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Do-It-Yourself (DIY) Question & Answer Forum
RCCB failure mode??
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<blockquote data-quote="Geoff1946" data-source="post: 490475" data-attributes="member: 28452"><p>I tried to paste in a circuit here, but can't for some reason, so perhaps I can describe so that you can visualise this:</p><p></p><p>The test circuit switches in a resistor between the live input and neutral output of the RCD. The current it sends hence passes through the neutral side of the balance transformer, but has bypassed the live side of it. Hence this imbalance trips the breaker. All is well.</p><p></p><p>NOW consider if that neutral output of the RCD is earthed by a fault. The test current will flow to earth rather than back through the transformer.</p></blockquote><p></p>
[QUOTE="Geoff1946, post: 490475, member: 28452"] I tried to paste in a circuit here, but can't for some reason, so perhaps I can describe so that you can visualise this: The test circuit switches in a resistor between the live input and neutral output of the RCD. The current it sends hence passes through the neutral side of the balance transformer, but has bypassed the live side of it. Hence this imbalance trips the breaker. All is well. NOW consider if that neutral output of the RCD is earthed by a fault. The test current will flow to earth rather than back through the transformer. [/QUOTE]
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RCCB failure mode??
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