load demand is 169KW, what size transformer? if 225KVA, do I size OC at 125%?

[charlston]

In my last test in Oregon there was a 10 units 1000 SQFT dwelling calculation. Each with 10KW range and 10KW heater. I came up with 169KW demand for this building using optional. There will be 480/208 3 phase transformer. now
1. Is optional method ok if didn't tell me which one to use?
2. I need only 169KW and next standard 3 phase is 225KVA, and is that the right choice?
3. So if I go with 225KVA then that is 625A and do I size OC at 125%? I heard I can size the secondary OC at lower size.
What size OC disconnect? (A)600A, (B)700A, (C)800A, (D)1000A.

If I size the OC at 125% it will be 800A but even 500A is enough for this building.

 

[Dennis Alwon]

In most cases the optional is the one to use but be careful with the exception

220.84 Multifamily Dwelling.
(A) Feeder or Service Load. It shall be permissible to calculate
the load of a feeder or service that supplies three or more
dwelling units of a multifamily dwelling in accordance with
Table 220.84 instead of Part III of this article if all the following
conditions are met:
(1) No dwelling unit is supplied by more than one feeder.
(2) Each dwelling unit is equipped with electric cooking
equipment.


Exception: When the calculated load for multifamily dwellings without
electric cooking in Part III of this article exceeds that calculated under
Part IV for the identical load plus electric cooking (based on 8 kW per
unit), the lesser of the two loads shall be permitted to be used.

 

[jumper]

In most cases the optional is the one to use but be careful with the exception

[/B]

OP said it was a test question. I would assume standard method is more usual than optional.

Like questions that do not state that one may use an exception unless the question states so or is allowed.

 

[Dennis Alwon]

OP said it was a test question. I would assume standard method is more usual than optional.

Like questions that do not state that one may use an exception unless the question states so or is allowed.

I have seen a question like that and it because there were electric ranges they expected you to use optional.

 

[jumper]

I have seen a question like that and it because there were electric ranges they expected you to use optional.

Darn test writers cannot even be consistent when writing the poorly worded questions.

Tis sad.