Earthing and bonding calculator
Size earthing, main earth and bonding conductors.
Reads AS/NZS 3000:2018. Tables checked 27 Sept 2026.
Try a job 6
Each job fills in example values. Replace them with your values.
- Size the earth for a shed submainThe protective earth for a 6 mm² copper submain to a shed.
- Size the main earth for large mainsThe main earthing conductor for 95 mm² consumer mains.
- Size the earth for an aluminium submainThe protective earth for a 120 mm² aluminium submain.
- Check an earth by the adiabatic equationThe earth conductor for a 6 kA fault cleared in 0.4 s, by calculation.
- Size the bond at a telecom terminalThe bonding conductor at a telecommunications earth.
- Size a bare copper earthThe earth with the k value of bare copper.
Inputs
Worked example with the default inputs. The live calculator replaces it when the page loads.
- Active conductor material
- Copper
- Largest active conductor
- 16 mm²
- Consumer mains active conductor
- 16 mm²
- Bonding case
- General equipotential bonding
- Check by calculation
- No
Protective earthing conductor
6mm²
- From the table
- 6mm²
- Main earthing conductor
- 6mm²
- Bonding conductor
- 4mm²
This result is a design aid. Verify it against the current standard.
Calculation steps
- Protective earthing conductor from the table6mm²
AS/NZS 3000:2018 Table 5.1
- Main earthing conductor6mm²
AS/NZS 3000:2018 Cl 5.3.3.2
- Bonding conductor4mm²
AS/NZS 3000:2018 Cl 5.6.3.2
- Selected protective earthing conductorResult6mm²
AS/NZS 3000:2018 Table 5.1
About this calculator
How this is calculated
The tool sizes the protective earthing conductor, the main earthing conductor and the bonding conductor. It reads AS/NZS 3000:2018. It starts from the size of the active conductor.
- Protective earthing conductor. You enter the active size and the conductor material. The tool reads the earth size from Table 5.1.
- Main earthing conductor. The tool reads Cl 5.3.3.2. It sizes the conductor from the consumer mains size you enter.
- Bonding conductor. You pick the bonding case. The tool reads the bonding conductor size from Cl 5.6.3.2.
- Adiabatic check. If you turn it on, you enter the fault current and clearing time. The tool then checks the selected conductor against the adiabatic equation. A larger size replaces the table size if it fails.
| Step | Table or clause | What it decides |
|---|---|---|
| Protective earth | AS/NZS 3000:2018 Table 5.1 | The earth size for the active size |
| Main earth | Cl 5.3.3.2 | The main earthing conductor size |
| Bonding | Cl 5.6.3.2 | The bonding conductor size |
Worked example
- 16 mm² copper active conductors. Consumer mains are also 16 mm², with the general bonding case. The protective earthing conductor is 6 mm². The main earthing conductor is 6 mm². The bonding conductor is 4 mm².
Limits
The table sizes cover the usual installation. The tool does not cover a special case. A long earth route can need a larger conductor for loop impedance. Use the loop impedance tool for that.
The tool does not choose the earth electrode or the earthing system. It does not check the conduit or cable support. The adiabatic check is off until you turn it on.
See also: The MEN system, Short-circuit withstand and the k factor and the fault rating tool.
Questions
Each answer describes what this tool calculates. The result is a design aid. Verify against the current standard.
What does the earthing tool do?
The tool reads the protective earthing conductor size for the largest active conductor. It reads the main earthing conductor size from the consumer mains. It applies the 4 mm² minimum and the 120 mm² maximum, and reports the bonding size. It can also check the size by calculation.
Which table gives the earthing conductor size?
AS/NZS 3000:2018 Table 5.1. The tool reads the copper active column or the aluminium active column. The main earthing conductor rule comes from Clause 5.3.3.2. The bonding sizes come from Clause 5.6.3.2.
How does the calculation option work?
It applies Equation 5.1 of Clause 5.3.3.1.3. The tool squares the fault current and multiplies by the disconnection time. It takes the square root of that and divides by K to get the area. It rounds the result up to the next standard size. The equation applies from 0.1 s to 5 s.
Which K value should I use?
Note 1 to Clause 5.3.3.1.3 gives 170 for bare copper. It gives 136 for PVC insulated copper not laid up in a cable with other conductors. An earthing conductor can be a core laid up in a cable with others. For that case, use the k factor from AS/NZS 3008.1.2 Table 52 instead.
What size is the MEN connection?
The tool sizes the main earthing conductor from the consumer mains active size. In copper, it is at least 4 mm², and it never needs to be larger than 120 mm². Aluminium active conductors below 16 mm² are not tabulated.
Clauses and tables this tool reads
- AS/NZS 3000:2018 Cl 5.3.3Earthing conductor size
- AS/NZS 3000:2018 Cl 5.6.3.2Bonding conductor size
- AS/NZS 3000:2018 Table 5.1Minimum earthing conductor size by active conductor size
- AS/NZS 3000:2018 Table 5.1Minimum copper earthing conductor size for aluminium active conductors
- Cl 5.3.3.1.3 Note 1K values for the protective earthing conductor adiabatic equation
Every clause and table, with how each was verified
Tables last checked on 27 Sept 2026.
Related tools
- Cable screen earthing selectorFind where to earth a screen, drain wire or armour.AS/NZS 3000
- Segregation and separation checkerCheck what may share an enclosure and the separation.AS/NZS 3000
- Cable size calculatorFind the smallest cable size that passes each check.AS/NZS 3008.1.2AS/NZS 3008.1.1AS/NZS 3000
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