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