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What this video covers

Fuses and circuit breakers protect conductors, not the devices at the end of a circuit — a point Nigel Calder calls a common and complete misunderstanding among sailors.0:35 A short circuit can drive hundreds of amps through a conductor, melting it along its entire run back to the battery; if that conductor runs in a bundle, it melts adjacent conductors and triggers multiple simultaneous short circuits.1:13 The fuse or breaker must sit at the source-of-power end of the circuit, not in front of the load, so it can interrupt the high-current flow before the conductor fails.1:46 Placing a fuse directly ahead of a device protects nothing upstream.2:27 Jan Attenstedt and Calder note the rule applies equally to DC and AC circuits, and that the fuse must be within a few centimeters or inches of the power source when exact placement is impractical.2:14 The discussion references the BoatHowTo Boat Electrics 101 course and a free primer article by Calder for detailed guidance on overcurrent protection device placement.2:58

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