Electrical devices can create an electromagnetic field at the instant of energizing your coil, so they are called electromagnetic keys. They are used to open or close contacts.

There are several types of electrical devices that command, regulate and protect electric motors and form the power elements of industrial electrical installations. Some are manual as the power switch and other automatic such as contactors and relays.

In the power contactor, the main contacts are identified with unit numbers from 1 to 6. These contacts withstand high currents, which depend on the power the motor will drive, and are always of the normally open type.              cluthes and brakes for boston gear

There are also the auxiliary contacts, which are used to drive electromagnets (coils), magnetic keys, signal lamps or audible alarms.

These contacts may be of the normally open or NF (normally closed) type and the contactors have the identification of their associated terminals and relays, informing their position and the function of each terminal. The coils are identified alphanumerically (A1 and A2) according to IEC 947-4.