Installing the Control Unit

concrete-encased ground—must be an electrode, consisting of one of the following:

at least 20 ft (6.1 m) of one or more steel reinforcing rods, each being at least ½-inch (1.27 cm) in diameter

20 ft (6.1 m) of bare copper conductor not smaller than

#4 AWG, encased in 2 inches (5 cm) of concrete.

This electrode must be located within and near the bottom of a concrete foundation or footing that is in direct contact with the earth.

ground ring-consists of at least 20 ft (6.1 m) of bare copper conductor not smaller than #2 AWG encircling the building. The ground ring must be in direct contact with the earth and buried at least 2.5 ft (77 cm) below the earth’s surface.

WARNING:

Do not use metal underground gas piping system—this is a safety risk.

Central Office Trunk Protection

The telephone company is responsible for providing the following protection of central office trunks at the entrance to the site:

carbon blocks or gas discharge tubes connected to an approved ground

adequate bonding of the central office trunk protector ground and the power company ground

2-14Power and Grounding

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AT&T Release 2.0 manual Central Office Trunk Protection