On Fri, 16 Dec 2005 22:55:09 GMT, Owen Duffy wrote:


Very often, the target of effective lighting protection of radio
installations is minimisation of voltage drops or potential
differences internal to an installation as a result of lightning
discharge current rather than trying to minimise the voltage to
"ground" resulting from the current.

I should have expanded that to say:

Minimisation of potential differences is often obtained by one or more
of:
- providing an alternate low impedance path to ground so that less
current flows through the equipment room;
- single point earthing to reduce the voltage drop in earthing
conductors internal to the equipment room;
- equipotential bonding to reduce the voltage drop between the
equipment room earth and other parts of the building, and other
services or structures (eg water, gas, telephone, power).

There may be standards or codes that apply to lighting protection in
your area, they are worth checking, and while they may not mandate
lighting protection, they may mandate the way in which it is done if
it is done. That may have implications for your insurance.

Effective lightning protection is a very expensive business, and if
you don't need "continuous operation" and have a simple configuration,
it is much cheaper and effective to ensure that feedlines and similar
conductors (like rotator cables) are totally disconnected from the
shack at times of high risk.

Owen
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