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。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 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.

繼電器之所以冠上了“中間”兩個字，可以理解成它并不是用來實現控制的，而是起到一個中間環節的轉接作用，“繼”就是繼接狀態的意思了。所以中間繼電器并沒有所謂的主觸點和輔助觸點的說法，它的目標是讓小電流變成稍微大一點的電流，甚至還繼續保留原來的小電流，而只利用了觸點的隔離功能。

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.