Make A Well-Grounded (Earthed)
Fence
Tips from a New Zealand grazing
farmer and consultant to keep your fence hot and your
livestock in.
By Vaughn Jones
Editor's note: Noted New Zealand grazing
farmer and consultant, Vaughn Jones, has been building
and troubleshooting electric fences since 1954. Here he
provides a checklist of advice and tips to solve one of
the most common causes of fencing failure: Poor
grounding -- or "earthing" as they say "down under."
For your fence to function correctly, your earth
(ground) system must be perfect. But very few are,
despite the instructions provided with most energizers.
Also I've not seen an instruction book with complete
details of how to achieve perfect earthing and
completely trouble-free operation in all respects. So
I'll give all I know here:
Most farms seem to have earth systems which can't cope
with the flow of electrons coming back to it from fences
with poor insulation, leakage into vegetation, and the
occasional wire which breaks and touches the ground or
touches a non-insulated wire. Energizers have become
more powerful, but many ground systems and their
recommendations have not kept up with them.
When the energiser (charger) earth system can't handle
the increased flow of electrons, they find other ways of
getting back to the power supply earth system.
Unfortunately they sometimes do this through the cows
and milking machine, and through steel water pipes or
the water in plastic pipes.
Guide to Good Grounding
When the energiser earth system can't absorb the
increased flow of electrons from leakage, electrons find
other ways of getting back to the power supply earth
system. Energisers put out thousands of volts, and just
one volt through the cow's mouth or teats can upset her.
Here are methods to follow to avoid that:
- The energiser earth system must be installed
well away -- at least 10 m (33 feet) from mains
power earth peg, preferably on the opposite side of
the building.
- Use 25-mm (1-inch) or larger diameter new or
near new galvanised pipe driven as deeply as
possible into a moist soil, each at least 10 m (33
feet) apart. Thin, black or rusty fence posts or
similar are not suitable. Rust is a bad conductor. A
large surface area is needed to give a large contact
area between the soil and pipe.
- One metre (3 feet) of earth pipe per joule of
output of the energiser is usually sufficient for
satisfactory earthing in conductive soils. Long
earth pipes which are driven deep into the soil give
far better earthing than the same total length at
shallower depths because soils are more moist and
have more conductive minerals at lower levels. Two
3- metre-long pipes are better than three
2-metre-long pipes when driven deeply this way.
Large diameter pipes have a greater soil contact
surface, so are better than thin rods.
- Install the earth system well way from water
pipes and bores which are being used. But an unused
steel pipe bore can be an excellent earth if it's
not rusted or broken.
- Connect the terminal marked Earth or Ground to
the earth pipes by one continuous length of double
insulated electric fence leadout cable -- not
household or industrial cables which are made for
only 400 volts, not for 10,000 volts. The cable
should contain 2.5-mm (16-gauge) galvanised wire --
not thinner and not copper wire, which
causes electrolysis at the joins. Bare and clamp the
cable securely to each pipe with galvanised clamps.
Ordinary galvanized wire can rust where it is
damaged or touches the ground. Using cable
eliminates this.
- It is best to have no voltage on the earth
system, but a maximum of 200 volts (and up to 300
volts on a large energizer) are acceptable when the
fence has been shorted out to as low a voltage as
possible.
- Soils are not good conductors, so electrons
spread out inclining towards moist and mineral soils
when travelling back to the energizer. Aim for a
moist area, work out a system of keeping the area
around the earth pipes moist. If necessary, take a
galvanised wire along the bottom of a fence to a
moist area, and then install more earth stakes at
that point. If the distance exceeds 100 metres, use
two wires. Better still, use aluminium or
aluminium-coated wire which is up to three times
more conductive than the same thickness galvanised
wire.
- Some soils are very bad conductors. If you have
dry peat, pumice, volcanic ash soils, etc., or soils
that are dry at any time of the year, and there is
no wet area within a few hundred metres which could
be used, a bentonite earthing system can be bought
and used. They are a good value. The bentonite mix
is made into a slurry and poured down 75-mm (3-inch)
diameter or larger holes with pipes set in the
centre. Keep them moist. This system can improve
earthing by up to ten times.
- In extremely dry areas and on snow, use an earth
wire return system. This is where there is an equal
number of live and earth wires kept well apart on
the fence. The earth wires are joined with joint
clamps (like the live wires) and connected to the
energized earth terminal. The earth wires should
also be earthed adequately (no voltage on them)
every kilometre. These also act as lightning
conductors, keeping it away from energizers.
Testing an Earth System
- Testing an earth system without the fencing
shorted out is a waste of time. You must create a
flow of electrons to load the earth system before
testing it.
- Also testing the earth by holding the last earth
pipe can be a waste of time if the wire between it
and the energiser is broken.
- To test the earth system, first short the fence
out with steel rods at least 100 metres from the
earth system. Then use a digital voltmeter to
measure the voltage between the energiser earth
terminal and an independent earth wire. This should
be pushed as far as possible (about one metre) into
damp ground in a position handy to the energizer and
several metres away from any other earth peg.
- To lower the voltage on the earth system add
more earth pipes and/or connect the earth wire to
the bottom wire of a conventional fence.
- Never use your water supply, bore or well
as a ground or allow a charger ground wire to touch
them or any part of buildings. It can cause shocks
in the water and stop animals from drinking, and
buildings can become a transmitting aerial for radio
and phone interference.
- Double insulated underground cable should be
used for the ground as well as the live wire. Unused
bore pipes or steel well liners are usually good
grounds.
- Many New Zealand farmers measure Joules (energy)
roughly by holding the live wire and feeling the
kick in good insulated gumboots standing on one foot
to halve the electrons flowing through your body.
Caution: Don't do this if you have a dicky
ticker or Pacemaker.
- High-power energizers are essential for to
controlling animals where long lengths of wire are
electrified. The high power is on for the very short
period of 0.0003 seconds which makes them safe.
- Voltage measured at the energizer is useless,
especially if the fence wire is thin, limited to one
wire or has bad connections. But voltage can be an
indicator of the energy when measured at the end of
a long fence.
- The latest, best New Zealand energizers have a
system of telling the farmer at the energizer the
effectiveness of the fence at various points, and
the earth condition, both of which are extremely
clever.
- The lower the voltage on the ground the better
it is. But with high-power energizers, it can be
difficult to get the voltage below 200 volts, which
figure is acceptable (provided it was measured when
the fence was shorted (grounded) a few hundred
metres from the energizer).
- Ensure that all electrical appliances wirings,
everything metal and all concrete steel reinforcing
are all connected by welding or strong galvanised
clamps, not electroplated ones which rust sooner.
- If your stock are going through fences, check
the earth first, followed by the joints on the whole
fence, and at the same time look for shorts.
- Test your earth by thoroughly shorting out the
fence at least 100 metres (330 feet) away from the
energiser with steel standards. Doing this creates
the maximum current flow so puts a load on the earth
system. If your earth pipes can't handle the flow
you'll get a voltage reading at the energizer
terminals. If there is no voltage, then your
earthing system is satisfactory.
- You should have a digital voltmeter, then
install an earth monitoring point by pushing a piece
of 4-mm (8-gauge) wire into the ground handy to the
energiser and measure between it and the energiser
earth terminal. Don't check the last earth pipe
because there could be a break in the wire to it, in
which case you'll think the earth is OK, but it may
not be.
- With the fence shorted out, there should be no
more than 200 volts, although no voltage reading is
best. The more voltage you read flowing to your
earth, the less power you will have on your fence
because it indicates that the earth is inadequate
and needs more pipes.
- To improve your earth system, increase the
number of earth pipes and put them in as deep as
possible. Tests on several soil types have shown
that depth is essential -- 2 m (6 feet) deep is the
minimum, and 3 m (9 feet) deep is twice as good.
Doing all the above reduces the chances of clicks on
your radio and telephone.
An inadequate earth system reduces the output of your
energiser and increases the chances of shocks in milking
parlors, yards and water troughs. It takes an expert
with sensitive measuring equipment left connected for 24
hours and a recorder to check for shocks in parlors.
There may be none during the day, but they can occur
when heaters, cookers, etc., are switched on in the late
afternoon.
Check your parlor twice a year and yards in many
positions at the height of dry weather and the height of
the wet period. See your energiser installation
instructions for more details on installing it and an
earth system.
Poor Earthing Costs Production
A common problem is having energiser earth pipes behind
the milking parlor. Leaked electrons (there are always
some) flow from the farm under the yard and parlor when
the soil is moist. But when it is dry, they look for
easier routes, which can be across a moist yard and
through parlor pipe work.
In wet weather, electrons can travel along the soil
surface and through the parlor, especially after cows
enter and pass their high mineral, highly conductive
urine. This can cause electrons to even flow across the
concrete surface and across pipe work, so affecting the
cows.
A short or weeds conducting power off a live wire close
to the parlor can result in electrons flowing through
the parlor and/or yard because it is the shortest route,
especially after cows enter and urinate. The above can
occur even when the earth system is perfect, simply
because the electrons are flowing to it via the best,
shortest and fastest route.
To avoid this, earth systems should be in a damp area
well to the side of the milking parlor, or even have
earth pipes well to both sides, but never in line with
the parlor. The earth leadout wire from the energiser
should be insulated, and not allowed to touch any other
wire, building or pipe.
Electrons can also move through water pipes, giving
shocks to cows when drinking in a paddock, so no wires
should be allowed to touch water troughs. Even if not
electrified, they can conduct induced current. Cows
standing around a full trough waiting to drink can be a
sign of power deterring them from drinking.
Where conventional fences have a live wire running with
them or as an offset wire, the conventional fence wires
can absorb induced current (more so in damp conditions)
and become electrified. So unelectrified wires must be
earthed or they can build up a voltage which can:
- Jump gaps (bad joins) and cause sparks and radio
and phone interference.
- Conduct current to water troughs they may touch.
Animals then won't drink so growth and milk
production suffer, and females can get cysts on
their ovaries through stress. This happened to a
herd near here causes calculated losses of $30,000
over the years it had been happening.
- Give people shocks when opening and closing
gates.
- Give animals shocks as they go through gateways
and brush against the wires tied around strainer
posts.
Earthing these conventional fence lines is easy because
being induced power, it is of low joules (energy or
power). All they need is a piece of soft galvanized wire
wrapped around all dead wires at the strainer posts and
pushed into the soil. These will need replacing when
they rust at ground level.
Shocks in sheds and water troughs have cost some farmers
small fortunes in lost production over several years,
until the problem was identified. New Zealand
manufacturers discourage grounding the fence circuit
though the earth or ground terminal of the charger to
the utility (power supply) grounding system because it
is illegal in many countries and can cause shocks in all
directions including in your shower. The power supply
ground is usually just a metre deep rod. A modern high
power New Zealand energizer needs ten to twenty times
more.
Safety Considerations
Keep these in mind when you build fence:
- Don't string wires across lanes or thoroughfares
without marking them clearly. Motor cyclists have
been injured through not seeing them.
- Never electrify barbed wire.
- Train and demonstrate the shock to children and
visitors with a long piece of grass.
The thought of 5,000 volt fences on farms near cities
could be frightening to townies, but thousands of human
contacts occur annually with nothing more than
discomfort. However, care should be taken to avoid
contact through the head because it is very
uncomfortable. Young children and elderly people should
be kept away from even low powered fences.
Electrified fences in any position where the public
could come in contact with them must be clearly marked
with approved warning signs at frequent enough
intervals so as to be easily seen.
Radio Interference
It is an offence to operate any appliance which causes
any electronic interference, so points to note include:
- Some energizers cause more radio and/or phone
interference than others, even if not on a fence.
Switch it off, disconnect the fence and earth
(ground) cables (wires) at the energizer (if they
were loose the sparking there could cause
interference) and switch on the energizer and check
for interference.
- If the interference is still there, return the
energizer to the supplier and try another unit or
brand. Some brands are bad.
- If the interference disappears when the fence
and earth are disconnected:
- Tighten all joins and clamps on the
energizer and fences. Those on some energizers
work loose because of the thump (vibration).
- Ensure that all wire connections are figure
of eight or reef knots, or are clamped and
tight.
- Tube insulators will crack and leak in time.
Even double tubes and those with steel inserts
leak and spark in some cases.
- Sparking causes radio and telephone
interference so insulators must be good quality
with adequate tracking distance to avoid arcing
over the surface as occurs with staple
insulators or through the insulator as occurs
with single tubing. Use quality insulators with
at least 25 mm (1 inch) of tracking distance
(length on insulator from the live wire to any
other point).
- Some cable can have breaks in it causing
sparking. Single insulated cable gets cracks
sooner than double. (Try bending a sheet of
cardboard and a wad of paper the same thickness
and you'll see why. The card will crack.) Some
of the orange cable from New Zealand cracked and
leaked soon after installing. Replace it all.
- Even the best cable when buried can become
damaged by a stone and then leak. It is
essential that all be threaded through 12 mm
(half-inch) or similar black plastic piping to
give it physical protection. If the distance is
long, push a piece of high tensile wire (with
its end bent back) through and then pull the
cable through. To check under gateways,
disconnect before each one and check if the
interference stops.
- Ensure that the earth is perfect. Check it
at the energizer, not at the last earth pipe as
shown on some instruction books. There could be
a break in the cable so there would be no
voltage at the last, or even first pipe.
- The earth cable should be one continuous
length of double insulated cable or be joined
with a good galvanised joint clamp, and must not
touch any building or pipe. Support the cable in
good insulators.
- Use a digital volt meter to test the earth
and to locate shorts and maintain tidy,
trouble-free fences.
- If you still have interference, tighten all
joins and clamps on the farm. This is best done in
summer when joint clamps have expanded.
- Walk along all fences and wires with a radio
tuned off the station and clicking. It will get
louder close to the interference cause.
- Shorting to vegetation or to any grounded object
can cause clicking, so disconnect the bottom wire
and/or clear the fence line with a weed wiper. Once
grass touches a live wire, stock won't graze it, or
anywhere near it, so the problem increases. Always
have the bottom wire able to be disconnected with a
flexible connector and do so before
vegetation touches it.
- The mains power supply (utility) earth and all
connections including power point terminals and
plugs must be adequate with no loose or old
verdigris connections.
- If wires run parallel with overhead phone wires
on underground phone cables interference can be
worse, so avoid the constructing of electrified
fences parallel to telephone lines or cables and
aerials, or parallel to other long fences which
could act as aerials.
You might find this difficult. Having changes in the
fence to under-gate cable reduces the length of "aerial"
electric fence wire. It is long lengths of electric
fence wire parallel with long lengths of telephone or
similar wires which cause the problem which can grow as
the fences are extended over time. The closer they are
the more the induction. The break causing the spark and
interference can then be on the induced wire.
Radio interference is worse in poor reception areas, and
if the radio is not tuned exactly on the station.
Telephone systems are not always perfect.
Lightning Protection
The long distances of electric fencing now used increase
the chance of a lightning strike, so an effective
protective system should be used. Lightning often hits
the power supply line and goes through the energizer to
its earth system blowing its fuse or components. The
power (utility) supply earth system should be good
enough to attract the lightning rather than have it go
through the energizer to its earth.
Finding Shorts
The solid state digital volt meter is important for
fault finding and for testing the earth system. It
enables accurate reading of the voltage and easy fault
finding, because of its extreme accuracy.
Start by going to the first switch (these must be
installed along fence lines to save going back to the
energizer to switch it off for repairs and for fault
finding) and see if the voltage before the switch
increases after opening the switch to stop current flow
down the farm.
If the voltage increases then go to the next switch. If
not check the fence between the switch and the
energizer. Neon fence testers are also available, but of
no use for finding small leaks or earth system faults.
Many are bought and not used for long before buying a
digital volt meter.
Electric or power fencing helps make animal farming
profitable and sustainable, so the effort required to
achieve the above suggestions is well worthwhile. If
installation is good and monitoring is done, the labour
required is less than with any other system and the
profit is greater.
If you have problems, read all the above again. There is
a lot to take in, but once you understand it, it becomes
second nature.
Take pride in your fencing and enjoy your animals.
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