Maglock Selection GuideAuthor: Brian Rhodes, Published on Dec 26, 2012
One of the most misunderstood yet valuable pieces of electrified hardware is the maglock. Few locks are stronger, but myths and confusion surround their proper use. Many access control designers avoid using them altogether, but should they? In this note, we examine maglocks, their proper application, and how to avoid problems when using them, including:
- Fail Safe vs Fail Secure Concerns
- The Core Components of a Maglock
- Legality of Maglocks
- Shear vs Conventional Pull Action options
- Bond Ratings
- Power Considerations
- Matching Maglock to Door Operation
- RTE / Fire Alarm Considerations
Designed to Fail Safe
Despite misconceptions about their safety, all maglocks fail safe. Unlike other pieces of electrified hardware that can be configured to fail secure - potentially complicating egress in an emergency - maglocks lose all holding force when power drops.
Because a maglock is essentially an electromagnet, if energy is not present - it simply does not operate. Unlike electronic cylinders or electric strikes that have moving mechanical components that can break or bind, a maglock has no moving pieces and does not wear over time.
While concerns perputually surround the 'life safety' of these devices, when they are properly installed they are safest locks available. The 'solid state' construction means that a maglock either operates according to design, or it does not operate at all.
Despite their 'high-tech' latching method, a maglock is a very simple device composed of just two pieces:
- Armature: This is a flat section of steel that matches the magnet 'box' installed on the frame. The armature must be securely fastened to the door in order to achieve a strong bond and keep the door shut.
- Magnet: The larger of the two components contains an electromagnet core. Unlike the armature, this piece never physically moves in relation to door swing, and is the only component that receives power during operation.
While not essential to keep doors secured, maglocks are often equipped with or require additional components that aid their function in access control deployments. Among these other elements are:
- Bond Sensor: A simple contact closure than confirms the maglock is energized and matched with the armature, signalling a valid 'bond'. This indicates the door is both closed and locked/secure.
- Integrated RTE PIR or REX: Some maglocks include a motion sensor or switch that drops power to the lock. This feature is required by life/safety codes (addressed below) so that in an emergency egress situation the lock drops power and permits exit.
- Door Closer: The closer returns the door to a 'closed' position. Because the door's armature must be in contact with the magnet to bond properly, a door closer device is necessary to always ensure the door is shut after opening.
- "MOV" , or "Metal Oxide Varistor": If not factory equipped, the maglock may require an MOV to be field installed, typically across the power leads of the lock. Because a maglock causes a magnetic field to collapse every time it is de-energized, it can backfeed a small but damaging surge into the power supply. A MOV dissipates this field and prevents this type of damage from happening.
Which Type Should I Choose?
Selecting the proper type of maglock for an application is not difficult, if a few basic parameters are addressed during specification. The basic questions that must be answered, and the order they must be asked are listed below:
- Legality/ AHJ requirements
- Action Type (Shear vs. "Conventional"/Pull)
- Bond Ratings
- Voltage Type
- Operation Type
- Required RTE Hardware/Fire Alarm Tie-In
The first, and most critical aspect that must be addressed is whether or not use of maglocks are permitted by the local code authorities, or what special restrictions apply to their use. Permission or prohibition is granted on a municipal level, and can vary from one town to the next. In general, a call to the local Fire Marshal or City Codes department will yield proper guidelines. In the examples below, note that accepted use may vary depending on door locations, door types, and maglock type:
Shear Action vs. "Conventional"/Pull Action
Maglocks are available in two functional types; either Conventional/Pull style or Shear style actions. The difference between these types is noted in the drawing below:
The action determines the intended mounting location of the maglock. As depicted in the drawing, the movement direction the lock is designed to 'hold' distinguishes the type. Because of the differences in coil windings, a 'conventional' maglock is not suited for use in a 'shear' application, and vice versa.
While the operating principle is the same, the installation locations and door preparations are different according to maglock types. In the sections below, we address the two types and how they differ:
This style of maglocks is ideally used where maglocks must be low-profile, as they can be completely recessed (hidden) into frames. Because these units are installed flush with exposed surfaces, they are tamper-resistant. However, shear style locks are less common than the 'conventional' type because both frames and doors must be previously fabricated with lock clearances in mind.
Since many, if not most, of electronic access control systems are 'after-market' or 'retrofitted' to existing doors (without the proper cut-outs), shear locks are not frequently used. However, because of their low-profile and strong bond in the intended direction of travel, special applications like gates or rolling grilles often employ shear locks.
Cost for shear locks is roughly equal compared to other maglock types, however due to the additional fabrication required to doors and frames to fit them, the deployment cost is higher.
Conventional / Pull Locks
The most common type of maglock installed today is the "Conventional/Pull" type. In contrast to the shear action, this type is installed with the magnet exposed, meaning the magnet must be installed on the 'secure' (or unexposed) side of the door. The direction of door swing can complicate this, since some doors will swing in - resulting in a modification to the installation position and armature bracket - a point we examine later.
Power cabling is typically installed inside the frame, and the armature plate is installed flush onto the door itself. Because this plate must be installed so it is integral with the door leaf itself, it is drilled and attached with through-bolts. While not an issue for hollow metal or wood doors, this can present a problem for frameless glass or thin bezel doors. In those applications, a 'low profile' maglock may need to be used instead.
Maglock holding force is measured in hundreds of pounds, frequently more than 1500 pounds per lock. This rating describes the amount of pulling force required to match the magnetic bond of the lock - any amount greater will overcome the electromagnetic bond.
Typically, the lowest bond rating available is 600 pounds, while the strongest models are rated to 2700 pounds. In general, the stronger the holding force the higher the cost anywhere from a few hundred dollars to more than $1800 for the strongest units. However, considering the structural elements of the door, (eg: leaf, frames, pull hardware) will fail before the maglock itself, it is exceedingly difficult and uncommon for the bond of a maglock to be defeated.
In general, exterior doors should not be secured with less that 1500 pound rated maglocks. Less expensive and weaker locks have a variety of uses (eg: securing cabinet doors, sliding gates, or closets), but they should not be used where a brute force attack using tow chains or mechanical come-alongs is possible.
Maglocks require power for operation. Most modern models are field selectable to either 12 or 24VDC, but other voltages and AC versions are available. Power for these locks is often recommended to be supplied by an independent, individually fused power supply. Because the effectiveness of these locks is entirely dependent on the strength and dependability of the power source, maglocks do not typically share power sources with surveillance equipment.
Additionally, while 'low-draw' maglocks are available, supplying power via door controller in the way that electric strikes are powered in not recommended. Unlike a strike that only intermittently draws power when activated, a maglock continually draws power during operation. The heavier duty-cycle of the maglock calls for a supply source that is more robustly built and able to handle the constant supply of current to the lock.
Matching Maglock to Door Operation
The next step in deciding which lock to use comes from examining the door itself. Because openings are constructed in several ways, maglocks must be specified to match the opening. We examine a few of the most common installation locations in the list below:
- Outswinging Door: This is the simplest, and default location that maglocks are installed. In this position, because the door swings away from the magnet, the maglock is installed beneath the top edge frame of the door, and the armature is mounted to match the location. While the lock will encroach into the 'headspace' of the opening, typically this is only a few inches. Given the standard 8 foot height of the door, the unit does not present a hazard.
- Inswinging Door: In this orientation, the swing of the door would interfere with the lock if hung in the 'outswinging' position, so the lock is moved up and mounted flush with the side of the top frame. In addition, the armature is moved outward and upward with a 'z-bracket', which may be an additional cost. Note in the picture below how the door swing affects installation location:
- Double-Door Units: Maglocks can be installed on 'dual-leaf' or 'double-doors'. Typically codes require adjacent door leafs to release simultaneously. While this can sometimes be achieved with two single-door maglocks, many electronic access door controllers are only able to be connected to a single locking device. In this case, a double-door unit must be used so a single release command will allow adjacent doors to open at the same time. In general, these units are able to be installed on the frame like single units, and the presence of a door mullion does not impede installation.
- Hold-Open Function: Maglocks are also used to hold doors open. Especially in applications like hospital corridors or busy hallways, fire doors may be critical opening that are only closed when absolutely necessary. Because maglocks can easily be integrated into fire alarm systems, they are sometimes used to lock doors in the 'open' position, and in a fire-alarm situation, the maglocks drop and associated door closer then shuts the doors. The image below shows a maglock used in this application:
Required RTE Hardware/ Fire Alarm Tie-In
Briefly stated, 'RTE', or 'Request to Exit' Hardware are accessories required by code where maglocks are installed. These devices, typically PIR motion sensors and/or 'Exit' pushbuttons, must be installed so a maglock loses power when people want to egress through the door.
While the topic is substantial, and will be addressed separately in a future post, the requirement to install RTE Hardware is often cited by the following passage in the IBC Code:
From the 2012 Edition:
1008.1.9.9: Electromagnetically locked egress doors. Doors in the means of egress in buildings with an occupancy in Group A, B, E, M, R-1 or R-2 and doors to tenant spaces in Group A, B, E, M, R-1 or R-2 shall be permitted to be electromagnetically locked if equipped with listed hardware that incorporates a built-in switch and meet the requirements below:
1. The listed hardware that is affixed to the door leaf has an obvious method of operation that is readily operated under all lighting conditions.
2. The listed hardware is capable of being operated with one hand.
3. Operation of the listed hardware directly interrupts the power to the electromagnetic lock and unlocks the door immediately.
4. Loss of power to the listed hardware automatically unlocks the door.
5. Where panic or fire exit hardware is required by 1008.1.10, operation of the listed panic or fire exit hardware also releases the electromagnetic lock.
Many jurisdictions require maglocks to automatically release when the fire alarm is activated, so that emergency egress in a fire is completely unabated by maglocks. Incidentally, the requirement to release maglocks upon activation of the fire alarm in addition to RTE hardware has been removed in the 2012 edition of the IBC code, but many jurisdictions will still require this integration despite the recent revision.
Because they are technically door hardware, maglocks are available from most 'traditional' door hardware conglomerates within the ASSA ABLOY, Ingersoll Rand, and Stanley brands. However, there are a few brands that specialize in offering maglocks or units with special designs. While not a comprehensive list, the follwing list details a few of these recogized names:
- DynaLock: A large manufacturer with a broad portfolio of action types, voltages, and integrated features.
- SDC: Electrified Hardware manufacturer that specializes in access control hardware, including low-profile, low current draw, and high bond rating maglocks.
- Rutherford Controls: This manufacturer was recently purchased by Dorma (a transaction we covered in this report) known for its line of 'multifunction maglocks' that incorporate delayed egress, visual/audio annunciation, and even CCTV cameras.
- Securitron: This ASSA company offers several lines of maglocks, including the low-profile M680 series, configurable to include an intergrated RTE PIR and CCTV camera in an architecturally styled finish. (See our report on this product for more details.)
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