The Clear-Com intercom line is intended to run on a shielded twisted pair of cable per channel of intercom. One conductor carries full duplex (two-way) audio, the other conductor carries the DC power for remote stations. The shield is used for ground return for audio and power. When choosing interconnect cable, keep the following considerations in mind:
1. DC resistance of the ground or common conductor affects crosstalk. For runs longer than 100 ft. (30.5 m) do not use wire smaller than 20 gauge. The total resistance of the ground return (the combined parallel sum of all shields to a location) to any point in the system should be under 1.5Ω
2. The capacitance of the interconnect cable affects system frequency response and sidetone stability. Total capacitance should not be greater than 0.25 uF (capacitance between conductor and shield) equivalent to an intercom system containing 5,000 ft. (1525 m) of cable at 50 pF per ft. (0.305 m).
Typical cable for portable system interconnections is flexible, two-conductor, shielded microphone cable. For runs less than 500 ft. (152.5 m) a cable made of 24-gauge wire is acceptable. For runs longer than 500 ft. (152.5 m) use a 20-gauge cable or larger.