Proper safety grounding of telecommunications equipment is one of the most important
but least understood elements of good installation practice. Earth neutral connections
provide numerous benefits to equipment owners including personal electric shock
safety, protection from voltage surges caused by lightning and power line delivery
variations, and reduction or elimination of electromagnetic interference from nearby
sources. Here are some basic tips to follow when designing an installation in which
grounding is an integral part:
- Start with the location. Electronic equipment, especially transmitting gear,
should always be located at ground level or below ground where the distance from
equipment chassis to the earth terminal connection point is as short as possible.
In all cases try to keep the ground leads less than 10 feet in length running
in a straight line. If an elevated site is mandatory then all connecting leads
such as transmission lines, rotator lines, AC feeder lines, etc. should reach
ground level first (where lightning protection can be installed) and then routed
to their proper destinations (antenna on roof, AC system, etc.).
- Choose an electrode wisely. Don't use cold water pipes or AC service neutrals
to achieve ground. both of these often travel very long distances before actually
reaching earth ground, and they are often full of joint connections, corrosion,
and dissimilar metal changes along the route. Making connections through these
sources in transmitting applications frequently increases local interference
because they become part of the radiation pattern at ground level. Grounding
should always be done with the shortest distance to the actual dirt entry point
where a rod may be driven. Ground rods come in many sizes but a length of 6 feet
or more is highly recommended. Use rods that have a bright dipped copper clad
finish to the steel core or solid brass for best long term results. Keep the
earth around the rod wet as often as possible to increase effectiveness and dissipation
- Always add weather protection to ground rod connections. Products such as "Liquid
Rubber", RTV Compound, commercial aquarium sealers, or roof patching tar
make fine coverings for electrical joints and they'll prevent corrosion and rust.
Use an anti-oxidant compound to coat the conductors before connecting them together
as a further protection from weatherization. Many are available, but among the
better ones are Burndy Penetrox, Ideal Noalox, or I.C.E. #601 or 602. All are
easily applied and available from electrical supply houses or hardware stores.
- What kind of wire to use in making ground leads? Copper definitely, but remember
that the length of ground leads is far more important than wire size or type.
Use conductors of #12 or larger, covered or bare. But keep 'em short!
- Always ground coaxial cable shields, but be sure to do it by routing the coaxial
cable to the ground rod joint. Don't ground cable shields by attaching a wire
to the shield in some convenient fashion and running a long length of wire from
that point to a ground rod. The effect is mostly lost that way. Route the cable
to the rod and insert a grounding block or some homebrew means, then route the
cable to the equipment. As always, keep the leads short!
- Check the condition of ground connections every six months or so. Keep in mind
that the rod connections are exposed to a big variety of outdoor vermin!