What size wire is used for a 7.5 hp 240 volt single phase motor?

Answer 1

The rule of thumb for a single phase 240 volt electric motor is 7 amps for each horsepower. As this is a 7.5 h.p. motor you should use a 60 amp breaker wired with AWG # 6 copper to be safe.

Answer 2

For calculation purposes the electric code book states that a 7.5 HP motor at 230 volts draws 40 amps. A #8 copper conductor with an insulation factor of 90 degrees C is rated at 40 amps. This wire will have to be up sized because the code states that conductor's ampacity has to be 125 percent of the motors full load amperage. The next larger size wire will be a #6 copper conductor.

Answer 3

Wire size is based on the amperage that the motor draws. Motors amperages vary within the same HP range. Without that an accurate answer can not be given.

For calculation purposes the electrical code book uses 17 amps as a usable amperage. The book amperages are usually high as compared to the actual motor's full load amperage. A motor feeder has to be rated at 125% of the motors full load amperage. 17 x 125% = 21 amps.

For short distances a #12 conductor will be suffice.

A #12 copper conductor with an insulation rating of 90 degrees C is rated at 20 amps.

A #10 copper conductor with an insulation rating of 90 degrees C is rated at 30 amps.

A breaker for a motor feeder has to be rated at 250% of the motors full load amperage to over come the starting current which is usually around 300% of the motor's full load amperage. 17 x 250% = 42.5 amps. In this case a two pole 40 amp breaker will be fine.

If you can find out the motors actual amperage just substitute the actual amperage for the 17 used for calculations supplied by the electrical code book.