400A Residential Service Wire Size

[SIRSPARKSALOT]

Just checking myself. I do not do 400A residential services. I have a 400A residential 120/240 1-phase service to do.

Transformer to 320 Meter Socket
(6)#3/0 CU (1) #3 in 3" PVC conduit underground from the transformer to the 320 meter socket
(6*0.3117)+(1*0.1134)=1.9836 in2
3" PVC=7.268in2 @ 40% =2.9072 useable conduit area
*Conduit correctly sized for wires

310.16 says #3/0 is good for 225A at 90C (derating off 90C if less than 75C terminations)
310.15(B)(2)(A) says 4-6 current carrying conductors derate 80%
Therefore 225A*.80=180A per phase conductor *2=360A
240.4(B) allows the next higher fuse size being 400A

Any help is appreciated. I want to make sure I have this correct in my head before proceeding.

Thanks!

 

[augie47]

IMO, you would need to show a load calculation showing 360 amps or less calculated load.

 

[A/A Fuel GTX]

Why not run a pair of 2" conduits from the transformer to the meter socket and not have to worry about it. It will be a lot easier pulling too.

 

[infinity]

If you only want to run one conduit then you can use 400 kcmil copper or 600kcmil aluminum in a 3" PVC.

 

[CONDUIT]

You would have to do any adjustment factors off of the 75 degree "c" column because the conductors in the conduit is considered a wet location! 200 x .8 = 160 x 2 = 320. Unless it has a -2 (THWN-2) see table 310.104(a) in the 2011.

 

[infinity]

You would have to do any adjustment factors off of the 75 degree "c" column because the conductors in the conduit is considered a wet location! 200 x .8 = 160 x 2 = 320.

That would depend on the insulation of the conductor. THWN-2 or XHHW-2 can be derated from the 90? C ampacity.

 

[SIRSPARKSALOT]

Agreed.

That should be very easy to do since the house really does not need anything more than 200A based on my load calculation. The owner is very much into over building. My favorite quote of his is, "Penny in...dollar in." I wish all of my customers were this way.

One other thing I was looking at is coming off the 320 socket...I thought I would use this allowance to run (2) #4/0 SER to (2) 200A panels inside the garage, but after reading I do not think this is possible as it describes "all loads that are part or associated with the dwelling units". I take this to mean all of the loads would have to be on one feeder...not across two.

Sound right?

 

[SIRSPARKSALOT]

That would depend on the insulation of the conductor. THWN-2 or XHHW-2 can be derated from the 90? C ampacity.

Planning on wet location ie. THWN-2/XHHW-2.

Thanks guys!

 

[A/A Fuel GTX]

Agreed.

That should be very easy to do since the house really does not need anything more than 200A based on my load calculation. The owner is very much into over building. My favorite quote of his is, "Penny in...dollar in." I wish all of my customers were this way.

One other thing I was looking at is coming off the 320 socket...I thought I would use this allowance to run (2) #4/0 SER to (2) 200A panels inside the garage, but after reading I do not think this is possible as it describes "all loads that are part or associated with the dwelling units". I take this to mean all of the loads would have to be on one feeder...not across two.

Sound right?

Yes......310.15(B)(7) would not apply here. You would have to go with 250Kcmil if you use AL conductors.

 

[SIRSPARKSALOT]

Planning on wet location ie. THWN-2/XHHW-2.

Thanks guys!

For clarification purposes...the conduit fill areas were based on THW-2.

Either way THWN-2 only leaves more available pipe space.

 

[kwired]

Agreed.

That should be very easy to do since the house really does not need anything more than 200A based on my load calculation. The owner is very much into over building. My favorite quote of his is, "Penny in...dollar in." I wish all of my customers were this way.

One other thing I was looking at is coming off the 320 socket...I thought I would use this allowance to run (2) #4/0 SER to (2) 200A panels inside the garage, but after reading I do not think this is possible as it describes "all loads that are part or associated with the dwelling units". I take this to mean all of the loads would have to be on one feeder...not across two.



Sound right?

If your load calc is under 200 and you have no reason for significant extra capacity, why not run 200 amp conductors, hit a single switch or breaker and feed 2 panels - you are likely just after extra circuit spaces, or get a 60, 72, or 84 circuit panel - if you can, they are now legal if 2008 or 2011 NEC applies.

 

[SIRSPARKSALOT]

If your load calc is under 200 and you have no reason for significant extra capacity, why not run 200 amp conductors, hit a single switch or breaker and feed 2 panels - you are likely just after extra circuit spaces, or get a 60, 72, or 84 circuit panel - if you can, they are now legal if 2008 or 2011 NEC applies.

2008 Code Cycle.

I thought of that, but the owner really wants additional load expansion possibilities. There are plans for an out building (workshop), pool, separate hot tub, etc. Whether these things ever happen only time will tell.

 

[kwired]

2008 Code Cycle.

I thought of that, but the owner really wants additional load expansion possibilities. There are plans for an out building (workshop), pool, separate hot tub, etc. Whether these things ever happen only time will tell.

Separate buildings can be supplied by a service - even if on same meter. It is not always fun trying to get into the house panel to feed other buildings - and tearing up the lawn/landscaping that was not going to be disturbed. Just something to think about.

 

[SIRSPARKSALOT]

Separate buildings can be supplied by a service - even if on same meter. It is not always fun trying to get into the house panel to feed other buildings - and tearing up the lawn/landscaping that was not going to be disturbed. Just something to think about.

Hmmm...You bring up a great point...400A to the 320 meter socket...200A inside...conduit under the driveway...capped for future 200A in the out building...No OCP until entrance to the out building...I like that!

Now you got me thinking about the pool...For some reason I think the light of the pool needs to be wired in conduit back to the main panel - not a sub panel...I guess just another conduit across the road...need to read more...

Thanks KWIRED!

 

[stickboy1375]

Now you got me thinking about the pool...For some reason I think the light of the pool needs to be wired in conduit back to the main panel - not a sub panel...I guess just another conduit across the road...need to read more...

Thanks KWIRED!

You can wire a pool light back to a sub panel....

 

[kwired]

You can wire a pool light back to a sub panel....

I would sure hope so. Not as much of a problem at a dwelling, but could be a big problem at a large hotel or resort if that were not allowed. Main panel may not have any provisions for small branch circuits but rather supplies several larger feeders.

 

[curt swartz]

Maybe I missed if it was asked but what is the #3 for? You don't run an equipment ground with the service conductors.