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Explain to me how an RCD protects a person when there is an isolating transformer in the circuit?

Well, it's in case somebody gets bored while sitting in the bath (trying to think of another song to sing!) and decides to unscrew the shaver outlet and start tinkering around with the primary connections....... [Linked Image]

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Could someone translate RCD? Acronyms are fun.

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RCD = Residual Current Device

Also formerly known as:

RCCB = Residual Current Circuit Breaker.

And before that, it was known as a current-operated or current-balance ELCB.

ELCB = Earth Leakage Circuit Breaker.

Personally, I think the old ELCB designation is much more descriptive.

There was another type known as a fault-voltage or simply voltage-operated ELCB. In times past, this was the type assumed when somebody talked about an ELCB in a domestic setting. The voltage ELCB worked on a rather different principle though, and has been considered obsolete for years. The IEE Wiring Regs. here ceased to recognize it in 1981.