What is Switched Live?

The switched live is the conductor in an electrical circuit that carries current only when a connected device is actively switched on. It is part of the switched circuit, meaning it becomes live (energised) when a switch (e.g., light switch, fan isolator) is engaged, allowing power to flow to the appliance.

Key Characteristics:

  • Typically coloured brown (UK wiring standards post-2004, harmonised with BS 7671:2018+A2:2022).
  • Must never be confused with the permanent live (always energised) or neutral (return path).
  • Critical for safe operation of lighting, extractor fans, and other switched appliances.

Practical Example:
In a UK residential lighting circuit:

  • The permanent live (from the consumer unit) connects to the switch.
  • The switched live runs from the switch to the light fitting, activating only when the switch is turned on.

Building Regulations & Compliance:

  • BS 7671 (IET Wiring Regulations, 18th Edition + Amendment 2:2022) – Mandates correct identification and segregation of conductors.
  • Approved Document P (Electrical Safety – Dwellings) – Requires safe installation practices in domestic buildings.

Related Essential Terms

  1. Permanent Live: The continuously energised conductor supplying power to a circuit. Must be isolated before maintenance.
  2. Neutral (N): The return path for current, completing the circuit. Typically blue in UK installations.
  3. Earth (CPC – Circuit Protective Conductor): Safety conductor providing a path for fault current, preventing electric shock. Coloured green-and-yellow.
  4. Double-Pole Switching: Isolates both live and neutral (e.g., for bathroom extractor fans, complying with Part F (Ventilation)).
  5. Part P of Building Regulations: Governs electrical safety in dwellings, requiring notification of certain works to Local Authority Building Control (LABC).
  6. Zoning (Electrical Installations): Specific rules for circuits in high-risk areas (e.g., bathrooms under Part P and BS 7671 Section 701).
  7. Consumer Unit (Fuse Board): Distributes and protects circuits via MCBs/RCDs. Must comply with BS 7671 and Amendment 3 (2015) fire safety updates.