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Fire alarm cabling lookup

Look up cable and circuit rules for fire alarm systems.

NZS 4512

Reads NZS 4512:2010. Tables checked 26 Sept 2026.

Try a job 4

Each job fills in example values. Replace them with your values.

Inputs

Worked example with the default inputs. The live calculator replaces it when the page loads.

Circuit type
Detector or manual call point circuit
Cores in the cable
2

Minimum conductor size

0.75mm²

Stranded conductor required
Yes
Insulation resistance above
5MΩ
Fire rating
Not set by this clause
Clause
402.1

This result is a design aid. Verify it against the current standard.

Calculation steps

  1. Clause that applies402.1

    NZS 4512:2010 Cl 402.2

  2. Cores in the cable2

    NZS 4512:2010 Cl 402.1

  3. Minimum conductor sizeResult0.75mm²

    NZS 4512:2010 Cl 402.1

  4. Stranded conductor requiredYes

    NZS 4512:2010 Cl 402.1

  5. Stranding applies below1mm²

    NZS 4512:2010 Cl 402.1

  6. Insulation resistance above5MΩ

    NZS 4512:2010 Cl 402.2

  7. Fire ratingNot set by this clause

    NZS 4512:2010 Cl 402.2

About this calculator

How this is calculated

The tool looks up what a fire alarm circuit needs from NZS 4512:2010 Clauses 402.1 and 402.2. It gives the conductor size, the stranding, the insulation resistance and the fire rating.

  1. Circuit. You pick the circuit: detector, alerting device, transmission, staged evacuation, data link or mains supply.
  2. Clause. The tool picks the clause. Cl 402.1 covers detector and alerting device circuits. Cl 402.2 covers the rest.
  3. Cores. You enter the number of cores in the cable. The size rule in Cl 402.1 reads it.
  4. Conductor size. The tool gives the minimum conductor size and says whether it must be stranded.
  5. Insulation resistance. From Cl 402.2 it gives the minimum insulation resistance.
  6. Fire rating. It gives the fire rating, or says that this clause does not set one.
StepTable or clauseWhat it decides
Conductor size and strandingNZS 4512 Cl 402.1The smallest conductor and its construction
Insulation resistanceCl 402.2The minimum test result
Fire ratingCl 402.2The rating, where the clause sets one

Worked example

A detector circuit in 2-core cable. The minimum conductor size is 0.75 mm². The conductor must be stranded. The insulation resistance must be above 5 MΩ. This clause sets no fire rating.

Limits

  • The tool reads Cl 402.1 and 402.2 only. Check the cable specification and the mechanical protection in Cl 402.1.
  • Clause 402.2(g) is the other size driver. Read it in full.
  • Check the earthing rules for zone circuit wiring in Cl 402.2(i).
  • Check the separation and identification rules in Cl 402.2(k).
  • The tool does not check voltage drop on the circuit.
  • NZS 4512:2021 supersedes the 2010 edition this tool reads.

See also: Fire alarm battery, Detector spacing and the segregation checker.

Questions

Each answer describes what this tool calculates. The result is a design aid. Verify against the current standard.

What size cable does a fire alarm circuit need?

NZS 4512:2010 Clause 402.1 gives 0.75 mm² per conductor for two-core cable and 0.5 mm² per conductor where the cable has more than two cores. AmpSize also reports the 1 mm² stranding threshold of the same clause. Read Clause 402.1 for the cable types and the protection it accepts.

Which fire alarm circuits need fire-rated cable?

AmpSize reports two cases. Clause 402.2(m) gives 15 min integrity to AS/NZS 3013 Classification WS11 for a transmission circuit. Clause 402.2(r) gives WS51W for staged evacuation cabling. Read both clauses in full, because each carries conditions this tool does not check.

Does the fire alarm need its own supply circuit?

Yes. Clause 402.2(f) calls for a separate subcircuit and a permanent label. AmpSize prints the label text the clause gives, FIRE ALARM. Read Clause 402.2(f) for where the subcircuit starts and where the label belongs.

What insulation resistance is expected?

Clause 402.2(j) sets the criterion above 5 MΩ, and AmpSize reports that figure. Clause 402.2(i) and Clause 402.2(k) carry the earthing and the separation rules for the same wiring. Read all three before you record a test result.

Does this tool confirm that an installation complies?

No. AmpSize reports the figures of NZS 4512:2010 Clauses 402.1 and 402.2 for the circuit you pick. It is a pointer, not a ruling. A fire alarm installation is checked against the whole standard and against the wiring rules.

Clauses and tables this tool reads

Every clause and table, with how each was verified

Tables last checked on 26 Sept 2026.

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