4.2 Grounding and Lightning Protection
Surges induced by lightning are one of the most common
causes of electronic controller failures in solar water pumps.
Damaging surges can be induced from lightning that strikes
a long distance from the system, or even between clouds.
The risk of damage is greatly reduced if these instructions
are followed.
Location of the pump controller Place the controller
close to the solar array, not the pump. This will reduce the
risk of lightning damage. Explanation: The controller’s input
circuitry is more sensitive to surges than its output. It is
safest to minimize the length of the input wiring.
Construct a discharge path to ground A properly
made discharge path to ground (earth) will discharge static
electricity that accumulates in the above-ground structure.
This helps prevent the attraction of lightning. If a lightning
strike occurs at close proximity, a well-grounded conduc-
tive structure can divert the surge AROUND the electrical
circuitry, greatly reducing the potential for damage. The
controller has built-in surge protectors, but they help ONLY
if the system is effectively grounded.
Earth connection – create an effective discharge
path It helps to picture this as a “drain field” for elec-
trons. Here are suggestions for grounding, in order of their
efficacy:
The best possible ground rod is a steel well casing 1.
located near the array. Drill and tap a hole to make
a strong bolted connection to the casing with good
metallic contact. Bolt on a brass terminal lug. After
the connection is made, seal the connection with
silicone sealant or other waterproof compound to
prevent corrosion. Protect the ground wire(s) from
physical damage so they aren’t stressed by being
stepped on, etc.
Install a copper plate or other specialized grounding 2.
devices designed for the purpose. Some systems use
salts to improve the conductivity of the surrounding
soil.
Install one or more copper-plated ground rods at 3.
least 8 ft (2.5 m) long, preferably in moist earth.
Where the ground gets very dry (poorly conductive),
install more than one rod, spaced at least 10 ft (3 m)
apart.
If the soil is rocky and does not allow ground rods to 4.
be driven, bury BARE copper wire in a trench at least
100 ft (30 m) long. If a trench is to be dug for burial
of water pipes, ground wire can be run along the
bottom of the trench. The wire size must be minimum
#6 (16 mm
2
) or double #8 (10 mm
2
). Connect one
end to the array structure and controller. Or, cut the
ground wire shorter and spread it in more than one
direction.
Dry or rocky locations To achieve good grounding at a
dry or rocky site, consult a local contractor who specializes
in lightning protection. It is best to plan the procedure in
advance, and to coordinate the effort with other earth-
excavating procedures that need to be done. Reference:
www.lightning.org
Bond (interconnect) all the metal structural compo-
nents and electrical enclosures Interconnect the PV
module (solar panel) frames, the mounting rack, and the
ground terminals of the disconnect switch and the control-
ler, using wire of minimum size #8 (6 mm
2
), and run the
wire to an earth connection.
Ground connections at the controller The controller
and junction box have redundant ground terminals inside.
They are all connected in common with the metal enclo-
sures of both the controller and the junction box. Ground
connections can be made to any of these points.
Ground connections to aluminum This applies to
connections at the solar array framework, and at the con-
troller’s enclosure box. Connections to aluminum must be
made using terminal lugs that have an aluminum-tocopper
rating (labeled “AL/CU”) and stainless steel fasteners. This
will reduce the potential for corrosion.
WARNING Failure to install and con-
nect an effective grounding system
will greatly increase the risk of
lightning damage and will void your
warranty. We suggest you wire the
grounding system FIRST so it is not
overlooked. The concrete footer of a
groundmounted array will NOT pro-
vide adequate electrical grounding.
DO NOT GROUND the positive or the negative of
the power circuit. The best lightning protection results
from grounding the metallic structure only, and leaving
the power system ungrounded. This is called a “floating”
system.
Explanation: With a floating system and a good structural
ground, lightning induced surges tend to reach ground
through the structure, instead of the power circuit. When
high voltage is induced in the power circuit, the voltage
in negative and the positive sides tend to be nearly equal,
thus the voltage BETWEEN the two is not so high, and
not usually destructive. This method has been favored for
many decades by most engineers in the remote power and
telecommunications fields.
Exception for battery systems: You can connect the
pump to a battery-based home power system that has
a negative ground. If the wiring distance to the pump
exceeds 100 ft (30 m), particularly in a high lightning area,
DC-rated surge protection devices are recommended.
Legal exception: If the local electrical authority requires
grounding of the power circuit, ground the PV ARRAY
NEGATIVE wire. This may increase the risk of lightning
damage.
Solar array wiring Bind the array wires close together,
or use multi-wire cable. Avoid forming loops. This helps
induced voltages in each side of the circuit to equalize and
cancel each other out.
Wire twisting for long runs Twisting wires together
tends to equalize the voltage induced by lightning. It
reduces the voltage differential between the wires. This re-
duces the probability of damage. This method is employed
in telephone cable, and in many other applications. Some
power cables are made with twisted conductors. To twist
wires yourself, you can alternate the direction of the twist
about every 30 ft (10 m). This makes the job much easier.
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