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.

中间继电器有交、直流两种。中间继电器的特点是触点数目较多，一般在3~4对以上，触点形式常采用桥形触点（与接触器辅助触点相同）。

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，一个电路当中，某台接触器只有两组常开辅助触点，但这个电路中却需要用到这个接触器三组常开辅助触点，不够用，怎么办？就可以加入一台带有多个常开触点的中间继电器，利用接触器的其中一组常开触点控制中间继电器线圈，当接触器得电吸合，常开触点闭合，中间继电器也就跟着吸合，然后再利用中间继电器的常开触点充当接触器辅助触点。这就是增加了触点数量。

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，晶体管型PLC输出电流一般很小，0.3安左右，如果用这个电流去驱动一台比较大的接触器，容量就不够了，那就可以加入一台小型中间继电器，用这0.3安电流驱动中间继电器线圈，中间继电器触点容量一般有5安，可以用中间继电器触点再去驱动接触器线圈。这样转换一下，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.

中间继电器还可以实现电压的转换。比如，PLC输出直流24V，但需要驱动的负载是交流220V的电压，比如接触器，怎么办？加入DC24V线圈电压的中间继电器，PLC输出控制中间继电器，中间继电器触点接220V交流电控制负载。

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.