7.5KW motor needs much, open, contactor, thermal relay

Answer:

7.5KW motor rated current of about 15A near the open capacity should be greater than the rated current of 1.4 times the rated current, take 25A is appropriate; contactor take 40A, thermal relay set current of 16A; 2.5 square copper cable.

D-type open 20A CJ20-25 AC contactor LR1-D16321 thermal relay Cable 1.5 square three-phase four-core

If the 7.5KW AC motor to work properly, the air switch should use 20A, if the frequent start, it should also enlarge some, added to 32A; contactor, 20A on it, if the feeling of small, the same can be enlarged to 25A, thermal relay using 25A or 32A, as for the cable Well, under normal circumstances, 2.5 square millimeters of enough, if the hope is better, 4 square millimeters absolutely no problem.

7,5 kilowatts three-phase asynchronous motor, rated current 7,5 * 2 = 15A, starting current is about more than twice that 15A * 2> 30A, according to the actual situation to avoid frequent malfunction, the air switch should be selected in the current More than twice, that is, 32A or 40A. Contactor optional 30A or more, such as frequent start, of course, the greater the life expectancy, 20A only life will be significantly reduced. The key is the thermal relay must be selected more than 15A rated range, generally adjustable to 16A-18A or so. There is no air switch does not advocate the election fuse, if elected 30A fast fuse. Cable according to the actual, the current density of 4A / mm2, need to select the actual 4 square millimeters full load current, consider most manufacturers are not enough amount of wire gauge, so should choose 6 square millimeters of copper is better.