Terminal Blocks

Terminal blocks are modular, insulated blocks that secure two or more wires together. Terminal blocks consist of an insulating body and a clamping device. Their flexibility allows wiring to be centralized and makes it easier to maintain complex control circuits. Terminal blocks can be single feed through, dual level, dual level bridged, three level, three level bridged, ground circuit terminals, disconnect or switch blocks, fuse holder or fuse blocks, thermocouple blocks, I/O blocks, sensor specific blocks, or electronic circuit blocks.

A single feed through terminal block is a type of basic terminal block used for wire-to-wire connections where the wire feeds through one side and out the other.  Single feed through terminal blocks have one input and one output contact.  Dual level blocks are also called double level and two tier, these terminal blocks have two levels of contacts. They are used to save space and simplify wiring.  Dual level bridged are also called double level and two tier, these terminal blocks have two levels of contacts. They are used to save space and simplify wiring. Bridged terminal blocks use a "bridge" to connect one level to another for increased circuit flexibility. 

Three level blocks are also called three tier, these terminal blocks have three levels of contacts. They are used to save space and simplify wiring.  Three level bridged terminal blocks are also called three tier, these terminal blocks have three levels of contacts. They are used to save space and simplify wiring. Bridged terminal blocks use a "bridge" to connect one level to another for increased circuit flexibility.  Ground circuit terminals are interchangeable with standard block. These units can be inserted as needed. Permits grounding of components that runs to a specific piece of equipment.  Disconnect or switch blocks allow a circuit to be easily disconnected without removing any wires. A knife switch uses a lever type of control handle to disconnect the circuit. A sliding link disconnect uses a link that can be slid to the side to disconnect the circuit. A plug disconnect has a removable plug to disconnect the circuit.  When a short circuit occurs, only the portion of the circuit connected to a fuse holder or fuse block is affected. This can also be a disconnect block if dummy fuses are inserted instead of standard fuses. A light gives visual indication of fuse condition. Also called circuit protection blocks. 

Thermocouple blocks are used for connecting to thermocouples. Provides consistent metal type connections for thermocouple sensors to measure temperature.  I/O blocks provide communication between a controller, usually a PLC or IPC, and some type of sensor level devices.  Sensor specific blocks handle three-wire or four-wire proximity sensors, three- or four-wire photoelectric sensors, or any other type of three- or four-wire device. Also enables high-density terminations.  Electronic circuit terminal blocks provides electrical circuit functionality such as rectification, voltage indication, etc.

The numbers of input and output terminals are important specifications to consider when searching for terminal blocks.  The maximum working voltage and maximum current rating is important electrical specifications to consider. In North America, wire area is measured by the American Wire Gauge (AWG) to indicate conductor size. The AWG is used to measure certain conductors including copper. The higher the AWG number the thinner the wire. This is because AWG stems from a measurement that represented the number of times the copper wire was run through a wire machine, which reduced the diameter of the wire. Thus 24-gauge wire went through the machine 6 more times than 18-gauge wire. Terminal blocks can accept conductor sizes larger than 0 AWG. AWG sizes also referred to as 00, 000, and 0000.  Sizes larger than 4/0 are called out in CM (Circular Mils) or MCM (Thousand Circular Mils).  Outside North America, countries measure conductor size by the size of the area of the wire, measured in mm².

Termination types for terminal blocks can include screw clamps, spring clamps, insulation displacement (IDC), and tab connections.  Common mounting types include universal mounting foot (rail), 15 mm DIN rail, 32 mm DIN rail, 35 mm DIN rail, panel mount, and PCB.  Features common to terminal blocks include pluggable, stackable, indicator lights, diodes, and 45-degree entry.  Manufacturer approvals can be CE conformity marks, CSA mark (US, C and US, NRTL/C), UL listing mark, UL recognized component mark (US and Canadian) and VDE component mark.

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Part Numbers for Terminal Blocks