300 volts to ground safely fuse on all
currents greater than the current-carrying capacity of
the primary protector, or associated insulated
conductors and of the primary protector grounding
conductor

(d) Where insulated conductors in accordance with

800.50(A) are used to extend circuits aerially to a
building from a buried or underground circuit that is unexposed to accidental contact with electric light or power conductors operating at greater than 300 volts to ground
Where insulated conductors in accordance with
800.50(A) are used to extend circuits to a building from
cable with an effectively grounded metallic sheath
member(s), and where (1) the combination of the primary
protector and insulated conductors is listed as being
suitable for this purpose for application with circuits
extending from a cable with an effectively grounded
metallic sheath members), and (2) the insulated
conductors safely fuse on all currents greater than the
current-carrying capacity of the primary protector and of
the primary protector grounding conductor
FPN: Section 9 of ANSI C2-2007, National Electrical Safety Code, provides an example of methods of protective grounding that can achieve effective grounding of telecommunications cable sheaths for cables from which communications circuits are extended.
(2) Fused Primary Protectors. Where the requirements listed under 800.90(A)(1)(a) through (A)(1)(e) are not met, fused-type primary protectors shall be used. Fused-type primary protectors shall consist of an arrester connected between each line conductor and ground, a fuse in series with each line conductor, and an appropriate mounting arrangement. Primary protector terminals shall be marked to indicate line, instrument, and ground, as applicable.
(B) Location. The primary protector shall be located in, on, or immediately adjacent to the structure or building served and as close as practicable to the point of entrance.
FPN: See 800.2 for the definition of Point of Entrance.
For purposes of this section, primary protectors located at mobile home service equipment located within 9.0 m (30 ft) of the exterior wall of the mobile home it serves, or at a mobile home disconnecting means connected to an electrode by a grounding conductor in accordance with 250.32 and located within 9.0 m (30 ft) of the exterior wall of the mobile home it serves, shall be considered to meet the requirements of this section.
FPN: Selecting a primary protector location to achieve the shortest practicable primary protector grounding conductor helps limit potential differences between communications circuits and other metallic systems.
(C) Hazardous (Classified) Locations. The primary pro tector shall not be located in any hazardous (classified) location as defined in 500.5 or in the vicinity of easily ignitible material.

Exception: As permitted in 501.150, 502.150, and

503.150.

(D) Secondary Protectors. Where a secondary protector is installed in series with the indoor communications wire and cable between the primary protector and the equipment, it shall be listed for the purpose in accordance with 800.170(B).
FPN: Secondary protectors on circuits exposed to accidental contact with electric light or power conductors operating at greater than 300 volts to ground are not intended for use without primary protectors.
800.93 Grounding or Interruption of Metallic Sheath Members of Communications Cables. Communications cables