In electric motors, relays are the indispensable devices of maneuver of electric charges, since they allow the combination of logic in the control, as well as the separation of the circuits of power and command. The simplest types of relays consist of a housing with five terminals.
The first two terminals correspond to the excitation coil. The third terminal is the input terminal, and the fourth and fifth terminals correspond to the NC contacts, normally closed, and the NC, normally open, respectively.
An important feature of the relays to be considered is that the voltage at the first two terminals can be 5 Vdc, 12 Vdc or 24 Vdc, at the moment simultaneously, terminals three, four and five can operate with 110 Vac or 220 Vac . In this way, there is no physical contact between the drive terminals and the working terminals.
This process allows the existence of two circuits in an electrical panel. One is the control circuit, in which the interface with the operator of the machine or device is found, working with low currents and / or low voltages. And the power circuit: is where the loads to be driven, as well as motors and heating resistors, among others, are found.