1. Electromagnetic relay Electromagnetic relays are divided into overcurrent and undercurrent. The overcurrent relay is determined according to the current. When the rated current exceeds the standard, it should be adjusted by 1.1 to 1.3 times. The undercurrent relay protects the DC motor, which is also determined by the current. Once the current exceeds the standard, the setting current will be less than the excitation current. 2. The choice of thermal relay The thermal relay is used on the motor, and it is selected according to the motor model, working location and load condition when purchasing. If the voltage is unstable or the environment is not good, a three-phase structure relay is suitable. On the contrary, the less commonly used motor can be selected according to the rated current, but if the electric motor needs to work repeatedly, it should be selected according to the starting time and current of the motor. 3. Selection of time relay There are many types of time relays, such as damping relays. The coil current and voltage are the same as the circuit. Delay relays are delayed or de-energized according to the circuit. Contact type relays are selected according to the closed form and number of contacts. .