Branch Circuits

[pressone]

Does anyone know how many branch circuits I need for a connected lighting load of 140KVA that consists of 120V fluorescent fixtures on a 20A circuits? I have a 120/208V 3 Phase Supply. Thank You! George

[suemarkp]

I believe you'll need 73 if you're willing to max them out and the amps can come to exactly 16 (16A on a 20A circuit is for continuous use commercial). I'd plan for more than that. This is a tremendous amount of lighting!

[pressone]

Hi Suemarkp,

Can you tell me how you came up with 73 branch circuits at 16A each by using the NEC guidelines for saftey?

Thank You So Much! George

[mdshunk]

140 KVA is 140,000 watts

volts x amps = watts
watts / volts = amps

140,000 watts / 120 volts = 1,166 amps

code permits continuous loading of a 20 amp circuit to 80%
20 amps x .80 = 16 amp

1,166 amps total load / 16 amps permitted per circuit = 73 circuits

Is this for fluorescent aisle lighting or fluorescent high bays in a grocery store or a warehouse type situation? That's enough lighting to do 60,000 - 80,000 square feet. This is the sort of stuff that's generally done under an engineer's supervision.