HomeTechnical notes › What Does a Fire Alarm Terminal Box Do? How Fire Interlock and Signal Transmission Work

05 Informational content / Technical articles 2026-09-11 Published ~ 11 min read GB 50116

What is the purpose of a fire terminal box?
How Fire Interlock and Signal Transmission Work

A fire alarm terminal box is the signal hub of a fire interlock system— how do smoke detectors, heat detectors, manual call points and fire hydrant buttons feed their signals back to the fire alarm control panel? This article follows GB 50116(Code for Design of Automatic Fire Alarm Systems) to explain the function and wiring of the fire alarm terminal box. Zhejiang Golden Unicorn produces 5,000+ fire alarm terminal boxes per year.

1. What Is a Fire Alarm Terminal Box? (Signal Transfer Box)

A fire alarm terminal box is thefield signal collection boxin a fire alarm system, installed on a floor or inside a fire compartment. Functions: ① collect signals from all detectors, manual call points and modules in that area; ② send them over the bus to the fire alarm control panel; ③ during maintenance, measure signals at the terminal box and isolate the faulty section.

SCHEMATICBusbarsTerminal blocksMain circuit breakerControl & protection devicesTerminal block outgoing cables
Figure — 1. What Is a Fire Alarm Terminal BoxCabinet structure diagram · photo pending

2. What a Fire Alarm Terminal Box Does (3 Key Functions)

FunctionWhat it should show
Signal CollectionCollects smoke, heat and manual call point signals from the local area
Branch IsolationIsolates a fault in that area without affecting other areas
Maintenance & TestingMeasure signal voltage at the terminal box, perform short-circuit tests, replace devices

3. How Fire Interlock Signals Travel (3-Layer Architecture)

Fire Interlock Signals 3-Layer Architecture:

  1. Field Device Layer: smoke detectors / heat detectors / manual call points / fire hydrant buttons → via RVS cable to the terminal box.
  2. Terminal Box Layer: signals collected at the floor fire alarm terminal box → via fire-resistant bus to the fire alarm control panel.
  3. Panel Layer: the fire alarm control panel receives the signals → interlocks start sprinkler pumps / smoke exhaust fans / sound and strobe alarms / elevator homing.
SCHEMATICBusbarsTerminal blocksMain circuit breakerControl & protection devicesTerminal block outgoing cables
Figure — 3. How fire alarm interlock signals are routedCabinet structure diagram · photo pending

4. Fire terminal box wiring requirements (GB 50116)

Code

GB 50116 Requirements:
① Fire terminal boxes shall be installed inthe floor's low-voltage room or within the fire compartment, surface-mounted, 1.3–1.5 m above floor level;
② UseFire-resistant cable / fire-resistant wirefor incoming and outgoing lines (NH-BV/NH-RVS);
③ Terminal block numbers correspond to circuit numbers, with clear labeling;
④ Bus terminals and interlock terminalsseparate zones, separated by a partition.

5. Fire terminal box selection (by number of circuits)

Circuit CountTerminalsEnclosure sizeInstallation
≤ 16 circuits2 rows × 8 positions300×400×150Surface mount
16–32 circuits4 rows × 8 positions400×500×200Surface mount
32–48 circuits6 rows × 8 positions600×600×200Surface-mounted / floor-standing

FAQ FAQ

What is the purpose of a fire terminal box?

It collects fire alarm device signals in the area (smoke detectors / manual call points / modules) and forwards them to the fire alarm control panel, providingbranch isolation and maintenance testingfunctions.

What wire is used for a fire terminal box?

You must useFire-resistant cable / fire-resistant wire(NH-BV/NH-RVS), which maintains power supply without interruption during a fire.

Where is a fire terminal box installed?

In the floor's low-voltage room or within the fire compartment, surface-mounted, 1.3–1.5 m above floor level for easy maintenance access.

Can a fire terminal box share a cabinet with a standard terminal box?

No. Fire terminal boxes must be installed independently, with a red enclosure and fire-resistant cable.

Related pages:Technical notes · Products · Industries · Resource center · FAQ · Get a quote

Related reading

Need Distribution box, distribution cabinet? Build to drawing · MOQ 1 unit · 15–25 day delivery

A source factory in Zhejiang (Fengchuan Industrial Zone, Tonglu — 5,000 sqm, a team of 20, 5,800+ units a year), holding ISO 9001:2015 / CE(LVD+EMC) / IP65 test report. Build-to-drawing service for distribution boxes, low-voltage assemblies, PLC control cabinets and VFD panels. Free drawing review, photo/video inspection before shipment.