Electric Shock From a Washing Machine Body
While using a washing machine in a ground-floor flat in Mumbai, the user gets a severe shock on touching the metal body. The machine is connected to a 6 A socket with a 16 A MCB at the board; there is no RCCB. The supply is 230 V. The earth pin in the socket is found disconnected, and the earth wire from the board to the pit is broken. The earth pit resistance measured with an earth tester is 14 Ω. On opening the machine, a live wire from the motor terminal is found loose and touching the metal frame. The MCB did not trip. The machine's insulation resistance between live and body is effectively 0 Ω at the fault point. The user's hands and the floor were wet. The user wants to know why the MCB gave no protection and what must be done before the machine is used again.
1. Explain why the MCB did not trip and why the body became live. Estimate the current through the user when touching the body.
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An MCB is an overcurrent device. It trips only when the current through it exceeds its rating. With the earth disconnected, the live-to-frame fault has no return path, so no fault current flows; the machine simply sits with its metal body at 230 V. The MCB sees only the normal motor current.
When the user touches the body while standing on a wet floor, the body becomes the path: current flows from live through the user to earth. With wet body resistance of about 1,000 Ω, I = V/R = 230/1,000 = 0.23 A = 230 mA. This is far above the lethal threshold; currents of about 30 mA can already be dangerous.
The severity is explained by the combination of a live frame, a broken earth, no RCCB and wet contact. The MCB was never designed to detect this condition.
2. List the tests you would perform, in order, with the expected values, before the machine is used again.
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- Visual inspection for loose live conductors, damaged insulation and water.
- Earth continuity from the plug earth pin to the machine frame: should be a low resistance, typically less than 1 Ω; here it is open.
- Insulation resistance from live to frame at 500 V DC: should be at least 1 MΩ for a healthy appliance; here it is about 0 Ω at the fault.
- Supply polarity and socket wiring.
- Earth electrode resistance with an earth tester: 14 Ω is too high for a domestic installation; a low value, commonly around 1 Ω or less, is required, and 14 Ω is clearly excessive.
- After repair, repeat the insulation and earth-continuity tests and check leakage current.
The machine must not be reconnected until the loose live conductor is repaired, the earth path is restored and the earthing is improved.
3. Recommend the repairs and protective measures, including consumer advice, and explain why repairing only the loose wire is insufficient.
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Repairs: remake the motor terminal connection and replace damaged wiring so that no live part can touch the frame; restore the earth conductor from the socket to the board and to the pit, replacing the broken wire; improve the earth electrode by driving an additional rod and using good backfill, then measure until the resistance is low; fit a 30 mA two-pole RCCB at the origin and test it; verify with an insulation resistance test and an earth continuity test.
Consumer advice: never touch a wet appliance with wet hands, never use an appliance with a missing earth pin, use an RCCB, and have the installation tested periodically.
Repairing only the loose wire leaves the broken earth and the absent RCCB in place. The next fault, even a small leakage, would again make the body live with no automatic disconnection. The earth and the RCCB are the layers of protection that turn a dangerous fault into a safe disconnection.