NEC POWERMATE P Manual page 39

Precautions When Using TV Tuner with External Antenna
The circuit of cable distribution system under consideration is TNV-1 circuit.
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The common sides or earthed side of the circuit are connected to the screen of the coaxial
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cable through an antenna connector of tuner and to all accessible parts and circuits (SELV
and accessible metal parts).
The screen of the coaxial cable is intended to be connected to earth in the building
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installation.
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