Mike Dolt Enterprises
Mike Dolt Enterprises
User: KHall, Location: Eighty Four,Pa.15330
Asked on: Saturday, March 26, 2011 at 8:03 pm EDT
Answered on: Tuesday, May 14, 2024 at 3:20 am EDT
Question: I have a 3 phase panel with 7 different 208V/1 phase loads. I calculated the load for each 2 pole circuit by multiplying the load amps by 208. The VA totals for each phase are as follows ...A = 18,242 VAB = 18,242 VAC = 16,224 VAHow do I convert this into a total connected load figure for this panel and would that (along with 25% of my largest motor) be the basis for sizing my feeder and main breaker?The system is 120/208, 3 phase, 4 wire.
Step 1: Convert VA to Watts
Multiply the VA totals by a power factor of 0.8 to convert them to Watts.A = 18,242 VA x 0.8 = 14,593.6 WB = 18,242 VA x 0.8 = 14,593.6 WC = 16,224 VA x 0.8 = 12,979.2 WStep 2: Calculate Total Connected Load
Add the Watts for each phase to get the total connected load.Total Connected Load = A + B + C= 14,593.6 W + 14,593.6 W + 12,979.2 W= 42,166.4 WStep 3: Determine Feeder and Main Breaker Sizing Feeder Sizing
The feeder must be sized for the total connected load plus 25% of the largest motor load. Assume the largest motor is 5 kW (5,000 W).Feeder Size = Connected Load + 25% of Motor Load= 42,166.4 W + 0.25 x 5,000 W=
47,166.4 W
Select a feeder with a current rating based on the feeder size. Main Breaker Sizing
The main breaker must be sized for the feeder size. Select a main breaker with a current rating greater than or equal to the feeder current rating.As the feeder size is 47,166.4 W, select a main breaker with a current rating of
60 A. Flag for review