Outbuilding earthing
Earth a shed: earth with the submain, or its own MEN.
Reads AS/NZS 3000:2018. Tables checked 1 Oct 2026.
Try a job 4
Each job fills in example values. Replace them with your values.
- Earth a shed through the submainThe earth to run with a 10 mm² submain to a shed.
- Set up a shed as its own MENThe PEN, main earth and rod depth for a 16 mm² submain.
- Check a sleep-out with a metal water pipeA separate MEN where a metal pipe joins the buildings.
- Earth a farm shed in AustraliaA separate MEN on a strip electrode for a 25 mm² three phase submain.
Inputs
Worked example with the default inputs. The live calculator replaces it when the page loads.
- Country
- New Zealand
- Outbuilding
- Individual: one structure with its own board
- Earthing arrangement
- Earth run with the submain
- Submain phases
- Single phase
- Submain active size
- 6 mm²
- Conductor
- Copper
- Metal services between the buildings
- No
Protective earthing conductor
2.5mm²
- Allowed for this outbuilding
- Earth with the submain, or a separate MEN
This result is a design aid. Verify it against the current standard.
Calculation steps
- OutbuildingIndividual
AS/NZS 3000:2018 Cl 1.4.88
- Earthing arrangementEarth run with the submain
AS/NZS 3000:2018 Cl 5.5.3.1(a)(i)
- Allowed hereYes
AS/NZS 3000:2018 Cl 5.5.3.1(a)(i)
- Protective earthing conductorResult2.5mm²
AS/NZS 3000:2018 Table 5.1
About this calculator
How this is calculated
A shed, garage, sleep-out or workshop with its own board, fed by a submain, is an outbuilding. AS/NZS 3000 gives it two ways to be earthed. The tool asks which outbuilding it is and which way you plan, then checks the plan and gives the sizes.
An individual outbuilding is one structure, separated by land from the building whose board supplies it. It may take a protective earthing conductor run with the submain, connected at the main switchboard. Or it may be a separate MEN installation: the submain neutral becomes a PEN, the outbuilding board has its own MEN link, and an electrode is driven at the outbuilding. Combined outbuildings share a foundation, a metal roof or a metal frame. They take the earth with the submain only, so a separate MEN for them fails.
The sizes come from the same table as the earthing tool. With an earth in the submain, it is the protective earthing conductor for the submain's active size. With a separate MEN, the lead from the outbuilding board to its electrode is a main earthing conductor, sized from the submain. The PEN must be at least the neutral the submain needs and at least that earthing conductor, so the tool gives the larger. The electrode is one of the types the electrode table accepts, driven to the depth or laid to the length and cover for your country.
| Step | Table or clause | What it decides |
|---|---|---|
| Individual or combined | Cl 1.4.88 and Cl 1.4.89 | Which arrangements the outbuilding may take |
| Earth with the submain | Cl 5.5.3.1(a)(i) and Cl 5.5.2.1 | Where the earth connects |
| Separate MEN | Cl 5.5.3.1(a)(ii) and (c) | The MEN link, the board and the main earthing conductor |
| Combined outbuilding | Cl 5.5.3.1(b) | No separate MEN |
| Earthing conductor sizes | Table 5.1 | The protective and main earthing conductors |
| PEN size | Cl 3.5.2(c) | The least PEN of the submain |
| Electrode | Table 5.2 and Cl 5.3.6.3 | The electrode, and its depth, length and cover |
Worked examples
- A shed on a 10 mm² submain, earthed through the submain. The protective earthing conductor is 4 mm². No electrode is needed at the shed.
- A shed on a 16 mm² submain as its own MEN. The PEN is at least 16 mm², the main earthing conductor 6 mm², and the rod goes at least 1.8 m deep.
- A sleep-out with a metal water pipe to the house. The PEN is at least 6 mm². The tool warns that the pipe can carry neutral current in parallel with the PEN.
- A farm shed in Australia on a strip electrode. The PEN is at least 25 mm² and the main earthing conductor 6 mm². The copper strip is at least 3 m long with 0.5 m cover.
- Two sheds on one slab as a separate MEN. The arrangement is Not allowed and fails: combined outbuildings take an earth with the submain only.
Limits
The tool does not size the submain itself; use the cable size or total voltage drop tools for that. It does not check the earth fault-loop impedance at the outbuilding, which the loop impedance tool does. It does not decide whether a structure is an outbuilding: that is the definition and your site. Bonding of water pipes and other services follows the earthing tool.
See also: Earthing an outbuilding: earth or its own MEN, Shed earthing on a 16 mm² submain and Earthing and bonding.
Questions
Each answer describes what this tool calculates. The result is a design aid. Verify against the current standard.
Does a shed need its own earth stake?
Not always. AS/NZS 3000 Cl 5.5.3.1 lets an individual outbuilding take an earth run with the submain, with no electrode. It may instead be a separate MEN installation, and then it needs its own electrode and MEN link.
What is the difference between an individual and a combined outbuilding?
An individual outbuilding is one structure with its own board, separated by land from the building that supplies it. Combined outbuildings share a foundation, a metal roof or a metal frame. Combined outbuildings take an earth with the submain only.
What size is the PEN to a separate MEN shed?
At least the neutral the submain needs, which is the active size for a single-phase submain, and at least the earthing conductor from Table 5.1. The tool gives the larger.
How deep does the earth electrode go?
A driven rod goes at least 1.8 m in New Zealand and 1.2 m in Australia. A strip in a trench has at least 0.5 m cover and is at least 7.5 m long in New Zealand or 3 m in Australia.
Why do metal pipes between the buildings matter?
With a separate MEN, the submain neutral is also the earth. A metal water pipe or walkway between the buildings can carry part of the neutral current in parallel. The tool warns, and an earth with the submain avoids it.
Clauses and tables this tool reads
- AS/NZS 3000:2018 Cl 1.4.88Outbuilding definition
- AS/NZS 3000:2018 Cl 3.5.2(c)PEN conductor to an outbuilding
- AS/NZS 3000:2018 Cl 5.3.6.3Installing an earth electrode
- AS/NZS 3000:2018 Cl 5.5.2.1Where the protective earthing conductor connects
- AS/NZS 3000:2018 Cl 5.5.3.1Earthing an outbuilding
- AS/NZS 3000:2018 Cl 5.5.3.1Earthing arrangements for an outbuilding
- 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
Every clause and table, with how each was verified
Tables last checked on 1 Oct 2026.
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