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 Lightning
Protection FAQ:
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Q - Why do you need lightning protection at
all? |
A - Pet Containment System transmitters
are vulnerable to lightning-induced
surges from the AC power line, as all AC-powered equipment is. But
there is an extra vulnerability for PCSs, because the loop acts as an
antenna, and can pick up lightning-induced currents/voltage from
lightning even hundreds of feet away. Lightning currents can be up to
100,000 Amperes, with voltages into the millions! Experience shows
that in difficult sites (frequent lightning, large loop, hilltop
locations) transmitters will be damaged several times per year unless
they are protected. |
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Q - Why can't I just use an ordinary AC protector? |
A - As stated above, PCS transmitters need to be protected BOTH on the
loop side and on the AC side. The loop protector needs to be specially
designed for the PCS frequencies/voltages. |
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Q - Can I use separate protectors for the loop and AC? |
A - You can, but it won't work, unless the installation is very
carefully done. It is MUCH better to have the loop and AC protectors
in one package. That eliminates connecting wiring, and is less
expensive, because only one housing is needed. |
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Q - Can't I ground the loop to a ground rod and protect the
loop that way? |
A - No. People tend to think, "Ground is ground." The reality is very
different. Depending on soil conditions, the resistance of an 8-foot
ground rod can be from 20 ohms or so to 1000 ohms, or even more in
rocky or dry earth. The resistance of a short (say 2 foot) rod would
be about 4 times larger- say 1000-4000 ohms! This can be easily
measured with an ohmmeter. Lightning currents coming into the loop
from direct lightning can be several thousand amperes. Ohm's law tells
you that a 1000 ohm ground isn't going to take much current away from
the loop.
Note that the NEC Article 250-52C requires that ground
rods be AT LEAST 8 FEET long. The NEC also requires (250-50) that all
grounding electrodes be bonded (i.e., connected together) with a heavy
conductor (Table 250-66). |
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Q - Don't I have to worry about lightning currents being
brought into the house by the loop? |
A - Yes, you do. The PCS loop is one of the many paths that lightning
can take to get inside the house. CATV, AC wiring, phone, and TV/DBS
antenna wires are other paths. The NEC describes how these various
lines have to be protected- basically, by passing lightning currents
into the building grounding system. That's what the protector does.
The protector is UL Listed (approved) as an AC protector, and ALSO
tested and approved as an "isolated loop protector" for the PCS loop.
The protector contains fusible links on the loop side to limit
the amount of lightning current that can come through to
values the protector can handle without damage. (About 20,000 ampere
surge on each loop wire.) |
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Q - What is the expected field life of the protectors? |
A - The few protectors that have been damaged suggest a field life (MTBF)
of AT LEAST 500 YEARS, and probably more, even in high-lightning
areas. |
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Q - If I bury the loop, do I still need a protector? |
A - YES! Lots of field experience shows that even with burial 3 feet
deep, wires and cables can be struck by lightning. This occurs, once
again, because soil is not a good conductor. So the lightning current
keeps going down until it finds something metallic. Shallow burial
(less than 1 foot deep) provides very little protection. |
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To Order:
sales@undergroundpetfences.com |
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