1, should be installed in the control circuit of the motor isolation of electrical and short circuit protection, but the main loop-powered by electric motor and when one of the following conditions are met, not the other installation:
(1) the rated current of the main circuit short circuit protective device does not exceed 20A.
(2) control circuit wiring is simple, lines are shorter and have a reliable mechanical protection.
(3) when the control circuit power failure would have serious consequences.
2, power supply and wiring control circuit should be safe, reliable, and meets the requirements of mechanical conditions make it simple.
TN and TT system when a ground fault occurs in the control circuit, control circuit wiring to prevent motor accidents starting or parking is not allowed, if necessary, can be installed in the control loop isolation transformer.
High reliability requirements of complex control loop, DC power can be used. DC control circuits should be used without grounding system and the installation of insulation monitoring.