General Lighting question for Store

[squaredan]

I have a queston on a practice test that i got wrong maybe someone can help me.. this question reads
" A store building measures 60ft by 80 ft and is supplied by a 240/120V 3 phase 4 wire delta system.. which of the following is the minimum allowed number of 2 wire, 20 ampere branch circiuts required to supply the genral lighting in this building?"

A) 6
B) 7
C) 8
D) 9



I got 60x80=4800sq ft times 3 VA (table220.12) = 14400VA divide by 120v = 120A divide by 20A = 6 circuits but is wrong.. the answer key says C) 8 but the key could be wrong

i thought maybe cuz of 3 phase that i would divde by 120* 1.732 but you get a lower number ofcourse...

 

[97catintenn]

If you have a 20amp circuit what is the min size circuit breaker required?

If you assumed that the 20amp circuit was good for 16amps, then you would need 7.5 20 amp circuits...or in reality 8.

 

[Sierrasparky]

here it depends on type of use.
Just not enough information

 

[raider1]

My guess is that the question assumes the lighting is a continuous load so the circuit could only be loaded to 16 amps not 20.

Chris

 

[infinity]

My guess is that the question assumes the lighting is a continuous load so the circuit could only be loaded to 16 amps not 20.

Chris

I agree with Chris and 97catintenn, 6 circuits if non-continuous or 8 if continuous.

As Sierrasparky said the question is lacking information or is making an assumption.

 

[squaredan]

If you have a 20amp circuit what is the min size circuit breaker required?

If you assumed that the 20amp circuit was good for 16amps, then you would need 7.5 20 amp circuits...or in reality 8.

that could be it, lights would be continous load...

 

[antenna2001]

that could be it, lights would be continous load...

That is what happens. In a store, lighting, per 210.19 or 215.2 must be a continuous load
120A * 125% = 150A
150/20 = 8 circuits