Ranges of unequal rating supplied by 3-phase 208Y/120 volt circuit. Used for instructional purpose or for multiple dwelling units. What is the demand load for the service or a feeder?
I come up with this: Ranges of unequal rating supplied by 3-phase 208Y/120 volt circuit.
6 ranges at 3 KW 10 ovens at 5 KW 14 ranges at 6 KW 45 ranges at 12 KW 25 ranges at 15 KW 1 3-phase range at 20 KWThis problem does not fit nicely within the rules of Section 220.55 or Table
220.55 and accompanying Notes.Divide ranges to balance load and find how many are on each two phases.
For the 3-phase range divide load by three and apply to each phase.
Phases AB AC BC 2 - 3 KW 2 - 3 KW 2 - 3 KW 4 - 5 KW 3 - 5 KW 3 - 5 KW 5 - 6 KW 5 - 6 KW 4 - 6 KW 15 - 12 KW 15 - 12 KW 15 - 12 KW 8 - 15 KW 8 - 15 KW 9 - 15 KW 1 - 7 KW 1 - 7 KW 1 - 6 KW _________________________________________ 35 - 366 KW 34 - 363 KW 34 - 359 KW
Select phases with maximum number of ranges which is AB.
2 x number of ranges/phase = 2 x 35 = 70Double the number of ranges for each category and use 8.8 KW for any value below 8 3/4 KW.
Using 24 - 8.8 KW, 30 - 12 KW, and 16 - 15 KW use section 3 to find demand.
Demand is 81.38 KW using Section 3.
81.38 KW /2 = 40.69 KWThe total demand load is 3 x 40.7 = 122.1 KW
The line current is:
I = 122,100 / (1.732 x 208) = 122,100 / 360.3 = 339 amperes
I used my calculator at:
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