Estimating available capacity based on peak demand

[katwalatapan]

Hello,

I wanted to inquire if it is possible to estimate available electrical capacity in an electrical distribution system based on only peak demand information available. For e.g. if an 800A, 347/600V, 3-phase electrical service has a peak demand of 175kW, would it be safe to assume the following calculation to estimate available electrical capacity at unity power factor:

800A x 0.8 = 640A (max. loading)
175kW = 600V x A x 1.732 i.e. A = 168A
Available capacity would be 640A - 168A = 472A.

Would the estimation of available capacity change if there are 600V - 208V step-down transformers downstream of the electrical distribution system?

Thank you.

 

[Paul Sweet]

I don't know about Canada, but the National Electrical Code 220.87 allows you to use the maximum demand for a one year period as the existing load. New loads would be calculated in accordance with NEC 220.40.

 

[katwalatapan]

Thank you. I believe there are demand factors as well which could be applied for existing load and new loads to be calculated based on applicable code section.

 

[Paul Sweet]

The demand factors in the NEC only apply to new loads. I have found that actual demand is often less than half the calculated load, so you can look at the actual demand as a real-life demand factor.