Low Voltage Circuits

Application of the Material in this Chapter                                                                                                                                                                                                                                                          This IRC chapter applies to low voltage circuits such as door bells, thermostats and HVAC control circuits, security and fire alarm systems, intercom systems, and garage door opener controls. These circuits usually operate at not more than (≤) 30 volts. This chapter does not apply to communication circuits such as cable and satellite TV, broadband cable TV systems, and telephone systems.

Low Voltage Power Sources

1. Use transformers or power supplies listed as a Class 2 power source to run low voltage systems. Install the Class 2 power source according to manufacturer’s instructions. An example of a Class 2 power source is a door bell transformer.                                                                                                                                                                                                                            2. You may use a dry cell batt ery rated not more than (≤) 30 volts as a Class 2 power source.                                                                                                                                                                 3. Do not connect the output (load) side of a Class 2 power source to the output (load) side of other Class 2 power sources unless manufacturer’s instructions allow the connection. Example: do not use two door bell transformers to supply the same door bell circuit unless the door bell manufacturer’s instructions allow the use of multiple transformers in the circuit.

Low Voltage Wiring Methods
1. Limit the electric power circuit that supplies a Class 2 power source to not more than 120 volt,20 amp.
2. Use at least (≥) #18 AWG wire to connect a Class 2 power source to the electric power supply  circuit. Limit the length of the Class 2 power supply connection wiring to not more than (≤) 12 inches if the connection wiring is smaller than (<) #14 AWG. Example: limit the length of the wires on the primary (line) side of a door bell transformer to not more than (≤) 12 inches if the primary side transformer wires are smaller than (<) #14 AWG.
3. Use cables listed as Class 2 cables to connect a Class 2 power supply to the low voltage device. Example: use cable listed for use with a door bell circuit between the door bell transformer and the door bell butt on and chime. Lamp cord or speaker wire may not have the same fi re and smoke resistance rating as listed Class 2 cable.

Low Voltage and Electric Power Wire Separation
1. Do not run low voltage wires and electric power wires in the same conduit, tubing, raceway, junction and device box, or enclosure unless one of two exceptions exist. Example: do not run NM cable and door bell wires in the same conduit. Example: do not run door bell wires or security system wires in a panelboard cabinet or in a junction box with electric power wires.
2. You may run low voltage and electric power wires in the same raceway, box, and enclosure if the wires are separated by a physical barrier. In enclosures, the physical barrier may be a raceway such as conduit. Example: you may place a door bell transformer and Class 2 wires in the same cabinet with electric power wires if the door bell transformer and Class 2 wires are separated from the electric power wires by a physical barrier.
3. You may run low voltage and electric power wires in the same cabinet or box when the electric power wires supply power to the low voltage power source. Example: you may run #14 AWG electric power wires and #18 AWG door bell transformer wires in the same junction box if the electric power wires supply power to the transformer. Maintain at least (≥) ¼ inch separation between electric power wires and Class 2 wires in cabinets and boxes.
4. Separate low voltage and electric power wires by at least (≥) 2 inches when run outside of conduit, cabinets, and boxes. Two inch separation is not required if all the low voltage wires or all the electric power wires are contained in metal or nonmetallic sheathing or are contained in raceways. Example: you may run sheathed NM cable and sheathed thermostat cable near each other in a bundle and through the same bored holes in joists and studs if the sheathing of the NM cable and thermostat cable remains intact over the entire length of the run.

Low Voltage Wire Installation and Support
1. Use building structural members such as joists and studs to support low voltage wires.
2. Do not use electrical conduit, tubing, raceways, or cables to support low voltage wires. This restriction does not apply if the raceway contains wires that supply power to the equipment associated with the Class 2 wires. Example: you may use a raceway containing electric power wires for a furnace or condenser to support the thermostat wires.
3. Install low voltage wires so that they will not be damaged by normal building use.
4. Install low voltage wires so they will not restrict access to service and maintenance panels including suspended ceiling panels. Example: do not run low voltage wires directly on top of suspended ceiling panels. Support the wires on the joists that support the suspended ceiling panels. Example: do not run thermostat wires so that they interfere with access to furnace maintenance panels.