How to size a terminal block: current rating, cross-section, creepage and clearance, and DIN-rail vs PCB types for panels and control gear.
A terminal block is where a panel is either reliable for twenty years or where it slowly cooks itself. The rating printed on the block is only half the story — the cross-section, the spacing between poles and the way it mounts decide whether it stays cool under load. This guide covers the choices that change the part number.
The current a block carries safely is set by its conductor cross-section, not its plastic body. A 2.5 mm² block is good for roughly 24 A, a 4 mm² for about 32 A, and a 10 mm² for around 57 A — always derate for ambient temperature above 40 °C and for blocks packed tightly together in a row. Sizing the block below the cable it terminates creates a heater; sizing it far above wastes rail space and money.
Creepage is the shortest path along the surface between two conductive parts; clearance is the air gap. Both must suit the system voltage and the pollution degree of the enclosure. A control panel in a clean air-conditioned room tolerates smaller spacing than a block in a dusty, humid pump house, where you need wider pitch or a higher-grade material. For mains separation, confirm the block is rated for reinforced or double insulation at the working voltage.
| Type | Mount | Use |
|---|---|---|
| Feed-through (DIN) | 35 mm rail | General wire-to-wire termination in panels |
| PCB terminal | Soldered to board | Internal wiring of controllers, power supplies |
| Disconnect / fuse terminal | DIN rail | Isolatable points for testing and maintenance |
| Ground / PE terminal | DIN rail | Earthing bar, often green-yellow marked |
Match the block family to how the wire enters: a pre-insulated bootlace ferrule needs a tunnel clamp that grips the sleeve, not bare strand. Using an open clamp on a ferruled wire leaves strands proud and raises contact resistance.
ELEHPD supplies DIN-rail and PCB terminal blocks, copper and pre-insulated terminals, and busbar in the cross-sections panel builders use every day.
Send the ratings, dimensions and quantities you are working to and we will confirm the closest match from the ELEHPD catalogue, the compliance documents available for it and the lead time. OEM branding, private model numbering and buyer-specific cartons are available on qualified volumes.