4.3 Control/Monitor Modules & FACU Hardware

4.3 Control/Monitor Modules & FACU Hardware

Quick Answer: On addressable systems, monitor modules bring dry contacts onto the SLC, control modules drive relays or NAC-style outputs for auxiliary functions, and isolator modules limit short-circuit damage along the loop. The FACU must be installed in an accessible, listed environment with correct primary and secondary power, and annunciators/network nodes must remain supervised. Level II depth is correct landing, addressing, supervision, and environment—not full network engineering.

Why Modules Exist

Not every input or output is a smoke detector head. Sprinkler switches, kitchen systems, HVAC dampers, magnetic door holders, elevator interfaces, and remote power supplies connect through modules that the panel can supervise and display as discrete points.

Addressable Monitor Modules

Monitor modules present a supervised initiating circuit to a dry contact:

• Waterflow and tamper switches on sprinkler systems
• Kitchen hood fire systems, clean-agent panels (as contacts), duct detectors that only provide contacts
• Door/window contacts when used for fire-alarm functions
• Conventional four-wire device zones via interface modules

Wiring concepts:

1. Use the module’s listed initiating circuit terminals—not random SLC taps.
2. Many monitor circuits need an EOL resistor at the end of the contact run (Class B style IDC on the module).
3. Keep initiating wiring away from high-voltage inductive noise where practical; follow manufacturer max distance.
4. Program/label the point with a meaningful descriptor (“Riser 2 Waterflow,” not “Module 47”).
5. Verify latching vs non-latching and supervisory vs alarm types match the sequence (tamper is typically supervisory; waterflow is alarm).

Scenario: A tamper switch is landed on a monitor module but the EOL is left at the module terminals instead of beyond the switch. Opening the switch may not show as expected, or the circuit may not be fully supervised. Place EOL at the end of the true supervised path.

Control Modules (Relay / NAC Style Outputs)

Control modules implement outputs:

Critical install rules:

• Contact ratings: Do not switch motor loads or high-voltage circuits directly if the module is rated only for pilot duty—use listed interposing relays/contactors.
• Fail-safe behavior: Door holders often de-energize to release on alarm or power loss; wire so loss of module power produces the intended safe state.
• Feedback: When the sequence requires proof of position, pair control outputs with monitor inputs (e.g., damper end switches).
• Silence/reset interaction: Some outputs remain active until system reset; others follow signal silence—match the sequence of operation, not personal preference.

Isolator Modules

Isolators (automatic short-circuit isolators) open when a short is detected so the rest of a Class A/X style SLC can keep working. Placement is a design decision shown on risers:

• Between floors, between tenants, or every N devices per manufacturer/design
• Both sides of high-risk segments

Installer traps:

• Skipping isolators to “save addresses”
• Landing T-taps that defeat isolation boundaries (see SLC topology in Chapter 3)
• Failing to test that a deliberate short isolates only the intended segment

Isolators are how pathway Class X short performance is realized in many systems—class is not magic wire; it is devices plus topology.

FACU Location and Environment

The fire alarm control unit is the brain. Installation requirements typically include:

Moving a panel to a broom closet that exceeds temperature limits voids listing and causes phantom troubles.

Primary and Secondary Power Connections

FACUs require:

1. Primary power — dedicated branch circuit where required by code/specs, correctly breaker-rated, identified as FIRE ALARM at the panelboard, with lock-on devices where required.
2. Secondary power — batteries (and charger) sized per Chapter 10 of NFPA 72 for standby + alarm duration; sealed lead-acid or other listed chemistry per equipment.
3. Supervision — loss of primary, battery charger issues, and low battery must trouble at the FACU.
4. Grounding/bonding — per NEC and manufacturer; shield drains as specified.

Do not share a random lighting circuit as “temporary permanent” power. Do not leave batteries disconnected after a “quick test.” Engine-driven generators, when used, follow code rules for what may serve as secondary—know that batteries remain the common secondary for protected premises panels.

Annunciators

Annunciators (LED, LCD, or graphic) repeat system status at remote locations—lobby, fire command center, nurse station:

• Pathway to the FACU must be supervised.
• Access levels: some annunciators acknowledge/silence/reset; restrict per AHJ and security.
• Labels must match field device descriptors so responders see “Floor 3 Waterflow,” not cryptic point numbers only.
• Mounting height and visibility matter for fire service use.

Network / Peer Awareness (Level II Depth)

Larger campuses use networked FACUs, peer-to-peer nodes, or gateways:

• Physical media may be copper, fiber, or Ethernet (Class N concepts from Chapter 3).
• Level II installers land network risers, SFPs, and supervised links per shop drawings; they do not freestyle IP addressing without the programmer/designer.
• A “network trouble” is a system impairment—treat it like any other pathway trouble.
• Peer systems may share events; verify during commissioning that the correct node displays and that survivability of the network path matches the design (link to survivability levels in Chapter 3).

Practical Sequence for Module-Heavy Floors

1. Mount modules in accessible enclosures; maintain wire bend radius and separation.
2. Land SLC in/out correctly for isolator segments.
3. Land monitor circuits with EOL at end devices; land control loads within ratings.
4. Address and label; print or load point lists from the programmer’s worksheet.
5. Function-test each point: open tamper → supervisory; flow → alarm; trip control → correct equipment action.
6. Confirm FACU power fail and battery trouble paths.
7. Confirm remote annunciator matches FACU events.

Master modules and FACU hardware and you connect the entire building’s fire-safety equipment into one supervised, maintainable system—exactly what Level II installation performance measures expect.