Calculating 3-Phase Hi Leg Service Size.

[Mirwin]

I am trying to perform a load calculation for a project that will feature a 3-phase, high-leg delta system with a 120/240V voltage. I have compiled all the load information for the project and applied the relevant demand factors to the appliance loads for this occupancy (a restaurant).
My total VA after demand factors are applied is 112,752 VA.

I am familiar with the formula for a 120/208V, 3-phase service.
Total VA / (volts x 1.732) = Amps

Does the same formula work for the hi-leg calculation?
For example: 112,752 / (240 x 1.732) = 271Amps.

I checked Annex D in the NEC and didn't see any hi-leg load calculation examples.

 

[winnie]

That formula is correct for the 3 phase load.

But the common use of a high leg delta is a composite of a three phase and a single phase service. The formula you are using isn't correct for the single phase portion of the load.

So say you've calculated that you have 72,000 VA of three phase and 40,752 VA of single phase you would use:
72000 / (240 * 1.732) to get 3 phase amps
and
40,752 / 240 to get single phase amps

On the high leg you only have 3 phase amps
On the single phase legs you have 3 phase amps + single phase amps. (This is approximate, since the phase angles are not quite aligned, but close enough)

You should double check: Some high leg services are essentially single phase services with small three phase on top; others are really intended for 3 phase loads with only a little bit of single phase L-N loading.

 

[Joethemechanic]

You should double check: Some high leg services are essentially single phase services with small three phase on top; others are really intended for 3 phase loads with only a little bit of single phase L-N loading.

Yeah
.
Look to see if it is a true delta or an open delta and the size of the transformers. Lots of them are open delta and only have a small transformer for the "high leg"