Terminal Block: Terminal blocks are modular, insulated blocks that secure two or more wires together. Terminal blocks are used tosecure and/or terminate wires and, in their simplest form, consist of several individual terminals arranged in a long strip. Terminals are useful for connecting wiring to a ground or, in the case of electrical power,for connecting electrical switches and outlets to the mains. Terminal bodies typically consist of a copper alloy with the same expansion coefficient as the wire intended for use. This not only prevents loosening because of differing expansion rates but also reduces corrosion caused by electrolytic action between two different metals Structure Types Single Feed Through Single feed products represent the basic type of terminal block, and are used for wire-to-wire connection. Single feed terminal blocks have one input and one output contact: two distinct wires are fed into either side of the terminal block and are connected within its housing. Dual Level Dual level terminal blocks have two levels of contacts; this arrangement saves space and simplifies wiring. Multi-level products may use abridgeto connect one contact level to another for increased circuit flexibility. Three Level Three level terminal blocks are essentially dual level products with an extra stacked level of contacts. Like dual level terminal blocks, they can also be bridged. Device Types Terminal blocks may also be grouped by application or type of device they connect. Ground circuit terminalsare used to ground components or systems. They are typically interchangeable with standard terminal blocks and can be inserted into a block as needed. -Fuse holdersconnect several fuses associated with numerous devices. When a short circuit occurs, only the wiring sections connected to the fuse holder are affected. -Thermocouple blocksare used for connecting thermocouples and providing consistent metal connections in order to measure temperature. -I/O blocksprovide communication between a device and a controller. -Sensor/actuator blockshandle three- or four-wire devices, such as proximity sensors and photoelectric sensors. -Power distribution blocksare used to terminate power cables. -Disconnect blocksallow a circuit to be easily disconnected usinga knife switch and without removing wires. They are also known as switch blocks.