The 2 pos selector switch symbol represents a rotary actuator that toggles between two distinct, maintained or momentary states—commonly used for On-Off, Hand-Auto, or Forward-Reverse control. On electrical schematics, it is drawn as a circle with a diagonal line and specific arrowheads indicating detent positions or spring returns. The exact graphic depends entirely on whether your prints follow IEC 60617 (global/modern US) or NEMA/IEEE 315 (legacy US industrial) standards. Below is the direct reference data you need to read, wire, and troubleshoot these components on the bench or jobsite.
Standard 2 Pos Selector Switch Symbol & Contact Table
The physical switch consists of two separate mechanical halves: the front operator (the knob and bezel) and the rear contact blocks. The schematic symbol only describes the operator's behavior; the pinout depends on the specific NO (Normally Open) and NC (Normally Closed) blocks stacked behind it. Review the table below to match your schematic symbol to the physical hardware behavior.
| Switch Function | IEC 60617 Symbol Description | NEMA / IEEE 315 Symbol Description | Typical Contact Block Pinout Action | Common Application |
|---|---|---|---|---|
| 2-Pos Maintained (On-Off) | Circle with a solid diagonal line. No arrows. | Circle with a straight cross-line or diamond shape. | Pos 1: NO closed, NC open. Pos 2: NO open, NC closed. |
Main power disconnects, simple motor starters, lighting overrides. |
| 2-Pos Spring Return (Momentary) | Circle, diagonal line, and a curved arrow pointing to the left detent. | Circle, cross-line, and a jagged spring symbol on the right side. | Pos 1 (Rest): NO open, NC closed. Pos 2 (Held): NO closed, NC open. Springs back to Pos 1. |
Start/Stop stations, reset buttons, inching/jogging controls. |
| 2-Pos Keyed (Key Remove Left) | Circle, diagonal line, and a small keyhole symbol on the left detent. | Circle, cross-line, and a key icon adjacent to the left terminal. | Pos 1 (Key removed): NO open. Pos 2 (Key turned): NO closed. Key cannot be removed in Pos 2. |
Security overrides, lockout enable circuits, HVAC master controls. |
| 2-Pos Selector (Hand-Auto) | Circle, diagonal line. Bezel text 'H' and 'A' often noted in parentheses next to symbol. | Circle, cross-line. Text labels 'Hand' and 'Auto' explicitly drawn on the schematic. | Pos 1 (Hand): Bypasses logic, direct coil energization. Pos 2 (Auto): Routes through PLC relays or sensors. |
Pump control, VFD bypass, generator transfer logic. |
| 2-Pos Illuminated (LED) | Circle, diagonal line, with a small internal lightbulb or LED diode symbol. | Circle, cross-line, with an adjacent lamp symbol tied to the switch node. | Includes an integrated LED module (e.g., 24VDC). Contacts operate identically to standard maintained. | Status indication combined with control (e.g., 'Alarm Acknowledge & Silence'). |
Regional Variants and Rows People Get Wrong
When reading legacy panels or imported machinery documentation, you will encounter regional variations in how these symbols are drawn. Furthermore, schematic symbols only tell half the story; the physical implementation is where most wiring errors occur.
Which Standard Applies to Your Region?
- IEC 60617 (Global / Modern US / EU): The dominant standard today. Uses clean geometric shapes (circles, solid lines, simple arcs). If you are working on modern PLC-controlled panels, Schneider Harmony (XB4/XB5), or ABB Compact (A22) series equipment, your prints will use IEC.
- NEMA / IEEE 315 (Legacy US Industrial): Common in older US manufacturing plants and heavy machinery built before the 2000s. Uses more complex, sometimes cluttered symbols (diamonds, explicit spring drawings). You will see this on legacy Allen-Bradley 800T or Eaton 10250T panels.
- Old BS 3939 (UK Pre-Harmonization): Rarely seen on new builds, but still present in older UK infrastructure. Used distinct graphical representations for rotary switches that often look like a series of interconnected nodes rather than a single circle.
The 'Rows People Get Wrong' Notes
Even experienced techs misinterpret specific aspects of 2-position switch schematics. Watch out for these common traps:
- The 'Operator vs. Contact Block' Fallacy: A 2-pos switch symbol does not mean the switch only has two wires or two contacts. The symbol only defines the front knob's two physical positions. On an industrial switch like the Allen-Bradley 800H series, you can stack up to four or six contact blocks on the back of a single 2-position operator. A single 2-pos symbol on a schematic might actuate four independent NO contacts and two NC contacts simultaneously. Always check the contact block schedule on the schematic's title block.
- Missing the Spring-Return Arrow: In dense ladder logic, the small curved arrow (IEC) or jagged line (NEMA) indicating a momentary spring-return is easily overlooked. Wiring a momentary 'Start' switch as a maintained 'On-Off' switch will cause the motor to run uncontrollably and bypass the safety stop logic.
- Confusing 'Off' with 'Neutral': In a 2-pos Hand-Auto switch, the 'Off' position (if it's actually a 3-pos Hand-Off-Auto switch mislabeled as 2-pos in a simplified diagram) breaks the control circuit entirely. However, in a true 2-pos setup, Position 1 might be 'Auto' (routing through a PLC) and Position 2 might be 'Hand' (direct hardwired bypass). There is no 'Off'—the circuit is always live in one mode or the other.
Safe Interpretation When Markings Are Faded or Missing
On a 20-year-old jobsite, UV exposure, oil mist, and physical abrasion will destroy the printed bezel markings on a selector switch. If the physical knob is blank, the mechanical cam is worn, and the original schematic is missing, you must reverse-engineer the switch behavior safely. Do not guess based on the physical angle of the knob.
Follow this bench-proven procedure to map an unknown 2-position selector switch, referencing standard multimeter continuity testing practices:
- Isolate the Terminals: Pull the wires off the contact block terminals. If you leave the wires connected, your multimeter will read 'ghost continuity' through parallel paths in the control circuit (like indicator lights or PLC input optocouplers), giving you false data.
- Identify the Block Type: Look at the physical contact block. Standard IEC blocks use specific terminal numbering. Terminals ending in 3/4 (e.g., 13/14) are Normally Open (NO). Terminals ending in 1/2 (e.g., 21/22) are Normally Closed (NC). If it's an older NEMA block, look for the stamped 'NO' and 'NC' letters on the phenolic resin housing.
- Map the Cam Lobes: Set your multimeter to the continuity/diode setting (the symbol with the sound wave). Place probes across the NO terminals (13 and 14). Turn the switch to Position 1. If it beeps, the cam lobe is depressing the plunger in Position 1. If it's silent, move to Position 2.
- Check for Momentary Action: While holding the probes on the contacts, twist the knob to the second position and let go. If the knob snaps back to the first position on its own, you have a spring-return (momentary) operator. If it stays where you left it, it is a maintained operator.
- Verify the Cam Mechanics: If the switch feels 'mushy' or doesn't snap cleanly between detents, the internal plastic cam or the metal detent spring inside the operator head has failed. In industrial environments, you cannot simply repair the plastic cam; you must replace the entire front operator assembly (e.g., swapping a worn Eaton 10250T knob while leaving the rear contact blocks intact).
By understanding that the switch type and schematic symbol only dictate the mechanical operator's behavior—and that the electrical pinout is entirely dependent on the stacked contact blocks—you can accurately wire, read, and troubleshoot any 2-position selector switch regardless of the standard or the condition of the physical hardware.
