Q. Are unlisted communications cables allowed to enter buildings?
A. Unlisted communications cables can be installed in building spaces other than risers, ducts, or plenum spaces as described in 300.22(C), if the length of the cable within the building from its point of entrance doesn't exceed 50 ft and the cable terminates in an enclosure or primary protector [800.48].
As outlined in Informational Note 2 of 800.48, the primary protector must be located as close as practicable to the point at which the cable enters the building [800.90(B)]. Therefore, unlisted outside plant communications cables may not be permitted to enter the building if it's practicable to place the primary protector closer than 50 ft to the point of entrance.
Remember that the "point of entrance" is defined as the point within the building where the cable emerges from an external wall, from a concrete floor slab, or from rigid metal conduit (RMC) or intermediate metal conduit (IMC) connected to an electrode by a grounding conductor in accordance with 800.100 [800.2].