Farm Forestry New ZealandThink before you form that new access track
Geoff Wishart, New Zealand Tree Grower May 2018.
Forming a new track beneath or close to a transmission line on your property may introduce an electrical hazard to yourself your workers or visitors. This will be a problem if the ground-to-wire clearance is not sufficient for vehicles to safely pass underneath.
Transpower operates the national grid and maintains the high voltage transmission lines which connect areas of generation to the local lines networks that supply your farms and homes with power. Most of these transmission lines are located on or across private land.
Constructing new tracks and other work around transmission lines can result in an electrical risk to machine operators and people working around them, especially if the vehicle or machinery encroaches the minimum electrical safe distances.
Electrical safe distances are set out in the New Zealand Electrical Code of Practice for Electrical Safe Distances issued under the Electricity Act 1992. Compliance with this code is mandatory, in other words, you have to follow it. A table in the code sets out the minimum safe vertical distances of wires from the ground. Transpower lines generally range from 50,000 volts to 350,000 volts.
Transmission lines have been built across some rugged terrain which was assessed as either traversable or not traversable. The code mentioned above recognises the difference between traversable or not traversable in terms of the minimum safe distances which are applicable. As shown in the table below, they specify distances to the ground for roads and driveways which can be greater than for other areas possibly traversable by vehicles. which is greater again than for areas not traversable by vehicles at all. Of course, those distances relate to when the line was built, and the use of the land underneath can change.
Land was defined as not traversable because at the time the line was constructed vehicles including mobile plant, were unable to travel beneath the lines. In these situations, the vertical clearance to the ground may be less. This includes ridges, steep side slopes and gullies.
As land use has intensified and properties subdivided, new areas of land have been opened up for farming and forestry. Areas that were once non-traversable may now be traversable, and other changes may make overhead transmission lines much closer to the ground.
If you are thinking about changing the nature of the land underneath lines, take care. We recommend you contact your local Transpower service provider to obtain some guidance on existing clearances and required clearances before you start. This will give you the confidence that you are not going to end up with a clearance problem once the project has been completed.
If you do end up working around transmission lines to bench cut a track, it is worth remembering that for voltages involved in transporting bulk electricity on the grid, you do not have to touch the wire for there to be a problem – the electricity can jump quite a gap. For that reason, you need to keep your vehicles and mobile plant at least four metres away from the wires.
Transpower, landowners and occupiers play an important role in ensuring everyone is kept safe when working on their land. Our local service providers can help you ensure that any proposed work around the lines is safe for you and the grid. Call 0508 526 369 for free advice when planning any work activity around the transmission lines.
| Circuit voltage | Vertical distance to the ground | Radial distance | ||
|---|---|---|---|---|
| Across or along roads or driveways | Any other land traversable by vehicles, excluding across or along roads | Any land not traversable by vehicles due to its inaccessibility | In any direction other than vertical on all land | |
| Not exceeding 1kV and insulated | 5.5 metres | 4.0 metres | 2.7 metres | 2.0 metres |
| Not exceeding 1kV | 5.5 metres | 5.0 metres | 4.5 metres | 2.0 metres |
| Exceeding 1kV but less than 33kV | 6.5 metres | 5.5 metres | 4.5 metres | 2.0 metres |
| Exceeding 33kV but less than 110kV | 6.5 metres | 6.5 metres | 5.5 metres | 3.0 metres |
| Exceeding 110kV but less than 220kV | 7.5 metres | 7.5 metres | 6.0 metres | 4.5 metres |
| Exceeding 220 kV | 8.0 metres | 8.0 metres | 6.5 metres | 5.0 metres |
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