Terminal Block
Connector
A modular connector for joining individual wires without soldering, commonly used for secure wire-to-wire or wire-to-board connections in control panels and industrial applications.
What it looks like
Terminal Block
A typical connector — exact shape, colour and markings vary between manufacturers.
Types & variants
Key specs
Current rating
Ampere (A)Max current the terminal can handle continuously without overheating.
Voltage rating
Volt (V)Max voltage the terminal can safely isolate between connections.
Wire gauge range
AWGMinimum and maximum wire sizes that fit properly in the terminal.
Number of positions
countNumber of independent connection points in the block.
Pitch
mmCenter-to-center distance between adjacent terminals.
Laws that govern it
- Ohm's lawV = I × R
A properly torqued screw gives microhms; a loose one gives ohms, and the volt drop across it is the diagnostic.
- Joule's law of heatingH = I² × R × t
That loose terminal dissipates I²R exactly where there is no heatsink — the single most common cause of burnt distribution boards.
Each law is stated in full — with its diagram, variables and worked meaning — on the electrical laws page.
Markings
Usually labeled with current rating (A), wire gauge range (AWG), manufacturer logo, and part number. Some may have terminal numbers.
Standard values
Common pitches: 3.5mm, 5.0mm, 7.5mm, 10.16mm (0.4 inch). Current ratings: 10A, 15A, 20A, 30A, 60A. Wire gauge: typically 12-22 AWG for standard blocks.
How to choose
1) Determine required current and voltage ratings. 2) Check wire gauge compatibility with your wires. 3) Choose pitch based on space and density needs. 4) Select mounting type (panel, DIN rail, PCB). 5) Consider screw type (slotted, Phillips, captive) for tool-less access if needed.
Pinout & package
Multiple terminals in a row with isolation between them. Each terminal has a screw/clamp for wire and a connection point (screw, tab, or pin) for mating. Available in various widths and mounting styles (DIN rail, panel mount, PCB mount).
Example circuits
- Power distribution in control cabinets
- Connecting sensors to PLCs
- Building custom test leads
- Creating junction points for wiring harnesses
- Ground bus bar connections
Common failures
Loose connections from under-tightened screws causing high resistance and heat; corrosion from environmental exposure; cracked plastic housings from physical stress; terminals breaking when wires are forcibly removed.
How to test
1) Visually inspect for cracks, discoloration, or loose screws. 2) With power off, check continuity between wire and mating connection point. 3) Check for continuity between adjacent terminals (should be open). 4) With power on, measure voltage drop across terminal connection (should be near zero).
Substitutes
Wire nuts, crimp connectors, solder lugs, or custom PCB layouts for high-density connections. For temporary use, alligator clips or jumper wires.