By Dr Clive Dalton
Making sure you can find sheep where you left them has been a challenge for shepherds since domestication. Sheep are the classical “follower” species and if one finds an escape route – the whole flock will follow it in no time. Some sheep are born to be escapologists and they can lead to terrible disasters on steep hill country when one finds a hole in the fence in a hollow, and the rest of the mob push up behind it waiting their turn to follow ending up in a massive smother. Hundreds of sheep can easily die in these events in minutes. The solution for the persistent escaper is the butchers! So having good fences in the correct locations is the first priority of sheep farming.
Fencing law - Fencing Act 1978
Rural fence specifications
Seven or 8 wire Fence
A substantial wire fence, having 7 or 8 wires properly strained, with up to 2 of these wires as galvanised barbed wire, or with 1 galvanised barbed wire and a top rail; barbed wires to be placed in a position agreed upon by the persons interested, or to be omitted if those persons agree; the posts to be of durable timber, metal, or reinforced concrete, and not more than 5m apart, and securely rammed and, in hollows or where subject to lifting through the strain of the wire, to be securely footed, or stayed with wire; the battens (droppers) to be affixed to the wires and of durable timber, metal or plastic, evenly spaced, and not fewer than 3 between posts; the wires to be galvanised and of 2.5mm high tensile steel or 4mm steel or its equivalent; the bottom wire to be not more than 125mm from the ground, the next 3 wires to be not more than 125mm apart; and the top wire or rail to be not less than 1m from the ground.
Nine or 10 wire Fence
A substantial wire fence having 9 or 10 wires properly strained, with or without battens (droppers) or lacing affixed to the wires between the posts or standards; the posts or standards to be durable timber, metal, or reinforced concrete, well and substantially erected, and not more than 5m apart, the top wire not to be less than 1m from the ground surface, the wires to be galvanised, and of 2.5mm high tensile steel or 4mm steel, or its equivalent, the space between the ground and the bottom wire not to exceed 100mm, the bottom 4 wires to be not more than 130mm apart.
Prefabricated (Netting) Fence
A substantial wire netting fence properly strained of a minimum height of 1m; the netting to have at east 7 horizontal wires, and, if necessary, extra wires above or below the netting, one of which may be a galvanised barb wire, all other wires to be galvanised in either 2.5mm high tensile steel or 4mm steel, or its equivalent; the vertical stays of the netting to be galvanised wire, and not more than 305mm apart. Posts or standards to be not more than 5m apart and of durable timber, metal or reinforced concrete, additional battens (droppers) may be installed between the posts if both parties agree; the overall fence to be well and substantially erected.
Fence types
NZ Standard boundary fence
- This is the basic legal boundary fence required under the law (The Fencing Act 1978) in New Zealand.
- It is the best stock-proof fence there is but it’s the most expensive.
- It has got to be a seven-wire, fully-battened fence, and is the perfect sheep fence if well erected.
- It usually has posts 5 m apart with 5 battens equally spaced between them.
- The gaps between the seven wires from ground level to top are at intervals of 120mm, 120mm, 130mm, 150mm, 170mm, 200mm and 250mm.
- So the “escape holes” at sheep height along the bottom are about 400mm long between the battens and either 130mm or 150mm high and these are great sheep stoppers.
- Goats dig holes at the base of fences that sheep will go through so if you have goats (feral or farmed) on sheep farms, then a hot wire on an outrigger along the bottom is a good investment (see later).
- Using wire netting fencing is an easy solution to keep sheep of all sizes at home and it’s quick to erect.
- It works best on flat country and is not suitable for the ups and downs of hill country.
- It’s notorious for ripping tags out of sheeps’ ears – but maybe the sheep are to blame and not the fence!
- The rectangular gaps in the netting are either 150mm or 300mm long and going up from ground level they are 100mm, 100mm, 100mm, 120mm, 140mm, 150mm, and 200mm. So it’s very stock proof for ewes and small lambs.
- You will need a wire along the top of the netting too and if you run cattle, put a hot wire along the top and never a barbed one.
- Barbed wire should be banned for the benefit of humans, farm dogs and stock of all species.
This is a very cost-effective solution to keeping in sheep, and New Zealand has led the world in its development. It can be used as a stand-alone power fence, or be added on to a standard fence. If your standard fence is in bad repair and cash is short, adding a hot wire to it is a great way to get a few more years out of it.
Advantages of power fencing
- Low cost.
- Easy to construct with light materials. It’s much easier to get power fencing materials out to the back of a farm than with standard fencing.
- It lasts a long time as there’s minimal stock pressure on it.
- It’s easy to use for subdivision of paddocks improving grazing control.
- It’s easy to modify to suit the stock and if you find it’s in the wrong place, it’s easy to shift.
- It does not damage stock and if there is a disaster like a smother, stock in panic will easily be forced through it without injury.
- It can be aesthetically more acceptable than a permanent fully battened fence.
How does a power fence work?
It’s important, especially with sheep that carry their own wool insulation, that you understand how a power fence works to get the most out of it.
- A power unit or energiser puts out current along the fence. The energizer can be fed from the mains supply, from a battery or a solar unit.
- The critical part of the fence is the earth peg or pegs. They acts like an aerial and collects electrons from the ground.
- If you have a big energiser than you need a big earth.
- The earth rule is to count 1 2 3 3. This says:
- Have ONE continuous wire from power source to earth pegs. The wire needs to be attached with nuts and bolts and not just twisted.
- Use ground pegs TWO metres long and knock them all the way into the ground.
- Have THREE ground pegs.
- Knock the pegs in THREE metres apart, if possible in a wet area.
- The energiser should be earthed at least 10m away form telephone cables and other electrical earths including water pipes.
- When the sheep out in the paddock or away at the back of the farm touches the wire, the current goes through the sheep (delivering the shock) and back to the earth peg. The sheep in effect completes the circuit and if it doesn’t then there is no shock.
- Modern energizers will power up to 360 km of fence and at long distances, it’s important to run an earth wire along the fence to help the current find the earth contact easier.
Are power fences safe?
- It’s a relevant question, as modern energisers get bigger to power longer distances of fence to be more cost effective. Some will now power over 300km of fence. New Zealand manufacturers defend the safety of their units.
- The shock is normally around 4000 volts but the pulse only lasts for 0.0003 seconds which is more than enough to get a response from animal or human!
- There have been cases of new-born and very wet lambs and calves being killed from entanglement with a hot wire and receiving constant shocks for a very long period.
- The pulse is very low amps and it’s amps that cause injury.
- But saying that, a long continuous series of pulses will kill wet newborn lambs (and calves) if they stumble their way and get trapped on a hot wire.
- Hot wires are also lethal to hedgehogs. Their spines hit the wire and they curl up and die. They don’t recoil back from the first shock!
- Also be aware about a bit of physics called “impedance”. This is the build up of current at the end of a very long power fence. So if you are at the very back of a hill country farm, you (or the dog) may find the fence to be a bit more than the expected 4000 volts. The dog will certainly remember the experience longer than you will!
- If the power at the end of the fence exceeds 4,000 volts, then something needs fixing
Poor fence performance checklist
Client surveys by manufacturers of power fencing have found that 40% of fences are not working to their full capacity for a number of common faults leading to low voltage. Here they are so you can check your fence:
- Poor earth. This is top of the list and most people don’t know because they are scared to grab the fence, and they don’t invest in a voltmeter to check the power and find out where the problem is. Keep checking the earth pegs and soaking them with water frequently if they are not in a wet area.
- Bad or corroded connections.
- Poor knots in wire. Don’t use reef knots; use a knot with plenty of twists to make good contact, or use the modern connections where the end of the wires lie parallel and are clinched together.
- Long lengths of wire that is too thin – restricting the power flow.
- Long distances of single-wire fence (again with poor earth).
- Rusty wire which can be a problem with salty air.
- Animals standing on dry areas (insulated) and only touching live wires and no earth wire on the fence.
- Leakage through poor insulation. Old plastic insulators that need replacing.
- Leakage through excess vegetation contacting the fence. Spray the area under the fence.
- Avoid running fences within 10m of telephone lines. Many phone lines are buried along the side of the road and may be directly under your power fence.
Wire spacings on power fences for sheep
Three-wire fences
- This is a low fence suitable only for internal fencing on small farms with very quiet sheep that respect a power fence.
- Posts can be up to 10m apart.
- Wire spacings from the ground upwards can be 200mm, 300mm, 350mm.
- The top wire can be set up to take current but is always kept switched off to allow safe climbing by people.
- The power in the lower two wires will keep the sheep in unless they get really short of feed or are panicked. You can always power the top wire if needed.
- This fence could be used if you run cattle as well as sheep, but another wire on the fence would be better for cattle (see below).
- It’s very low cost and low maintenance.
Four-wire fences
- This is suitable for internal fencing for sheep and cattle.
- Spacings between wires from the ground upwards can be 180mm, 150mm, 225mm and 350mm.
- Posts can be up to 10m apart.
- The first and third wires can be dead and the second and fourth hot.
- Or use spacings from the ground upwards of 160mm, 190mm, 250mm, 300mm.
- Alternative wires can be hot or you can make it a standard practice that all top wires are prepared to take power but are kept switched off for ease of climbing over.
- Power the top wire if you have cattle.
- Some farmers have the bottom wire dead as it is the one most easily shorted by herbage and it allows safe passage for hedgehogs.
- This is suitable for internal fencing for sheep and cattle.
- Spacings between wires from the ground upwards can be 150mm, 150mm, 190mm, 200mm, and 210mm.
- Posts can be up to 10m apart.
- Alternative wires can be hot or only the first and third from the ground upward.
- You can make it a standard practice that all top wires are powered but kept dead for ease of climbing over.
- Power the top wire if you have cattle.
- Some farmers have the bottom wire dead as it is the one most easily shorted by herbage and it too allows safe passage for hedgehogs.
- This is netting made of plastic cord into which hot wires are woven, so all of it is hot.
- It’s only a temporary fence and is very useful when controlling pasture or crops by strip grazing and other odd jobs around the farm to direct sheep for a short term.
- If it’s correctly put up and kept tight, it works well. It’s easy to move and transport, and works if no pressured from large numbers of sheep– and where sheep have been trained to respect a shock.
- Before you start power fencing the farm draw up a good plan so that different areas of the farm can be isolated by switches conveniently placed around the farm.
- Put gateways on high points rather than in low points where sheep may rush down hill and smother.
- If you buy sheep that are not used to power fences then they will need time to learn. Put them for a spell in a paddock with a good seven-wire fence with a hot wire about 500 mm from the ground. Leave them in there till the feed gets short and they start fancying the feed in the next paddock!
- If you have metal gates, make sure there are no leaks from the fence to the gate. Grabbing a hot gate is not a nice experience, especially if it’s your entrance one! Nicely-brought-up people say some funny things when they are surprised by 4000 volts!
Scrim (Hessian)
- A large roll of scrim (Hessian) has been used by shepherds to get ewes and lambs into the pens at docking for generations.
- The ewes and their small lambs cannot see through it, and apart from the ones that jump over, you can drive them into pens or yards. The skill is to keep the pressure on them and never let them have space to get a run at the fence you have created.
- So if you ever need a visual barrier, a bit of scrim is ideal, being light and not bulky when rolled up.
This material is provided in good faith for information purposes only, and the author does not accept any liability to any person for actions taken as a result of the information or advice (or the use of such information or advice) provided in these pages.
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