What Is an Electric Strike?
To understand the electric strike, one first must understand the term “strike.” In the context of door hardware, “strike” means a metal plate or assembly that is installed into or onto a door frame on the lock side to receive a latch or bolt and hold it secure. When locking a pair of doors with a single-point lock, the strike is installed on the inactive leaf, that is, the door that is locked in place with flush bolts. When locking a pair of doors with vertical rod exit devices, the strikes are installed into or onto the header and threshold, or sometimes just the header.
At right is a picture of a standard ANSI (non-electric) strike in a hollow metal frame. When the latch contacts the lip of the strike, it is forced back into the door, allowing the door to close. When the door is fully closed, the latch drops into the “D”-shaped hole, securing the door. One would say that the door is then positively latched.
The term “positive latching” relates to compliance with the fire code in the sense that fire-rated doors are required to be equipped with positive latching devices, that is, locks that latch positively. Since the electric strikes you may install must comply with the fire code, this is an important concept.
How Electric Strikes Work
This mechanism is not called an “electric door opener” because it does not open the door. They only allow a person to open the door. The force that opens the door comes entirely from the person.
An electric strike holds the latch, just like a non-electric one, but can also electrically release it.
Electric Strike Anatomy
Above is an illustration of a classic, single-keeper electric strike showing its visible external parts when not installed—a simple mechanism, in spite of how complicated it sounds.
- The Faceplate: This has mounting holes in it through which screws are inserted to fasten the electric strike to the door frame.
- The Keeper: This is a movable cavity into which the latch projects when the door is closed. The keeper pivots outward when the strike is activated, releasing the latch.
- The Lip: This bridges the gap between the faceplate and the edge of the door frame and provides a path for the latch to enter or exit the electric strike.
- The Body: This contains the internal electrical and mechanical parts of the electric strike.
Faceplate Considerations
- Height and width dimensions
- Finish
- Round or square corners
For installation in wood door frames, a larger faceplate with square corners is recommended. For hollow metal frames, like the electric strike in my illustration above, the faceplate should be 4-7/8 inches tall by 1-1/4 inches wide with square corners. For aluminum frames, a round-corner faceplate is generally called for, and there are a variety of sizes to accommodate various applications.
Keeper Considerations
- Depth
- Placement
For typical installation of an electric strike to release a cylindrical lock in a hollow metal door and frame, you will need to be at least 1/2 inch deep in order to accommodate a standard 5/8 inch deadlatch, given a standard 1/8 inch gap between the frame and the door.
For the cylindrical lock application described, the keeper will be centered in the strike. For installation with a mortise lock, the strike will need to have an offset keeper because, with a standard mortise lock prep, the hole for the latch in its non-electric strike will be offset (as shown in the illustration below).
Lip Considerations
Electric strike lips come in different lengths for different applications. The lip must extend far enough to reach slightly past the surface of the door frame. A standard electric strike has a lip that protrudes slightly from a hollow metal frame. For other applications, such as a center-hung glass and aluminum storefront door, an electric strike would need an “extended lip.” Lip extensions are available for many strikes to accommodate these variable conditions.
For installation in a pair of doors, a shorter lip is not required, but it does make for a much more aesthetically pleasing installation.
Body Considerations
Electric strike bodies are designed for specific applications. Most electric strikes are designed for hollow metal or aluminum doors and frames. For wood doors and frames, strikes are available with different body designs that leave more room in the prep for the mounting holes. If the screws are too close to the body cutout in a wood frame, the wood may split, weakening the installation.
In a pair of wood doors in which the strike will be installed in the inactive leaf, there is little room for error. It is best to get an electric strike that is designed for this specific application.
Electric Strike Applications and Pitfalls
Although I write about this in more depth elsewhere, the simple rule is: The electric strike you choose will depend upon the lock you use.
Therefore, when you go shopping for your electric strike, the first thing you need to know is what lock you will be releasing. The second thing you need to know is the characteristics of the opening: its composition and dimensions. An electric strike application is made up of the type of lock and the type of opening.
Here are some typical electric strike applications:
- Cylindrical lock, hollow metal door and frame
- Mortise lock, aluminum storefront door and frame
- Rim exit device, hollow metal door and frame
- Rim exit device, aluminum storefront door and frame
- Mortise lock, hollow metal door and frame
- Mortise exit device, hollow metal door and frame
Electric Strike Pitfalls
A common (and expensive) mistake made when specifying electric strikes is to specify them for use on interior stairwell doors because, in most jurisdictions, stairwell doors must be unlocked and positively latched when the fire alarm has been activated and/or when the building experiences a power outage. If the strike is fail secure, the door will not be unlocked. If the strike is fail-safe, the door will not be positively latched.
Worse, fire-rated frames are only supposed to be modified in a fire-rated shop, so if you have cut electric strikes into the door frame of the field, the AHJ (authority having jurisdiction) would be fully within their rights should they order you to replace all the frames, in addition to removing all your electric strikes. You can see how this very rapidly might add up to a big loss.
Another electric strike no-no is vertical rod exit devices. There is no law against this, but the application works so poorly that it is hard to justify. First, the bottom rod must be removed from each exit device to be released by an electric strike. With the bottom rod removed, when you pull on the door, you will probably be able to pull the door out a couple of inches. Add to that the electric strike, which will also add a certain amount of mobility, and you’ve got a door that feels very insecure. And if later the door sags a little over time, the door will not be secure at all.
Electric Strike Examples
Above: HES 1500 electric strike. Available with faceplate kits for cylindrical or mortise locks. Used with hollow metal doors.
Above: Dormakaba RCI 0162 strike for rim exit devices
Above: Dormakaba RCI 12C compact electric strike for modified ANSI A115.3 prep in hollow metal or wood frame.
Special Application Electric Strikes
In addition to the applications discussed and shown above, there are situations require special electric strikes such as these:
- Electric strike installed in the inactive leaf of a pair of doors
- Electric strike for all glass door with overhead locking push/pull device
These strikes are shown below:
Above: Von Duprin 6223 for inactive leaf of a pair of doors
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Above: Dormakaba RCI electric strike for all glass doors with surface vertical rod exit device
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