400amp single phase temporary service

[Dsg319]

Am I correct to say that parallel 4/0 aluminum conductors are undersized for a 400amp single phase service. 400amp meter(320) than our to two different 200amp panels.

There are no real calcs that I’m aware of for the service as it’s feeding temporary job trailors. I know the service conductors just need to be sized for the load. Think we should have any problems with inspection?

Duke energy midwest.

4/0aluminum ampacity-180amperes

180x2=360amperes

Derate for 4CCC

360x.80= 288ampacity.

 

[infinity]

Why derating are you using a single raceway? Since there is no calculated load seems like you're fine with parallel #4/0.

 

[Dsg319]

Why derating are you using a single raceway? Since there is no calculated load seems like you're fine with parallel #4/0.

Yes single raceway.

But as you said being there is no calculated load for the temporary job trailers there is really no way to say the #4/0 is too small.

 

[kwired]

If you had an actual load calculation it is possible to feed these two service disconnecting means with whatever conductor ampacity is equal or greater than the load calculation results. If you had 150 amps load calculation then 150 amp conductor would be acceptable even though you have 2-200 amp main breakers.

What you did mention however would be limited to a load calculation of 288 amps.

 

[wwhitney]

4/0aluminum ampacity-180amperes
180x2=360amperes

That's the termination ampacity for parallel 4/0 Al.

Derate for 4CCC
360x.80= 288ampacity.

For derating, you can start at the 90C ampacity (assuming 90C insulation) of 205A. So after derating you have 2*205*.8 = 328A. Needs to be protected by a 350A breaker.

Or if these aren't actually in parallel (you mention supplying two panels), each needs to be protected by a 175A breaker. Unless the two runs occupy the same conduit for only a short distance (less than 10% of the total run, and under 10'), then you can ignore the derated ampacity, and the termination ampacity will control as usual.

Cheers, Wayne

 

[electrofelon]

That's the termination ampacity for parallel 4/0 Al.

For derating, you can start at the 90C ampacity (assuming 90C insulation) of 205A. So after derating you have 2*205*.8 = 328A. Needs to be protected by a 350A breaker.

Or if these aren't actually in parallel (you mention supplying two panels), each needs to be protected by a 175A breaker. Unless the two runs occupy the same conduit for only a short distance (less than 10% of the total run, and under 10'), then you can ignore the derated ampacity, and the termination ampacity will control as usual.

Cheers, Wayne

But there is the "loophole" of being able to size service conductors that are serving multiple disconnects to the load calc so it may be fine. Of course in the absence of a load calc, some inspectors may want to see full size conductors,

 

[wwhitney]

But there is the "loophole" of being able to size service conductors that are serving multiple disconnects to the load calc so it may be fine.

OP's one line isn't clear to me, but it would be unlikely to have the two sets of 4/0 Al in parallel where they are in a common raceway and then separated to go to two different service disconnects.

But you are correct that it is possible: Meter - parallel 2 sets of 4/0 Al - junction box with 4-port Polarises to join the parallel 2 sets to two separate sets of 4/0 Al - separate runs to two service disconnects.

In that scenario, each service disconnect could be 200A, and the only limit is that the individual load on each service disconnect is under 180A, and the combined load is under 328A.

Cheers, Wayne

 

[electrofelon]

OP's one line isn't clear to me, but it would be unlikely to have the two sets of 4/0 Al in parallel where they are in a common raceway and then separated to go to two different service disconnects.

But you are correct that it is possible: Meter - parallel 2 sets of 4/0 Al - junction box with 4-port Polarises to join the parallel 2 sets to two separate sets of 4/0 Al - separate runs to two service disconnects.

In that scenario, each service disconnect could be 200A, and the only limit is that the individual load on each service disconnect is under 180A, and the combined load is under 328A.

Cheers, Wayne

I am assuming the parallel is on the line side of the meter and two sets (not parallel) to each disconnect.

 

[wwhitney]

I am assuming the parallel is on the line side of the meter and two sets (not parallel) to each disconnect.

Yes, that just occurred to me, say an overhead service with one mast and parallel 4/0 Al in the mast to the meter. Agreed that is quite likely.

Cheers, Wayne

 

[Dsg319]

That's the termination ampacity for parallel 4/0 Al.

For derating, you can start at the 90C ampacity (assuming 90C insulation) of 205A. So after derating you have 2*205*.8 = 328A. Needs to be protected by a 350A breaker.

Or if these aren't actually in parallel (you mention supplying two panels), each needs to be protected by a 175A breaker. Unless the two runs occupy the same conduit for only a short distance (less than 10% of the total run, and under 10'), then you can ignore the derated ampacity, and the termination ampacity will control as usual.

Cheers, Wayne

Ahhh yes I’ve been out of the book too long.
Forgot to start my derating at 90c. And they are parallel going into the meter can then split from there.

 

[Dsg319]

I am assuming the parallel is on the line side of the meter and two sets (not parallel) to each disconnect.

Correcto

 

[Dsg319]

Thanks all!

 

[Dsg319]

Yes, that just occurred to me, say an overhead service with one mast and parallel 4/0 Al in the mast to the meter. Agreed that is quite likely.

Cheers, Wayne

Yes this is correct.

 

[electrofelon]

FWIW I usually do 400 amp services pretty similar to this. The situation with most of the ones I do is the load is not very large and would likely even be fine with even a 200 amp service. Also the inspectors dont ask for load calcs so its kinda "whatever i want" to use for the conductors. IF I am feeling generous I might go with 250's, but often Ill just use double 4/0. Single 500 is an option too.