MT Fire Alarm cheat sheet

NFPA 72 defines four signal types: alarm, supervisory, trouble, and (since 2010) carbon monoxide - each has distinct annunciation and priority rules.

Initiator spacing: spot-type smoke detectors on smooth ceilings use the 30 ft (9.1 m) rule; for ceilings above 10 ft, spacing increases per the 0.7 × ceiling height formula (NFPA 72 17.6.3.1.1).

Manual pull stations must be within 5 ft (1.5 m) of each exit door and mounted 42–48 in (1.07–1.22 m) above finished floor to the operating handle.

Notification appliance circuits (NACs) are typically 24 VDC and supervised for opens, shorts, and grounds; end-of-line (EOL) resistor value must match the panel's listed value.

Two-wire conventional detection zones supervise detectors via a compatible EOL; four-wire systems use separate power and supervised signal circuits with relay bases.

Addressable devices report individually; SLC (signaling line circuit) is supervised and typically supports 99–318 devices per loop depending on panel listing.

Audible notification must be at least 15 dBA above ambient or 5 dBA above maximum 60-second ambient, whichever is greater (NFPA 72 18.4.1.1).

Voice evacuation systems require intelligible voice: STI ≥ 0.50, STI ≥ 0.45 in rooms with 0.20–0.80 s reverberation, or CIS ≥ 0.70 (NFPA 72 18.4.11).

Smoke detector spacing on sloped ceilings: detectors may be spaced per the horizontal projection of the ceiling area, with the first detector within 3 ft of the peak.

Ohm's law: E = I × R; power: P = E × I = I²R = E²/R. Voltage drop on a two-wire circuit: VD = 2 × K × I × L / CM (K ≈ 12.9 for copper).

NEC Article 760 covers fire alarm systems: Part I general, Part II non-power-limited, Part III power-limited. FPLR/FPLP/FPL cable listings govern permitted uses.

Class 2 vs Class 3 circuits: Class 2 limited to 100 VA and specific voltage/current tables (NEC 725.121); Class 3 exceeds Class 2 limits but is still power-limited.

Conductor ampacity: 14 AWG copper = 15 A, 12 AWG = 20 A, 10 AWG = 30 A (NEC 310.16, 60°C column for small conductors).

NEC 760.41: non-power-limited fire alarm conductors must be installed in raceway, MC, AC, or as Type FPLR/FPLP where permitted.

Battery calculations per NFPA 72 10.6.7: standby capacity = 24 h (or 60 h for voice) plus 5 min alarm; use manufacturer derating for end-of-life (typically 80% capacity).

Ground fault detection: a ground on a supervised circuit causes current imbalance; typical threshold is 10–50 kΩ depending on panel.

Voltage drop limit for NACs: 10% maximum from panel terminals to the last appliance (NFPA 72 10.14 and manufacturer listings).

Series circuit: total R = sum of resistances; parallel: 1/R_T = 1/R1 + 1/R2 + ...; parallel voltage is the same across branches.

Montana fire alarm work falls under the State Electrical Board (Department of Labor & Industry) per Title 37, Chapter 68, MCA - the electrical contractor license covers fire alarm installation.

The Montana Electrical Board issues journeyman, master, and contractor licenses; a fire alarm installer working under a licensed electrical contractor may be an apprentice or licensed electrician.

Continuing education: Montana electricians renew every 3 years and must complete 24 hours of approved CE, including code update hours (verify current cycle requirements).

License renewal and CE deadlines follow the license expiration date; late renewals may require reinstatement fees and additional CE.

Plan review and inspection: fire alarm shop drawings may require review by the AHJ (local building/fire department); permits are obtained through the jurisdiction, not the state board.

Montana adopts the NEC by administrative rule; the adopted edition is updated periodically - always confirm the current edition before design.

Unlicensed practice is a violation under 37-68-201, MCA; penalties include fines and possible misdemeanor prosecution.

Reciprocity: Montana has limited reciprocity with certain states for electricians; verify with the Board before relying on an out-of-state license.

Apprentices must be registered with the Department of Labor & Industry and work under direct supervision of a licensed journeyman or master.

Lockout/tagout (LOTO) per OSHA 29 CFR 1910.147: disconnect and lock the FACP primary and battery power before servicing; verify zero energy.

Arc flash: NFPA 70E requires an incident energy analysis or PPE category table; energized work requires an energized electrical work permit.

Battery handling: lead-acid batteries produce hydrogen gas - no open flames or sparks; use insulated tools and eye protection; recycle per EPA/DOT rules.

Ladder safety: 4-to-1 rule for extension ladders (1 ft out per 4 ft up); maintain 3-point contact; inspect before each use.

Fall protection required at 4 ft or more in general industry (29 CFR 1910.28); 6 ft in construction.

Confined space entry requires permit, atmospheric testing, attendant, and rescue plan (29 CFR 1910.146).

Hearing protection: use when noise exceeds 85 dBA TWA; fire alarm horns can exceed 110 dBA at close range - do not stand near horns during testing.

Smoke detector testing uses canned smoke or manufacturer-approved aerosol; notify the monitoring company and building occupants before any test.

Personal protective equipment: safety glasses, hard hat, and insulated gloves when working near energized circuits; verify glove class matches voltage.

NFPA 72 defines four signal types: alarm, supervisory, trouble, and (since 2010) carbon monoxide - each has distinct annunciation and priority rules.

Initiator spacing: spot-type smoke detectors on smooth ceilings use the 30 ft (9.1 m) rule; for ceilings above 10 ft, spacing increases per the 0.7 × ceiling height formula (NFPA 72 17.6.3.1.1).

Manual pull stations must be within 5 ft (1.5 m) of each exit door and mounted 42–48 in (1.07–1.22 m) above finished floor to the operating handle.

Notification appliance circuits (NACs) are typically 24 VDC and supervised for opens, shorts, and grounds; end-of-line (EOL) resistor value must match the panel's listed value.

Two-wire conventional detection zones supervise detectors via a compatible EOL; four-wire systems use separate power and supervised signal circuits with relay bases.

Addressable devices report individually; SLC (signaling line circuit) is supervised and typically supports 99–318 devices per loop depending on panel listing.

Audible notification must be at least 15 dBA above ambient or 5 dBA above maximum 60-second ambient, whichever is greater (NFPA 72 18.4.1.1).

Voice evacuation systems require intelligible voice: STI ≥ 0.50, STI ≥ 0.45 in rooms with 0.20–0.80 s reverberation, or CIS ≥ 0.70 (NFPA 72 18.4.11).

Smoke detector spacing on sloped ceilings: detectors may be spaced per the horizontal projection of the ceiling area, with the first detector within 3 ft of the peak.

Ohm's law: E = I × R; power: P = E × I = I²R = E²/R. Voltage drop on a two-wire circuit: VD = 2 × K × I × L / CM (K ≈ 12.9 for copper).

NEC Article 760 covers fire alarm systems: Part I general, Part II non-power-limited, Part III power-limited. FPLR/FPLP/FPL cable listings govern permitted uses.

Class 2 vs Class 3 circuits: Class 2 limited to 100 VA and specific voltage/current tables (NEC 725.121); Class 3 exceeds Class 2 limits but is still power-limited.

Conductor ampacity: 14 AWG copper = 15 A, 12 AWG = 20 A, 10 AWG = 30 A (NEC 310.16, 60°C column for small conductors).

NEC 760.41: non-power-limited fire alarm conductors must be installed in raceway, MC, AC, or as Type FPLR/FPLP where permitted.

Battery calculations per NFPA 72 10.6.7: standby capacity = 24 h (or 60 h for voice) plus 5 min alarm; use manufacturer derating for end-of-life (typically 80% capacity).

Ground fault detection: a ground on a supervised circuit causes current imbalance; typical threshold is 10–50 kΩ depending on panel.

Voltage drop limit for NACs: 10% maximum from panel terminals to the last appliance (NFPA 72 10.14 and manufacturer listings).

Series circuit: total R = sum of resistances; parallel: 1/R_T = 1/R1 + 1/R2 + ...; parallel voltage is the same across branches.

Montana fire alarm work falls under the State Electrical Board (Department of Labor & Industry) per Title 37, Chapter 68, MCA - the electrical contractor license covers fire alarm installation.

The Montana Electrical Board issues journeyman, master, and contractor licenses; a fire alarm installer working under a licensed electrical contractor may be an apprentice or licensed electrician.

Continuing education: Montana electricians renew every 3 years and must complete 24 hours of approved CE, including code update hours (verify current cycle requirements).

License renewal and CE deadlines follow the license expiration date; late renewals may require reinstatement fees and additional CE.

Plan review and inspection: fire alarm shop drawings may require review by the AHJ (local building/fire department); permits are obtained through the jurisdiction, not the state board.

Montana adopts the NEC by administrative rule; the adopted edition is updated periodically - always confirm the current edition before design.

Unlicensed practice is a violation under 37-68-201, MCA; penalties include fines and possible misdemeanor prosecution.

Reciprocity: Montana has limited reciprocity with certain states for electricians; verify with the Board before relying on an out-of-state license.

Apprentices must be registered with the Department of Labor & Industry and work under direct supervision of a licensed journeyman or master.

Lockout/tagout (LOTO) per OSHA 29 CFR 1910.147: disconnect and lock the FACP primary and battery power before servicing; verify zero energy.

Arc flash: NFPA 70E requires an incident energy analysis or PPE category table; energized work requires an energized electrical work permit.

Battery handling: lead-acid batteries produce hydrogen gas - no open flames or sparks; use insulated tools and eye protection; recycle per EPA/DOT rules.

Ladder safety: 4-to-1 rule for extension ladders (1 ft out per 4 ft up); maintain 3-point contact; inspect before each use.

Fall protection required at 4 ft or more in general industry (29 CFR 1910.28); 6 ft in construction.

Confined space entry requires permit, atmospheric testing, attendant, and rescue plan (29 CFR 1910.146).

Hearing protection: use when noise exceeds 85 dBA TWA; fire alarm horns can exceed 110 dBA at close range - do not stand near horns during testing.

Smoke detector testing uses canned smoke or manufacturer-approved aerosol; notify the monitoring company and building occupants before any test.

Personal protective equipment: safety glasses, hard hat, and insulated gloves when working near energized circuits; verify glove class matches voltage.