How to Create a Basic Man Trap System

A mantrap (otherwise known as a security interlock system) is a locking system that prevents one door opening before another is closed. One very popular application for a mantrap is on a clean room, where it is vital to control the flow of air (and dust) in and out of the secured space.

Every mantrap I have helped design is based on electromagnetic locks (AKA magnets or maglocks). There is a good reason for this. Maglocks are very good for this application because they are inherently fail safe, and, except in detention applications, it is desirable to use fail safe electrified locks in a mantrap application.

Typically a mantrap is used on two consecutive openings (see illustration below):

As long as the magnets are supplied with power, they are locked.

1. To enter the secured space, a person activates the access control (keypad, pushbutton switch, keyswitch, prox reader, etc.).
2. The access control closes a contact on the matrap relay for perhaps 10 seconds, telling it to unlock the first door for that amount of time.
3. The person opens the door, changing the state of the door position switch, which tells the matrap relay to keep the second door locked.
4. When the first door closes, the door position switch on the first door returns to its original state, which signals the mantrap relay to release the second door.
5. When the person opens the second door, it changes the state of the door position switch on the second door, which tells the mantrap relay to keep the first door locked.
6. When the second door closes, and the door position switch on the returns to its original state, the mantrap relay relocks both doors.

Similarly from the inside, pressing the first request to exit button releases the inside door while simultaneously locking the outer door. The outer door cannot be opened until the inner door is shut.

Please visit the links at the bottom of the page for wiring diagrams.

If you have further questions, don't hesitate to contact me at

tomr@rubecom.us