Anelectromagnetic door holder (electromagnetic door holder and release orhold-open device, sometimes informally called amag hold open orelectric doorstop) is a simpleelectromechanical mechanism which can be used to hold afire door or security door open until given a signal to release. Afire alarm control panel or a similar emergency control system usually powers and controls the door holder.
A simple electromagnetic door holder consists of a strongelectromagnet, usually attached to a wall or mounted in a floor pedestal enclosure, next to the door it controls. The mechanism may be mounted near the floor, at the upper corner of the open door, or at any convenient height along the latch edge (away from the hinged edge).
A steel plate, often mounted on aball joint orswivel joint, is attached to the door so that it can contact the electromagnet when the door is fully opened. An electric current typically energizes the electromagnet to attract and hold the steel plate, keeping the door open. Unlikeelectromagnetic locks, the magnetic attraction of an electromagnetic door holder is usually weak enough that it can be manually overpowered at any time by anyone, allowing the door to close.[citation needed]
If a fire alarm control panel,burglar alarm control panel, or similar emergency system is triggered, it will cut electrical power to the electromagnetic door holders under its control. The door holders release, allowing the doors to close automatically usingdoor closers.[1][2] The electric power to keep the doors open is typically 12 VDC, 24 VDC (common), 24 VAC, 120 VAC, or 240 VAC.
The closed doors may or may not mechanically latch or lock in the closed position. Many fire doors do not lock, to allow building occupants to move within the building to find an exit easily. On the other hand, security doors may close, latch, and lock, to prevent passage. Other designs are used to secure sliding or overhead doors similarly, holding them open until a signal to release the doors to close automatically.
In life safety and security applications, electromagnetic door holders must be very reliable; the simplicity of the mechanisms helps considerably. They are designed to befail-safe in that anything interfering with their operation (such as a power failure) will cause them to release the doors and allow them to close.[2]
To overcome possibleremanent magnetism, which could cause the electromagnet to fail to release, some door holders are equipped with a spring-loaded pin that helps push the magnetic plate away from the electromagnet when the power is cut.
| Fundamental concepts | |
|---|---|
| Lock hardware | |
| Keys | |
| Mechanical locks | |
| Electronic locks | |
| Other lock types | |
| Lock picking | |
| Door hardware | |
| Emergency access/exit | |
| Security alarms |
|
| Miscellaneous | |
