Electromagnetic Lock Deployment Considerations
The misunderstood electromagnetic lock. The device was initially designed as a solution to secure doors in large stadiums while safely releasing them in case of emergency. Should an emergency arise in this setting, a sea of humanity could come running to the exits, causing massive pre-load situations on the existing latch-based electrified hardware available at the time. The maglock was a way to safely release access-controlled doors in these settings without utilizing moving parts. It had an inherently safe mechanical design but had electrical control and code compliance considerations to achieve this safety goal. The Montreal Forum was the first location to have maglocks installed. The first maglocks were a line of magnetic fire door holders lined up on a bracket. Devices typically used to hold the door open were now used to keep it shut. But they have improved and have found their way into more general applications. Some hate and want to ban them, and some deploy them successfully daily. Properly installing maglocks can be complicated but can be a solution when used correctly.
The late Irving Saphirstein was the inventor of the direct pull maglock, and he worked with other engineers to improve the design over time to evolve it into the design we have today. This was the start of the Locknetics company. As a young engineer, I worked for him later in his career and learned not only about electrical considerations but also the construction of maglocks. I learned about the installation pitfalls that can occur if deployed incorrectly. Today, I see installations and am shocked at how incorrectly they are deployed and the lack of deployment knowledge. Here are details to consider.
Proper armature installation. Most installers believe that the main part of the lock is what is important, but good performance starts with the armature. The armature is the part of the lock that gets mounted on the door and is what the main component of the lock attracts to. The most common mistake I see with maglocks is mounting an armature to the door in a rigid manner. Maglock armatures are attached to the door with a central through-bolt quirkily called a “sexnut” and a series of washers. DON’T OMIT THESE WASHERS. Follow the manufacturer’s assembly diagram. Washers allow the armature to flex with a few degrees of movement in horizontal and vertical directions, even when the middle armature bolt is completely tightened. There are also usually at least two roll pins at the back of the armature, which stop the armature from rotating about the central fastener. Installers need to make sure that the holes drilled into the door to accommodate these roll pins are larger than the pins. The size and locations of these holes are typically printed on the template. An installer just has to use the correct drill. That armature needs to move around freely but not bang into the door at its ends. Without this freedom of movement in the armature, the locking performance is lost completely.
Utilize filler plates for mounting. The main part of the lock is mounted on the header of the door. Usually, headers have different profiles based on the manufacturer. Many poor installations I run into have most of the central part of the lock hanging off the header with no support, which severely limits the mounting rigidity. This causes mounting fasteners to loosen and break, potentially causing a lock to fall off the header. To manage this, a filler plate is used to create a landing area for the central part of the lock on the header. A filler plate is usually a piece of aluminum with a thickness that is the same as the header height, with several screw holes pre-drilled into it. You fasten filler plates to the frame using these pre-drilled locations before installing the lock to the header.
Avoid alignment issues. Maglocks come with exhaustively designed mounting templates that need to be used for proper installation. You can efficiently mark drilling and mounting locations on the door and header with a good template. Don’t just throw the paperwork in the trash along with the shipping box. Templates not only get the alignment between the armature and lock correct, but they also provide proper mounting spacing between the face of the armature and the lock, which avoids preload situations and door overtravel for good performance.
Use the specified mounting fasteners. Maglocks come with mounting fasteners from the manufacturer. If mounting on a wood frame, you want to use solid lag-type screws that are long enough to anchor themselves into the header and framing. If drilling into a metal header, mark and drill the holes, but consider tapping the holes before applying the screw. The self-drilling screws wander off during their application and have less strength than properly formed pre-tapped holes. Use the correct size tap drill when tapping into a metal header.
Inspect frame, hinge and door quality. You want to make sure that the frame and door is strong enough to accommodate the lock. The frame should not be sectional without welding and bust at the seams over time. There are a lot of forces put on a frame that may not have been designed to be applied in that location. If the frame needs reinforcement or replacement, do this service before installing the lock. Inspect the hinges for suitability and replace them if they are worn.
Inspect doorstops. You want to make sure, just like with electric strikes, that doorstops are properly adjusted so that the lock and armature are not acting as a doorstop. The stop should butt the door just as the armature meets the face of the maglock.
Review lock frame location. Most maglocks are mounted horizontally at the corner of the door on the open side. This is done for clearance and cosmetic issues. Despite this, mounting the maglock horizontally improves the physics of the system. Although considered a high-end installation, horizontal installations can use a continuous lock cover that extends over the entire vertical opening. A full-length cover prevents sharp corners in the opening and may accommodate multiple maglocks to overcome door warping by holding at multiple points. Adding additional maglocks to a single door does reduce the possibility of door warp but does not increase the maximum door force required for breakaway.
Consider surge suppression. Most modern maglocks have surge suppression integrated. Maglocks have large coils that can briefly generate thousands of volts when de-energized. For maglocks that don’t have integrated suppressing, add a MOV to them to shunt the back EMF. Even with integrated units, it’s not a bad idea to include an additional external MOV that can be replaced on a scheduled basis. Although it’s okay, discourage the use of diodes as surge suppressors as in some instances they can cause the lock not to release quickly.
Consider proper scaling. Maglocks have two main sizes. Standard 1200-1500 lb. units for full-performance door security and smaller 600 lb. units. The smaller units were not designed for security but mainly for traffic control. Lighter frames may not be able to accommodate a full-size unit due to the forces involved. Make sure the maglock is scaled to the frame and door strength.
Proper wire selection. Due to their high current needs, don’t use thin wire with a maglock. Use a quality 18 AWG wire with a plenum jacket. Using thinner wire will not only degrade holding performance but may heat excessively and may stop the lock from quickly releasing when de-energized.
Consider power supplies with backup batteries. If a maglock loses power, the door is completely unlocked. This is called a fail-safe operation. Some maglock systems are for security more than traffic control, so power supplies for maglocks often include a battery backup system. These systems are often based on low-voltage lead-acid alarm batteries that need to be changed every two years. Some jurisdictions do not allow these battery backups, and some only when tied into a central fire alarm. It’s important to consult with the local authority to determine when deploying a battery backup is allowed.
Be cautious for residual magnetism. Maglocks can come in a wide range of prices, from imports as unbelievably low as $22 to high-quality units costing over $900, depending on the quality and configuration. There is a reason for the higher construction costs of branded maglocks. Maglocks with little rubber bumpers or spring-loaded metal buttons on their armatures are units made from poorer grades of steel. These mechanical mechanisms are added to overcome residual magnetism caused by using low-grade steel in their laminations. The bumper mechanisms aid in unlocking when power is removed. This works fine until the bumping mechanism wears out, and then the lock starts not unlocking smoothly, causing a service call and perhaps a dangerous situation. Maglocks constructed of quality grades “grain-oriented” transformer steel will unlock immediately without bumping mechanisms. A robust installation will utilize a model of lock made from high-quality steel that unlocks immediately without mechanical helpers.
Egress accessories. Maglocks do not have a mechanical interface to the mechanical locking hardware on the door like a lever or exit device, so they need additional hardware added to the system for safety. Additional hardware, of course, raises costs and limits applications, so this is an area where poor installation companies love to skimp. To meet NFPA 101, a maglock requires two forms of egress. One of those is a push button that is labeled PUSH TO EXIT. This pushbutton must hold open the door independent of the electronics of the access control and must cut the power directly to the lock. This is a mechanical or electronic timer switch, depending on the jurisdiction. In addition to the button, a second form of egress is required, usually a motion sensor or an exit device (a.k.a. crash bar) with an internal switch. With the motion sensor, the door unlocks automatically when someone walks up to the door on the unsecured side. If that should fail, then the button is used as a backup release. With an exit device, depressing the device will cause the switch to close, de-energizing the lock and allowing egress. The button is also used as a backup release in this configuration. Use of touchless buttons may be used additionally, but they are not a replacement for an approved, listed egress push button assembly.
Fire alarm interfacing. The entire system should be connected to a fire alarm relay if the building has a central fire alarm system. The relay releases power to the lock in the case of a fire. This is often a big area of contention as making the connection to the fire alarm can involve a different qualified vendor. The fire alarm should use a maintained closed, but normally open, relay contact controlled by the fire alarm system to allow power to the maglock.
Regular cleaning. Maglocks can have obstructions and dirt between the armature and the lock over time, degrading performance. Since the armature can float, grains of sand and debris can cause a grinding action that can remove surface plating, exposing the steel directly and causing rust. It’s good practice to not only clean the surface of a maglock and armature regularly but also inspect the maglock for purposeful obstructions used to prevent the lock from bonding.
Sensors. Maglocks can be equipped with sensors for two main functions.
Door Position Switch (DPS) sensors are used to monitor the position of the door and report this status to an access control system. DPS signals can be used by the access control system to do an anti-tailgating function where the door locks immediately at re-closing, negating the remainder of the passage mode interval.
Magnetic Bond Sensors (MBS) are used to monitor the locking performance of a lock. This is a lesser utilized maglock option. When the lock has an MBS, the MBS will close when the lock meets the armature properly and is energized. This signal tells you that the lock is performing well and does not have an obstruction between its face and the armature. This status can be reported back to an access control panel or other monitoring station equipment like an illuminated switch panel.
Use cases. There are applications where maglocks are convenient, but many can also be addressed with modern latches and electric strikes. Electrified exit devices, electric strikes for exit devices, and surface-mounted strikes all provide higher levels of security but may be more challenging to install. Using these devices, you can often avoid the additional egress hardware and fire alarm tie-in that maglocks require while achieving a higher level of holding force on the door.
Many applications don’t have the preload requirements that maglocks are typically noted for, and many modern mechanical designs offer good pre-load performance. Careful consideration of hardware selection is important to meet budget and performance parameters.
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Credits: Mr. Dan DeMerchant’s Post (President at Highpower Security Products LLC)