sizing panel boards

[SiddMartin]

NOTE: I only want to know how to get the answer

I was taking Mike Holt's lovely online pre-test and got this question:

When selecting and sizing panelboards and conductors, we must balance the line loads in amperes. Balance a 120/240V, 3-phase panelboard in amperes for the following loads: one 18 kVA 3-phase heat strip, two 5 kVA single-phase 240V loads, and three 2 kVA 120 V loads.

a)the largest Line is 98A
b)the smallest Line is 81A
c)each Line equals to 90A
d)a and b

I only want to know how to get the answer

Thanks for your help

 

[mdshunk]

A = 18+5+2
B = 18+5+5
C = 18+5+2+2

Red is the 18 kw 3 phase load
Blue is the first 5 kw single phase 240 volt load
Green is the second 5 kw single phase 240 volt load
Purple is the three 2kw 120 volt loads

This panel schedule ought to get you started, now you just have to do some math.

 

[SiddMartin]

ok, here's what I got:

18kw = 43A
5kw = 20.8A
2kw = 16.6A

A = 43 + 20.8 + 16.6 = 80.4
B = 43 + 20.8 + 20.8 = 84.6
C = 43 + 20.8 + 16.6 + 16.6 = 97

so the answer would be (d)

Is this the correct way?

 

[hdpeng]

With the loads given, that's as balanced as you're going to get. Yes, D.