Right. You’re here because a door is doing the opposite of what it should. Again. The beeping is incessant, the fire marshal’s face is a particular shade of purple reserved for contractors, and you’re holding a wiring diagram that makes less sense than the procurement policy for left-handed scissors. Welcome to the circus. This isn’t a tutorial; it’s an intervention. We’re going to talk about fire alarm relays and electromagnetic locks, and why your “standard install” is probably a violation waiting to happen.

Act I: The Delusional Cast List

Before you connect a single wire, understand you’re not building a system. You’re managing a dysfunctional family of components that actively hate each other.

The Fire Alarm Panel (FACP): The paranoid, overbearing parent. It sees a spec of dust and screams “FIRE!” Its only useful contribution to this endeavor is a set of dry-contact relays. They are stupid switches. Not power sources. Switches. Remember this, or everything that follows is useless.
The Relay (Field or Panel): The moody teenager. It does what the FACP says, but only if you ask it in the exact right way. Its entire personality is defined by three terminals: Common (C), Normally Open (NO), and Normally Closed (NC). Mess this up, and it will rebel spectacularly.
The Power Supply (PS): The only responsible one. It feeds the beast (the lock). It must be UL-listed for this specific purpose. Using anything else is not “cost-saving,” it’s “future-lawsuit-funding.”
The Electromagnetic Lock: The simple, expensive brute. It has one thought: “Power on, I stick. Power off, I let go.” It is fail-safe. This is the one non-negotiable truth in this whole mess. No power = open door.
The Access Control System & REX: The annoying in-laws. They handle the day-to-day drama of letting authorized people in and out. Their job is security. They are irrelevant to the fire alarm. The fire alarm override is a divorce-level event that supersedes all their rules. They do not get a vote.

Act II: The “Synchronization” Farce

“Syncing” implies harmony. There is none. This is about using the fire alarm relay to perform a single, violent action: break the circuit powering the maglock. That’s the entire dance.

The catastrophic, industry-standard beginner’s error goes like this:

Take the PS (+) wire.
Connect it to the relay’s Common (C) terminal.
Connect the relay’s Normally Open (NO) terminal to the maglock’s (+) terminal.
Connect PS (-) to maglock (-).

Result: In normal conditions, the relay is dormant, C-to-NO is open, the circuit is broken, the maglock has no power, and the door is unlocked. When the fire alarm activates, the relay energizes, closes C-to-NO, completes the circuit, powers the maglock, and locks everyone inside a burning building. You have just engineered a trap. A round of applause, please.

Act III: The Correct, Grumpy Wiring Reality

To have a door normally locked and unlocked on alarm, you must use the relay’s Normally Closed (NC) contact. The relay’s default, un-energized, resting state must complete the circuit.

The correct, non-deathtrap wiring:

PS (+) -> Relay Common (C).
Relay Normally Closed (NC) -> Maglock (+).
PS (-) -> Maglock (-).

The Logic:
Normal Day: Relay is sleepy. C-to-NC is a closed path. Power flows freely. Door is locked. Security is happy.
Fire Alarm: FACP screams, relay energizes and pulls in. This physical action breaks the C-to-NC connection. The circuit is severed. Power dies. Maglock releases. Door is unlocked. People can escape. The AHJ might not yell today.

This isn’t advanced physics. It’s understanding that the relay’s activation should interrupt the normal state.

Act IV: The Real-World Sewer of Complications

If it were just a relay, a PS, and a lock, even your apprentice could manage it. But it’s not.

The Access Control Menace: Now your PS is a “door controller” with software programmed by someone who left for another company last Tuesday. You wire your fire alarm relay to its “Fire Alarm Input.” You must physically test that this input, upon contact closure (or opening), kills the lock output immediately. Do not trust the programming interface. Trust the door. Yank on it. If it’s locked during an alarm simulation, the software is wrong. This is the most common post-install failure.
Supervision (The Part Everyone Ignores): The fire alarm system needs to know if the wire you just ran to the maglock is still connected. If a painter, janitor, or rogue rodent severs it, the FACP must throw a trouble signal. This is done with a supervised monitor module (e.g., an MMX, ICM) watching that circuit. It uses end-of-line resistors. Omitting this is criminally lazy. It means you have no idea if your safety circuit is intact from one day to the next.
Power Supply Pedantry: It must be UL 294/UL 10C listed for access control, with appropriate fire alarm compatibility. Its battery must be sized to hold the lock during a primary power failure (until the alarm triggers). And for the last time: THE FIRE ALARM RELAY DOES NOT POWER THE LOCK. It is a signal. The dedicated PS provides the amperage. Using the relay as a power carrier will fry it, eventually.
The 15-Second Delay Debacle: Some codes permit a brief (≤15 sec) delay on unlocking for security. This delay is enacted downstream by the door controller, never by delaying the fire alarm signal itself. The fire alarm relay must trigger instantly. The controller can then, if programmed, wait 15 seconds before cutting lock power. Document this explicitly for the inspector.

Act V: The “It Worked in Test!” Hallucination

You pressed the test button on the panel. The relay clicked. The door unlocked. You called it a day. You are a fool.

Your test was a fantasy. Did you:

Verify supervision by disconnecting a wire at the lock to ensure the FACP shows a Trouble?
Kill primary power to the door PS to confirm battery backup maintains the lock until an alarm triggers?
Test every initiating device—a smoke detector, a pull station, a flow switch—not just the convenient panel menu test?
Confirm the Request-to-Exit (REX) motion sensor or button still works normally when the fire alarm is not active?

No? Then you didn’t test the system. You performed a magic trick for yourself.

Act VI: The Grumpy Procurement Manager’s Checklist

Demand Documentation: Before you buy or approve anything, get the UL-listed installation guides for the FACP, relay, power supply, and lock. They must be compatible as a system.
Insist on a Riser Diagram: The installer must provide a single-line diagram showing every connection, supervision point, and power source. If they can’t draw it, they can’t install it.
Verbalize the Logic: Make them explain it back to you: “So, when the alarm triggers, the relay opens the NC contact, breaking the constant power from the PS to the lock. Correct?” If they hesitate, stop.
Contract for AHJ Liaison: The installer’s scope must include submitting the diagram to the Authority Having Jurisdiction (AHJ) for review and shepherding it through approval. This is non-negotiable and should be a line-item cost.
Link Payment to Certification: Final payment is contingent upon the installer providing a signed AHJ approval document (the “NFPA 72 Record of Completion” or local equivalent) and demonstrating every test in Section V above to you or your representative.

AHJ WARNING – YOUR GET-OUT-OF-JAIL-FREE CARD IS VOID

Listen carefully. The grumpy truths above are just that—truths. They are not code. I am not your AHJ.

The Authority Having Jurisdiction—the fire marshal, the building official, the insurance carrier’s engineer—is God, King, and Supreme Arbiter. Their interpretation of NFPA 72, NFPA 101, and local amendments is the only one that matters. They have pet peeves, obscure memos from 1998, and a deep, abiding distrust of your entire profession.

Your installer’s “standard practice” is irrelevant. The manufacturer’s “typical wiring diagram” is merely a suggestion. The only thing that stands between you and catastrophic liability, rework, and fines is the AHJ’s written, stamped approval of your specific installation plan.

Procurement’s role is to enforce this. Do not release funds. Do not grant access. Do not consider the project complete until you have that paper in hand. Otherwise, you have not purchased a fire safety system. You have purchased an enormous, expensive liability and a future starring role in an incident report. Do your job.

The Inevitable Catastrophe: Syncing Fire Alarm Relays with Maglocks