Tech Tips: Electric Strike Considerations

Last month we discussed power transfers which enable us to get power to a lock which is installed on a moving door. Devices such as electrified exit devices and electrified locksets are two kinds of locks which require power onto the door. Other devices which might require you to get wires onto the door include door cameras and request to exit touchbars.

Frame-mounted electric locking hardware is a very important category which includes electric strikes and electromagnetic locks.

The very first steps in the entire process are to determine if the door is fire rated, and inspect the door to be sure it is in working order.

If the door is a fire door, your options for locking it are limited. Just for starters you need to use a fire rated strike, and you cannot use a strike which will involve excessive alteration the frame or the door.

Hopefully the door will have a label identifying it as a fire door, but no visible label does not mean the door is not fire rated, or release you from responsibility to be sure the electric lock you are installing and other work you are performing is appropriate.

Some of the 11 Point Fire Door Inspection offers some details of the door and its operation which can serve as a handy punch list whether you are working on a fire door or not. You may wish to learn more about Fire Door Inspections and how they can add to your list of services and revenue stream. But the items covered in a fire door inspection cover essential items on a door and frame which you need to verify and correct if you expect to perform a successful electric lock installation. Some of the items on the list are fire door specific, so the following list includes the items which apply to any door when it is being surveyed for an electric lock upgrade.

• No holes or breaks in door or frame.
• Door, frame, and hardware are in proper working order.
• No missing or broken parts.
• Door clearances are within allowable limits.
• Door closer/spring hinges are operational and door is self-closing.
• Door is self-latching in the closed position.
• Opening is not equipped with auxiliary hardware items which interfere with operation.
• No field modifications have been performed that void the label.

Two potential scenarios involve electric strikes. One is the planned installation of locking devices as part of a access control project, and the other is the unscheduled spur-of-the-moment situation where you are dispatched and find out what you are doing when you arrive.

There are so many different scenarios you might encounter, but you cannot realistically carry around dozens of strikes for every scenario.

Installing an electric strike in a conventional door and frame is very interesting and challenging from the standpoint of the specification of all the elements and the skill sets that will be required to complete the installation.

Whether it is a new installation or a retrofit, there are parameters and details which are best considered before you reach for your screwdriver.

Size of the existing strike plate. 4-7/8”; or 2-3/4”: many commercial doors have 4-7/8”, which is a good thing because the majority of electric strikes use a 4-7/8” faceplate. (Notable exceptions are the Trine #014 and Trine #3000 Series with the 234; 234-375, or 334 Faceplate)

Space behind the strike: The type of frame will determine the space behind the electric strike. Metal frames wrap around behind the strike opening, and limit the depth available for the electric strike. Also if the frame is in poured concrete, there may be issues as well as possible problems running your wires to the electric strike. The only way to really know is to measure the depth. You may be able to insert a pencil through the hole in the strike and use it as a depth gauge, or you may have to take the strike out and take a look.

Metal frames are bent and curled around inside the wall, so be sure you get the right measurement, which is smallest depth. This dimension is one of the parameters which must be considered when specifying an electric release.

Latch type and length of latch: You must consider the type of latch and the length of the latch.

The length of the latch is usually referred to as the ‘throw’. Typical throws are ⅝” and 1”.

The portion of the extended latch which can fit into the hole in the strikeplate or fall behind the strike’s gate is partly determined by the gap between the door and the frame.

Also since latches are extended by spring pressure, the latch may not fully extend if obstructed.

As a practical matter, there needs to be enough latch behind the ‘gate’ of the electric strike so that the latch cannot be pulled past the gate and allow the door to open. Turning the lever or shaking the door might move the latch a little bit.

In some situations, the latch can be shimmed with a thin piece of metal, a credit card or other similar implement. If the latch can be shimmed, then either the lock does not have a deadlocking feature, or the deadlocking pin is not being held in the proper position for it to work.

Deadlatch Pin: On a cylindrical latchbolt you will usually see that the latchbolt has two pieces: the large bolt that does the work of securing the door and a small bolt that moves somewhat independently of the large bolt. This is the deadlatch pin. When adjusted correctly, the latchbolt is extended into the strike and the deadlatch pin is not fully extended- it’s held by the strike’s gate.

When the deadlatch pin is not extended (held in), the latchbolt cannot be moved and therefore the latch cannot be shimmed. Deadlatch pins are part of the latch bolt on a cylindrical lock. On mortise locks, they are mounted in another part of the lock. Locks that don’t have some version of deadlatch pins are really not designed for security applications. 

If you are planning on installing an electric strike on a door, make sure that the faceplate on the strike you choose maintains the deadlatch functionality.

A family of door accessories referred to as pry guards or anti-jimmy plates can be mounted on the door to cover the latch area and limit the opportunities for bypassing the latch by shimming or spreading.

So start with an properly adjusted and working door with functioning lockset, then specify a door strike which is designed with a deep enough pocket for the latch to fully extend.

Door Issues. If the door is warped or if the door closer is too small or undersized for the door, you will have problems if the latch does not seat properly behind the strike gate, or if the latch presses against the gate when the door is closed. When the latch presses against the gate (or the strike), it is referred to as loading.

For the door to provide the expected, (rated) level of security, the door must be adjusted to compensate loading vs excessive horizontal door movement when the door is closed.

“Excessive” in this case is the thickness of the deadlocking pin. Loading can be caused by many things, including: pedestrians pushing on the latched door, wind pressure, warping in the door or a faulty closer not able to maintain latch pressure on the closed door.

Finally I wanted to mention the possible problem when the latch resists passing over the ramp on the strike so it will reliably lock when it swings shut. If the latch is too long, or if the ramp on the strike is too short for the width of the frame, the latch may bounce off the frame rather than allow the door to come to a fully closed position. Many electric strikes offer an extended lip option to overcome this problem.