A relay is an electrically operated switch. Relays use an electromagnet to operate a switching mechanism mechanically. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays were used extensively in telephone exchanges and early computers to perform logical operations .
An electromagnet is a magnet made with electricity. Normal magnets are called permanent magnets. An electromagnet has the same properties as an ordinary magnet. It has a north and south pole and it attracts steel and iron. It is different from a permanent magnet because it can be turned on and off. When electricity flows in a circle of wire, it makes a magnet. One side of the wire is a north pole, the other side is a south pole. If there are many loops of wire, the magnet is stronger.
Within the relay there will be switch contacts, each separate switch is referred to as a “Pole”. The poles within the relay will have a “Current rating” which is shown in “Amps”. The higher the current rating the more current it is able to switch.
MT Relay The MT Relay is another widely used general purpose Relay, these are also know as octal relays as their pins are In a circular configuration. The MT is available in 2 and 3 pole types 10amps.