Alltec Protection Systems Pvt. Ltd. Becomes the First Company in India to be Certified by Underwriters Laboratories in the Installation of Lightning Protection
The attenuation of an electromagnetic wave as it passes through a shield. This loss is due primarily to induced currents and the associated resistance loss.
Air Discharge
A form of lightning discharge similar to a cloud discharge, in which the lightning channel propagates away from a cloud charge center into apparently clear air where it terminates.
Air Terminal
A type of strike termination device intentionally installed for the purpose of intercepting lightning flashes. These items are sometimes referred to as lightning rods.
Ambient Field
The electric field strength of the atmosphere at rest, in clear air and under static-free conditions. Generally thought to be some 150-300v/m at standard temperature and pressure.
Amperage
The unit measure for current flow. One (1) ampere equals one (1) coulomb of electrons passing a point in a circuit in one (1) second.
ANSI
American National Standards Inst
Anvil-to-Ground Lightning
A form of positive lightning, since it emanates from the anvil top of a cumulonimbus cloud where the ice crystals are positively charged. The leader stroke issues forth in a nearly horizontal direction until it veers toward the ground. These usually occur kilometers/miles from (often ahead) of the main storm and will sometimes strike without warning on a sunny day. An anvil-to-ground lightning bolt is a sign of an approaching storm, and may occur in a largely clear sky.
Arc
A low-voltage, high-current electrical discharge that occurs at the instant two points, through which a large current is flowing, are separated.
Atmospheric Electric Field
A term denoting the electric field strength of the atmosphere at any specified point in space and time. In areas of fair weather, the atmospheric electric field near the earth’s surface typically is about 100 volts per meter and is directed vertically in such a sense as to drive positive charges downward to the earth. In areas of fair weather this field decreases in magnitude with increasing altitude, falling for example, to only about 5 volts per meter at an altitude of about 10 km. Near thunderstorms, and under clouds of vertical development, the surface electric field varies widely in magnitude and direction, usually reversing its direction immediately beneath active thunderstorms. It is now believed that thunderstorms, by replenishing the negative charge to the earth’s surface, provide the supply current to maintain the fair-weather electric field in spite of the continued flow of the air-earth current that tends to neutralize that field. During fair weather, a potential difference of 200,000 to 500,000 volts exists between the earth’s surface and the ionosphere, with a fair weather current of about 2×10-12 Amperes/meter2. It is widely believed that this potential difference is due to the worldwide distribution of thunderstorms. Present measurements indicate that an average of almost 1 Ampere of current flows into the stratosphere during the active phase of a typical thunderstorm. Therefore, to maintain the fair weather global electric current flowing to the surface, one to two thousand thunderstorms must be active at any given time, producing on the order of 100 flashes per second.
