range

[treyp3]

what is the equivalent 3 phase demand load in va for 10 - 11kw household electric ranges installed in an apartment complex supplied by a 120\208v, 3 phase, 4 wire system
a. 23,400
b. 30,500
c. 34,500
d. 38,200
220.55 coulum c says 23, at least thats the answer as I see it. So, is a. a good answer? Is this why they state "equivalent"? Or, am I doing this wrong?

 

[Dennis Alwon]

Look at art.220.55--- I believe we are to assume the ranges are single phase but the feeder is 3 phase.

 

[david luchini]

I believe the answer is C) 34,500VA

There are 4 units max between any two phases, which means figure 8 units. The demand for 8 units is 23kW per T220.55, or 11.5kW per phase.

The "equivalent three phase" load would be 11.5kW per phase * 3 phases =34.5kW.

 

[jumper]

David is correct. See example D5(a) in Annex D in your NEC.

 

[Dennis Alwon]

David is correct. See example D5(a) in Annex D in your NEC.

I agree that's why I referenced art. 220.55 because the fpn took you to the annex D with the exact example. I should have said read the fpn...:grin:

 

[treyp3]

Look at art.220.55--- I believe we are to assume the ranges are single phase but the feeder is 3 phase.

Yea, I guess I have to assume that the ranges are 1 phase as the question does not specify.

Aha! 23kw/2 phases =11.5kw per phase x the 3 phases = 34.5kw. Thanks for the help!

 

[jumper]

I agree that's why I referenced art. 220.55 because the fpn took you to the annex D with the exact example. I should have said read the fpn...:grin:

I did not even read 220.55, I just remembered there was an example with ranges in the annex and looked it up. It was a coincidence that the example was 10 ranges also.

 

[jumper]

Yea, I guess I have to assume that the ranges are 1 phase as the question does not specify.

Aha! 23kw/2 phases =11.5kw per phase x the 3 phases = 34.5kw. Thanks for the help!

You can also do the math:

23,000 VA / 240V= 95.8A
34,500 VA / 208V / 1.732 = 95.8A