I have a customer that currently is in a building with a 1000 Amp CT cabinet that is fed from a TAP box with (4) 500MCM type THHN-2, through a 4" conduit. His new equipment has a total calculated load of 606 Amp, 208V 3 Phase. Article 220 states that I can use the highest KW usage from his utility bills over the last 12 months X 125% plus the new load. Can I derate the new load or do I have use the total. If I can derate, by what factor? NEC is geared more towards residential dwelling units or farm equipment. I don't have a clear referance for industrial equipment.
Derating Industrial equipment
- Thread starter DTH
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- Lockport, IL
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- Semi-Retired Electrical Engineer
There really aren't many demand factors that apply to non-dwelling units. Whatever method you used to calculate the new load, whether or not that method included any derating factors, that is the value you must add to the existing load. The utility's report of peak demand, times 125%, plus the new caculated load, must be within the capacity of the existing equipment, or else you have a problem on your hands.
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