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 ELECTRICAL
Ground Test (Lightning Protection)-Continued
n Measurement of Ground Resistance:
A copper-clad steel rod from 3/8 inch to 1 inch in diameter and long enough to be
driven into the ground so it makes good contact with permanently moist soil should be
used for the test ground. The diameter of the rod has little effect on the magnitude of
the electrical resistance to ground.
n Method of Test:
Primary and secondary lightning protection systems shall be tested as follows:
Primary System:
One lead of the test instrument should be connected to the test ground and
the second lead in turn to each of the air terminals. The resistance to ground for each
air terminal shall be recorded.
Secondary System:
The resistance to ground and the electrical continuity of all grounded doors,
windows, gutters, downspouts, shutters, trusses, columns, girders, reinforcing rods, and
other metal objects in buildings and magazines should be tested by securing one lead of
the test instrument to the part being tested and the other lead to the test ground.
n Electrical Connections:
In order to assure low contact resistance, the metallic surfaces forming each electrical
contact must be carefully scraped until they are bright and shiny to remove any paint
and oxide film. The teeth of terminal clips should similarly contact a bright and shiny
metallic surface. If the surface film is not removed, sufficient pressure must be applied
to terminal clips to cause their teeth to break through to the basic metal conductor un-
derneath.
7.2.12 Grounds and Grounding Systems: Comply with all current safety
precautions. The condition of the grounding system is important both for proper opera-
tion of the distribution system to obtain indications of improper or unsafe conditions af-
fecting operation of the system and to protect personnel from electric shock that might
result in injury or death. Grounds and grounding systems require maintenance at
much higher levels of perfection than most other facilities, to assure the required de-
gree of safety to personnel. Because a current as low as 5 milliamperes is considered
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