Which of the following is an allowed entry method for transmitting station lead-ins when the shielding is not present or not grounded?

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When shielding isn’t present or isn’t grounded, the entry path for transmitting station lead-ins must provide solid physical and electrical isolation to prevent RF leakage and arcing. A rigid noncombustible, nonabsorbent insulating tube or bushing accomplishes this by surrounding and protecting the conductor, preventing contact with combustibles and nearby materials. Securing entrance conductors in an opening designed for that purpose with a minimum clearance of two inches ensures adequate separation to avoid arcing and heat transfer. Entering through a drilled window pane is another allowed method when it’s arranged to maintain shielding integrity while allowing the lead-in to pass through. Since each method meets the safety objective of containing the lead-in when shielding isn’t used or isn’t grounded, all of the options are acceptable.