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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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. Electromagnetic locks are fail-safe locking mechanisms that require constant power to remain locked. They are designed to provide basic traffic control up to a medium level of security.

The basic electromagnetic lock is normally installed onto the jamb of an out swinging door. The ferrous metal armature plate is mounted onto the face of the door in alignment with the bonding surface of the electromagnet. When the door is closed and the electromagnetic lock is energized, the current flowing through the wire coils produces a magnetic field. This magnetic field attracts the armature plate mounted onto the door. The armature is drawn against the electromagnetic lock with sufficient force to prevent the armature (door) from being opened.

When power is removed from today's magnetic locks, the magnetic field immediately dissipates and the door is immediately unlocked. Earlier models of magnetic locks have suffered from residual magnetism that caused electromagnets to retain a portion of the magnetic field, building in strength over the years. This would eventually cause the door to remain bonded, resulting in difficulty separating the armature from the magnet (opening the door) in the unenergized state.

Electromagnetic locks have increased in popularity as the potential applications have increased and the costs have decreased. In this article, we will discuss the operation, types, advantages and disadvantages and generalized installation considerations.

An electromagnet is a piece of metal that is wrapped with wire and then electrified. The electromagnetic lock in its basic form is a locking device that has no moving parts, depending upon a produced magnetic field to lock the armature (strike) against the magnet. To electrify the magnet, loops (coils) of wire surround the metal, while electrical circuitry is used to control the direct current (DC). Current draw for most electromagnetic locks is minimal, costing much less than a conventional light bulb to operate.

The electromagnet component consists of a metal alloy formed in a specific shape. The goal is to produce as large a magnetic field as possible within a limited sized housing. The specific chemical composition of the alloy is different for each lock manufacturer and is a closely guarded secret. The reason is specific metals' molecular structure will align with each other to greatly enhance the magnetic flux density (armature holding power).

Securitron, a manufacturer of electromagnetic locks, uses special metal alloy formed in “E” shaped plates. The size and number of “E” plates and number of coils of wire used in a specific electromagnetic lock determine the current and the holding power of the magnet. The holding power of an electromagnet starts at approximately 200 pounds and goes up to to almost 2,000 pounds for the larger units. Electromechanical models can have a holding force of 4,000 pounds.

The shape of the electromagnet is usually rectangular with a flat face to maximize the electronic bonding capability of the armature. The early mounting choices were header mount and face mount. The header mount meant there were holes running vertically on the sides of the magnet housing. Face mount was horizontal holes. Over the years, manufacturers developed a variety of mounting variations for magnetic locks using specially designed brackets and spacers. As an example, top jamb mounting kits will accommodate in-swing door applications.

Electromagnetic locks have evolved in the way they operate and are installed. An early improvement eliminated magnetic residue. A later development was dual voltage (12/24VDC) electrical circuitry that could identify and accommodate voltage. Upgradeable electromagnetic locks were designed so components could be replaced, either to upgrade the capability of the electronic lock mechanism or to replace non-functioning components.

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