Electric strikes were invented over a century ago to do one job: to remotely release a locked door. Early electric strikes operated on alternating current. An electro-magnet in the electric strike was actuated each time the current alternated. The electro-magnet attracted a spring-loaded 'flapper' which caused a buzzing sound as it vibrated in unison with the actuating electro-magnet. Most old electric strikes were prone to early failure and were sealed so parts could not be easily replaced. The result was frequent electric strike replacement.
At one time electric strikes were only available in about a half dozen different face sizes. These early strikes were designed to operate with spring latches in mortise vestibule locksets or with rim night latches. Large cutouts were necessary for mortised electric strikes due to the large box required to house the electro-magnet and flapper parts. Since most electric strikes are installed on exterior exit doors, these doors usually open out to satisfy fire codes. Spring latches can be easily knifed open so electric strikes were used for convenience with security secondary.
Modern electric strikes have come a long way since those early days. Electronic access control systems often depend on electric strikes to release locked doors but access control systems also require more security than older electric strike designs provided. Electric strike manufacturers have responded with products which simplify the installation and increase usage with several additional features.
Fail-Safe and Fail-Secure
These are terms used to describe how an electric strike will act during a power failure. Electric strikes set in a fail-safe mode use continuous DC electrical power to remain in a locked position. In case of power failure, the electric strike will automatically unlock to allow free access through the door opening.
Fail-secure electric strikes are mechanically locked at all times. Fail-secure electric strikes unlock only when power is applied. In case of a power failure a fail-secure electric strike remains in a locked mode. Many electric strikes are field settable for fail-safe or fail-secure operation.
Latch Bolt Monitoring
Some electric strikes have a monitoring switch located in the strike pocket area. When the door is securely closed, the lock latch enters the strike pocket which moves the monitoring switch to a non-alert position. If the door remains ajar and the lock latch does not fully enter the strike pocket, the monitoring switch is set to an alert position and will send a signal to building personnel that the door is not securely locked.
Correct placement of the electric strike pocket is essential to smooth and dependable electric strike operation. Several electric strike models allow adjustment for either horizontal or vertical requirements. Adjustment may be needed after a new installation or may be needed due to minor door warpage or frame movement. An optimum installation is when there is only a small amount of in-out movement of the door when it is locked but just enough looseness to prevent binding between the lock latch and the electric strike keeper.
Electrical sources are most often alternating current. This causes the electric strike to 'buzz' as the current alternates. Rectifiers are designed to change AC current to DC current. This will eliminate any objectionable buzzing noise emanating from the electric strike. Electric strike manufacturers often feature replacement face plates. The electric strike body can be installed on different sized face plates depending on the ANSI cutout dimension requirements.
To read additional Locksmith Ledger articles on electric strikes, visit http://tinyurl.com/strikes314.
Aiphone's EL-12S is a non-industrial, compact, mortise electric strike. Designed for quick, convenient installation, the EL-12S can be installed with little or no modification to the mounting frame. Simply remove the existing strike plate, remove the dust box if present and install. Operates on a 12V AC/DC power source with a current consumption of; AC: 125mA, DC: 200mA. More Info: www.aiphone.com.
Camden's new 20 Series pre load strikes feature German engineered design, BHMA Grade 2 performance and competitive value. These strikes work with all major center-line cylindrical locks and feature an adjustable keeper, 12/24V AC/DC operation, left or right handing, to 5/8" throw, fail safe/fail secure operation and latch monitoring. Series 20 pre load strikes are available with a selection of faceplates and the CX-EPD2850L EZ Fit model avoids the need to cut or drill the door frame, and provides both horizontal and vertical faceplate adjustment. Camden 20 Series pre load strikes are supported by a five-year warranty. More Info: www.camdencontrols.com.
Dortronics’ 3300 Series strikes feature heavy duty construction and versatility. A simple field adjustment with a screw driver will convert these electric strikes from the factory default fail-secure to fail-safe operation. They can also be adjusted for 12 or 24 volt DC input voltage and are rated for continuous duty. Additional features include universal strike plates, a deep latch bolt pocket and latch bolt sensor option. More Info: www.dortronics.com.
Hager's 2930 Heavy Duty Electric Strike is designed for easy installation in a standard ANSI strike prep without additional cutting for access control of cylindrical, mortise locksets and mortise exit devices. The choice of application faceplates eliminates the need for centerline relocation, making this an ideal choice for new or retrofit, high security access control applications. This strike is dual voltage, 12/24 VDC, and field reversible between fail safe and fail secure. In addition, it is available with monitoring options that include latchbolt monitor, door secure monitor, and deadbolt monitor to further enhance security. More Info: www.hagerco.com.
The 9600 series Genesis is a windstorm rated, surface mounted electric strike designed to accommodate rim exit devices with a 3/4" throw latchbolt. All components are completely encased within its 3/4" thick stainless steel housing, so no cutting on the frame is required for installation. Simply place the electric strike on the surface of the frame, align it with the exit latchbolt and install. It is field selectable for fail secure and fail safe operation, and for 12 or 24VDC. More Info: www.hesinnovations.com.
The ROFU 2400 KIT has become the best seller in ROFU’s line-up of electric strikes. Installers find that its features meet most any situation they run into. Dual voltage (12 and 24 Volt) has been around for some time. The 2400 Kit also accepts AC or DC power input. The strike depth of 1 ¼” makes it suited for most any kind of installation, including glass store fronts. Keeper depth is ½”, so with a 1/8” door gap, the strike allows for a 5/8” latch projection. Field reversal from fail safe to fail secure (and back) is simple. The strike comes with two stainless steel faceplates so that most any existing opening can be filled. It comes with a UL listing for Burglar Protection and is RoHS compliance. More Info: www.rofu.com.
SDC’s 55 UniFLEX® Series Electric Strikes are ideal for high traffic, high security access control and multi-brand applications. Designed for installation in hollow metal frames, they provide rugged, robust and proven integration of cylindrical, mortise locksets and mortise exit devices with electronic access control technology. A choice of six application faceplates eliminates the need for centerline relocation, making them the perfect universal strike for new or ANSI 4-7/8” strike prep retrofit applications. 55 UniFLEX® Series Electric Strikes are non-handed, field reversible failsafe/failsecure, and are used with 5/8” latch bolts, or up to 3/4” latch bolts with 1/8” door gap. More Info: www.sdcsecurity.com.
The SECO-LARM Universal Door Strike (SD-996C-NUQ) is a UL-listed door strike that comes with three differently-sized faceplates, making it suitable for nearly any door type. The door strike has field selectable 12 or 24-volt operation and fail-safe or fail-secure operation. The strike's is built with a symmetrical design, making it suitable for either right-hand or left-hand doors. The SECO-LARM Universal Door Strike is engineered with convenience in mind, easily integrating into nearly any door type and installation. More Info: www.seco-larm.com.
An installation tool is now available for the Trine 4850 surface mounted electric strike. This unique 4850-ITL tool has the identical 4850 shape and throat cutout dimensions. Internal magnets attach the 4850-ITL tool to metal frames. The installation tool lets you "feel the door" on the frame. When the installation tool is accurately mounted in position on the frame, a custom center punch furnished with the installation tool is used to quickly mark the exact pin, bolt, wire and LB wire hole drilling locations. A 1/4" spacer is included with the installation tool when there a 3/4" dimension between exit device and frame. More Info: www.trineonline.com.