[wxqc] Grounding of anenometer mast

[Mark Wyman]

Lighting protection and grounding are all ugly things to deal with. No
matter what, the short distances in your house are nothing to a one mile
long plus lightning strike.

The idea of lightning protection is to prevent lightning from forming in the
first place. On the top of large radio towers, barns, houses, etc. are a
series of sharp points designed to bleed off charge before enough can gather
to form a lightning bolt. The other end of these "brushes" and lightning
rods are grounded extremely well deep in the ground. The best ones on towers
are large stainless steel arrays of spikes that look downright nasty. They
however have hundreds of very sharp points, and could drain off current in
the hundreds of amps which essentially locally shorts out the charge in the
storm to prevent the voltage from getting high enough to form a bolt. Still,
this sometimes doesn't even do the trick.

Needless to say, grounding your mast vs. leaving it floating wont make much
difference, both will attract lightning as a conductive rod in air is better
than plain air. The best thing is to leave the unit wireless, ground the rod
around the outside of the house (to divert any discharge around the house
rather than through it), and do NOT run any wires into the house, or you are
asking for a serious fire and more damage than just your weather setup.

-Mark

-----Original Message-----
From: wxqc-bounces at lists.gladstonefamily.net
[mailto:wxqc-bounces at lists.gladstonefamily.net] On Behalf Of Dennis Maier
Sent: Tuesday, March 14, 2006 1:14 PM
To: 'Discussion of weather data quality issues'
Subject: [wxqc] Grounding of anenometer mast

As soon as it's safe to climb up on my second story garage roof I intend to
extend the height of my anemometer from about 7' to maybe 15' or more above
the roof.

At the present time the Davis Vantage Pro anemometer is connected to their
Wireless Anemometer Transmitter mounted on the mast just above the tripod.
Also mounted on the same mast a couple feet below the anemometer is a large
TV antenna used to pickup On-Air HDTV. The TV antenna coax is routed into
the garage through the roof eaves vent down to the ground floor and into a
metal patch panel enclosure and grounding block then into the house. The
enclosure and a coax grounding block are grounded with #4 copper wire
through the wall outside to a ground rod. I did it this way to preserve the
appearance (no unsightly wires) of the newly vinyl sided house and garage.
At this time the mast is not grounded.

Was this, routing the wires inside the building before the ground block, an
unsafe decision from a lightning standpoint?

Because of occasional missed data packets from the Wireless Anemometer
Transmitter when I extend the mast I will probably hardwire the anemometer
to the Davis ISS and do away with the Wireless Transmitter. So that will be
additional wires running from the mast to inside the home.

I live on the waters edge of Saginaw Bay off Lake Huron in the Thumb of
Michigan. A few years ago lightning struck the electrical wires entering my
home at the utility pole, so I know it likes my area.

What are forum members thoughts about grounding the mast? I worry that
grounding the mast will just attract more lightning strikes.


Dennis Maier
CW4869

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