Electrical Relays

Electrical Relays



Relays are electrically operated switches that open and close under the control of another electrical circuit. The current that flows through the coil of the relay leads to creation of a magnetic field that attracts a lever and changes the switch contacts. Relay switches have two switch positions as the coil current can be on or off.

A relay can also be considered as an electrical amplifier because it is able to control an output circuit of higher power than the input circuit.

Types of Electrical Relay
There are different types of relay available in the market depending on the end use. These are:

* Latching Relay
* Reed Relay
* Polarized Relay
* Mercury-Wetted Relay
* Machine tool Relay
* Relay Circuit
* Contactor Relay
* Solid-state contactor Relay
* Solid state Relay
* Overload protector Relay

Pole and Throw Configurations
Relay is a type of switch and thus can have the following configurations:

* SPST - Single Pole Single Throw
* SPDT - Single Pole Double Throw
* DPST - Double Pole Single Throw
* DPDT - Double Pole Double Throw
* QPDT - Quadruple Pole Double Throw

Specifications to be Considered
There are certain important specifications that must be considered while selecting an appropriate relay for a particular application. These are: Selection of an appropriate relay for a particular application requires evaluation of many different factors:

* Number and type of contacts: These can be normally open, normally closed, or changeover (double-throw).

* Rating of contacts: While small relays switch a few amperes, there are large contactors that are rated for up to 3000 amperes.

* Voltage rating of contacts: This can vary depending on the type of relay. While control relays are rated 300 VAC or 600 VAC, automotive types to 50 VDC, special high-voltage relays to about 15,000 V.

* Package/enclosure: The packing or enclosures of relay can be open, touch-safe, double-voltage for isolation between circuits, outdoor, oil-splash resistant and explosion proof.

* Mounting: This can be plug board, rail mount, panel mount, through-panel mount, enclosure for mounting on walls or equipment.

* Regulatory approvals: Relays approved from agencies assure high quality to customers.

Electrical Relays Applications
Relays are used in numerous applications including:

* Modem
* Automobiles
* Aerospace
* Telecommunications