 3/0 AL would give him 465 A of ampacity but I think he would need more than one conduit.

Unless it is a very short pull, I can't imagine a 1000 kcm conductor making much sense either.

(3) 1/0 Copper might make more sense. that would be nine CCC in a conduit. would give you 357 A worth of ampacity. that might be enough depending on his actual load.

I would run 3 separate conduits, each with 3 # 3/0 and a ground.

 

[petersonra]

I would run 3 separate conduits, each with 3 # 3/0 and a ground.

i would not run a ground unless it was plastic conduit.

 

[infinity]

I would run 3 separate conduits, each with 3 # 3/0 and a ground.

Why 3 conduits and #3/0? Two conduits with aluminum 250's would work.

 

[petersonra]

Why 3 conduits and #3/0? Two conduits with aluminum 250's would work.

maybe he does not like 250 kcm wire.

 

[infinity]

maybe he does not like 250 kcm wire.

Knowing his approximate labor cost running an extra 225' of raceway seems like a good way to waste money.

Besides 250 Al is a piece of cake.

 

[Julius Right]

From NEC Table 4 EMT 3-1/2" 40% 4.618 in^2
From Table 5 for XHHW, XHHW-2,XHH 600 kmil 0.8709 in.^2 or for THHW 0.9729 in.^2
900 kmil 1.2351 or 1.3561 in.^2.; #2 0.1333 in.^2.
Table 310.15(B)(16) 75oC 600 kmil copper 420 A 900 kmil Al 425 A.
Area 3*900 +#2 =3*1.3561+0.1333=4.2<4.618 in.^2
From Table 9 for 900 kmil Aluminum in steel [750 kmil] 0.052
DV=SQRT(3)*420*0.052*225/1000=8.51 V 1.77% of 480 V

 

[kwired]

Knowing his approximate labor cost running an extra 225' of raceway seems like a good way to waste money.

Besides 250 Al is a piece of cake.

I agree. When you need more then 250 kcmil is when you typically should start to consider paralleling the conductors from my experiences.

 

[electrofelon]

I agree. When you need more then 250 kcmil is when you typically should start to consider paralleling the conductors from my experiences.

250 vs 750 is a good example of how inefficient large conductors are. 3x 250 AL 615 amps. Single 750 Al 385 amps. Ouch. Now of course AL is pretty cheap so I could see other considerations winning oUT sometimes, particularly if the run isn't very long, but copper.......

 

[Julius Right]

In my opinion, you need 2 * 3 * 400 kcmil of aluminum [2*270 A must be multiplied by 0.8 for 6 loaded conductors] if 420 A is required.

 

[kwired]

In my opinion, you need 2 * 3 * 400 kcmil of aluminum [2*270 A must be multiplied by 0.8 for 6 loaded conductors] if 420 A is required.

ampacity adjustment for number of current carrying conductors would only apply if all conductors are in one raceway.

 

[JFletcher]

3 600 MCM copper in 1 conduit is kind of an odd set up... 420 amps ampacity is well over what a 400 amp breaker can carry continuously, it is 80% of a 500 amp breaker, (though I do not know if they make such an animal), the run is not so long that voltage drop should be that much a concern... again, what ampacity do you need, and what size breaker are these coming from?

675 ft of copper versus aluminum.... may wind up close to a wash by the time a second 3.5" ENT conduit is run and extra-time terminating is taken into consideration.

Eta: looks like you can pull up to 8 400 MCM wires in one three and a half inch conduit, so if another Raceway isn't needed, aluminum will definitely be the way to go here

 

[kwired]

3 600 MCM copper in 1 conduit is kind of an odd set up... 420 amps ampacity is well over what a 400 amp breaker can carry continuously, it is 80% of a 500 amp breaker, (though I do not know if they make such an animal), the run is not so long that voltage drop should be that much a concern... again, what ampacity do you need, and what size breaker are these coming from?

675 ft of copper versus aluminum.... may wind up close to a wash by the time a second 3.5" ENT conduit is run and extra-time terminating is taken into consideration.

Eta: looks like you can pull up to 8 400 MCM wires in one three and a half inch conduit, so if another Raceway isn't needed, aluminum will definitely be the way to go here

standard sizes from 240.6 include 300, 350, 400, 450, 500, 600. If your conductor ampacity is 420 amps after adjustments -it would need to be protected with a 450 amp device and calculated load would still be limited to 420.

 

[infinity]

3 600 MCM copper in 1 conduit is kind of an odd set up... 420 amps ampacity is well over what a 400 amp breaker can carry continuously, it is 80% of a 500 amp breaker, (though I do not know if they make such an animal), the run is not so long that voltage drop should be that much a concern... again, what ampacity do you need, and what size breaker are these coming from?

600 kcmil is very common for us. For a 400 amp transformer secondary it would be the minimum size for one set.