Lorentz PS200 Instructions For Installation Operation Service page 17

Grounding and Lightning Protection continued
DO NOT GROUND the positive or the nega-
tive of the power circuit. The best lightning
protection results from grounding the metal-
lic 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
feet (particularly in a high lightning area), DC-
rated surge protection devices are recom-
mended.
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 reduces the probabil-
ity of damage. This method is employed in
telephone cable, and in many other applica-
tions. Some power cables are made with
twisted conductors. To twist wires yourself,
you can alternate the direction of the twist
about every 30 feet (10 m). This makes the
job much easier.
Float switch cable A long run of control cable
to a float switch in the storage tank can pick
up damaging surges from nearby lightning.
The best protection is to use shielded,
twisted-pair cable . Shielded cable has a
metallic foil or braid surrounding the two
wires. Ground the cable shield as illustrated
in Section 5.10.
Low water probe cable A long horizontal run
of wire to the low-water probe at the pump
can pick up damaging surges from nearby
lightning. Wire twisting is helpful. The best
protection is to use shielded, twisted-pair
cable, same as recommended for a remote
float switch. This product is suitable for direct
burial, but not for submersion in the well. At
the wellhead, make a transition to submers-
ible probe wires.
Additional lightning protection The controller
has built-in surge protection devices. How-
ever, additional grounding measures or
surge protection devices are recommended
under any of the following conditions:
1. Isolated location on high ground in a
severe lightning area
2. Dry, rocky, or otherwise poorly conductive
soil
3. Long wire run (more than 100 feet / 30m)
from the controller to the wellhead, or to the
float switch.
Additional lightning protection devices (surge
arrestors) can be obtained from your pump
supplier. The device(s) for the controller's PV
input, float switch and probe connections,
must be rated for DC. The device(s) for the
controller's AC output to the motor must be
rated for 3-phase AC. In each case, the
clamping (bypass) voltage should be 90V or
higher, but not much higher.
In extreme cases, it is best to employ the
service of a local lightning protection contrac-
tor.
Reference www.lightning.org
CAUTION
Ground the
cable shield at
the controller
end only, not at
the float switch.
WARNING
Isolate solar
pump wiring
from electric
fence systems.
Do not connect
the pump system
to the same
ground rod as an
electric fence. Do
not run power or
float switch cables
close to an
electric fence.
17