A fire alarm system has several kinds of circuit. Each kind has its own cabling rule. A detector circuit does not follow the rule for a transmission link. This page shows what the tool reads for each circuit type.
One clause, many circuits
The cabling rules sit in Cl 402 of NZS 4512:2010. Cl 402.1 sets the minimum conductor size by the number of cores. Cl 402.2 adds the rules for each circuit type.
The tool takes two inputs: the circuit type and the number of cores in the cable. It reports the clause that applies. It also reports the minimum size and whether the conductor must be stranded. It reports the insulation resistance limit and any fire rating.
Circuit types
The tool offers six circuit types.
- Detector or manual call point circuit
- Alerting device or loudspeaker circuit
- Transmission circuit to a receiving centre
- Staged evacuation cabling across a firecell
- Dedicated supervised data link
- Mains supply subcircuit
Case 1: a detector circuit on a two‑core cable
A detector circuit uses a cable with 2 cores. The tool applies Cl 402.1.
- Minimum conductor size: 0.75 mm²
- Stranded conductor required: yes
- Stranding applies below: 1 mm²
- Insulation resistance above: 5 MΩ
- Fire rating: not set by this clause
Open the cabling tool with this circuit.
A cable with more cores may use a smaller conductor. Run the same circuit with 4 cores. The minimum size falls to 0.5 mm². The stranding rule and the 5 MΩ limit stay.
Open the cabling tool with four cores.
Case 2: a transmission circuit
A transmission circuit joins the panel to a receiving centre. The clause that applies is Cl 402.2(m).
- Minimum conductor size: not set by Cl 402.1
- Fire rating: AS/NZS 3013 WS11
- Minimum integrity time: 15 minutes
- Insulation resistance above: 5 MΩ
Cl 402.1 does not name this circuit, so it gives no size. The tool says to read Cl 402.2(m) in full. The fire rating is the main change. The cable must keep working in a fire for the stated time.
Open the cabling tool with this circuit.
The other circuit types
The tool reports these results for 2 cores.
- Alerting device circuit. Cl 402.1 applies. The size is 0.75 mm² and the conductor is stranded.
- Staged evacuation. Cl 402.2(r) applies. The size is 0.75 mm², the conductor is stranded and the fire rating is AS/NZS 3013 WS51W.
- Data link. Cl 402.2(q) applies. Cl 402.1 sets no size. There is no fire rating from the clause.
- Mains supply subcircuit. Cl 402.2(f) applies. The subcircuit carries the label FIRE ALARM.
What the tool does not decide
The tool gives the minimum size from the cabling clause. Cl 402.2(g) is another size driver. Read it in full. The tool shows this reminder on every result.
Other rules need your own reading. They cover the cable specification, mechanical protection, earthing of zone wiring, separation and identification. The tool lists the clause for each.
Voltage drop, battery size and detector spacing are separate checks. The battery tool and the spacing tool cover those.
Where it goes wrong
The detector rule is used for every circuit. The transmission and staged evacuation circuits carry a fire rating. A detector rule does not.
The core count is ignored. A cable with more cores can use a smaller conductor. The tool gives a different minimum for each count.
Stranding is forgotten. A conductor below 1 mm² must be stranded in the cases above.
A not-set result is read as no rule. The tool says when Cl 402.1 sets no size. A rule may still apply in Cl 402.2.
This page is a design aid. Verify every value against the current edition of the standard.
See also: Control panels and PLC wiring, Testing to Section 8 and PLC panel 24 V DC battery backup.