Screw Terminal (2-pos) Symbol
Definition: The Screw Terminal (2-pos) symbol represents a 2-position screw-clamp connector used in circuit diagrams to denote a mechanical connection point where two conductors are secured with set screws, as recognised under IEC 60617 and ANSI Y32.2 / IEEE 315 connector conventions.
Also known as: 2-way screw terminal, 2-position terminal block, TB2, 2-pole screw connector, WAGO 2-pin equivalent.
What the Screw Terminal (2-pos) symbol means
The 2-position screw terminal symbol denotes a two-conductor mechanical interface block that accepts stripped wire ends and clamps them with screw pressure. In schematics it marks the physical boundary where wired field connections enter or leave a circuit board, enclosure, or control panel.
In a circuit diagram the two pins P1 and P2 identify the first and second connection positions respectively. Each position is electrically isolated from the other; current can flow through an external load connected between them or a single conductor can be fed from the terminal to the rest of the circuit.
How to identify the Screw Terminal (2-pos) symbol
The 2-position screw terminal symbol typically appears as a small rectangular block with two vertical lines or slots indicating the screw openings, side by side, with one wire entry lead extending from each position. Pin labels P1 and P2 mark the first and second positions. The symbol width spans two pitch positions (typically 5 mm or 5.08 mm pitch), and the block outline is drawn as a closed rectangle.
Function in a circuit
A 2-position screw terminal block provides two independent, tool-secured electrical connection points that allow field wiring to be attached or removed without soldering. Each position accepts one conductor, making it ideal for terminating two separate wires that must be individually disconnectable, such as a supply line and a neutral, or a sensor positive and a sensor negative.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617 connector/terminal block category; the symbol uses a rectangular block outline with two internal divisions representing the screw positions. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315 does not define a unique screw-terminal symbol but the connector block convention uses a rectangle with pin stubs, consistent with general terminal designations. |
| Key difference | IEC practice labels terminal blocks with the prefix TB and numbers positions 1–N; ANSI/IEEE uses J or TB designators. Graphically the symbols are essentially identical in modern CAD tools. |
Terminals / pins
| Pin | Name |
|---|---|
| p1 | P1 |
| p2 | P2 |
Typical values
Standard pitch: 2.54 mm, 3.5 mm, 3.81 mm, 5 mm, 5.08 mm, 7.5 mm. Current ratings: 8 A–32 A (300 V–600 V) typical for PCB types; cage/clamp terminal blocks rated up to 125 A. Wire gauge: AWG 28–AWG 10 (0.08 mm²–6 mm²) depending on model.
Where the Screw Terminal (2-pos) symbol is used
- Power supply outputs connecting to load wiring on PCBs and control panels
- Sensor signal wiring termination (temperature, pressure, position sensors)
- Motor control panels: L and N mains feed termination before contactors
- Lighting circuits: phase and neutral brought into a driver board
- DIN-rail panel field wiring: PLC I/O modules and relay output modules
- Prototype and lab breadboard-adjacent wiring where solderless connection is needed
Example
In a 24 V DC LED driver circuit, P1 of the screw terminal accepts the positive supply conductor from the DIN-rail PSU and P2 accepts the return (0 V) conductor; the driver board's internal rails connect directly to P1 and P2, allowing the field wiring to be changed without disturbing soldered components.
Key facts
- The Screw Terminal (2-pos) symbol designator is TB (terminal block) followed by a reference number, e.g. TB1, in both IEC and ANSI schematic conventions.
- The two pins are labelled P1 (position 1) and P2 (position 2); each pin is a fully independent electrical node in the schematic netlist.
- Standard PCB-mount screw terminals conform to 2.54 mm (0.1 in) or 5.08 mm (0.2 in) pitch grids, which are also common breadboard and through-hole PCB pitches.
- Screw terminal blocks are rated by voltage class (300 V, 600 V, 1000 V) and current class (8 A, 15 A, 20 A, 32 A) — both parameters must be met for safe wiring.
- IEC 60947-7-1 governs low-voltage terminal blocks for industrial use, specifying creepage and clearance distances that determine the physical spacing between adjacent positions.
- Unlike solder pads or IDC connectors, screw terminals are field-wire-compatible: they accept standard insulated stranded or solid copper wire without special crimp tools.
- A 2-position terminal block can be used as a 2-pin power connector (positive + negative), a 2-conductor signal connector, or as two independent single-wire anchor points in the same panel row.
- WAGO spring-clamp terminals are functionally equivalent to screw terminals in schematics and use the same TB symbol even though the clamping mechanism differs physically.
Frequently asked questions
What does the screw terminal 2-position symbol look like?
The 2-pos screw terminal symbol is drawn as a compact rectangular block with two side-by-side internal divisions, each representing a screw clamp position, with short wire-stub leads extending from each position. Pin labels P1 and P2 identify the two terminals.
What does the screw terminal symbol mean in a circuit diagram?
The screw terminal symbol marks the physical point where external field wiring connects to a circuit board or panel. It signifies a removable, tool-secured electrical connection that can be wired and re-wired without soldering.
What is the designator letter for a screw terminal?
Screw terminal blocks use the designator TB (terminal block) in most IEC and ANSI schematics, numbered sequentially as TB1, TB2, TB3, etc. Some older drawings use the letter J (jack/connector) instead.
What is the difference between IEC and ANSI screw terminal symbols?
Both IEC 60617 and ANSI Y32.2 / IEEE 315 represent terminal blocks as rectangular connector blocks with pin stubs. The graphical difference is negligible; the primary distinction is in designator convention: IEC uses TB, ANSI may use J or TB.
What voltage and current ratings do 2-position screw terminals have?
Common PCB-mount screw terminals are rated 300 V or 600 V and 8 A to 32 A depending on pitch and construction. Industrial DIN-rail terminal blocks (IEC 60947-7-1) are available up to 1000 V and 125 A.
What pitch sizes are standard for 2-position screw terminals?
The most common screw terminal pitches are 2.54 mm, 3.5 mm, 3.81 mm, 5 mm, 5.08 mm, and 7.5 mm. PCB-mount low-voltage types typically use 2.54 mm or 5.08 mm; power-wiring types use 5 mm or 7.5 mm.
Can a 2-position screw terminal be used as a 2-wire power connector?
Yes. A 2-pos screw terminal is routinely used as a 2-wire power connector, with P1 carrying the positive or line conductor and P2 carrying the negative or neutral conductor, providing a removable interface between the power supply and the circuit.
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