Protectors are surge arresters designed for the specific requirements of
communications circuits. They are required for all aerial circuits not
confined with a block. (Block here means city block.) They must be
installed on all circuits with a block that could accidentally contact
power circuits over 300 volts to ground. They must also be listed for the
type of installation. Other requirements are the following:
Metal Sheaths of any communications cables must be grounded or interrupted
with an insulating joint as close as practicable to the point where they
enter any building (such point of entrance being the place where the
communications cable emerges through an exterior wall or concrete floor
slab, or from a grounded rigid or intermediate metal conduit).
Grounding conductors for communications circuits must be copper or some
other corrosion-resistant material, and have insulation suitable for the
area in which it is installed.
Communications grounding conductors may be no smaller than No. 14.
The grounding conductor must be run as directly as possible to the
grounding electrode, and be protected if necessary.
If the grounding conductor is protected by metal raceway, it must be bonded
to the grounding conductor on both ends.
Grounding electrodes for communications ground may be any of the following:
- The grounding electrode of an electrical power system.
- A grounded interior metal piping system. (Avoid gas piping systems for
obvious reasons.) - Metal power service raceway.
- Power service equipment enclosures.
- A separate grounding electrode.
If the building being served has no grounding electrode system, the
following can be used as a grounding electrode:
- Any acceptable power system grounding electrode.
- A grounded metal structure.
- A ground rod or pipe at least 5 feet long and 1/2 inch in diameter.
This rod should be driven into damp (if possible) earth, and kept separate
from any lightning protection system grounds or conductors.
Connections to grounding electrodes must be made with approved means. If
the power and communications systems use separate grounding electrodes,
they must be bonded together with a No. 6 copper conductor. Other
electrodes may be bonded also. This is not required for mobile homes.
For mobile homes, if there is no service equipment or disconnect within 30
feet of the mobile home wall, the communications circuit must have its own
grounding electrode. In this case, or if the mobile home is connected with
cord and plug, the communications circuit protector must be bonded to the
mobile home frame or grounding terminal with a copper conductor no smaller
than No. 12.