Test Prep on range.

[daiashi]

A 120/208 volt,three phase,four wire feeder supplies 16 single phase ranges rated 10 kw @ 240 volts.These ranges are installed in a home economics classroom within a school.What is the total calculated amperage load for these ranges? answer says 113 amps according to 220.55. Not what I was getting.
Any ideas?

 

[Jim Shorts]

113 is correct. Check out the text in 220.55 for single phase ranges on a 3 phase feeder or service and then look at the example in Annex D.

6 ranges max per any 2 phases x 2 = 12
Demand for 12 ranges in column C = 27 kw
27,000 / 2 = 13,500 (load in watts per phase)
13,500 x 3 = 40,500 (total load for all 3 phases)
40,500 / (208 x 1.732) = 112.5 amps