Strictly speaking, relays are only used for medium voltage current. Because of the mechanism of the relay, the two electric shocks of the relay will not be too far apart, that is to say, the working voltage cannot be too high (0~380v), and the contact of the relay also limits its working current (0~ 10a). If the voltage is high, the relay is not suitable for large current, and mechanical switch is generally used.

However, for ordinary electronic switches (such as triodes and field effect transistors), the working voltage (0~380) of relays is still relatively high, and the working current (0~ 10) is not relatively large. Another advantage is that the control part and the controlled part are electrically isolated, which cannot be realized by many electronic switches.

Then combining the above relay with ordinary mechanical switches and electronic switches has the following advantages.

1; It can realize automatic control, and this mechanical switch is not easy to do.

2; The control part and the controlled part are isolated, so the electronic switch is not easy to do.

3; Higher working voltage and current (compared with electronic switch)

So how to choose in the process of use depends on the actual situation.

One more thing: with the progress of science and technology, the above is not easy, and with the development of production technology, the contrast may become less obvious.