Emergency Stop Symbol
Definition: The Emergency Stop symbol represents a safety-rated manually-actuated electromechanical device that immediately interrupts power or control circuits to halt a machine in a dangerous situation, as defined in IEC 60947-5-5, ISO 13850, and NFPA 79, depicted on electrical schematics as a mushroom-head pushbutton with a normally-closed (NC) contact and a latching-lock mechanism, with designator ES or S (sometimes ES1, E-STOP).
Also known as: E-stop, emergency stop button, mushroom head button, kill switch, emergency stop switch, safety stop, emergency stop pushbutton.
What the Emergency Stop symbol means
The Emergency Stop symbol denotes an operator-actuated safety device designed for immediate de-energisation of hazardous machine functions when pressed. The symbol appears in electrical and control schematics to mark the position and circuit connection of the E-stop device, which opens a normally-closed contact in the machine control circuit, dropping out the main contactor, cutting servo drives, or triggering a safety relay when the mushroom head is depressed.
On safety-related control diagrams the E-stop symbol is critical for hazard and risk analysis, CE marking, and compliance with safety integrity levels (SIL) or performance levels (PL). The latching mechanism (twist-release or key-release) ensures the machine cannot restart accidentally after an E-stop event — the operator must deliberately unlock the device before the circuit can be re-energised.
How to identify the Emergency Stop symbol
The Emergency Stop symbol is drawn in two ways: as a schematic contact (a normally-closed switch symbol — two parallel lines with a diagonal slash — with a mushroom-head button actuator annotation above it) or as a functional block (a rectangle labelled 'E-STOP' with In and Out pins). The mushroom-head shape is indicated by a circle with a cross (+ symbol) on top in some IEC conventions. The contact is normally-closed (NC), meaning the circuit is complete when the button is NOT pressed and opens when pressed. The designator is typically ES1 or S1 on the control wiring diagram.
Function in a circuit
Pressing the Emergency Stop button mechanically forces the NC contact to open. This interrupts the control circuit (or power circuit in direct-wired systems), causing the main contactor, safety relay, servo amplifier, or drive controller to de-energise immediately, removing power from the hazardous machine element. The latching mechanism keeps the contact open after the operator releases the button, so the machine cannot self-restart. Deliberate operator action — twisting, pulling, or inserting a key — is required to release the latch and restore the NC contact to its closed state before the machine can be re-started by the normal start sequence.
Standards: IEC vs ANSI
| IEC 60617 | IEC 60947-5-5 defines the requirements for electrical emergency stop devices with mechanical latching function. ISO 13850 specifies design and application principles for emergency stop functions in machinery. IEC 62061 (SIL-rated safety systems) and ISO 13849 (performance level PL) govern the safety integrity of the E-stop circuit. The mushroom-head button must be RED with a YELLOW background per IEC 60204-1 clause 10.7.4. |
|---|---|
| ANSI/IEEE 315 | NFPA 79 (Electrical Standard for Industrial Machinery) Section 9.2.5 requires emergency stop devices on all industrial machines. ANSI B11 series machine safety standards reference emergency stop requirements. In ANSI diagrams the E-stop contact is shown as an NC contact symbol with a mushroom-head actuator annotation or 'ES' label. |
| Key difference | IEC 60947-5-5 and ISO 13850 are the primary international standards; NFPA 79 governs North American industrial applications. IEC requires a RED mushroom head on YELLOW panel background; NFPA 79 similarly requires RED. Safety category requirements (PLd Cat.3 or SIL2 minimum for most machinery) are defined in ISO 13849 (IEC) and ANSI B11.19 (ANSI). |
Terminals / pins
| Pin | Name |
|---|---|
| in | In |
| out | Out |
Typical values
Contact type: NC (normally-closed), opening on actuation. Contact rating: typically 10 A at 240 V AC (IEC AC-15) or 24 V DC. Latching: twist-release, pull-release, or key-release. Colour: RED actuator, YELLOW mounting collar (IEC 60204-1). Response time: mechanical, essentially instantaneous (<10 ms). Safety performance: up to PLe / Cat.4 (ISO 13849) or SIL3 (IEC 62061) for dual-channel monitored configurations.
Where the Emergency Stop symbol is used
- Industrial machine control panels: E-stop mushroom buttons on the machine front panel and at operator stations interrupt the main contactor holding circuit
- Robotic work cells: E-stop buttons at all entry points and on teach pendants de-energise robot servo drives immediately when pressed
- Conveyor belt and material-handling systems: pull-cord E-stop switches along conveyor length allow workers anywhere along the line to stop motion
- CNC machining centres: E-stop on the control pendant and machine body stops axis servos, spindle, and coolant pump simultaneously
- Safety PLC and safety relay systems: E-stop contacts wire into dedicated safe-input modules for PLd/SIL2 certified emergency stop function monitoring
- Electrical test and laboratory equipment racks: bench-mounted E-stop cuts power to DUT (device under test) circuits during fault or personnel-safety events
Example
In a 3-phase motor control panel, the Emergency Stop (ES1) normally-closed contact is wired in series with the START pushbutton and the main contactor coil (K1) in the 24 V DC control circuit. When ES1 is pressed, the NC contact opens, the coil de-energises, and K1's main contacts open, disconnecting the motor from the 400 V supply. The motor cannot restart until ES1 is twist-released to restore the NC contact, and the operator presses the START button again to re-energise K1.
Key facts
- The Emergency Stop symbol represents a latching normally-closed (NC) safety contact: the circuit is CLOSED when the button is not pressed, and OPENS immediately when the mushroom head is pressed, de-energising the machine.
- Per IEC 60947-5-5 and ISO 13850, the E-stop actuator must be RED and mounted on a YELLOW background; no other button in a control panel may use the RED mushroom-head form factor.
- The two schematic pins are In (x=20,y=0) and Out (x=20,y=50); the NC contact between them opens on actuation, breaking the control circuit and causing upstream safety devices (contactors, drives, relays) to de-energise.
- After actuation, a latching mechanism (twist-to-release, pull-to-release, or key-release) keeps the contact open until deliberate operator action releases it, preventing accidental machine restart.
- E-stop safety performance is classified under ISO 13849 Performance Levels (PLa–PLe) and IEC 62061 Safety Integrity Levels (SIL 1–3); most machinery requires PLd / SIL2 minimum, achieved using dual-channel monitoring safety relays.
- NFPA 79 Section 9.2.5 requires at least one E-stop device on every industrial machine; machines with multiple operator stations require an E-stop at each station and at the main control panel.
- The E-stop category per IEC 60204-1 Stop Category 0 (immediate de-energisation) is distinguished from Category 1 (controlled stop, then de-energise) and Category 2 (controlled stop, power maintained); most E-stop buttons implement Category 0.
Frequently asked questions
What does the emergency stop symbol mean in a circuit diagram?
The emergency stop (E-stop) symbol marks the location of a latching normally-closed (NC) safety pushbutton that immediately opens the machine control circuit when pressed. It tells the circuit reader that pressing this device will cut power to the machine and that the machine cannot restart until the button is deliberately released and the normal start sequence is repeated.
What does an emergency stop button symbol look like in a schematic?
The E-stop symbol is drawn as a normally-closed (NC) contact — two parallel lines with a diagonal slash indicating normally-closed state — with a mushroom-head actuator annotation (a circle with a cross) above it. Alternatively it appears as a functional block rectangle labelled 'E-STOP' with In and Out pins. The designator is ES or S (e.g., ES1).
Is the emergency stop contact normally-open or normally-closed?
The emergency stop contact is NORMALLY-CLOSED (NC). The circuit is complete (machine can run) when the button is not pressed. Pressing the mushroom head OPENS the contact, interrupting the control circuit. This fail-safe design means that a broken wire or disconnected terminal also de-energises the machine, which is the required fail-safe behaviour per ISO 13850.
What standard governs emergency stop buttons?
IEC 60947-5-5 defines the device requirements (latching, force, IP rating) for electromechanical E-stop buttons. ISO 13850 specifies E-stop application principles in machinery safety. IEC 60204-1 defines colour (RED actuator, YELLOW background) and stop categories. NFPA 79 governs industrial machinery in North America.
Why must the emergency stop button be RED?
IEC 60204-1 clause 10.7.4 and ISO 13850 both mandate RED for emergency stop actuators, with YELLOW as the background colour, because RED universally signals immediate danger or stop in safety colour conventions (IEC 60073). No other pushbutton function is permitted to use RED in a control panel, ensuring the E-stop is instantly identifiable in an emergency.
What is the difference between emergency stop category 0 and category 1?
IEC 60204-1 Stop Category 0 removes power immediately and simultaneously to all machine actuators — the quickest stop but potentially causing mechanical shock or uncontrolled machine movement. Stop Category 1 performs a controlled deceleration before removing power. Most mushroom-head E-stop buttons implement Category 0 for simplicity and maximum speed of hazard removal; Category 1 is used when an uncontrolled stop itself is hazardous.
How is the E-stop connected in a control circuit?
The E-stop NC contact is wired in series with the main contactor coil circuit. The 24 V DC (or 110/230 V AC) control supply passes through the E-stop NC contact, then through the run/start logic, to the contactor coil. Opening the E-stop contact drops the coil voltage to zero, de-energising the contactor and disconnecting the motor or machine from the power supply.
Place the Emergency Stop symbol on a wiring diagram or schematic in the free online circuit diagram maker — no download required.