be pro- vided on each circuit run partly or entirely in aerial wire or aerial cable not confined within a block. Also, a listed primary protector shall be provided on each circuit, aerial or underground, located within the block containing the building served so as to be exposed to accidental contact with electric light or power conductors operating at over 300 volts to ground. In addition, where there exists a lightning exposure, each interbuilding circuit on a premises shall be protected by a listed primary protector at each end of the interbuilding circuit. Installation of primary protectors shall also comply with 110.3(B).
FPN No. 1: On a circuit not exposed to accidental contact with power conductors, providing a listed primary protector in accordance with this article helps protect against other hazards, such as lightning and above-normal voltages induced by fault currents on
power circuits in proximity to the communications circuit.
FPN No. 2: Interbuilding circuits are considered to have a lightning exposure unless one or more of the following conditions exist:
(1) Circuits in large metropolitan areas where buildings are close together and sufficiently high to intercept lightning.

(2) Interbuilding cable runs of 42 m (140 ft) or less, di- rectly buried or in underground conduit, where a continuous metallic cable shield or a continuous metallic conduit containing the cable is connected to each building grounding electrode system.

(3) Areas having an average of five or fewer thunderstorm days per year and earth resistivity of less than 100 ohm-meters. Such areas are found along the Pacific coast.

(1) Fuseless Primary Protectors. Fuseless-type primary protectors shall be permitted under any of the conditions given in (A)(1)(a) through (A)(1)(e).
(a) Where conductors enter a building through a cable with grounded metallic sheath member(s) and where the conductors in the cable safely fuse on all currents greater than the current-carrying capacity of the primary protector and of the primary protector grounding conductor

(b) Where insulated conductors in accordance with

800.50(A) are used to extend circuits to a building from
a cable with an effectively grounded metallic sheath
members) and where the conductors in the cable or
cable stub, or the connections between the insulated
conductors and the plant exposed to accidental contact
with electric light or power conductors operating at
greater than 300 volts to ground, safely fuse on all
currents greater than the current-carrying capacity of
the primary protector, or the associated insulated
conductors and of the primary protector grounding
conductor

(c) Where insulated conductors in accordance with

800.50(A) or (B) are used to extend circuits to a building
from other than a cable with metallic sheath
member(s), where (1) the primary protector is listed as
being suitable for this purpose for application with
circuits extending from other than a cable with metallic
sheath members, and (2) the connections of the
insulated conductors to the plant exposed to accidental
contact with electric light or power conductors
operating at greater than 300 volts to ground or the
conductors of the plant exposed to accidental contact
with electric light or power conductors operating at
greater than