Screw terminal blocks
A screw drives a clamp onto the wire or ferrule. Simple and universal; needs correct torque and periodic checks in vibrating equipment.
Wire terminations
Electrical Terminals and Terminal Connectors
An electrical terminal is the fitting on the end of a wire that connects it to a stud, screw, busbar or mating contact. The right terminal depends on the conductor size and metal, the current, the way the joint is made (crimp, screw, plug-in or spring clamp) and the environment. Metline supplies aluminium and bimetal copper-aluminium terminals and cable lugs, and the aluminium and copper-clad aluminium stock used to make terminals, to panel builders and equipment makers worldwide.
- Types
- Crimp, lug, plug-in, ferrule, block
- Wire range
- 0.5 mm² to 1000 mm²
- Metline range
- Al and bimetal Cu-Al
- Finishes
- Tin, nickel, silver
What electrical terminals do
Every wire has to end somewhere: on a breaker, a relay, a motor, a battery or another wire. A terminal turns the loose end of a stranded or solid conductor into a defined, repeatable connection that can be bolted, screwed, plugged or clamped. A good terminal keeps contact resistance low for the life of the equipment, holds the wire mechanically, and is quick to fit correctly.
Terminals fall into four broad families: crimp terminals for small and medium wires, cable lugs for high-current power cables, screw and plug-in terminals for equipment that is connected and disconnected, and wire-end ferrules and pins that prepare stranded wire for screw or spring clamps. Terminal blocks and power distribution blocks then gather these connections inside panels.
Main types of electrical terminals
| Terminal | How it connects | Typical use |
|---|---|---|
| Ring terminal | Closed ring over a stud or screw; cannot slip off if the screw loosens | Power and earth connections, vibration-prone equipment |
| Spade / fork terminal | Open fork slides under a loosened screw | Terminal strips where quick removal is needed |
| Blade / pin terminal | Flat or round pin inserted into a clamp | Terminal blocks and breakers with box clamps |
| Quick-disconnect (faston) terminal | Male tab and female receptacle push together, commonly 6.3 mm (0.250 in) | Appliances, HVAC, automotive and control wiring |
| Bullet terminal | Round male and female pieces push together | Automotive and low-voltage connections |
| Butt connector | Joins two wires end to end by crimping | Splicing and repairs |
| Cable lug | Heavy barrel crimped to cable, palm bolted | Power cables 10 mm² and above |
| Battery lug | Heavy-wall lug for battery posts and studs | Vehicles, UPS, energy storage |
| Wire-end ferrule | Sleeve crimped over stranded wire before clamping | Screw and spring-clamp terminals in panels |
| Twin ferrule | One sleeve for two wires into a single clamp | Looping and bridging in control panels |
Insulated crimp terminal colour code and sizing
Pre-insulated crimp terminals carry a coloured sleeve that shows the wire range. The colour system below is widely used for ring, fork, blade, butt and quick-disconnect terminals:
| Sleeve colour | Wire range (mm²) | Approx. AWG | Typical stud sizes |
|---|---|---|---|
| Red | 0.5 – 1.5 | 22 – 16 | M3 – M8 |
| Blue | 1.5 – 2.5 | 16 – 14 | M3 – M10 |
| Yellow | 4 – 6 | 12 – 10 | M4 – M12 |
Above 6 mm², uninsulated copper tube terminals and cable lugs are used, with heat-shrink sleeving for insulation. Always crimp with a ratchet tool whose die matches the terminal colour or size; a ratchet will not release until the full crimp is made, which prevents under-crimped joints.
Nylon-insulated terminals tolerate higher temperatures and crimp forces than PVC-insulated ones, and heat-shrink insulated terminals add a moisture seal for automotive, marine and outdoor use.
Terminal materials and finishes
| Material | Properties | Typical terminals |
|---|---|---|
| Copper (Cu-ETP, C11000) | About 100 % IACS conductivity, ductile, ideal for crimping | Crimp terminals, cable lugs, ferrules |
| Brass (Cu-Zn) | Lower conductivity (about 25 – 28 % IACS) but stronger and easy to stamp | Small ring and fork terminals, quick-disconnects, terminal block parts |
| Phosphor bronze / copper alloys | Springy, keeps contact force | Female receptacles and spring contacts |
| Aluminium (1050, 1060, 1350) | About 61 % IACS, light, must be used on aluminium conductors | Aluminium cable lugs and connectors |
| Copper-aluminium bimetal | Copper palm, aluminium barrel | Aluminium cable to copper terminal |
| Finish | Purpose |
|---|---|
| Tin plating | The standard finish: protects against tarnish, keeps contact resistance stable, compatible with aluminium |
| Nickel plating | Resists oxidation at high temperature; used near engines, heaters and furnaces |
| Silver plating | Lowest contact resistance; high-current and high-reliability equipment |
| Bare | Acceptable in dry, clean indoor panels |
Terminal blocks, DIN rail and distribution blocks
Spring-clamp and push-in blocks
A spring holds the wire with constant force, resisting vibration loosening; ferrules make insertion easier with stranded wire.
DIN rail mounting
Modular blocks clip onto a 35 mm top-hat rail (EN 60715), allowing panels to be built and changed quickly.
Power distribution blocks
One large incoming cable split into several outgoing circuits, often with aluminium or copper bodies.
Pluggable PCB terminals
Board-mounted headers with removable plugs, for electronics that must be swapped or serviced.
Earth and neutral bars
Copper or brass bars with multiple screw holes for protective and neutral conductors.
How to choose the right terminal
- ConductorIdentify conductor metal (copper or aluminium), cross-section and class (solid, stranded, fine-stranded flexible).
- Connection pointStud or screw size, clamp type, tab size or busbar hole pattern on the equipment.
- Current and temperatureRated current, ambient temperature and any continuous high-temperature exposure, which can rule out PVC insulation or tin finishes.
- EnvironmentMoisture, salt, vibration and chemicals: choose heat-shrink sealed, tin- or nickel-plated and ring-type terminals for harsh conditions.
- MaintenancePlug-in or fork terminals where frequent disconnection is expected; ring and lug terminals where it is not.
- ApprovalCheck the terminal is listed or tested to the standard your market requires.
Standards for terminals and connections
| Standard | Scope |
|---|---|
| IEC 60352-2 | Solderless connections: crimped connections, requirements and tests |
| IEC 61210 | Flat quick-connect terminations |
| IEC 60947-7-1 | Terminal blocks for copper conductors in low-voltage equipment |
| UL 486A-486B | Wire connectors for copper and aluminium conductors |
| UL 310 | Electrical quick-connect terminals |
| DIN 46228 | Wire-end ferrules |
| EN 60715 | Mounting rails (35 mm top-hat DIN rail) for low-voltage equipment |
Applications
- Industrial power distribution and control: panels, motor control centres and PLC cabinets
- Battery and energy storage: copper and aluminium lugs and terminals matched to cable and post metals
- Automotive and marine: sealed crimp terminals, battery lugs and quick-disconnects
- Building services: distribution boards, lighting, HVAC and lift controls
- Renewable energy: inverter, combiner box and transformer terminations
- Appliances and electronics: quick-disconnects, PCB terminals and internal wiring
References and standards
- IEC 60352-2 – Solderless connections: crimped connections
- IEC 60947-7-1 – Low-voltage switchgear and controlgear: terminal blocks for copper conductors
- UL 486A-486B – Wire Connectors
- IEC 61210 – Connecting devices: flat quick-connect terminations for electrical copper conductors
- DIN 46228 – Wire-end ferrules
Electrical terminals: frequently asked questions
What is the difference between a terminal and a connector?
A terminal terminates one wire at a fixed point such as a stud, screw or clamp. A connector joins wires or devices to each other, often with mating halves that can be separated. In practice the words overlap, and many products, such as quick-disconnects, are both.
When should I use a ring terminal instead of a fork terminal?
Use a ring terminal wherever vibration or a loose screw could let the wire slip off: it stays captive on the stud. Fork terminals are for places that need quick removal without fully taking out the screw.
What do the red, blue and yellow terminal colours mean?
They show the wire range: red for about 0.5 – 1.5 mm² (22 – 16 AWG), blue for 1.5 – 2.5 mm² (16 – 14 AWG) and yellow for 4 – 6 mm² (12 – 10 AWG).
Do I need ferrules on stranded wire?
For fine-stranded flexible wire in screw clamps, ferrules are strongly recommended and often required by panel standards. They stop strands splaying or breaking under the screw and give a consistent clamping surface.
Are aluminium terminals safe?
Yes, when used on aluminium conductors with the correct crimp tooling and contact compound. For aluminium cable on copper equipment, use bimetal terminals.
Can you supply terminals and conductive metal together?
Yes. Metline supplies aluminium and bimetal terminals and lugs alongside aluminium busbar, strip, tube and copper-clad aluminium for the same project, shipped worldwide with certificates.
Selecting terminals for a panel or project?
Send wire sizes, stud sizes, conductor metals and quantities. We will recommend terminal types and quote aluminium or bimetal terminals at a delivered price.
