Push Button NO Symbol
Definition: The Push Button NO symbol represents a momentary normally-open (NO) push button — standardised in IEC 60617-07 and ANSI Y32.2/IEEE 315 — whose contact is open (non-conducting) in the resting state and closes momentarily when the button is pressed, used as the Start button in motor starter control circuits, with terminal designations In and Out and reference designator S per IEC 60947-5-1.
Also known as: push button normally open, NO push button, Start button, momentary NO switch, make push button, normally open momentary switch.
What the Push Button NO symbol means
The Push Button NO (normally open) symbol represents a momentary contact switch that is in the open (non-conducting) state when not actuated and closes its contact when the button cap is pressed. The contact returns to its open state automatically when the button is released, making it a momentary action device with NO (make) contact function.
In industrial motor starter control circuits, the NO push button is universally used as the Start button: pressing it momentarily closes the control circuit, energising the contactor coil and starting the motor. A holding (self-seal) contact in parallel with the Start button latches the coil energised after the button is released. Start buttons are coloured Green per IEC 60204-1 and ANSI/NEMA Z535 safety colour standards. The reference designator is S in IEC practice.
How to identify the Push Button NO symbol
The Push Button NO symbol is drawn as two short horizontal parallel lines with a visible gap between them (representing the open contact blades), and a downward-pointing arrow or push actuator symbol above the contact gap, indicating the push button operating mechanism. In IEC 60617-07 notation, the NO push button shows a make-contact symbol with a spring-return push actuator. The ANSI/IEEE symbol is similar: a make-contact with a manual push actuator indicator. The symbol reads as 'this contact is open at rest and closes when pushed'.
Function in a circuit
The NO push button, when not pressed, presents an open circuit between its In and Out terminals, blocking current flow. When the button is pressed, the spring-loaded contact mechanism brings the contact blades together, completing the circuit for the duration the button is held. Upon release, the spring restores the contact to its open (non-conducting) position. In a DOL motor starter, pressing the Start button (NO push button) closes the control circuit, energising the KM1 contactor coil; the coil then closes the main power contacts (connecting the motor to 3-phase supply) and simultaneously closes the holding contact in parallel with the Start button to maintain coil energisation after the button is released.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60617-07 defines the normally-open (make) contact symbol with a spring-return push actuator for the NO push button. IEC 60947-5-1 governs low-voltage control circuit devices including push buttons, specifying AC-15/DC-13 ratings, IP protection, and colour coding. IEC 60204-1 (Safety of machinery) requires Start push buttons to be coloured Green. |
|---|---|
| ANSI/IEEE 315 | ANSI Y32.2 / IEEE 315 represents the NO push button as a make-contact symbol with a push actuator indicator. NEMA ICS standards govern push button assembly ratings for North American industrial applications. ANSI/NEMA Z535 and NFPA 79 require Start push buttons to be Green. |
| Key difference | IEC 60617-07 and ANSI Y32.2/IEEE 315 NO push button symbols are very similar: both show a make-contact with a spring-return push actuator. IEC schematics typically represent the actuator as a short downward arrow or T-bar; ANSI schematics show a push actuator circle or arrow. The contact function and circuit wiring are identical in both standards. |
Terminals / pins
| Pin | Name |
|---|---|
| in | In |
| out | Out |
Typical values
Contact configuration: 1 NO (make). Rated voltage: 230/400 V AC, 24–250 V DC. Rated current: 6–10 A (AC-15 category per IEC 60947-5-1). Actuation force: 1.5–5 N. Contact resistance: < 10 mΩ. Mechanical life: ≥ 1,000,000 operations. IP rating (front): IP65 standard for panel-door-mount push buttons. Colour: Green (Start function per IEC 60204-1). Terminal designators: In and Out (identified by circuit position and label).
Where the Push Button NO symbol is used
- DOL motor starter Start button: NO push button momentarily closes control circuit to energise contactor coil and start the motor
- Conveyor belt Start station: NO push button at operator station initiates conveyor belt movement
- Machine tool start control: NO push button on machine control panel provides operator start function
- PLC input wiring: NO push button wired to PLC digital input to provide software-readable start command
- Remote start stations: additional NO push button in parallel with the main Start button for multi-station motor start control
- Test and jog functions: momentary NO push button used for brief motor jog or inching operations during machine setup
Example
In a standard IEC DOL motor starter control circuit wiring diagram, the Green Start push button (NO, terminals In-Out) is wired in parallel with the KM1 holding contact (also NO), and this parallel combination is in series with the Red Stop push button (NC) and the overload relay NC contact (95-96). Pressing Start momentarily closes the Start push button contact, energising the KM1 contactor coil (A1-A2); the KM1 holding contact immediately closes in parallel and maintains coil energisation after the Start button is released.
Key facts
- The Push Button NO is a momentary normally-open (make) contact switch: it is open (non-conducting) at rest and closes only while the button is pressed, returning to open on release.
- IEC 60947-5-1 governs push button devices; IEC 60204-1 requires Start push buttons to be Green and wired as NO contacts that momentarily energise the motor contactor coil.
- In a DOL motor starter, the NO Start push button is wired in parallel with the contactor holding contact: pressing Start briefly energises the coil; the holding contact then latches the coil on without requiring the Start button to remain pressed.
- The reference designator for push buttons in IEC schematics is S (e.g. S2 for Start); in ANSI/IEEE schematics the designator is PB (push button, e.g. PB2).
- IEC 60617-07 defines the make-contact symbol with spring-return actuator used for the NO push button; ANSI Y32.2/IEEE 315 uses a visually similar make-contact with push actuator.
- Start push buttons (NO type) must be Green per IEC 60204-1 and ANSI/NEMA Z535; this colour coding is mandatory in industrial machine safety panels to immediately communicate the start/run function to operators.
- Multiple NO Start push buttons can be wired in parallel to create multi-station start control for a single motor or machine — pressing any one Start button energises the contactor coil.
Diagrams that use this symbol
- dol starter diagram
- contactor wiring diagram
- dol starter control diagram
- dol starter connection diagram
- dol starter wiring diagram
- motor starter connection
- motor starter wiring diagram
- 3 phase dol starter wiring diagram
Frequently asked questions
What does the push button NO symbol look like?
The Push Button NO symbol shows two short parallel lines with a gap between them (the open contact, non-conducting at rest) and a small downward arrow or actuator symbol above, representing the push button mechanism. In IEC 60617-07 schematics the symbol shows a make-contact with a spring-return push actuator. The ANSI/IEEE symbol is visually similar with a push actuator indicator above the open contact gap.
What does NO mean on a push button?
NO stands for Normally Open — meaning the push button contact is in the open (non-conducting) state when the button is not being pressed. The contact closes (circuit makes) only while the button is actively pressed and held down. When released, the spring returns the contact to its normally open position. NO push buttons are used as Start buttons in motor control circuits.
Why is the Start button a NO (normally open) push button?
The Start button uses an NO push button so the motor does not start automatically on power-up or on restoration of power after an outage — a safety requirement per IEC 60204-1 (protection against unintended restart). An NO Start button requires a deliberate operator press to start the motor each time. If the Start button wiring breaks (open circuit), the motor simply cannot start, which is the safe default condition.
What is the difference between a NO and NC push button?
A NO (normally open) push button is open at rest and closes when pressed — used as a Start button. An NC (normally closed) push button is closed at rest and opens when pressed — used as a Stop button. In a motor starter control circuit, the NO Start button is in parallel with the holding contact, and the NC Stop button is in series with the contactor coil.
What standard defines the push button NO symbol?
IEC 60617-07 defines the normally-open make-contact symbol with spring-return actuator used for the NO push button in IEC schematics. IEC 60947-5-1 specifies push button construction, ratings, and testing. ANSI Y32.2/IEEE 315 defines the equivalent make-contact symbol for North American schematic practice.
What colour should a NO Start push button be?
IEC 60204-1 (Safety of Machinery) and ANSI/NEMA Z535 both require Start push buttons to be Green. This is a mandatory safety colour coding convention in industrial machine control panels: Green = Start/On; Red = Stop/Off/Emergency Stop. Using a non-green colour for a Start button is a non-conformance with both IEC and ANSI safety standards.
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