Kaiwhakarerekē rahi taura imperial

How this is calculated#

The tool finds the largest fuse or circuit-breaker for an old imperial-size cable. You use it when you alter or repair existing wiring. It reads AS/NZS 3000:2018 Appendix I, Table I1.

1. Wires. You pick the size as the wire count and the wire diameter in inches, such as 7/.029.
2. Calculated area. The tool works out the conductor area from the wire count and the diameter. This is a calculation. It is not a table value.
3. Nearest metric size. It gives the nearest metric size for that area.
4. Method and insulation. You pick how the cable is installed, unenclosed or partially surrounded, and the insulation, V75 or V60.
5. Circuit-breaker rating. The tool reads the maximum circuit-breaker rating from Table I1.
6. Existing device. It also reads the maximum rating for an existing rewireable fuse or plug-in circuit-breaker.

Worked example#

A 7/.029 conductor, unenclosed, with V75 insulation. The calculated area is 2.98 mm². The nearest metric size is 2.5 mm². The maximum circuit-breaker rating is 32 A. The maximum existing fuse or plug-in breaker is 20 A.

Limits#

• Check the scope of Appendix I. It is written for existing imperial conductors.
• The second rating is for a device already in place. Read Clause 2.5.2 before you plan a new device.
• The two notes under Table I1 set conditions. Read them on the page.
• Do not use the area for conductors in parallel. Read Paragraph I3 and Table I2.
• The tool does not check voltage drop or the condition of the old insulation.

See also: Cable size calculator, What size breaker for 4 mm² cable and Checking an existing circuit.