RCD question

[BenStiller]

When you activate the test button on a rcd, this is supposed to generate an earth fault.
My question is, lets assume all the connections are sound and in their proper place, i push the test button and everything works fine.

Now i disconnect the actual earth going to the rcd (shower enclosure type), will this still trip, even though there is no actual earth connected to the circuit?

 

[pdcelec]

It is dangerous to remove an earth from a live circuit. This practice should not be done!

 

[andy]

When you activate the test button on a rcd, this is supposed to generate an earth fault.
My question is, lets assume all the connections are sound and in their proper place, i push the test button and everything works fine.

Now i disconnect the actual earth going to the rcd (shower enclosure type), will this still trip, even though there is no actual earth connected to the circuit?

it creates an 'earth leak' inside the RCD between ingoing neutral and outgoing live (or the other way around). it has no connection to earth

and there is also a wiring diagram on most RCDs. go look at it

 

[BenStiller]

Yes andy i know how they work, i think i never explained better what my point is, but inadvertantly you might have answered it.
What you are saying is, the earth leakage fault actually gets picked up by the rcd.
Even though we all wire this up to the actual main incoming earth what im saying is, technicaly speaking, is there a need to?

 

[andy]

Yes andy i know how they work, i think i never explained better what my point is, but inadvertantly you might have answered it.
What you are saying is, the earth leakage fault actually gets picked up by the rcd.
Even though we all wire this up to the actual main incoming earth what im saying is, technicaly speaking, is there a need to?

earth is sometimes connected (mostly in RCBO's) so that it the neutral fails it still has something other than live. not sure why tho

 

[ban-all-sheds]

Yes andy i know how they work, i think i never explained better what my point is, but inadvertantly you might have answered it.
What you are saying is, the earth leakage fault actually gets picked up by the rcd.

No - there is no "earth leakage" generated by an RCD test button - how can there be when there is no connection to earth?

RCDs do not detect earth leakage, per se, they detect an imbalance between the current flowing in the live conductor and that flowing in the neutral one, hence the term Residual Current Breaker, and not Earth Leakage Circuit Breaker.

In practice, of course, a genuine fault which creates an imbalance is likely to be because current somewhere is flowing to earth, and it is the possibility that it is flowing to earth via someone's body that drives the advisability and performance characteristics of RCDs. But as we have seen many times in postings on this forum, an imbalance can be created by connecting the neutral of a circuit to the wrong side of a split board. In that case nothing is leaking to earth, but the discrepancy between live & neutral currents is detected and the RCD trips.

AFAIK, the test button on an RCD connects a resistor between the upstream live and downstream neutral (or vice-versa; would work just as well), thus generating an imbalance across the RCD.

 

[slippyr4]

wikipedia's RCD page is quite useful for learning about RCD. Just train your mind to ignore all the yankified wording.

 

[BenStiller]

Cheers fellas

 

[Spark123]

RCDs do not detect earth leakage, per se, they detect an imbalance between the current flowing in the live conductor and that flowing in the neutral one, hence the term Residual Current Breaker, and not Earth Leakage Circuit Breaker.

There are two types of earth leakage circuit breaker (ELCB), current operated and voltage operated. The current operated ELCB is the same as an RCD (residual current device). The voltage operated ELCB was removed from IEE regulations back in 1981.

 

[nickyross]

When you activate the test button on a rcd, this is supposed to generate an earth fault.
My question is, lets assume all the connections are sound and in their proper place, i push the test button and everything works fine.

Now i disconnect the actual earth going to the rcd (shower enclosure type), will this still trip, even though there is no actual earth connected to the circuit?

A dumb question from a novice: isn't disconnecting the earth an incredibly stupid thing to want to do?

Why do you want to do this Ben?