SHOCK THERAPY

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

Down conductors: Each lightning rod needs to be connected to two conductors leading to separate grounds. A one-way path running to a separate ground is limited to 40' in length on a roof lower than the main roof; dead ends that lead back to the main conductor system may be no longer than 16' . These conductors have to be at least 16-gauge copper or 14-gauge aluminum, may not turn more than 90° in one bend and may not make any turn with a radius of less than 8". Conductors should be kept as far as possible from other metal objects to avoid flashovers. If this proves difficult, the metal objects should be connected to the household ground. Down conductors should be protected from physical damage to 6' above ground level.

Ground: Grounding rods are usually 1/2"-diameter, 8'-long solid copper, copper-clad steel or stainless steel. In some instances, such as where soils are very shallow, they may take the form of thick plates about 2' square, or even 16-gauge cables that encircle the entire building. In any case, the connection between the ground and the down conductor should be clamped or welded.

Different soils require different grounding techniques to achieve sufficiently low resistance. Deep, moist clay soils can get by with a single rod penetrating 10' below the surface in compacted soil. In sand or gravel, however, two of these 10'-deep rods, spaced at least 10' apart, are needed. In shallow clay soils, a conductor in a 2'-deep, 10'-long trench will do, while shallow sand or gravel can be accommodated with a 2'-deep, 24'-long trench and conductor.

The lightning-protection ground must be connected to all the other electrical grounds in the building, including those for the electrical service; the telephone; any antennae; gas lines; underground pipes such as water, sewer and well casings within 25 '; and other metal conduits.

The human body can serve as a very effective lightning rod.

Protecting Electronics

Because their logic circuits operate at low voltage, electronics such as televisions, stereos and computers are especially susceptible to damage from lightning. Either the direct effects of lightning's high voltage or the induced surge indirectly produced by a nearby strike can easily ruin such equipment.

If lightning strikes your house or a utility pole on your side of the utility's electrical transformer (it's that metal can hanging on the power pole), only drastic measures will suffice. An uninterruptible power supply will generally save equipment in such a situation, though the supply itself may be sacrificed (at a cost of from $800 to several thousand dollars). The only alternative is to unplug when lightning threatens.

RSS | Comments | E-mail | Print