800 Amp 3 Phase Service

[djcrzysounds@yahoo.com]

Just checking... 800 Amp 3 Phase 120/208 Volt Service. Incoming conductors to be 4 parallel 4/0 feeds (4 wires each phase).

 

[roger]

You could do it with (4) sets of 3/0 75 deg conductors.

Roger

 

[djcrzysounds@yahoo.com]

I was trying to get away with only 2 conduit runs. Sorry for not explaining... Also is it possible to run 2 sets of Service conductors in the same conduit.(As seen in a separate thread in NEC Section)

 

[roger]

I was trying to get away with only 2 conduit runs. Sorry for not explaining... Also is it possible to run 2 sets of Service conductors in the same conduit.(As seen in a separate thread in NEC Section)

As long as you adjust the conductors ampacity per table 310.15(B)(2)(a)

Roger

 

[djcrzysounds@yahoo.com]

As long as you adjust the conductors ampacity per table 310.15(B)(2)(a)

Roger

Please check my math. Using XHHW-2 Copper Conductors.
4/0 @ 260Amps
x2(sets of conductors per Conduit) 520 Amps
/1.25 (For derating) = 416 Amps
x2 (For 2 sets Conduit) = 832Amps

 

[infinity]

Please check my math. Using XHHW-2 Copper Conductors.
4/0 @ 260Amps
x2(sets of conductors per Conduit) 520 Amps
/1.25 (For derating) = 416 Amps
x2 (For 2 sets Conduit) = 832Amps

Looks good. :smile:

 

[augie47]

Unless the major portion of your load is non-liner, then your neutral would count as currrent carying and you would need to look at the calculated load.

 

[roger]

Looks good. :smile:

I agree.

Roger

 

[djcrzysounds@yahoo.com]

Thanks Guys... when it doubt.. just post it..lol... now comes the fun part... how do I get 8 wires through a weatherhead? The only ones I can find have holes for 7 conductors.

 

[infinity]

Thanks Guys... when it doubt.. just post it..lol... now comes the fun part... how do I get 8 wires through a weatherhead? The only ones I can find have holes for 7 conductors.

What size conduit?

 

[djcrzysounds@yahoo.com]

Not sure yet... might depend on the Weatherhead... could be from 3" RMC or PVC through 4"

 

[LarryFine]

how do I get 8 wires through a weatherhead? The only ones I can find have holes for 7 conductors.

Maybe you can re-calculate your neutral load and use a single neutral conductor.

 

[djcrzysounds@yahoo.com]

Maybe you can re-calculate your neutral load and use a single neutral conductor.

I thought even with 120/208V 3-phase you could not derate the neutral. So if for an 800amp service you would need one or more conductors that had an ampacity of 800Amps or more.

 

[jrannis]

I gotta say thats a new one for me. Eight wires in a weatherhead. Is it Delta by any chance? Maybe just one larger neutral?

 

[don_resqcapt19]

I thought even with 120/208V 3-phase you could not derate the neutral. So if for an 800amp service you would need one or more conductors that had an ampacity of 800Amps or more.

The grounded conductor only has to be as large as required by the load calculations and 220.61.

 

[infinity]

The grounded conductor only has to be as large as required by the load calculations and 220.61.

I'm curious, if you used that method could you ever add any single phase 120 volt loads to the service in the future?

 

[augie47]

The grounded conductor only has to be as large as required by the load calculations and 220.61.

if I might add
with the requirements of 250.24(C)

 

[don_resqcapt19]

I'm curious, if you used that method could you ever add any single phase 120 volt loads to the service in the future?

No different than adding any loads to an existing service or feeder...you have to do a new load calculation.

 

[don_resqcapt19]

if I might add
with the requirements of 250.24(C)

Thanks for adding that point, Gus. In some cases, those with small neutral loads, that section will require a larger grounded conductor than does the load calculation.

 

[djcrzysounds@yahoo.com]

Thanks for adding that point, Gus. In some cases, those with small neutral loads, that section will require a larger grounded conductor than does the load calculation.

I come up with a Neutral (Unbalanced load) of approximately 280 Amps. So if I call it 400 Amps and run two 4/0s (One per run) it will keep me at 7 wires per run and should not be a problem with conductor ampacity. The majority of my loads is a 200Amp 3 Phase Heater and about a dozen 3 phase motors Most of which are 30FLA and 2-3 are 5.5 FLA and a little HVAC(not 3 phase). Does anyone see a problem with this?