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Passive RCD unit


dor

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If we are talking about houses here, our house didn't have an RCD or RCBO at all. Neither have any houses I've previously lived in, except the one in Borneo. For some inexplicable reason we are still alive, although when I redid the bathroom I did route the power for the heated towel rail/underfloor heating/heated mirror through a new RCD.

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I'm sure RCDs have saved many lives.  My brother cut through the mains lead of a Flymo hover mower and then picked up the cable and put his thumb over the end, 'to see if it was hot'.

It was, but not in the way he anticipated! and the in-line RCD probably saved his life.

But just Google "RCD discrimination" and there's lots to read.

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4 minutes ago, mross said:

I'm sure RCDs have saved many lives.  My brother cut through the mains lead of a Flymo hover mower and then picked up the cable and put his thumb over the end, 'to see if it was hot'.

It was, but not in the way he anticipated! and the in-line RCD probably saved his life.

But just Google "RCD discrimination" and there's lots to read.

I'm sure there are lots of people who would cut through a cable and then stick it in their mouth to see if the power was still on - now, post RCDs. But before RCDs, Darwinism made sure these people were few and far between.

  • Greenie 1
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1 hour ago, Chewbacka said:

If the test button were to put an actual current between L and E - which would be the 'best' way to test...

I don't see why that would be 'the best' way. An RCD detects an imbalance between L & N currents. The diagram Nick showed is, I believe, a not very commonly used method of 'testing' an RCD these days. It's cheaper and simpler to simply insert a resistance between L prior to the coil and N after the coil. The RCD then genuinely detects an imbalance and trips out. 

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21 minutes ago, WotEver said:

I don't see why that would be 'the best' way. An RCD detects an imbalance between L & N currents. The diagram Nick showed is, I believe, a not very commonly used method of 'testing' an RCD these days. It's cheaper and simpler to simply insert a resistance between L prior to the coil and N after the coil. The RCD then genuinely detects an imbalance and trips out. 

Yes I think that's the case but a quick Google only turned up that diagram, which nevertheless makes the point that an earth connection doesn't come into it.

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42 minutes ago, WotEver said:

I don't see why that would be 'the best' way. An RCD detects an imbalance between L & N currents. The diagram Nick showed is, I believe, a not very commonly used method of 'testing' an RCD these days. It's cheaper and simpler to simply insert a resistance between L prior to the coil and N after the coil. The RCD then genuinely detects an imbalance and trips out. 

The main reason I thought it may be 'best' (but impractical) is because it would also confirm in a 'normal' domestic type installation that there is a reasonable protective conductor back to the neutral, but probably a simple internal test mode is better for testing the RCD rather than including the wiring as well.  Test the wiring as a separate test is probably more sensible if it's required.  

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17 minutes ago, Chewbacka said:

The main reason I thought it may be 'best' (but impractical) is because it would also confirm in a 'normal' domestic type installation that there is a reasonable protective conductor back to the neutral, but probably a simple internal test mode is better for testing the RCD rather than including the wiring as well.  Test the wiring as a separate test is probably more sensible if it's required.  

Yeah, when I had the wiring checked out at work it involved all kinds of stuff that I'm not up to speed on including earth loop impedance and more. 

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4 hours ago, system 4-50 said:

Um, I believe the latest edition calls for 2 RCDs per household, in readiness for when divorce proceedings start.

None of the editions so far have outlawed predecessors though, thus many houses are wired to previous standards; and additions have been additions to this, rather than a complete rewire or complete replacement of the consumer unit.

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11 hours ago, nicknorman said:

Yes I think that's the case but a quick Google only turned up that diagram, which nevertheless makes the point that an earth connection doesn't come into it.

Here you go...Wiring-Methods-for-Lighting-Circuits-101

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1 hour ago, WotEver said:

Here you go...Wiring-Methods-for-Lighting-Circuits-101

Yes I think this is the normal way of doing it. However the only thing with that diagram, bearing in mind my purpose was to demonstrate that an earth connection doesn't come into it, is that it shows earth connections and doesn't clearly differentiate which bits are inside the RCD and which bits are part of the external circuit. It would be easy for the untechnical to look at it and go "yeabut there ARE earth connections".

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14 hours ago, mross said:

I'm sure RCDs have saved many lives.  My brother cut through the mains lead of a Flymo hover mower and then picked up the cable and put his thumb over the end, 'to see if it was hot'.

It was, but not in the way he anticipated! and the in-line RCD probably saved his life.

But just Google "RCD discrimination" and there's lots to read.

Darwin award!

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