It can be used in relay protection and automatic control system to increase the number and capacity of contacts. It is used to transmit intermediate signals in the control circuit. The contact capacity of the intermediate relay is generally small, in other words, there is no main contact, but all auxiliary contacts, which is characterized by more contacts. Therefore, the intermediate relay is generally used in the control circuit.

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。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 need to be used in this circuit, which is not enough. An intermediate relay with multiple normally open contacts can be added. 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 will close, and the intermediate relay will also close. 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.

继电器之所以冠上了“中间”两个字，可以理解成它并不是用来实现控制的，而是起到一个中间环节的转接作用，“继”就是继接状态的意思了。所以中间继电器并没有所谓的主触点和辅助触点的说法，它的目标是让小电流变成稍微大一点的电流，甚还继续保留原来的小电流，而只利用了触点的隔离功能。

The reason why the relay is crowned with the word "middle" can be understood as that it is not used to achieve control, but to play a role in the transfer of an intermediate link. "Following" is the meaning of the following state. Therefore, there is no so-called main contact and auxiliary contact in the intermediate relay. Its goal is to change the small current into a slightly larger current, and even keep the original small current, and only use the isolation function of the contact.