Topic 3 of 4
Live, neutral, earth and the plug
The three wires have different roles. Understanding where each connects explains both normal operation and why a switch must break the live connection.
A sustained current needs a complete conducting path. A break can stop current while a potential difference still exists. Review circuit connections if you need help following the paths.
Identify each conductor
- Live: L, brown
- Live is at a substantial alternating potential difference relative to earth. Together with neutral, it supplies the normal load circuit.
- Neutral: N, blue
- Neutral is the normal return conductor, maintained near earth potential in the simplified supply model. It carries normal load current. Its name does not make it safe to touch in every real circuit.
- Earth: E, green and yellow
- Protective earth connects exposed conductive parts, such as a metal casing, to the protective return path where required. It normally carries negligible current in a correctly operating appliance.
Mains is an alternating supply: current direction reverses. Calling neutral the return conductor describes its circuit role; it does not mean charge always travels in one direction through the appliance.
Read the plug connections
Identify terminals in an inside wiring view
The cable enters at the bottom. This labelled schematic shows connections inside the plug; it is not the pin-facing view or a complete circuit.
- L: liveBrown
- N: neutralBlue
- E: earthGreen/yellow
The fuse is in the live connection. The grip holds the outer sheath so a pull on the cable is not taken directly by the terminal connections.
The brown core connects to L through the fuse, the blue core to N, and the green/yellow core to E. Use the terminal letters and the stated viewpoint: looking at the pins from the opposite side reverses left and right in the drawing.
The grip secures the cable's outer sheath so that a pull on the cable is not transferred directly to the core connections. The insulating covering around each core keeps the conductors apart. The plug view shows these connections; the fault circuit explains how the earth connection works with protection.
Open the live connection
An open circuit can still contain parts connected to live
Both circuits have the same idealised a.c. supply and resistive load. An amber band marks connection to live potential; it is not a current arrow. Brown and blue still identify the cores.
Open a single-pole switch in live
The open gap disconnects the load from live. The load remains connected to neutral in this simplified circuit.
Open only the neutral wire
Current is zero, but the load and the blue segment between the load and the open gap remain connected to live. Stopping operation has not disconnected live.
Live alternates in potential relative to earth. In this model neutral is maintained near earth potential; that does not make neutral universally safe to touch.
A single-pole switch opens one conductor. Placing it in live breaks the connection between the live supply and the appliance when the switch is open.
If the switch opens only neutral, the normal circuit is incomplete and the appliance stops operating. However, the load remains connected to live. In the ideal no-current model, there is no voltage drop across the load, so even the load-side segment of the opened neutral connection can be at live potential. Its blue insulation still identifies its intended wiring role.
For the same reason, a fuse or circuit breaker must interrupt live when it operates. Interrupting only neutral can stop operation while leaving the appliance connected to live. Some devices open more than one conductor; the essential protection here includes breaking the live connection.