Electromagnetic Lock Basics

Important: Before installing electronic locks, it is important to check with the “Local Authority Having Jurisdiction” (LAHJ). An electromagnetic lock is designed to provide security for a door or gate that closes against a solid jamb or stop...


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Mounting and installation modifications have included the addition of a splice chamber and trapezoid shaped mounting bracket and slot mounting in the lock's case. The splice chamber has been incorporated into the housing of some magnetic locks. The splice chamber normally contains the circuit board with sufficient area to connect the wires.

When installing a “block” style magnetic lock containing existing mounting holes either vertically or horizontally positioned, the installer would have to hold the magnet in position and start several of the mounting bolts in order to hold the magnet in place.

The development of the trapezoid mounting bracket enables this bracket to be first installed into the header. Then slide the electromagnetic lock into place and determine what final adjustments would be necessary. Several of the mounting holes in the trapezoid mounting bracket are elongated, permitting front to back adjustment in order to locate the magnet for maximum attraction. Once in position, existing set screws are tightened, securing the magnetic lock in place.

SDC (Security Door Controls) developed the interlocking EZ mount assembly on their EMLocks®. The EZ mount bracket is installed onto the header, using the magnet to set the bracket's position. A captive mounting screw locks the magnet in position. The EZ mount assembly simplifies the installation of the Emlock electromagnetic lock.

The armature or strike plate is a thick piece of ferrous metal that is attracted to the magnetic field produced by the electromagnetic lock. The armature is usually about the length and height dimensions of the electromagnet. It is normally is “float” mounted onto the door, allowing it to rock into position flush against the face of the magnet. To accommodate this needed movement, lock manufacturers usually include rubber washers to install between the armature and the face of the door. Secondary locating pins are installed into the armature, having holes drilled into the door face to permit movement without rotation. In addition, energy absorbing sex bolts are available with an internal spring designed to absorb and dissipate the force of a blow aimed at disengaging the magnetic bonding in order to gain unauthorized access.

Additionally, manufacturers have developed offset mounting hole and split armatures. The offset armature is designed for an installation where it is necessary to raise or lower its position to better accommodate the electromagnetic lock. The split armature (strike) can be used to enable one electromagnetic lock to secure a double door opening using traffic control holding force.

For applications that require delayed egress, some electromagnetic locks are designed to delay exiting through the door for 15 or 30 seconds while sounding an alarm, notifying personnel of an attempted exit. Once the delay period has expired, power is removed and the door can be opened. This type of lock mechanism complies with the NFPA Life Safety Code 101, Special Locking Arrangements. A few of the applications for this type of lock mechanism can be to deter shoplifting, employee theft, patient wandering or baby abduction.

A specialized application for the surface mount electromagnetic locks is for sliding doors. The electromagnet is recessed into the lock side of the jamb leg. The armature is recessed onto the lock edge of the sliding door. When the door is closed, the armature comes into close contact with the electromagnetic lock. When powered, the electromagnet secures the door.

Another specialized type of electromagnetic locks are the shear locks. These concealed magnetic locks were designed for providing traffic control for Herculite (glass) doors, while exhibiting no visible signs of a lock or locking mechanism. Unlike the standard electromagnetic lock, the shear lock provides its greatest power against the armature being pulled across the face of the electromagnetic lock (i.e. opening the door).

The face of the shear lock separate from the electromagnet has recesses into which raised shear locator posts built into the spring loaded armature engage when the door is closed and the electromagnet is powered. The purpose of the raised shear locator posts is to stop the armature (strike plate) from sliding off from the shear lock. When power is removed, the shear strike plate retracts, disengaging the shear locator posts from the magnet, releasing the door.

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