What Is a Terminal Block? Types: DIN Rail, Junction Box and Barrier Strips
What terminal blocks do; DIN rail, junction box, barrier strip, earth, fused and disconnect terminal blocks, a size-to-current table and selection rules.
A terminal block joins two or more conductors without solder or tape, in a removable and safe contact. By place of use there are three main groups: DIN rail terminal blocks in panels (IEC 60947-7-1), junction box connectors for installation joints, and barrier (screw) terminal strips for appliance connections.
> Related Category: Browse all types and sizes in Terminal Blocks, DIN Rail Terminal Blocks and Junction Box Terminal Blocks.
1. Terminal block types
| Type | Mounting | Use |
|---|---|---|
| DIN rail terminal block | 35 mm DIN rail | Panel input and output wiring, terminating field cables |
| Earth terminal block | DIN rail; foot contacts the rail | Protective conductors (green-yellow body) |
| Neutral terminal block | DIN rail, blue body | Collecting neutral conductors |
| Fused terminal block | DIN rail | Protecting control and sensor lines with a glass fuse |
| Measuring and disconnect terminal block | DIN rail | Testing and shorting current transformer and metering circuits |
| Junction box connector | Inside boxes and luminaires | Installation joints; 2–8 conductors |
| Barrier (screw) strip | Screwed to a surface or free | Luminaire, appliance and motor connections; 12-way strips cut to length |
| Porcelain terminal block | Free | High temperature: heaters, ovens, floodlights |
2. Connection technology: screw, spring, push-in
| Technology | Connection | Strength | Note |
|---|---|---|---|
| Screw | Tightened with a screwdriver | Wide size range, high current | Can loosen under vibration; needs correct torque |
| Spring | Spring opened with a screwdriver | Vibration-proof, maintenance-free | Lower maximum size |
| Push-in | Ferruled or solid conductor pushed straight in | Fastest wiring | Stranded wire needs a ferrule |
See Screw vs Spring vs Push-in Terminal Block Difference for a full comparison.
3. DIN rail terminal block size and current
A terminal block is named by its rated cross-section; typical rated currents per IEC 60947-7-1:
| Rated cross-section | Rated current |
|---|---|
| 2.5 mm² | 24 A |
| 4 mm² | 32 A |
| 6 mm² | 41 A |
| 10 mm² | 57 A |
| 16 mm² | 76 A |
| 35 mm² | 125 A |
- Close the open side of a group with an end plate and fix both ends with end stops.
- Link terminals at the same potential with a jumper instead of wire.
- Put a separator plate between voltage groups and number the terminals with labels.
- These parts are under terminal block accessories.
4. Choosing junction box connectors
- Lever connector: lift the lever, insert the conductor, close the lever. Accepts solid, stranded and fine-stranded conductors without ferrules; typical ratings are 0.2–4 mm², 32 A, 450 V. Reusable.
- Push-wire connector: solid conductors are pushed straight in; quick for concealed wiring, not suitable for stranded wire.
- Screw connector: conductors clamped into a common brass body; economical but needs periodic tightness checks.
Twisted joints wrapped in insulating tape loosen and heat up over time and are a leading cause of fires. Quick cable splice connectors replace them.
5. Selection and wiring rules
- Rated cross-section must match the conductor, and rated current must be equal to or above the circuit fuse.
- Stranded conductors go into screw terminals with a ferrule; for sizes see the DIN Rail Terminal Block, Ferrule and Cable Lug Guide.
- One conductor per clamping point; for two, use a double-entry terminal or a twin ferrule.
- Strip to the length printed on the terminal; too long leaves bare copper, too short traps insulation in the contact.
- Aluminium conductors need terminals marked as suitable for aluminium.
- Above 100 °C ambient use porcelain terminal blocks and heat-resistant cable.
Frequently asked questions
What does a terminal block do?
It joins cables to each other or to a device without solder, removably and safely, keeping panels tidy and making maintenance and fault finding easier.
What is the difference between a DIN rail terminal block and a junction box connector?
A DIN rail terminal block mounts on rail in a panel and terminates incoming and outgoing wires one by one. A junction box connector is not rail-mounted; it joins several conductors at one point inside a box or luminaire.
How many amps does a 2.5 mm² terminal block carry?
Per IEC 60947-7-1 a 2.5 mm² DIN rail terminal block is rated 24 A. The exact figure is on the maker's label.
Is a ferrule required on stranded wire?
Yes for screw and push-in terminals; it holds the strands together and secures contact. Lever connectors and most spring terminals accept stranded wire without one.
Why does a terminal block overheat or melt?
The usual cause is a loose connection: contact resistance rises and the point heats up. Other causes are an undersized terminal and more than one conductor in a clamping point.