1. What's on a Terminal Block Wiring Diagram? (4 Categories of Information)
| Information | Example | Function |
|---|---|---|
| Terminal number | 1/2/3… | Unique number on the terminal block |
| Internal wiring | To equipment/instruments | Wires from inside the box to equipment |
| External wiring | From the upstream source | Wires from outside into the box |
| Wire number | L1-1-W1 | Circuit + phase sequence + cable number |
2. Terminal Block Numbering Rules (Top to Bottom / Left to Right)
Terminal block numberingTop to bottom, left to rightIncrementing: single-deck terminal blocks start at No. 1; double-deck terminal blocks use odd numbers on the upper deck and even numbers on the lower deck. Each terminal is marked withterminal number + circuit number + destination. For example, "Terminal 3 → Circuit 1L2 → to Motor 1"
3. Single-Deck vs. Double-Deck Terminal Blocks (Comparison)
| Type | Terminals per block | Numbering rule | Application |
|---|---|---|---|
| Single-deck | 20–40 positions | 1,2,3… | Few circuits |
| Two-tier | 40–80 positions | Odd top, even bottom | Many circuits / compact enclosure |
| Three-tier | 60–120 positions | Tiered numbering | Large terminal box |
4. Terminal Block Wiring Principles (3 Items)
① One wire per terminal— Each terminal takes only one wire; two wires maximum and only with a feed-through terminal; ② Separate inside and outside— Inner wires (to equipment) and outer wires (from the upstream source) land on opposite sides of the terminal; ③ Separate PE/N rails— PE terminal rails and N terminal rails are mounted separately and must not be mixed.
5. How to Read a Wiring Diagram: 3 Steps (Hands-On)
- Find the terminal number: Match the terminal number on the drawing to the physical terminal in the box.
- Check the destination: See which equipment the inner wire of that terminal goes to, and where the outer wire comes from.
- Verify the wire number: The wire number on the cable matches the wire number on the drawing.
FAQ FAQ
How do I read a terminal block wiring diagram?
First find the terminal number (1/2/3…), then check where that terminal's inner wire goes and where its outer wire comes from, and finally verify the wire numbers match.
How are two-tier terminal blocks numbered?
Odd-numbered terminals on the top tier (1/3/5…), even-numbered on the bottom tier (2/4/6…), which saves enclosure height.
Can one terminal take two wires?
Not recommended. One wire per terminal is the most reliable; multiple wires under one clamp cause poor contact. Use two-tier or feed-through terminals for special cases.
What does the terminal block model UK-2.5 mean?
UK is Phoenix Contact's terminal block series; 2.5 means maximum cross-section 2.5mm² and rated current 24A.
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