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What this video covers

Galvanic isolators that lack a "fail safe" label can fail open — severing the safety grounding connection to the dock — without triggering any alarm.▶ 0:00 Nigel Calder explains that early galvanic isolators used two sets of counterposed diodes; when either set fails open, the shore-power grounding path is lost and the boat gives no warning.▶ 1:07 ABYC revised its standards in the early 2000s to require a failure alarm, but that proved too costly to implement, so the standard shifted to requiring fail-safe design: diodes that fail shorted, preserving the dock grounding connection.▶ 1:48 Any isolator meeting that standard carries a "fail safe" label and an ABYC compliance statement.▶ 1:56 An isolator without that label should be replaced.▶ 2:09 The trade-off: a fail-safe unit that fails shorted still passes DC current and creates a galvanic corrosion risk, so periodic testing is necessary to confirm the device is still functioning as an isolator and not simply acting as a wire.▶ 2:32 Jan Attenstedt notes that testing procedure is covered in the BoatHowTo advanced marine electrics course.▶ 2:43

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