The electric strike provides remote electrical control to unlock a door. The electric strike was originally patented in the late 1880s so New York City high rises could have a locked common entry door, while residents could grant access and physically unlock the door from inside their apartments.
Today, there are a number of different styles of electric strikes. The basic style is the recessed electric strike mounted into the doorjamb at the location corresponding to the centerline of the lock's latch.
The standard recessed mounted electric strike appears as a modified strike plate with a strike lip and an attached case. Instead of a fixed opening for the latch to enter and become trapped, a movable jaw or keeper is in the front of the strike faceplate. As the door closes, the latch slides along the electric strike's lip. The latch retracts as it slides over the movable jaw that is in the locked condition. As the latch passes over the jaw it extends within the opening in the electric strike, becoming trapped. The strike opening will usually be either one-half of an inch or deeper to accommodate the different length latch/bolts.
Once the latch is within the opening, the straight edge of the extended latch cannot slide back over the jaw. The door can be opened in one of two ways -- retract the latch by operating the knob/lever or electrically release the movable jaw. When electric strike is remotely released, the jaw tilts out of the way as the door is opened by having the latch slide out of the electric strike in the extended condition.
Most recessed electric strikes are designed for a 1-3/4" thick door in a standard jamb. When installed, the edge of the electric strike lip is flush with the edge of the jamb. This enables the lock's latch to use the lip as a ramp to slide into the electric strike without contacting or damaging the jamb material. To accommodate thicker doors and larger jamb sizes, some electric strikes have optional lip extensions, available in different sizes. Lip extensions for fire-rated electric strikes must be factory installed.
The internal mechanism for controlling the operation of an electric strike is different for most manufacturers. Most are controlled by a solenoid, operating a mechanism that controls the jaw or keeper. For the purpose of this article, I will use Adams Rite electric strikes as the examples and illustrations.
The Adams Rite 7100 Series is an ANSI/BHMA Grade 1 electric strike designed for operation with cylindrical latches that have a 1/2" to 5/8" projection. The 7100 Series electric strike has a 1" x 3-3/8" x 1-5/8" deep zinc-aluminum alloy case. The strike lip is designed for operation with a 1-3/4" thick door, when installed into a standard jamb. The faceplate is 1-1/4" x 4-7/8" to fit into an opening designed for an ANSI strike plate. The faceplate has radiused corners to accommodate aluminum and wood installation. The radiused corners can help prevent splitting of the wood or cracking of an aluminum jamb.
The AR 7100 Series electric strikes are available with 12, 16, or 24 volt AC and DC solenoids. The voltage and duty of the solenoid determine the operation of the electric strike. A solenoid is the housing that surrounds a coil of wire around a metal rod. When the solenoid is powered, the rod moves in one direction. When power is removed, the rod moves back to the original position. The difference between an AC or DC solenoid operating on 12, 16 or 24 volts is the number of windings. In addition, there is a difference between an intermittent duty and a continuous duty solenoid. An intermittent duty solenoid is designed to be energized for no more than 30 seconds. The intermittent duty solenoid is used in a fail-secure electric strike application. A continuous duty solenoid is designed to be energized without break or interruption. A continuously duty solenoid can be used in a fail-safe or fail-secure electric strike application. A continuous duty electric strike requires less power than an intermittent duty electric strike.
The Adams Rite electric strikes have two adhesive labels attached to each electric strike. The larger label indicates the model, voltage, amperage, date of manufacture, the duty rating, and UL listing (if applicable). The smaller label indicates the model of the electric strike, the static strength, the dynamic strength, and the endurance. For this 7100-510 electric strike, the static strength is 1,500 lbs.; the dynamic strength is 70 ft-lbs, and the endurance is 500,000 cycles.
An AC-rated electric strike's solenoid will buzz when power is applied. Alternating Current, which regularly reverses direction, causes the buzzing noise. DC power does not buzz as Direct Current flows only in one direction. To eliminate the AC buzz, install a rectifier anywhere between the transformer/power supply and the electric strike.
A continuous duty electric strike can be operated as either fail-secure or fail-safe. A fail-secure electric strike unlocks when powered. If power should fail, the electric strike remains in the locked condition. A fail-safe electric strike locks when powered. If power should fail, the electric strike unlocks and remains in the unlocked condition. For this reason, if a fail-safe electric strike is used for the locking mechanism in a building, there must be a back-up battery system installed in case of power failure. Note: Before installing an electric strike contact the local authority having jurisdiction.
The Adams Rite 7100 Series electric strike operates using the solenoid located on a shuttle that slides to either lock or unlock the jaw when power is applied. For a fail-secure electric strike, when no power is applied, the shuttle keeps the latch arm in the unlocked position. In this position, the blocking arm is free to move, allowing the jaw to tilt out of the way when the door is swung open. When power is applied, the latch arm moves against the blocking arm, locking it in place. In this position, the blocking arm keeps the jaw from tilting, not allowing the latch to exit the electric strike or the door to open without first retracting the latch.
The AR 7100 Series electric strikes have field reversible operation. A fail-safe electric strike can be converted to a fail-secure electric strike without any additional components or specialized tools or operations or vice versa.
To convert a fail-safe electric strike to fail-secure:
Step 1. Remove the faceplate and strike lip.
Step 2. Remove the screws securing the cover onto the case. Lift off the cover.
Step 3. Carefully remove the blocking arm return spring.
Step 4. Lift off the blocking arm.
Step 5. Lift off the latch arm.
Step 6. Lift off the separation plate.
Step 7. Carefully remove the solenoid from the case.
Step 8. Carefully lift out the shuttle and the shuttle spring.
Step 9. Place the shuttle spring into the opposite end of the shuttle.
Step 10. Install the shuttle into case, spring end first. Make sure the spring compress properly.
Step 11. When the shuttle is seated, install the solenoid in the reverse direction. There is an opening for the wiring on each end of the case.
By changing the position of the shuttle spring and the direction of the solenoid, the electric strike operation is reversed.
Step 12. Install the separation plate, latch arm, blocking arm, spring, case cover, strike lip and faceplate. Test the operation of the electric strike.
With the case cover removed, a fail-safe configured AR 7100 Series electric strike can be identified by the position of the blocking arm tip that must be with the latch arm notch. This way when power fails, the jaw cannot push be pushed open because the blocking arm is locked in place within the latch arm notch.
With the case cover removed, a fail-secure configured AR 7100 Series electric strike can be identified by the tip of the blocking arm just out of the latch arm notch when power fails. In this configuration, the when pressure is exerted against the jaw, the blocking arm will tilt out of place, and the latch can be moved out of the electric strike.
To convert back to a fail-safe operation, repeat the above steps. Be careful not to loose the springs. They are available separately.
Over the years, there have been a number of developments in the design, operation, and security features of the electric strike. For me, the most important development was the movement of the solenoid on a heavy duty electric strike from extending out of the case to within the case. This has made installation of electric strikes into concrete poured jambs much easier, as you no longer have to hammer and drill through the concrete to provide space for not only the solenoid, but space for sliding the electric strike into the opening. Additionally, electric strikes have become smaller. Today many models of the recessed electric strikes require minimal modification of the jamb.
An additional development is the surface and the semi-rim mounted electric strike. The surface electric strike is mounted onto the surface of the jamb without any modification. The semi-rim mounted electric strike is only partially recessed. These two types of electric strikes are mainly used for Pullman-style bolt on rim exit devices.
Depending upon the application, some electric strikes are UL Listed for Burglary Resistance and some are UL 10C, a three hour rating for Fire Door Assemblies. To identify a fire-rated electric strike, a capital letter "F" will be stamped into the faceplate. The faceplate will be made of stainless steel and the strike lip will be made of either stainless steel or high temperature steel. The faceplate will be held on with tamper-resistant screws.
Monitoring capabilities have been added to electric strikes. Adams Rite offers two types of monitoring for their electric strikes; latch bolt monitoring and jaw monitoring. The latch bolt monitoring is accomplished by have a sensor switch in the base of the jaw. When the door is closed and secured, the latch bolt contacts the sensor switch, illuminating an LED or other signal. When the latch bolt is retracted or no longer against the jaw, the LED turns off indicating the door is no longer secured.
Jaw monitoring has a sensor within the case that indicates if the blocking mechanism is blocked. When the blocking mechanism is not blocked, the LED extinguishes indicating the door is no longer secured.
When installing an electric strike, there are three considerations. The first is the type and location of the electric release. The second is the type and location of the power supply. The third consideration wiring the electric release, power supply and power source to the electric strike. If you have questions regarding the installation of an electric strike including the type and size of power supply, wire, and release button, contact your local locksmith wholesaler or the manufacturer's technical support group.
For the purpose of this article, we will install a 7100-510 electric strike into a portion of jamb channel. The jamb channel was pre-cut to accommodate the electric strike and the mounting clips. The opening required for the electric strike can be cut using a router and template or the old-fashioned way, using a drill, saber saw and file. Once the opening has been cut and checked for size, drill two holes for attaching the mounting clips onto the jamb.
Note: when install an electric strike using the old fashioned method, be sure to cut the opening slightly smaller. This way, a file can be used to enlarge the opening. A too large opening is much more difficult to repair.
The 7100-510 electric strike comes with mounting clips and adhesive shims to accommodate installation. To install the electric strike:
Step 1. Install the power supply/transformer, release mechanism, and if necessary, the rectifier.
Step 2. Cut out the opening for the electric strike. Check to be certain the electric strike will fit in the opening.
Step 3. Attach the mounting clips onto the top and bottom of the electric strike cut-out. Secure using Phillips head screws.
Step 4. Make the necessary electrical connections.
Step 5. Slide the electric strike into the opening. Secure using Phillips head screws. Test the operation of the electric strike.
Adams Rite electric strikes are available in different configurations for most types of lock hardware. The faceplates are available with different finishes to match hardware, and varying length lip extension up to three inches to accommodate most door and jamb sizes.
For more information, contact your local locksmith wholesaler or Adams Rite, 260 Santa Fe Street, Pomona, CA 91767. Telephone: 800-872-3267. Fax: 800-232-7329. Web site: www.adamsrite.com.