Lighting Panel Main Breaker Rating

[eestudent]

Suppose you have a Lighting Panel with 3 phase, 4 wire, 415/240v 30kva,
with an unbalaced (lighting) load on each phase (L1N, L2N,L3N). Is it correct to get the largest unbalanced load then multiply it by 1.25 then divide the answer by 80%? What is the reason behind this approach? Could anyone give me a reference (Codes and the likes). Thank you very much.

 

[LarryFine]

1.25 and 80% are reciprocals. Multiplying by 1.25 and then dividing by 80% would be applying the same function twice. You only need to it once.

Now, multiplying by 1.25 and then multiplying by 80% would give you the original number again.

1.25 = 5/4
0.8 = 4/5
5/4 x 4/5 = 1
1.25 x 0.8 = 1

 

[bsh]

NEC 210.19(A). I usually assume that the load is continuous and size the circuit for 125% of the load.

 

[petersonra]

NEC 210.19(A). I usually assume that the load is continuous and size the circuit for 125% of the load.

Not an unreasonable approach. it also gives you some headroom in case the load increases by a small amount down the road.