The absence of earthing doesn't mean a device will "malfunction" — quite the opposite: it may continue working completely normally for years, while the real danger lurks silently until the moment a single fault occurs.
What Happens When Current Leaks to the Body of an Unearthed Appliance?
Imagine an electric water heater with a metal body, in which a minor insulation fault occurs in the heating element such that the phase touches part of the metal body. If the body is earthed, the fault current flows directly through the earth wire, and the breaker usually trips instantly. If the body is not earthed, the entire metal body stays "live" silently — nothing visible happens, until someone touches it while in contact with the ground (standing on damp ground, or touching a metal sink connected to the water supply), at which point their body becomes the current's path.
Why Won't a Normal Breaker Alone Protect You from This Risk?
The shock current through a human body, despite its potentially fatal danger, is usually far smaller than the rating of a normal breaker (MCB) — so it won't trip it. A normal breaker protects against large currents that threaten the wire, not small currents that threaten a person. The absence of earthing combined with the absence of an earth leakage breaker (RCD) is the most dangerous combination, because there's no line of defense at all between the internal fault and the person's body.
Appliances More Exposed to This Risk
- Electric water heaters: Metal body, direct proximity to water, and a heating element exposed to degradation over time.
- Washing machines: Metal body, connection to water and drainage, and continuous exposure to moisture and vibration.
- Refrigerators and freezers: Large metal bodies, operating continuously for years without being switched off.
- Electric cooking ovens: Metal bodies, high-power heating elements.
Proper earthing and an RCD breaker work together as two complementary layers: earthing provides a low-resistance path that makes the fault current large enough to trip the normal breaker or RCD quickly, while the RCD detects even very small leakages that may not produce a current large enough to trip the normal breaker on its own.
Sample answer: When an internal insulation fault occurs that causes the phase to touch the appliance's metal body, the absence of earthing leaves the entire body "live" silently without any breaker tripping, because the leakage current through a human body is usually far smaller than the rating of a normal breaker. The first to discover the fault may be a person touching the device, whose body becomes the current's path to earth. Appliances with metal bodies near water (heaters, washing machines) are more exposed to this risk.
Believing that a device "working normally for years" is proof that its earthing or insulation is sound. The absence of earthing doesn't prevent a device from operating normally at all — the danger only appears when an internal insulation fault occurs, which can happen at any moment after years of apparently "normal" operation.
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