Lead-in conductors for transmitting stations entering a building when not protected by a continuous metallic shield that is grounded may enter by which method?

• A. Any of the above
• B. through a rigid noncombustible nonabsorbent insulating tube or bushing
• C. through an opening provided for the purpose in which the entrance conductors are firmly secured so as to provide a clearance of at least 2 inches
• D. through a drilled window pane

Answer: (A)

When lead-in conductors from transmitting stations enter a building without a continuous grounded metal shield, the code requires a listed method to protect the conductors where they pass into the building. The idea is to provide a safe, protected path that prevents physical damage, avoids arcing, and preserves the building envelope.

One acceptable approach is routing the conductors through a rigid, noncombustible, nonabsorbent insulating tube or bushing, which gives a secure, insulated channel and minimizes movement or abrasion. Another valid method is to enter through an opening that is specifically provided for this purpose, with the conductors firmly secured so there is a clear clearance of at least 2 inches to prevent contact or arcing and to accommodate movement or vibration. A third permissible path is to pass through a drilled window pane, using appropriate protective devices to maintain insulation, sealing, and fire/weatherproofing.

Because all of these methods meet the requirement for a protected entry when a grounded metallic shield is not present, any of the above is allowed. The overarching concept is balancing physical protection, electrical insulation, and the building’s envelope while permitting the lead-in to enter.