What should be done with unused conductors in copper unshielded or shielded twisted-pair network cables?

Question

Options

• Aterminate in their characteristic impedance
• Btrim back and properly insulate
• Cconnect to protective earth
• Dsplice to a used conductor

• A
  94% (29)
• B
  3% (1)
• C
  3% (1)

Explanation

Unused conductors in twisted-pair cables must be terminated in their characteristic impedance (typically 100Ω for standard Cat5e/6 UTP) because unterminated conductors act as antennas - they radiate and pick up electromagnetic interference, degrading signal integrity on the active pairs through crosstalk and reflections. Option B (trim and insulate) is tempting but wrong: an open-ended conductor floating inside the cable jacket still capacitively and inductively couples to active pairs, introducing noise. Option C (connect to earth) is dangerous - grounding unused conductors can create ground loops and inject 50/60 Hz noise or DC offset into the cable environment. Option D (splice to an active conductor) would short or corrupt the active pair's signal, which is the opposite of what you want.

Memory tip: Think of it as "ending the conversation" - an unterminated wire keeps "talking" (radiating/reflecting), so you give it a proper termination resistor to make it go quiet without disrupting the active lines.

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