So I'm aware of the standard rule of thumb, keep high and low voltage away from each other, preferably on opposite sides of a stud. However, while looking at some properties, I'm seeing telephone and cable lines in the same junction box as an electrical outlet. Under what conditions is this permitted by NEC?
High and low voltage conductors in the same junction box must be separated by a barrier. Outdated NEC reference: 800-52(a)(1)c.1.Exception 1.
In the typical dbl. gang box installation, power in one half and phone and data in the other, there needs to be a partition in the box separating the two classes of conductors.
800.133 Installation of Communications Wires, Cables, and Equipment. (A) Separation from Other Conductors. (1) In Raceways, Cable Trays, Boxes, and Cables. (c) Electric Light, Power, Class 1, Non–Power-Limited Fire Alarm, and Medium-Power Network-Powered Broadband Communications Circuits in Raceways, Compartments, and Boxes.
Communications conductors shall not be placed in any raceway, compartment, outlet box, junction box, or similar fitting with conductors of electric light, power, Class 1, non–power-limited fire alarm, or medium-power network-powered broadband communications circuits.
Exception No. 1: Where all of the conductors of electric light, power, Class 1, non–power-limited fire alarm, and medium-power network-powered broadband communications circuits are separated from all of the conductors of communications circuits by a permanent barrier or listed divider.
Exception No. 2: Power conductors in outlet boxes, junction boxes, or similar fittings or compartments where such conductors are introduced solely for power supply to communications equipment. The power circuit conductors shall be routed within the enclosure to maintain a minimum of 6 mm (0.25 in.) separation from the communications circuit conductors.
Exception No. 3: As permitted by 620.36.
620.36 Different Systems in One Raceway or Traveling Cable. Optical fiber cables and conductors for operating devices, operation and motion control, power, signaling, fire alarm, lighting, heating, and air-conditioning circuits of 600 volts or less shall be permitted to be run in the same traveling cable or raceway system if all conductors are insulated for the maximum voltage applied to any conductor within the cables or raceway system and if all live parts of the equipment are insulated from ground for this maximum voltage. Such a traveling cable or raceway shall also be permitted to include shielded conductors and/or one or more coaxial cables if such conductors are insulated for the maximum voltage applied to any conductor within the cable or raceway system. Conductors shall be permitted to be covered with suitable shielding for telephone, audio, video, or higher frequency communications circuits.