In electric motors, relays are the essential components of electric charge manipulation, as they allow the combination of logic in the control, as well as the separation of power and command circuits.
The most common are made up of a housing with five terminals. The terminals (1,2) correspond to the excitation coil. The terminal (3) is the input, and the terminals (4,5) are equivalent to the normally closed (NF) and normally open (NO) contacts, respectively.
A fundamental peculiarity of the relays is that the voltage at the terminals (1,2) can be 5 Vdc, 12 Vdc or 24 Vdc, while simultaneously the terminals (3,4,5) can work with 110 Vac or 220 Vac.
That is, there is no physical contact between the drive terminals and the working terminals. This definition allowed the advent of two circuits in an electrical panel:
Control circuit: this is the interface with the operator of the machine or instrument and, in the meantime, operates with low currents (up to 10 A) and / or low voltages. NJ 406 MA/C3P
Power Circuit: this is the circuit where the loads to be connected are located, such as motors, heating resistors, among others. In this can circulate electric currents of the order of 10 A or more, and reach tensions of up to 760 V.