Cable selection
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My pump is three-phase and 5.5 kilowatts in capacity; it starts directly. For some reason, a C20 circuit breaker and a contactor with a capacity of up to 5.5 kilowatts (BC7-30-10) have been installed. The cables used are three-core wires with a cross-sectional area of 2.5 square millimeters. It’s not easy to make any changes now. Should there be no major problems with the current setup?
1. For contactors, there is no need to consider the starting current; it is sufficient as long as the rated current meets the requirements. Theoretically, for a 5.5 KW system, an AC contactor with a current rating of 12A or higher will suffice, unless the operating conditions require very frequent start-ups and stoppages； 2. The circuit breaker needs to be able to handle the starting current; it is recommended to replace the C20 circuit breaker with a D20 or D16 one. Of course, you can also check whether the actual starting current will cause the circuit breaker to trip – if it doesn’t trip, then using it is fine ； 3. It’s fine to use 2.5 square millimeter wire for 5.5KW motors.
1. The rated current of the motor is approximately 10A. A PVC cable with a cross-sectional area of 2.5 mm2 can carry a current of 15A when installed in air; so there should be no problem. 2. If the distance between the circuits is long, it is advisable to increase the voltage rating by one level, which facilitates the starting of the motor ； Additionally, if the motor starts frequently, the rating should also be increased by one level. 3. The long-term tripping current of the circuit breaker should not exceed the current-carrying capacity of the cable.
Since it is urgently needed and no suitable component can be found in a short time, the main concern now is whether a tripping will occur and affect normal production; if not, then there’s no need to worry