Relays and contactors are both electromagnetic switching appliances, but the former belongs to the switching electrical appliances working in the control loop, while the latter belongs to the switching electrical appliances working in the main circuit.

1. Relay

Ultrathin relay
Definition of relay: Relay is an automatic electrical appliance, which is suitable for long-distance switching and disconnection, DC small-capacity control circuits, and is used for control, protection and signal conversion in the electric drive system. The input amount of the control relay is usually the current and voltage and other electricity, or it can be the temperature, pressure, speed and other non-electricity, and the output amount is the electrical signal emitted when the contact is operated or the parameter change of the output circuit. The characteristic of the relay is that when the change of its input amount reaches a certain program, the output amount will undergo a step change.

1. When expressed in a single letter, use K
2. When expressed by double letters, there are:
KA—- instantaneous, with or without relay, AC relay
KL—- latching contact relays, bistable relays
KM—- contactor
KP—- polarization relay
KR—- reed relay, countercurrent relay
KT—- delay, with or without relay


Definition of contactor: Contactor is divided into AC contactor (voltage AC) and DC contactor (voltage DC), which is used in power, distribution and power consumption occasions. In a broad sense, contactors refer to electrical appliances that use the current flowing through the coil to generate a magnetic field and close the contacts to control the load.

1. The graphic symbol of the contactor is shown in the figure below, and the text symbol is KM.

The graphic symbol of the contactor is shown in the figure below, and the text symbol is KM

(a) Coil (b) Main contact (c) Auxiliary contact

2. The wiring method of the contactor




Third, the difference between relay and contactor
1. The role is different:
The primary function of the relay is signal detection, transmission, conversion or disposal, and the circuit current it is on and off is generally small, generally used in the control circuit to control weak signals.

The primary function of the contactor is to turn on or off the main circuit. Main circuit refers to whether a circuit is working or not is marked by whether the circuit is turned on or not. The main circuit concept corresponds to the control circuit. Generally, the current passed through the main circuit is greater than that of the control circuit.

Contactors with large capacity are generally equipped with arc extinguishing covers. The contact capacity of the relay generally does not exceed 5A, the contact capacity of the small relay is generally only 1A or 2A, and the contactor contact capacity is as small as 9A; The contactor contact generally has three pairs of main contacts (the main contacts are normally open contacts), and several pairs of auxiliary contacts.

The contacts of the relay are generally not divided into main and auxiliary; The contacts of the relay are sometimes arranged in pairs, that is, the normally open contact and the normally closed contact are combined together, while the contactor is not set in pairs; Relays for specific needs, will be combined with other equipment planned into time relays, counters, pressure relays, etc., have additional functions, while contactors generally do not.

2. The opening and closing of the contact is different:
In addition, contactors are used to turn on or off loads with large power, used in the (power) main circuit, the main contact can have interlocking contacts to indicate the opening and closing of the main contact. Relays are generally used in electrical control circuits to extend the contact capacity of miniature or small relays to drive larger loads.

For example, the contact of the relay can be used to connect or disconnect the coil of the contactor. Generally, relays have more opening and closing contacts, of course, relays can also complete some special functions through appropriate connections, such as logical operations.

3. The arc extinguishing device has one without:
In fact, looking at contactors and relays, one of the most important differences is that contactors have arc extinguishing devices, while relays do not.