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When you plug a device into a wall socket, electricity flows along a predictable path: from the distribution board, through the live wire, into your device, and back out via the neutral wire. But what happens when something goes wrong? What if a live wire inside your toaster touches the metal casing?
Next time an electrician spends 20 minutes testing your sockets with a yellow meter, remember: they aren’t checking your wiring—they’re checking your . Disclaimer: Electrical testing should only be performed by qualified persons. The values and regulations mentioned vary by country; always refer to your local wiring standard (NEC, IEC, BS 7671, AS/NZS 3000). fault loop
According to Ohm’s Law, the current flowing during a fault is equal to the supply voltage divided by the total impedance of the fault loop (I = V / Z). If the loop impedance is too high, the fault current will be too low. A low fault current might not trip a circuit breaker or blow a fuse quickly—or at all. This is dangerous because the metal casing of a faulty appliance could remain live indefinitely, waiting for someone to touch it. Engineers distinguish between two main scenarios: When you plug a device into a wall