By supplying a safe, resistance-free path for lightning to follow, a decently grounded protective system allows the charges to travel harmlessly through on their way to the ground. The system starts with a series of air terminals or rods which protrude above the roof so that strokes would contact them before touching other parts of the house. The rods are attached to each other by heavy cables, and these in turn are linked up by equally thick wires to metal plates, pipes or rods buried deep in permanently moist earth. Each rod is linked to at least two conductors so that the path of the bolt is split on its way to the ground.
Installation of these protective systems is decidedly not a job for do-it-yourselfers. Professional installers, using equipment approved for this function by the Underwriters' Laboratories, are needed. For guaranteed results, the contractor must provide a Master Label plate indicating that the materials used are acceptable and that the installation was done with a sufficient number of conductors, grounds and rods. A Master Label also guarantees the owner that proper installation procedures have been observed and that only approved materials and fittings have been used.
Though installation costs are lowest when a system is installed while the house is being built, suitable protective systems can also be set up on existing homes. In numerous cases insurance rates would go down anywhere from 10 to 15 per cent, thus amortizing a considerable part of the cost.
Besides installation of grounded lightning rods, houses which stand out on open areas must have television antennas grounded and outfitted with suitable lightning arresters. Water pipes, waste lines and wiring systems must also be grounded and equipped using protective devices. Tall trees near a house (particularly if on an exposed hill) must be protected by installing lightning rods connected by cables to a ground. Metal fences that have wooden posts should likewise be grounded (by driving pipes into the ground at 100-foot intervals), since these can become hazardously charged even when not struck directly.