Emergency stop button: how it works, wiring

An emergency stop button is used to stop a machine in a dangerous situation. It is a red mushroom-head button, and if there is a background around it, the background is yellow.

How it works

When pressed, the button latches in the pressed position and its NC contacts open.
The button stays down until it is released on purpose, usually by turning or pulling it.
Releasing the button must not start the machine. The emergency stop is reset separately, and only after that is the machine started in the normal way.

Direct opening contacts

The NC contacts of an emergency stop button have direct opening action, often called positive opening. The movement of the button separates the contacts mechanically, without relying on a spring, so even a contact that has welded shut is forced open. This is marked next to the contact with an arrow inside a circle.

Wiring

In a simple control circuit, the NC contact of the emergency stop button is in series with the whole control circuit, so it breaks the coils of all the contactors. On more demanding machines, the emergency stop is wired with two contacts to a safety relay, which monitors both channels.

In your region

Showing notes for

UK & Ireland

In Great Britain EN ISO 13850, the standard for the emergency stop function, is a designated standard for machinery.

Source: UK government: designated standards for machinery (list v16, 2026)

Europe

The emergency stop function is designed to EN ISO 13850, a harmonised standard under the Machinery Directive. From 20 January 2027 the Machinery Regulation (EU) 2023/1230 replaces the directive.

Source: European Commission: harmonised standards for machinery (summary list) · European Commission: Machinery Regulation (EU) 2023/1230

Australia & New Zealand

Australia and New Zealand use AS/NZS 4024.1604, which is ISO 13850:2015 with national modifications.

Source: Standards Australia: AS/NZS 4024.1604:2019 (ISO 13850:2015 MOD)

United States

The same red button on a yellow background is used. NFPA 79 keeps the red and yellow combination for emergency stops only, and the red of an illuminated emergency stop button must not depend on its lamp.

Source: Rockwell Automation: emergency stop white paper 800-WP008 · NFPA 79 First Draft report, 2021 edition (Table 10.3.3, 9.1.1)

United States, Canada

On ladder diagrams the emergency stop is drawn as a normally closed pushbutton with a mushroom head, and marked ESTOP.

Emergency stop

Source: NFPA 79 First Draft report, 2024 edition (13.2.3, Annex E Table E.1 device designations) · Square D (Schneider Electric): Wiring Diagram Book 0140CT9201, symbols and examples

Other IEC countries

No regional notes on this page yet. If something is different in your country, please send feedback.

Frequently asked questions

How do you reset an emergency stop button?

First release the button, usually by turning or pulling it. Releasing it must not start the machine. The emergency stop is then reset with the reset button, and only after that is the machine started normally.

How do you wire an emergency stop button?

In a simple control circuit, its NC contact is in series with the whole control circuit and breaks the coils of all the contactors. On more demanding machines, two contacts of the button go to a safety relay.

When does an emergency stop need a safety relay?

When the risks of the machine require that a single fault must not prevent stopping. A safety relay monitors the emergency stop on two channels and also detects wiring faults and a welded contactor.

What does positive opening mean on an emergency stop?

The movement of the button separates the contacts mechanically, without relying on a spring, so even a welded contact is forced open. The standard calls it direct opening action. The mark is an arrow inside a circle.

What colour is an emergency stop button?

Red. It is a red mushroom-head button, and if there is a background around it, the background is yellow.