Basic knowledge of high and low voltage switchgear

1. Contactor

The contactor consists of two parts: the electromagnetic mechanism and the contact system. The most common coil voltages of the contactor are AC220V, AC380V and DC220V.

The electromagnetic mechanism of the contactor is composed of a coil, a moving iron core (armature) and a static iron core; the contactor contact system consists of a main contact and an auxiliary contact. The main contact is used to turn on and off the main circuit, and the auxiliary contact is used to control in the circuit.

Contactor text symbol is: KM

2. Intermediate relay

The principle of the intermediate relay is a relay that turns an input signal into multiple output signals or amplifies the signal (that is, increases the capacity of the relay contacts). Its essence is a voltage relay, but it has many contacts (up to 8 pairs), the contact capacity can reach 5-10A, and the action is sensitive.

When the number of contact pairs of other electrical appliances is not enough, intermediate relays can be used to expand their contact pairs, and there are also intermediate relays to achieve the expansion of electric shock capacity.

Intermediate relay text symbol: KA

3. Transfer switch

The universal transfer switch consists of an operating mechanism, a panel, a handle and several contact bases.

Universal transfer switch text symbol: SA

The on-off state of each contact when the handle is turned to different gears is indicated by black dots, with black dots indicating that the contacts are closed, and no black dots indicating that the contacts are open.

4. Button

In practical applications, the button is usually selected according to the number of contacts required, the occasion of use and the color. The commonly used LA18, LA19, LA20 series buttons are suitable for AC500V, DC440V, rated current 5A, and the control power is in the control loop of AC300W and DC70W.

Button text symbol: SB

Button color requirements:

(1) The "stop" button and "emergency stop" button must be red. The device must be stopped or powered off when the red button is pressed.

(2) The color of the "Start" button is green.

(3) The buttons for the alternate action of "start" and "stop" must be black, white or gray, and red and green buttons shall not be used.

(4) The "jog" button must be black.

(5) "Reset" (if there is a reset button of the protection relay) must be blue, and when the reset button has a stop function at the same time, it must be red.

5. Indicator light

The function of the indicator light:

(1) Indicates the running or stopping state of the equipment.

(2) Monitor whether the power supply of the control appliance is normal.

(3) Use the red light to monitor whether the tripping circuit is normal, and use the green light to monitor whether the closing circuit is normal.

6. Thermal relay

Thermal relays are relays that operate inversely in time using the principle of thermal effect generated by current passing through components.

Thermal relay text symbol: FR