Intermediate relay is used in relay protection and automatic control system to increase the number and capacity of contacts and transmit intermediate signal in control circuit to achieve the purpose of control signal distribution and power amplification.

中間繼電器有交、直流兩種。中間繼電器的特點是觸點數目較多，一般在3~4對以上，觸點形式常采用橋形觸點（與接觸器輔助觸點相同）。

There are AC and DC intermediate relays. The characteristic of the intermediate relay is that the number of contacts is more than 3 ~ 4 pairs, and the contact form often adopts bridge contact (the same as the auxiliary contact of the contactor).

比如，一個電路當中，某臺接觸器只有兩組常開輔助觸點，但這個電路中卻需要用到這個接觸器三組常開輔助觸點，不夠用，怎么辦？就可以加入一臺帶有多個常開觸點的中間繼電器，利用接觸器的其中一組常開觸點控制中間繼電器線圈，當接觸器得電吸合，常開觸點閉合，中間繼電器也就跟著吸合，然后再利用中間繼電器的常開觸點充當接觸器輔助觸點。這就是增加了觸點數量。

For example, in a circuit, a contactor has only two sets of normally open auxiliary contacts, but three sets of normally open auxiliary contacts of the contactor need to be used in this circuit, which is not enough. What should we do? An intermediate relay with multiple normally open contacts can be added, and one group of normally open contacts of the contactor can be used to control the coil of the intermediate relay. When the contactor is powered on and closed, the normally open contacts close, and the intermediate relay will also close, and then the normally open contacts of the intermediate relay can be used as auxiliary contacts of the contactor. This is increasing the number of contacts.

再比如，晶體管型PLC輸出電流一般很小，0.3安左右，如果用這個電流去驅動一臺比較大的接觸器，容量就不夠了，那就可以加入一臺小型中間繼電器，用這0.3安電流驅動中間繼電器線圈，中間繼電器觸點容量一般有5安，可以用中間繼電器觸點再去驅動接觸器線圈。這樣轉換一下，就是增加容量。

For another example, the output current of transistor type PLC is generally very small, about 0.3 A. if this current is used to drive a relatively large contactor, the capacity is not enough, then a small intermediate relay can be added, and the 0.3 a current is used to drive the intermediate relay coil. The contact capacity of intermediate relay is generally 5 A, and the intermediate relay contact can be used to drive the contactor coil. This conversion is to increase the capacity.

中間繼電器還可以實現電壓的轉換。比如，PLC輸出直流24V，但需要驅動的負載是交流220V的電壓，比如接觸器，怎么辦？加入DC24V線圈電壓的中間繼電器，PLC輸出控制中間繼電器，中間繼電器觸點接220V交流電控制負載。

The intermediate relay can also realize the voltage conversion. For example, PLC output DC 24 V, but need to drive the load is AC 220 V voltage, such as contactor, how to do? Add the intermediate relay with DC24 V coil voltage, PLC output control the intermediate relay, and the contact of the intermediate relay is connected with 220 V AC control load.