Earth wire (conductor de protección, protective conductor)

What the conductor de protección is

The conductor de protección is the earth wire (ground wire in the US) of the installation, the one with green and yellow insulation. It runs through every circuit alongside the live and neutral and reaches each earthed socket, each metal light fitting and the metal bodies of appliances such as the washing machine, oven or water heater.

What it does

Normally it carries no current. Its job starts when something fails: if a bare wire touches the metal casing of an appliance, the current finds an easy path through the earth wire to the earthing system. That leak trips the RCD before anyone touches the casing and gets a shock.

How it should be installed

• Green and yellow, a colour reserved for earth only under ITC-BT-19.
• Continuous from the earth bar in the consumer unit to the last socket, with no breaks or doubtful joints.
• In the usual home cable sizes, the same cross-section as the circuit’s live wire.
• Connected to the building’s earth electrode, whose resistance must be measured.
• Never joined to the neutral inside the home.

What happens if it is missing

In many old Seville flats (apartments) the sockets have no earth, or the wire exists but goes nowhere. The RCD only acts once the leak is already passing through a person, and a faulty appliance can give you a shock. A tingle when you touch the shower tap (faucet) or a casing is a warning sign.

How it is checked

The electrician measures the continuity of the earth wire to every socket and the resistance of the earth. If it fails, a new conductor is run or the earthing is improved. See electrical safety testing in Seville, Spain.