Electrical
Earthing and RCD Protection Explained: Why Your Home Needs Both
Short answer
Earthing gives fault current a safe path to the ground so that protective devices trip quickly and metal parts do not stay live. An RCD (residual current device) detects even small leakage to earth, typically at 30 mA for socket circuits, and cuts power in a fraction of a second to prevent electric shock. Every home should have both.
What earthing does
If a live wire touches a metal appliance case, the case becomes live. With a good earth connection, a large fault current flows to ground, which trips the breaker fast and keeps the case at a safe voltage. Without an earth, the case stays live until someone touches it.
What an RCD does
An RCD compares the current going out on the live wire with the current coming back on the neutral. If some current leaks, for example through a person, it trips within milliseconds. A 30 mA RCD is commonly used for additional protection on socket and outdoor circuits.
Earthing vs RCD vs breaker
| Device | Protects against | Trips on |
|---|---|---|
| Circuit breaker (MCB) | Overload and short circuit, cable overheating | Excess current |
| RCD | Electric shock and some fires from leakage | Small leakage to earth |
| Earthing | Live metal parts, makes protection work | Not a switch; a safe path to ground |
| Surge protector (SPD) | Voltage spikes from the grid or lightning | Diverts surge to earth |
Signs of poor or missing earthing
- Tingling or mild shocks from appliance cases, taps or metal fittings.
- Two-pin sockets or no earth pin connected.
- Old boards with no RCD.
- Appliances or electronics failing after storms.
Earthing for solar and generators
Solar arrays, inverters and generators must be earthed correctly, with surge protection on DC and AC sides. Good earthing reduces damage risk from lightning and faults. This is part of every proper solar installation and generator installation.
Test your RCD
Press the test button on your RCD about once a month. It should trip. If it does not, have it replaced. An electrician can also test the earth resistance.
Common questions
Can I add an RCD to an old house?
Yes. An electrician can fit an RCD at the distribution board, but it works best with proper earthing and sound wiring.
Does an RCD replace earthing?
No. They work together. Earthing is what lets faults trip protection and keeps metal parts safe.
How do I know if my house is earthed?
An electrician can test the earth connection and loop impedance. Look for an earth pin connection at sockets and an earth conductor at the board.