Electric Strike Evolution

Early in my career as a locksmith, I installed mainly two brands of electric strikes, Adams Rite and Trine. Trine electric strikes were 00 Series, installed mainly into light commercial application wooden jambs. The electric strike was relatively small with the components contained within the body. This made the installation relatively easy if the lock side jamb molding could cleanly be removed to run the wiring.

The Trine electric strike was the main electric strike for jewelry stores, liquor stores (after 8 p.m.) and other small businesses that wanted the ability to see the customers before they entered their business. After all these years, Trine Access Technology still includes the 00 Series Electric Strikes in their product line. As recently as 10 years ago, I found out that a few of these strikes were still in operation.

The transformers, wiring and the momentary buttons were purchased from the doorbell section in one of the hardware supply houses or a department/hardware store. Unlike a power supply, a transformer simply changes the voltage from 120VAC to a lesser Alternating Current Voltage (VAC); it does not convert the voltage from AC to DC. In those days, the most common voltage was 16VAC. Alternating current solenoids are only used for intermittent duty. Intermittent is ten seconds or less power. An advantage is the AC electric strike buzzes when powered. This eliminated the need to install a noisemaker to notify the customers when to push or pull open the door.

Adams Rite electric strikes were used for high traffic applications. These heavy duty electric strikes had the solenoid extending out from the body. Various models had the solenoid pointing out the back or one end of the body. Installing one of these Adams Rite electric strikes into a concrete fill jamb was very time consuming.

Adams Rite has expanded their electric strike product line to control access for mechanical and electromechanical locks in hollow metal, wood and aluminum doorjambs. An example is the UltraLine 74R1 Electric Strike, a semi mortised strike for rim exit devices that can be installed into any of the three doorjambs providing UL1034 Burglary Listing. This electric strike can accommodate exit devices with ¾" Pullman type latchbolts and is capable of opening under 35 pounds of pre-load.

Electric Strike Basics

Electric strikes are relatively simple mechanisms, invented in the late 1800s. The five basic components of an electric strike are the body, keeper, faceplate, lip and solenoid. The lip, which can be a black plastic/aluminum separate component or a portion of the faceplate, is the bridge between the keeper cavity and the edge of the jamb. The keeper mechanism enables the latch to retract and project into the cavity as the door is being closed. To open the door, the keeper either pivots outward or releases the deadlatch and provides a ramp mechanism to retract the latch when the strike is activated. Keeper depth (cavity) determines the projection (length) of the latch/bolt. The solenoid has one of two purposes: it can be used either to unlock the keeper mechanism (Fail Secure) or to lock the keeper mechanism (Fail Safe).

Many commercial grade electric strike solenoids have been reduced from the approximate 1-1/2" in diameter and two to three inches in length. Today, most heavy duty electric strikes have their AC and/or DC solenoid located within the housing. Some institutional/detention electric strikes have external solenoids.

In the early days, the standard action for an electric strike was Fail Secure. Power is required to release the latch. Some electric strikes were non-handed. However, many of the faceplates were non-standard sizes. The only option was finish and having the ability to radius a faceplate using a file.

Technological Advances

Then technological advances began. The continuous duty (DC) solenoid came to the market. Plug-in power supplies were introduced for light duty applications, making it easier and inexpensive to offer direct current (DC) powered electric strikes, which do not buzz when powered. Using DC current also enabled electric strikes be Fail Safe, as continuous power is required to remain locked. Loss of power unlocks the electric strike. Continuous duty solenoids today can have a long, relatively cool and productive life. Continuous duty is considered 10 seconds to constant on power.

Continuous duty electric strikes will often run cooler and longer when using an in-line power controller. For example, the HES Smart Pac III is able to receive input voltages from 12 to 32V AC or DC. It has a built-in bridge rectifier. The continuous duty timer reduces initial voltage by 25% to extend the life of the electric strike. The Smart Pac III includes built-in resettable fuse, Metal-Oxide Varistor (MOV), voltage regulation and input status LED.

Electric strike applications expanded to include various mortise lock latch configurations; fire rated cylindrical locks, deadbolt locks and rim exit devices. For mortise locks, the latch mechanism does not necessarily follow the centerline of the lock. Plus, the changes in latch design and deadlatch placement affects the location of the strike plate openings and necessary size of the electric strike keeper cavity. Some electric strikes and faceplates were developed to operate with dissimilar styles of locks. To match the faceplate with the application, interchangeable faceplates were introduced for the same model electric strike body. Over the years, some companies include multiple faceplates with some of their electric strikes.

The electric strike lip provides a path for the latch to enter and exit the pocket by bridging the gap between the faceplate and the edge of the doorjamb molding. To install a lip-equipped electric strike, the jamb has to be cut out to accommodate the lip. Lip sizes and lengths can vary by manufacturer and model.

Compact electric strikes are designed to fit into the strike plate cutout in the jamb by using a modified strike plate. Some have a concealed design that appears to have an exposed lip from a standard strike plate when the door is closed. For example, the HES 8000 Series cylindrical lock electric strike has unique keeper pin locking design. When unlocked, it allows the deadlatch to extend fully, permitting the latch to be pushed into the door edge so the door be opened.

The BEA 10STRIKENC is designed to fit into a standard ANSI frame and does not require any major frame cutting. The electric strike's body is less than 1" deep minimizing modification to the dust box. The 10STRIKENC works with cylindrical locks equipped with a 1/2" latch projection.

A change to the electric strike offering is the ability to use one electric strike body with different faceplate configurations to operate with different types of locks. SDC UniFLEX 55 Series Electric Strikes are designed to retrofit existing ANSI 4-7/8" strike preparation. The electric strike is designed for hollow metal frames to control access when using cylindrical, mortise locks or mortise exit devices. SDC provides six different faceplates, which eliminate the need to relocate the electric strike in order to accommodate the centerline of the lock.

For fire rated openings, fire labeled electric strikes are available for mortise locks, cylindrical locks and exit devices. Rutherford Controls (RCI) F2 Series Electric Strikes are designed for offset and center line latch entry. The RCI F2 Series electric strike meets UL 10C, fire-rated, 3 hour (fail secure only). This electric strike is vertically adjustable using the "Saw-tooth Adjustment Locator." The locator aligns the deadbolt keeper and deadlatch ramp vertically to the proper operational position. This electric strike comes with a second faceplate designed for centerline latch entry.

The Von Duprin 6211 Electric Strike is ANSI 156.5 Grade 1, with a holding force of 1500 pounds. This burglary and fire resistant electric strike has stainless steel construction. Endurance has been tested for 1 million cycles. To ensure proper operation, the strike box is adjustable.

Not all electric strikes are installed into the doorjamb. For night latch applications, the electric strike is mounted onto the edge of the frame since the night latch is surface-mounted on the interior side of the door. The Von Duprin 6114 Electric Strike has four mounting screws and requires a ½" hole drilled into the edge of the frame. The offset electric strike keeper is 1-5/8" tall.

For rim exit devices, some electric strikes have evolved to a surface mounted unit that does not require cutting into the jamb. Trine Axion 4800 Series Electric Strikes are surface-mounted, offering two different thicknesses of spacers to accommodate different latch projections. Rim exit device applications include the Trine 4800F fire rated. The Trine 4850 surface mount electric strike is ½" thick and comes with a 1/8" and ¼" spacers to accommodate different door gaps. The on-board electronics accommodate 11-28 VDC input, having built-in surge and kickback protection. There are two low current draw models, the 4850-LCD draw of .135 Amps @ 24VDC and the 4850-PoE draw of .260 Amps @ 12VDC. These open cavity surface mount electric strikes are field selectable Fail Safe/Fail Secure. They have a one-piece mechanism with one solenoid meeting BHMA Grade 1 electric strike requirements. Options include latchbolt monitoring.

Note: PoE electric strikes can be powered and remotely unlocked using Ethernet Cables run through a company’s network.

Troubleshooting

If a door is misaligned in the jamb, the strike and lockset are normally misaligned, making it more difficult for access and egress. Misalignment can be caused by construction issues, the door being or becoming warped, or issues with stack pressure, seals and weather stripping. Any of these problems can result in the door locking mechanism not operating smoothly.

These issues can cause the latch to put pressure on the door and in turn, pressure is exerted against the electric strike keeper. Too much pressure (pre-load) can result in an electric strike preventing smooth unlocking by not releasing the keeper. If the keeper is not released, door cannot be remotely opened. Pre-load usually results in premature wear to the electric strike, the solenoid and lock.

There are two basic methods to resolve pre-load. First, offer an electric strike with the ability to adjust the vertical location of the keeper. This can resolve permanent alignment problems. For example, Rofu 1700 Series Electric Strikes have an adjustable keeper that allows 1/4″ vertical adjustment to compensate for misalignment, warpage, seals and weather stripping.

Second, use an electric strike designed to override the temporary pre-load problem from stack pressure and east facing metal doors that warp because of high temperatures. For example, Camden 20 Series Electric Strike Fail Secure models are capable of overriding pre-load amounts from 20 (12-24VAC) to 65 pounds (24VDC).

With the effort of going green and operational financial savings, most electric strike manufacturers have been working towards low power consumption electric strike. Some manufacturers offer PoE and/or low power electric strikes operating with solenoids. Rutherford Controls (RCI) has introduced five models of electric strikes using their micro-motor technology. Electric motor technology does not necessitate as large power inrush that can be required to operate a solenoid. Motorized locking mechanisms can release easier, which lessens the problems of pre-load. However, motors require start and stop circuitry to ensure proper operation.

RCI models include the surface mounted model 0563 for ½" Pullman latch rim exit devices, the 5114/5314 no-cut 5/8" projection cylindrical lock and the 5164/5364 no-cut ¾" projection mortise lock applications electric strikes. These field selectable Fail Safe/Fail Secure electric strikes operate on 26mA to 30mA, auto-sensing 12-24VDC. According to RCI, they provide 1500lbf static and 70ft-lb dynamic strength. Two models of the ANSI template electric strikes are available with 3 hour fire rating. All five RCI models have a five-year limited warranty.

Options for electric strikes can include multiple faceplates, in line conditioners and latchbolt monitoring. Latchbolt monitoring is for detecting bolt engagement within the electric strike. Latchbolt monitoring on some models must be ordered when purchasing the electric strike. On other models, latchbolt monitoring can be added at any time.

The electric strike has been sold and installed for more than 120 years. Being jamb mounted, a power transfer mechanism is not required. With today's compact and no cut electric strike choices, installation time has been dramatically reduced. Using the proper equipment as part of an access control component installation, the electric strike might be a better option.