How to Wire an Electric Strike to an Access Controller

Why this matters

An electric strike job fails in ways that look like the strike's fault and almost never are. The door will not release when someone leans on it, because the latch is preloaded against the keeper. The controller's relay contacts pit and stick after a few months, because nothing absorbed the voltage spike the strike coil throws every time it drops out. The log fills with "door forced" every time an employee walks out, because the exit sensor sees them a moment too late. And a strike sold for a fire-rated door is the wrong fail mode. Each of these is decided at the wiring stage, and each is cheaper to get right than to diagnose later.

Which fail mode a door needs, and when a maglock is the better choice, is in Electronic Strike vs Maglock, Fail-Safe vs Fail-Secure Selection. This card takes that decision as made and wires it.

Safety before you start

Line voltage. The lock power supply runs from 120 V. A plug-in supply on a nearby outlet is low-voltage work from its output terminals onward; a hardwired supply is a 120 V connection, which goes to an electrician where your state or locality requires it, and is de-energized, locked out and proved dead with a tester checked on a known live source before and after (NFPA 70E Article 120, current edition) before anyone touches it.

Batteries. A lock supply or controller with a standby battery is live from that battery even with AC off. Disconnect the battery before landing wires, and reconnect it last.

Cutting the frame. Cutting or grinding a hollow metal frame throws hot metal fragments: eye and face protection. Many hollow metal frames in masonry walls are filled with grout or mortar, which releases silica when cut; use a tool with a shroud and dust collection, clean with a HEPA vacuum, and never clear the cut with compressed air.

Fire doors. Look for the fire label on the frame and on the hinge edge of the door before ordering anything. A fire-rated door must stay positively latched in a fire (NFPA 80, in the edition your authority having jurisdiction has adopted), so a strike on one is fail-secure and listed for use on fire doors. Do not cut a labeled frame beyond what the strike's listing and the frame maker allow.

The circuit you are building

LOCK PSU 12 VDC             CONTROLLER
 +12V --------------------> LOCK RELAY COM
                            LOCK RELAY NO ---+
 0V  ---------+                              |
              |                              |
STRIKE AT     v                              v
THE FRAME   (-) term ----->|---- (+) term <--+
            diode across the strike terminals,
            cathode band on the (+) side
DOOR CONTACT  -> controller IN1 and COM
REX, dry NO   -> controller IN2 and COM

This is a fail-secure strike: locked with no power, unlocked while powered. The relay's normally open contact closes on a valid credential and sends +12 V to the strike for the unlock time. For a fail-safe strike (unlocked with no power), the same circuit uses the relay's normally closed contact instead, so the strike is powered and locked until a grant opens the contact. The diode sits across the strike coil in reverse, so it carries nothing while the strike is powered and clamps the coil's voltage spike when the relay opens.

The procedure

The door in this example is the back door of a small office: exterior, single-swing, hollow metal frame, cylindrical lockset with a lever, no fire label on the frame or door. Fail-secure was chosen so the door stays locked through a power outage; the inside lever retracts the latch mechanically, so free egress never depends on power.

1. Confirm the lockset gives free egress. The inside lever must retract the latch at all times. A strike only replaces the keeper; it does nothing about a lockset whose inside lever can be locked, and pairing a strike with that hardware traps people. Here the lever is a storeroom function: outside lever always locked, inside always free. Correct for a strike.

2. Size the supply and check the voltage at the strike. Add every load the supply carries, and check the strike gets enough voltage at the end of its wire run. The figures below are illustrative for this door; use the ratings on your hardware.

SUPPLY AND WIRE CHECK, ONE DOOR, 12 VDC
strike, continuous duty            0.45 A
controller board                   0.25 A
card reader                        0.12 A
total load                         0.82 A
supply rating                      1.50 A
load share, 0.82 / 1.50            55 percent
strike run 60 ft, 18 AWG pair
loop length, 2 x 60 ft             120 ft
18 AWG copper, about 6.4 ohm per 1000 ft
loop resistance, 0.120 x 6.4       0.77 ohm
drop at strike, 0.77 x 0.45 A      0.35 V
volts at strike, 12.0 - 0.35       11.65 V
strike's rated range, per its sheet
                                   10.8 to 13.2 V

The supply is at 55 percent, which leaves room for the battery to recharge while it carries the load. 11.65 V is inside the strike's range. Had the run been 200 ft on the same wire, the loop would be 400 ft: 0.400 x 6.4 is 2.56 ohm, times 0.45 A is 1.15 V, leaving 10.85 V at the strike: barely inside the range, with no allowance for a cold morning or a dropping battery. That run would get heavier wire.

3. Install the strike and test it under preload. Cut the frame to the strike maker's template, mount the strike, and adjust the keeper so the latch sits fully engaged with a little free play. Then the test that most installs skip: with the strike powered from a temporary lead, push the door firmly closed against its weatherstrip as if someone were leaning on it, and release. A strike that releases only when the door is not pressed will trap a user who pushes as they badge in. If it binds, adjust the keeper or fit the strike's preload-rated option.

4. Pull the wire. Strike pair through the frame to the controller location, door contact in the frame head, exit sensor above the door on the inside. Keep the strike pair separate from the reader cable if the controller maker asks for it.

5. Land the suppression at the strike, not at the controller. Fit the diode across the strike's two terminals, cathode band to the (+) terminal, unless the strike's sheet says it has suppression built in. On an AC strike, a diode will not work; use the varistor the maker specifies. Why at the strike: the spike is generated by the coil, and a diode at the far end of a 60 ft run lets the spike travel the whole cable first, arcing the relay contacts and radiating into the reader cable. What breaks if you skip it: the relay contacts pit, and a few months in, the strike stays unlocked because the relay welded shut.

6. Wire the lock relay for the fail mode. Supply +12 V to the relay common, relay normally open to the strike (+), strike (-) back to the supply 0 V, as drawn. Set the unlock time in the controller (5 seconds here).

7. Wire and configure the inputs. The door contact goes to IN1 and is set as a door position input; the exit sensor's dry normally open contact goes to IN2, set as request-to-exit. Configure the request-to-exit to shunt the door-forced alarm, and set it not to pulse the strike, since the lever already lets people out and an unlock on every exit is an unlocked door for 5 seconds every time someone leaves. Set the door-held-open time (30 seconds here).

8. Power up. Plug in the supply, reconnect the batteries, and confirm 12 V at the supply output and at the strike when the relay is energized.

Finish test: every event logs

Run each of these and check the controller's event log after each one:

• Credential: badge in. The log shows an access-granted event with the user's name, the strike releases, and the door contact logs open and closed.
• Exit: walk out using the inside lever. The log shows a request-to-exit and door open, and no door-forced alarm.
• Forced: open the door from outside with the mechanical key. The log shows door forced.
• Held open: prop the door past 30 seconds. The log shows door held open, and it clears when the door closes.

The test that failed. On the first exit test, the log showed request-to-exit and door forced on the same exit. The exit sensor was aimed at the floor a step in from the door, and a person reaching for the lever while standing beside the frame opened the door a fraction of a second before the sensor saw them. Re-aimed so its pattern covers the lever and the space directly in front of it, the next five exits logged clean. A sensor that sees people late fills the log with false forced-door alarms, and a log full of false alarms teaches everyone to ignore the real one.

What changes the method

A fire-rated door. Fail-secure and listed for the door, as above, and every frame modification checked against the listing. If the door also needs to unlock when the fire alarm goes off for a reason the owner gives you, that is a different design, because a fire door that unlatches has stopped being a fire door. Stop and route the question to the authority having jurisdiction.

A door with a panic bar. The keeper is part of the exit device, not the frame; use electrified exit hardware or a strike made for that device's latch, not a standard frame strike.

A 24 V strike or a dual-voltage strike set to 24 V. Current halves for the same power, so voltage drop on a long run matters far less. Check the strike's jumper or wiring for the voltage before power goes on; a 12 V coil on 24 V burns out.

References

• NFPA 80, fire doors and positive latching, in the edition your authority having jurisdiction has adopted
• NFPA 70E Article 120 (current edition), for any 120 V connection
• See related: Electronic Strike vs Maglock, Fail-Safe vs Fail-Secure Selection
• See related: How to Install a Maglock with Request to Exit and Fire Release
• Strike, lock power supply and controller maker installation instructions