Answer:
<em>Use a 150-amp breaker and No. 1/0 copper conductors</em>
Explanation:
An installation consists of a 10-kVA, single-phase transformer with a 440-volt primary and a 110-volt, 2-wire secondary using insulation type THWN copper conductors. No secondary OCPD is installed. The secondary loads are considered to be noncontinuous loads. Calculate the minimum size secondary conductors required to handle the secondary full load current for this transformer
Calculate primary full-load amps:
10 kVA ÷ (440 volts ÷ 1000) = 22.72 amps
Calculate required feeder breaker size and conductor ampacity:
22.72 amps x 1.5 = 34.09 amps
Use an 80-amp breaker and No. 3 AWG copper conductors 1
Calculate secondary full-load amps:
10 kVA ÷ (110 volts ÷ 1000) = 90.9 amps
Calculate required secondary breaker size and conductor ampacity:
90.9 amps x 1.25 = 113.6 amps
Use a 150-amp breaker and No. 1/0 THWN copper conductors.
