What Is an RCD and Why Do You Need One?
A Residual Current Device (RCD)—also called a Ground Fault Circuit Interrupter (GFCI) in the U.S.—is a crucial electrical safety device that protects people from electric shock and prevents electrical fires caused by insulation faults.
Unlike circuit breakers, which only protect against overloads and short circuits, RCDs detect leakage currents—even as low as 10–30mA—that indicate a dangerous fault in the system.
Key Functions of an RCD:
✔ Prevents fatal electric shocks from faulty wiring or damaged appliances.
✔ Protects against electrical fires caused by insulation breakdown.
✔ Automatically shuts off power within 30 milliseconds when a leak is detected.
How Does an RCD Work?
An RCD monitors the balance between the incoming (live) and outgoing (neutral) electrical current.
✔ Under normal conditions, both currents are equal.
❌ If a leakage occurs (e.g., current flows through a person or faulty wire), an imbalance is detected, and the RCD instantly shuts off the power.
Common Causes of RCD Tripping:
✔ Damaged appliance insulation (e.g., old frayed cords).
✔ Water contact with live wires (e.g., in kitchens or bathrooms).
✔ Faulty electrical wiring (especially in older homes).
RCD vs. Circuit Breaker: What’s the Difference?
| Feature | RCD (GFCI) | Circuit Breaker (MCB/RCB) |
|---|---|---|
| Protects Against | Electric shock & leakage | Overloads & short circuits |
| How It Works | Detects current imbalance | Detects excessive current flow |
| Response Time | 30 milliseconds | 0.1–1 second |
| Installation Location | Bathrooms, kitchens, outdoor outlets | Main panel, branch circuits |
| Required for Safety? | Yes (for ground fault protection) | Yes (for circuit protection) |