Calculating Phase Converters
How to Calculate Phase Converter Conductors and OCPD
Phase Converters
Per 455.6, the ampacity of the conductors for phase converters is determined by the type of load that is connected to it. The load can be variable or fixed.
A variable load is a load where the current fluctuates. When the loads are variable, the conductor ampacity shall not be less than 125% of the phase converter nameplate 1-phase input full-load amps.
A fixed load is a load where the current does not fluctuate. For fixed loads, if the conductor ampacity is less than 125% of the phase converter nameplate 1-Phase input full-load amps, the conductors shall have an ampacity of not less than 250% of the sum of the full-load; 3-Phase current rating of the motors and other loads served where the input and output voltages of the phase converter are identical. Where the input and output voltages of the phase converter are different, the current (as determined by this section) shall be multiplied by the ratio of output to input voltage.
The procedure for determining overcurrent protection for phase converters is found in 455.7. The OCPD shall not have a rating of less than 125% of the phase convertor’s 1-Phase input rating for variable and for fixed loads. If the required OCPD is not a standard rating, use the next higher-rated OCPD per 240.6.
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