Electric strikes are the access control component most often specified incorrectly on commercial door hardware projects. The mistakes fall into two categories: the wrong fail mode for the door's life safety function, and the wrong strike type for the lock installed on the door. Both errors are easily avoided with a clear understanding of how each selection is determined. This guide covers both.

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How an Electric Strike Works

A standard fixed strike plate is a passive piece of hardware bolted to the door frame. The latchbolt from the lock extends into the strike pocket and the door stays closed until someone operates the lever from inside or uses a key from outside. An electric strike replaces this fixed plate with an electromechanical device where the keeper (the curved piece that holds the latchbolt) is connected to a solenoid. When the solenoid is activated, the keeper pivots or retracts out of the way, allowing the latchbolt to pass through without being retracted mechanically. The door opens by being pulled or pushed, with the latch still extended, because the keeper is not blocking it.

When the door closes again, the latchbolt re-engages the keeper and the door is latched without any electrical input. The solenoid only needs to activate long enough for the door to be opened: a brief pulse (typically 1 to 5 seconds) is sufficient. This is why electric strikes are energy-efficient in fail-secure mode: they only draw power during the unlock event, not continuously.

The trigger for the solenoid comes from the access control system: a card reader credential event, a keypad code entry, a push-button release, a motion sensor, or a remote switch all send a signal to the access control panel which then applies or removes power from the strike.

Fail-Safe vs Fail-Secure: How Each Works and When Each Is Required

The fail mode is the single most important specification decision for any electric strike. It is determined entirely by the door's role in the building's life safety plan, not by preference, security level, or budget.

Fail-Secure (Fail-Locked)

In fail-secure mode, the strike remains locked when power is lost. Power must be applied to the solenoid to unlock the keeper. When power is removed (either as the normal locked state or during a power failure), a spring extends the keeper and the latchbolt is held positively in the strike. The door cannot be opened from outside without a credential or mechanical key. Free egress from inside is always available through the mechanical lever or push bar, which retracts the latchbolt directly regardless of the strike's electrical state.

Fail-secure is the correct specification for perimeter security doors, storeroom doors, server room doors, restricted area doors, and any door where unauthorized entry during a power failure would be a security breach. It is also the correct specification for fire-rated doors, for reasons explained below.

Fail-Safe (Fail-Open)

In fail-safe mode, the strike unlocks when power is lost. Power must be continuously applied to the solenoid to hold the keeper in the locked position. When power is removed, the keeper releases and the door can be pushed or pulled open without any credential or key. Fail-safe is required on doors that are on a required means of egress and where the door does not have a mechanical means of free egress from inside when the lock is energized.

The life safety code basis for fail-safe is clear: IBC and NFPA 101 require that all egress doors be operable without a key, tool, or special knowledge during emergency evacuation. A fail-secure lock on a required egress door that loses power during a fire leaves occupants unable to exit through that door. Fail-safe eliminates this risk by ensuring the door always unlocks on power loss.

Why Fire-Rated Doors Require Fail-Secure Electric Strikes

This is the most commonly misspecified aspect of electric strikes, and the one with the most significant life safety consequence. The misspecification goes in the direction you might not expect: people install fail-safe strikes on fire-rated doors thinking "fail-safe is safer," and they are wrong about fire doors specifically.

NFPA 80 requires that fire door assemblies be positively latching at all times when closed. The latchbolt must engage the strike and hold the door in the closed position. A fire on one side of a door creates pressure that can force the door open if the latch is not positively engaged. If a fail-safe electric strike is installed on a fire-rated door, the keeper retracts when power is lost. With the keeper retracted, only the spring-loaded latch is making contact with an open pocket in the strike. Under fire pressure, the latch can be pushed right through the open pocket, the door opens, and the fire separation is compromised.

A fail-secure strike keeps the keeper extended when power is lost, maintaining positive latching. The latchbolt is held in the keeper as firmly as it would be in a standard fixed strike plate. The fire door performs as designed. This is why NFPA 80 effectively requires fail-secure on fire-rated doors, and why Von Duprin fail-secure strikes carry UL listings for both fire and burglary, while fail-safe strikes carry UL listings for burglary only. The listing label difference is the physical documentation of this code requirement.

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Lock Type Compatibility: Cylindrical, Mortise, and Rim Exit Device

Electric strikes are not interchangeable between lock types. Each lock type presents a different latchbolt geometry, projection length, and mounting position that requires a specifically designed strike keeper. Installing the wrong strike type produces a latch that either cannot engage the keeper, binds against the frame, or provides insufficient security engagement.

Cylindrical Lock Electric Strikes

Cylindrical locks (Schlage ND Series, AL Series) use a spring-loaded latchbolt with a 1/2-inch to 5/8-inch throw. Standard ANSI electric strikes are designed for this geometry and are the most common commercial electric strike type. The ANSI prep in hollow metal frames (the standard cutout for the fixed strike plate) accommodates most ANSI electric strikes with minimal additional frame preparation. One critical installation detail: the deadlatch auxiliary plunger on a cylindrical lock must not contact the electric strike keeper edge. If the plunger falls behind the keeper when the door is closing, it can bind the strike and prevent the keeper from resetting after the door closes. Verify clearance between the deadlatch plunger and the strike keeper edge during installation.

Mortise Lock Electric Strikes

Mortise locks (Schlage L Series) have a latchbolt throw of up to 3/4 inches, which requires a deeper keeper pocket than a cylindrical strike provides. Mortise electric strikes have this deeper keeper pocket. An important limitation: mortise electric strikes only release the latchbolt. The separate deadbolt on a mortise lock is a true deadbolt with no spring return. The electric strike cannot capture and hold a deadbolt: if the deadbolt is extended when the door is opened, the deadbolt projects out and the door closes with the deadbolt extended into empty space. The deadbolt must be retracted before entry through a mortise electric strike, either by keying the deadbolt or with electrified mortise trim that controls the deadbolt electrically.

Rim Exit Device Electric Strikes

Rim exit devices use a Pullman-type latchbolt that is geometrically different from a cylindrical or mortise latch. Rim electric strikes are specifically designed for this geometry and are significantly larger and heavier-duty than cylindrical strikes. They semi-surface mount rather than recess fully into the frame. For double doors with surface vertical rod (SVR) exit devices, the bottom rod is typically deactivated and locking occurs only at the top of the door with a single rim electric strike. The top rod latch type (Pullman, carriage, pin) must be confirmed before selecting the keeper style in the rim electric strike.

Browse Von Duprin electric strike parts for cylindrical, mortise, and rim applications at SecurityParts.com.

Power: 12V vs 24V DC, AC Buzzing, and Wire Run Sizing

DC vs AC: Why Buzzing Happens and How to Fix It

AC-powered electric strikes buzz. The solenoid vibrates at the frequency of the alternating current (60 Hz), producing the characteristic noise. DC-powered strikes operate quietly: the solenoid activates with a soft click and holds silently. For any commercial installation where the electric strike is in a lobby, office entry, or anywhere occupants can hear it, DC power is the correct specification. AC is acceptable only in industrial or mechanical areas where ambient noise masks the buzzing.

If an existing installation is buzzing, add a rectifier between the transformer and the strike to convert AC to DC without replacing the power supply. A rectifier converts the AC waveform to pulsing DC, which significantly reduces solenoid vibration. For the quietest operation on a retrofit, replace the AC supply with a dedicated DC power supply.

12V vs 24V: Voltage Drop on Long Wire Runs

Both 12VDC and 24VDC are standard for electric strikes. For new installations, 24VDC is the better specification: at equal current draw, 24V delivers twice the power, and voltage drop over long wire runs is half as significant as at 12V. For wire runs over 200 feet, a 12V system may not deliver sufficient voltage at the strike to reliably actuate the solenoid. Check the manufacturer's voltage drop tables before finalizing wire gauge and run length. If an existing 12V installation shows intermittent strike release (works sometimes but not others), check the voltage at the strike terminals under load (when the access control panel triggers the release). If the voltage has dropped below the strike's minimum operating voltage, increase the wire gauge or switch to 24V.

Power Supply Sizing: Inrush Current, Not Holding Current

Sizing the power supply to the steady-state holding current is the most common power supply error in electric strike installations. Electric strikes have a momentary inrush current when the solenoid first activates that is significantly higher than the holding current. Size the power supply at 150 percent of the peak inrush current of all strikes that could activate simultaneously. A power supply sized only to holding current may actuate one strike reliably but fail to actuate multiple strikes when they trigger at the same time.

Common Electric Strike Troubleshooting

Strike Not Releasing When Triggered

Check voltage at the strike terminals under load (while the access control panel is sending the unlock signal). Use a multimeter. If voltage is present but the strike does not release, the solenoid may be failed and the strike needs replacement. If voltage is low or absent, check the power supply output, wire connections at the panel, and wire continuity. Voltage drop over long runs is the most common field failure cause.

Strike Releases But Door Does Not Open

The keeper has released but the latch is still engaged in the keeper pocket under door preload pressure. Door preload occurs when the door is pressing against the frame (from air pressure, tight weather stripping, or a slight warp). The latch presses against the keeper even when it retracts. The fix: check door gap at the strike side, adjust the door stop if it is pulling the door too tightly against the frame, and verify that the strike lip is aligned correctly. Some strikes have adjustable lip length to accommodate door gap variation.

Deadlatch Plunger Binding the Keeper

On cylindrical lock installations, the auxiliary deadlatch plunger sits beside the main latchbolt. If the strike keeper geometry allows the plunger to fall behind the keeper edge rather than riding over it, the plunger binds the keeper in the retracted position and the keeper cannot reset after the door closes. This prevents the door from latching on the next closure. The fix: verify that the strike is the correct model for the lock, check the plunger clearance in the strike pocket, and if necessary use a strike with a guard plate or plunger deflector.

Strike Buzzing on DC Power

If a strike that should be DC-powered is buzzing, check whether the power supply output is truly DC or actually AC using a multimeter on the AC voltage setting. Some inexpensive power supplies labeled as DC output deliver unfiltered rectified AC that still contains significant AC ripple. Replace with a filtered, regulated DC power supply.

For electric strike troubleshooting support and OEM replacement parts, contact SecurityParts.com at 845-935-0301 or the SecurityParts.com contact page.