The IEC selector switch symbol (governed primarily by IEC 60617 and IEC 60947-5-1) represents a rotary actuator that mechanically opens and closes specific electrical contacts based on its angular position. Unlike standard pushbuttons, selector switches maintain their state along a rotational axis or spring-return to a center detent. If you are reading an international schematic or designing a control panel for global export, recognizing the exact IEC graphical symbol—and understanding how it maps to physical contact blocks—is mandatory to prevent dead shorts or unintended machine starts.

Below is the direct reference chart for the most common IEC selector switch configurations, followed by regional variations, common misinterpretations, and a concrete decision path for selecting replacement hardware.

The Complete IEC Selector Switch Symbol Reference Table

IEC 60617 Symbol Description NEMA ICS 19 Equivalent Contact Logic (Positions) Typical Bezel Marking Common Application
2-Position Maintained
(Single line, two ticks, no return arrow)		 Target symbol with solid diagonal line Pos I: NO closes
Pos O: NO opens		 I - O
(On / Off)		 Main control power isolation, E-Stop reset enable
3-Position Maintained
(Single line, three ticks, no return arrow)		 Target symbol with solid diagonal line, 3 positions Pos I: Ckt A closes
Pos O: All open
Pos II: Ckt B closes		 I - O - II
(Fwd / Off / Rev)		 Motor reversing, Hand-Off-Auto control stations
3-Position Spring Return from Right
(Three ticks, curved arrow pointing from Pos II to O)		 Target symbol with dashed return line on right side Pos I: Maintained
Pos O: Normal
Pos II: Momentary		 I - O - >II
(Run / Off / Jog)		 Inching/Jogging circuits, momentary override resets
Key-Operated Selector (2-Pos)
(Standard symbol with superimposed key icon)		 Target symbol with keyhole graphic Pos I: Locked/Closed
Pos O: Unlocked/Open		 I - O
(Key removable in O)		 Security interlocks, unauthorized access prevention
Multi-Position (4+ Pos) Maintained
(Single line, multiple sequential ticks)		 Multi-position drum switch target Sequential contact making/breaking per cam profile 1 - 2 - 3 - 4 Speed selection, multi-tap transformer voltage selection

Regional Variants: IEC vs. NEMA vs. Legacy UK

While the physical switches often look identical on the panel door, the way they are drawn on schematics varies drastically by region. Assuming a single standard applies universally is a primary cause of wiring errors in imported machinery.

Standard Identification: IEC symbols use abstract geometric lines and dots. NEMA symbols use pictorial 'target' representations. Always check the title block of the schematic for the governing standard (e.g., IEC 60617, NEMA ICS 19, or IEEE 315) before wiring.
  • IEC (Global/EU/Asia): Uses a dotted mechanical linkage line connecting the rotary actuator symbol to the specific contact blocks. The actuator itself is drawn as a simple line intersecting positional ticks. This separates the physical operator from the electrical contacts, allowing complex stacking of multiple contact blocks to be drawn cleanly.
  • NEMA (North America): Draws the switch as a 'target' (a circle with a diagonal line indicating the wiper). The wiper points to the active contact. Mechanical linkages are shown with dashed lines. NEMA diagrams often bundle the switch and contacts into a single pictorial block, which is easier for beginners to read but becomes incredibly cluttered on large 480V motor control schematics.
  • Legacy UK (BS 3939): Before harmonizing with Europe (EN 60617), the UK used BS 3939. You will still find these on machinery built prior to the late 1990s. BS 3939 used a mix of pictorial and abstract symbols, often drawing the rotary knob as a literal semi-circle with a pointer. If you see a literal drawing of a knob rather than an abstract line-and-tick, you are looking at legacy BS or early NEMA, not modern IEC.

The 'Rows People Get Wrong' Notes

Even experienced panel builders misinterpret specific nuances of the IEC selector switch symbol. Pay close attention to these three common failure points:

1. Confusing Maintained vs. Spring-Return (The Arc Arrow)

The most critical error is missing the small curved arrow on the spring-return symbol. In IEC 60617, a curved arrow pointing from an outer position back to the center 'O' indicates a momentary spring-return. If that arrow is absent, the switch is maintained (latching) in all positions. Wiring a maintained switch into a circuit designed for a momentary 'Jog' function will result in the machine running continuously when the operator releases the knob, creating a severe safety hazard.

2. Assuming '0' Means Electrically Open

The '0' (or center tick) represents the mechanical center detent, not necessarily an electrically open state across all circuits. In a 'Hand-Off-Auto' (I-O-II) selector switch, the 'O' position opens the Hand (I) and Auto (II) control circuits, but it may simultaneously close a separate contact block used to illuminate an 'Off' indicator light or engage a mechanical brake. Always read the truth table for the specific contact block, not just the bezel marking.

3. Key-Switch Directionality

For key-operated selectors, the symbol often implies key removal is only possible in one specific position (usually '0' or 'O'). However, the IEC symbol alone does not dictate which positions the key can be turned to or removed from; that is defined by the physical cam and lock cylinder (e.g., Ronis or Fortress interlock systems). Never rely solely on the schematic to determine key-trap logic.

Decision Path: Sizing and Selecting Your Selector Switch

Use this decision matrix to terminate your design process with a concrete, orderable part number. This assumes a standard 22mm panel cutout, 24VDC or 120VAC control voltage, and IP65/IP67 environmental requirements typical of modern industrial enclosures.

If Your Application Is... Then You Need This IEC Symbol Type Required Contact Blocks Concrete Part Pick (Schneider Harmony XB4 / Siemens 3SU1)
Motor Reversing (Fwd/Rev)
Operator must select a direction and walk away.		 3-Position Maintained
(I-O-II)		 2x NO (Normally Open) blocks, mapped to Pos I and Pos II. Schneider XB4BD25
(Black knob, 3-pos maintained, 2NO)
Inching / Jog Control
Operator holds the switch to move, releases to stop.		 3-Position Spring Return from Right
(I-O->II)		 1x NO block mapped to the momentary Pos II. Siemens 3SU1100-0AA60-1AA0
(3-pos, spring return right, 1NO)
Security / Lockout
Prevent unauthorized mode changes.		 2-Position Key Maintained
(Key symbol, I-O)		 1x NO, 1x NC (for interlock feedback). Schneider XB4BG03
(2-pos key switch, 1NO+1NC, key removable at O)
Multi-Speed Selection
Selecting VFD presets or tap changers.		 4-Position Maintained
(1-2-3-4)		 4x NO blocks, sequentially actuated by custom cam. Siemens 3SU1150-0AA40-1AA0
(4-pos selector, requires stacking 4x 3SU1030 contact blocks)

Safe Interpretation When Markings Are Faded or Missing

On legacy equipment, UV exposure, chemical solvents, and physical abrasion often destroy the bezel markings and schematic labels. Never guess the switch logic based on the physical 'clicks' of the detent. A 3-position switch might be wired as a 2-position circuit, or the internal cam might be rotated 90 degrees from the bezel.

SAFETY PROTOCOL: Selector switches in motor control centers frequently sit upstream of contactor coils but downstream of control circuit fuses. Treat all control wiring as live until proven dead. De-energize the control circuit, apply Lock-Out/Tag-Out (LOTO), and verify dead using a CAT III or CAT IV rated multimeter before touching any terminals.

Step-by-Step Ringing Procedure:

  1. Isolate and Verify: Shut off the control transformer breaker. Test your multimeter on a known live source, then verify 0V across the switch line/load terminals, then test the meter again (Live-Dead-Live test).
  2. Set Meter to Continuity: Switch your multimeter to the audible continuity/diode test mode. This allows you to listen for the beep without taking your eyes off the switch shaft.
  3. Map the Terminals: Identify the common (C), normally open (NO), and normally closed (NC) terminals on each stacked contact block. IEC blocks are typically marked with numbers (e.g., 13/14 for NO, 21/22 for NC).
  4. Rotate and Probe: Place one probe on the common terminal (13 or 21) and the other on the corresponding output. Rotate the switch through every mechanical detent. Note exactly which position causes the meter to beep.
  5. Draft a New Truth Table: Write the results on masking tape and affix it to the inside of the panel door. Update the facility's master schematic immediately. Do not leave the panel relying on memory.

By strictly adhering to the IEC 60617 symbol conventions and verifying physical contact logic with a meter, you eliminate the guesswork that leads to cross-wired control circuits and unintended machinery actuation.