Mushroom Button (Mushroom-Head Actuator)
A control element used in emergency stop circuits, with a head wide enough to be pressed with the palm and which latches mechanically when pressed. ISO 13850 requires a red body on a yellow background for this element, a latching construction, and reset by a deliberate action.
The mushroom head is not accidental: it is designed wide and protruding so it can be pressed with a gloved hand, with an elbow or with the palm in a moment of panic. When pressed, no spring returns it; it holds its contact position until the head is pulled, turned or reset with a key.
- Colour code: a red actuator with a yellow background immediately behind it. This combination is reserved for emergency stop only; it is not used on a normal stop button.
- Contact construction: a normally closed contact with positive opening is used; even if the contact welds, the mechanism physically separates it.
- Access: it must be reachable without obstruction from every point where the operator stands.
On radio-controlled cranes the mushroom button is usually found in two places: on the machine panel or at a fixed operator station. In the panel, the receiver supply or relay output line is routed through this button's contact; that way, whatever the remote control says, the contactor coils cannot be energised while the button is pressed. Do not assume that the stop key on the remote control unit replaces the mushroom button.
The context in which this term is used: Wireless Crane Remote Control Selection Guide