Tom has 17 years experience as a commercial locksmith and over 20 years in door hardware distribution.
The "Strike" Concept
Please observe the drawings below. These drawings are important because you can use them to determine what strike your lock has now. The strike your lock has now will play a major role in your choice of electric strikes.
First a little vocab:
- Latchbolt - spring loaded part of a lock that actually holds the door closed
- Lock Front - the part of the lock that is visible only when the door is open. The latchbolt projects from this part.
- Strike - a piece of metal installed into or onto a door frame for the purpose of receiving a latch
- Electric Strike - a device installed into or onto a door frame for the purpose of receiving a latch mechanically and releasing it electrically
Criteria for Electric Strike Choice
The first thing you need to know in order to choose an electric strike is what kind of lock you have. A couple of good clues to help you find out what kind of lock you have are the kind of strike and the size of the lock front. Using the drawings above, you can determine what kind of lock you have.
The top-most illustration at right shows an "ANSI" strike with a centered keeper. That is hardware-speak for, 'The strike is 4-7/8 inches high, 1-1/4 inches wide and has the latch hole in the middle." This type of strike usually means you have a cylindrical lock and a hollow metal frame. You can confirm what kind of lock it is by comparing the latch front in your door to the second illustration from the top. If it is a cylindrical lock it will most likely match. For this type of application, I would suggest the HES 5000 series electric strike with 501 option faceplate, the Adams Rite 7240 electric strike, the Von Duprin 6211, or the RCI 4114.
The third picture down depicts a mortise lock front and its corresponding strike. Notice how the keeper (hole) is offset toward the bottom of the strike. If you have a mortise lock your choices are much more limited. For most mortise locks I would suggest the Von Duprin 6210, the HES 1006 with K, KD, or KM faceplate option, or the HES 4500.
The next picture down shows a mortise lock with a deadbolt. Your best bet is to change out your mortise lock so it looks like the third picture. Typically storeroom function mortise locks are used with electric strikes.
For a rim exit device on a wood or hollow metal door, the easiest installation is the HES 9600 on a single door. A more durable strike is the Von Duprin 6111 or 6112. Less expensive alternatives include the Adams Rite 74R1 and the RCI 0161.
If the rim device is on an aluminum storefront door, your choices are more limited. You would need a strike with a thinner faceplate such as the Von Duprin 6113 or an Adams Rite 74R2.
The last picture shows a rim exit device in a double door installation. For a double door you would need a surface mounted strike such as the Von Duprin 6121.
Questions to Answer
When ordering an electric strike, these are the facts you need to know:
- What kind of lock will it release?
- What voltage does it run on?
- Fail safe or fail secure?
- What is the finish?
Additionally it is good to know the faceplate size especially if you are replacing an existing electric strike.
"Fail secure" means that when there is no power supplied to the strike it is locked. If the strike was fail safe it would be unlocked when no power is supplied.
Fail safe electric strikes must be supplied with constant power (or energized) to be locked. Another term for fail safe is "fail unlocked." Since they are locked when energized they tend to be warm or even hot to the touch when locked. This is normal, but it does tend to decrease the life of the strike. This can be mitigated by a 'line conditioner' device installed between the power supply and the strike. Generally what this does is provide the strike with sufficient current to change states (from locked to unlocked or vice versa) and then reduce that current to a "holding current" to keep it in that state.
Fail safe electric strikes are used when access from the locked side must be free during a power outage or often when they will be used in an application in which they will be unlocked for long periods of time. For example, a commercial self service laundry might have a timer that unlocks the door at 6am and locks it back up at 11pm automatically. Since the fail safe strike is unlocked with de-energized it is not hot to the touch when customers are using the door.
The down side of that scenario is that should there be a power outage the laundry will be unlocked.
Almost all fail safe strikes are not fire rated because they do not allow the door to be positively latched in the event of a power outage.
Wiring an Electric Strike
The illustration below shows a basic fail secure electric strike system.
A simple loop of one-conductor wire connects the components. Starting at either terminal of the power supply, one wire runs directly to one of the two power inputs of the electric strike. The other wire runs from the other power input of the strike to the normally open switch which creates a gap in the loop until the switch is activated, closing the gap, and from the switch back again to the remaining power output terminal of the power supply.
If the electric strike had been a fail safe strike everything would be the same except for the switch, which would be normally closed instead of normally open.
A switch can take many forms. It might be a momentary push button mounted in a surface mount box under a desk for use by a security guard or receptionist, or it could be a keypad or card reader on the locked side of the door, or a wireless receiver. The principal of the loop in the illustration remains basically the same.
Basic Electric Strike System
The video below shows the ease of installation of the HES 5900 electric strike. This can be a real time saver for installations with cylindrical locks on hollow metal doors and frames.
Since this article was written the HES 5900 has been replaced by the 8000 series and that line has been expanded to include fire rated offerings and strikes to accommodate mortise locks.