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One thing that has to be remembered about a plain vanilla Residual Current Device. That's all it does, is sense an imbalance between Phase and Neutral in a circuit. A RCBO, has two functions, it senses like the RCD does, but it has the features of a Circuit Breaker built in to it.
There's certainly some confusion in the less enlightened DIY circles here as to the difference.

In this regard, the American GFCI fitted to a panel to protect one branch circuit is thus equivalent to the RCBO here (except for the lower trip current).

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However, Voltage Operated ELCB's were a different kettle of fish, they were only used where the basics of earthing could not be provided and used to trip if the voltage got above 22VAC, with reference to earth (cold water pipe).
For those across the pond who are having trouble visualizing how these devices worked, have a look at this diagram , which is in the U.K. power systems thread in the reference area.

This shows how the voltage ELCB was wired to provide whole-house protection. Note that the protective grounds from throughout the house are not grounded directly but are instead connected via the operating coil of the ELCB. The rod connected to the other side of the coil to provide an earth reference had to be located outside of any overlapping resistance gradient of other rods/pipes.

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Considering that they were sealed by the local Power Company here, the Home-owner was not allowed to reset them.
What was the idea behind that? [Linked Image]

The British ELCB was/is part of the homeowner's apparatus, and thus fully accessible for reset (or for testing with the button which deliberately connects the line to the coil through a suitable resistance).

Although obsolete for a good many years, there are still plenty of voltage ELCBs still in service in rural areas.

See this thread for some pictures of a typical old voltage-operated ELCB as used in domestic wiring:

Voltage-Operated Earth-Leakage Circuit-Breaker


[This message has been edited by pauluk (edited 12-01-2006).]