The difference between relay and contactor

- Jul 19, 2019-

Many friends of budding electricians are familiar with contactors, understand its use and performance, but when it comes to intermediate relays, they are a little squishy, do not know what intermediate relays are used for, and some intermediate relays and contactors are very close to each other.

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


Relay definition: Relay is an automatic appliance, it is suitable for long-distance switching and division of cross-cutting, DC small capacity control circuit, and in the electric drive system for control, protection and signal conversion. The input of the control relay is usually current, voltage, etc., or temperature, pressure, speed, etc., and the output is the change of the electrical signal or the parameters of the output circuit when the contact action is made. The characteristic of a relay is that the output changes step-by-step when the input volume changes to a certain program.


1, with a single letter, with K

2, with double letters, there are:

KA---- instantaneous, with or without relays, AC relays

KL---- closed contact relay, dual steady-state relay

KM ---- Contactors

KP---- Polarization Relay

KR---- reed relay, reverse flow relay KT---- delay, with or without relays


The definition of contactors: Contactors are divided into AC contactors (voltage AC) and DC contactors (voltage DC), which are used in power, power distribution and power use. Contactors in a broad sense refer to industrial electrical appliances that use coil scurrent scurrent to generate a magnetic field and close the contact to control the load.


1, contactor graphic symbol is shown below, the text symbol is KM.


(a) Coil (b) main contact (c) auxiliary contact

2, contactor wiring method





The difference between a relay and a contactor

1, the effect is not the same

The primary function of the relay is to detect, transmit, convert or dispose of the signal, it is generally smaller circuit current, generally used in the control circuit, control weak signal. The primary function of the contactor is to turn on or disconnect the main circuit. The main circuit is whether a circuit is working or not is marked by whether the circuit is turned on. The main circuit concept corresponds to the control circuit. The main circuit generally passes a larger current than the control circuit.

High-capacity contactors generally have an arc-out cover. Relay's contact capacity generally does not exceed 5A, small relay contact capacity generally only 1A or 2A, and contactor contact capacity is the smallest also has 9A; The contact of the relay is generally regardless of the main auxiliary, the contact of the relay is sometimes set in pairs, that is, the normal open contact and the normalclosed contact together, and the contactor is not set, the relay about the specific needs, will be combined with other equipment planning time relay, counter, pressure relay, etc., has additional function, and the contactor generally does not.

2, the contact open and closed is not the same

In addition, the contactor is used to turn on or disconnect the high power load, used in the (power) main circuit, the main contact can be with a chain contact to indicate the main contact open and closed condition.

Relays are generally used in electrical control circuits to expand the contact capacity of small or small relays to drive larger loads. If the contacts of the relay can be used to switch on or disconnect the contactor coil. General relays have more open and closed contacts, of course, relays through the appropriate docking can also complete some extra function, such as logic operations.

3, arc ingress device one has one no

 in fact, look at contactors and relays, one of the most important difference is that the contactors have an arcing device, and relays do not.