1. Terminal Box Types (3 Main Types)
| Type | the enclosure material | terminal blocks | Application |
|---|---|---|---|
| Wiring terminal box | Steel / stainless steel | UK series | Power/control wiring |
| Signal terminal box | Steel sheet/ABS | PTB series | Instrument/low-voltage signal |
| Explosion-proof terminal box | Cast aluminum/cast iron | AK series | Hazardous area |
2. Wiring Terminal Boxes (Power/Control)
Wiring terminal boxes are used forbranching and transition of power cables or control cables, with UK series terminal blocks inside (such as UK-2.5/UK-6/UK-16). Each row of terminals carriesterminal numbers, circuit numbers, and destination labels, so maintenance staff can trace by number. Typical enclosure sizes run from 300×400×150mm to 600×800×200mm.
3. Signal Terminal Boxes (Instrument/Low-Voltage Signal)
Signal terminal boxes are used forInstrument signals, DCS/PLC signalsaggregation and distribution. Terminal blocks are PTB series or dedicated signal terminals. Key characteristics:high terminal density(20–40 positions per rail), with shielded grounding terminals for noise immunity. Cabinets often includeZener safety barriersfor intrinsically safe circuits.
4. Terminal Block Specifications Comparison (UK series)
| Model | Cross-section | Current | Terminal width |
|---|---|---|---|
| UK-2.5 | 0.2–4mm² | 24A | 6mm |
| UK-6 | 0.5–6mm² | 41A | 8mm |
| UK-10 | 2.5–10mm² | 57A | 12mm |
| UK-16 | 5–16mm² | 76A | 15mm |
5. Terminal Box Marking Requirements (3 types of marking)
① Terminal number: each terminal carries a unique number (1/2/3…); ② Circuit label: identifies the circuit the terminal belongs to and where it runs; ③ Enclosure nameplate: model / voltage / current / ingress protection (IP) rating. All three marking types are required for compliance.
FAQ FAQ
What is the difference between a terminal box and a junction box?
A terminal box containsterminal blocksfor centralized multi-circuit transition; a junction box typically handles only 1–2 runs for branching or transition. Terminal boxes are larger and more complex.
How do I choose between UK-2.5 and UK-6 terminal blocks?
Select by conductor cross-section: 2.5 mm² uses UK-2.5, 6 mm² uses UK-6. Terminal width and rated current differ.
Can signal terminal boxes be used on power circuits?
No. Signal terminal blocks have a small cross-section (0.2–1.5 mm²); high power circuit current will burn them out.
Where are explosion-proof terminal boxes used?
Used inexplosive gas atmospheres(Zone 1/Zone 2), for instrument and signal circuits in chemical and oil & gas plants. Requires an explosion-proof certificate.
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