Consumer unit replacement cost

[JohnW2]

You cannot say that testing the RCD with appliances in circuit is the way to go because there is no way you can account for what may be attached to the circuit at any one time.

The bit of that I've highlighted is obviously true, so is going to leave some uncertainties (about what will happen with future loads). However ....

On my C&G courses, we were all taught only to test RCDs in isolation.

Were you really taught that if, when tested on an installation 'as it was at the time', the RCD failed to trip (or failed to trip satisfactorily), maybe even to the extent that it didn't trip when one pressed its test button, you could/should "pass" the installation if the RCD tested satisfactorily "in isolation'?

In any event, this whole discussion may be a bit hypothetical since, apart from all the recent discussions about 'types' of RCD, I thought that the main problem with testing RCDs in situ is that they may appear to be 'too trigger happy' (i.e. trip too easily, at test residual currents less than should cause them to trip), because of pre-existing residual/leakage currents due to connected loads - rather than a failure to trip (or to trip quickly enough) when they should. Is that not the case?

What would you suggest the correct procedure would be if you found the RCD to fail to complete the test process?

There's no short answer to that, since there are so many possible situations. What I would not do is 'pass' the installation if I had no reason to be confident that an L-E fault arising 5 minutes after I left would, with the installation 'as is', result in the RCD operating. At the very least I would conclude that 'further investigation was required'.

That's surely rubbish, and dangerous rubbish at that, isn't it?

No, I don't believe it is.

As above, I can't really change my view. To take the 'worst case', would you really 'pass' and installation and 'walk away' if you knew that pressing the RCD's test button would not result in a trip, just because it had 'tested OK in isolation'?

Kind Regards, John

 

[securespark]

No, when I say the RCD tests OK, that would include operation of the test button.

I would like to press you to answer the question I asked.

It's not really an answer to explain what you wouldn't do, especially as you have repeatedly voiced that opinion previously.

 

[JohnW2]

No, when I say the RCD tests OK, that would include operation of the test button.

I may be getting a bit confused. To be clear, are you talking about a situation in which:

With the RCD in situ, it trips in response to the test button being pressed
With the RCD in situ, it 'fails' and RCD test
With the RCD in isolation, it passes the RCD test
?

if so, I think I need to know more about the sort of 'fail' (when in situ) you are talking about. Are you perhaps merely talking about it tripping with too low a current (on a ramp test)?

I would like to press you to answer the question I asked. It's not really an answer to explain what you wouldn't do, especially as you have repeatedly voiced that opinion previously.

OK. However, as above, before I can answer that, I need to know what sort of 'fail' (when tested in situ) you are talking about - since that will determine my answer (as I said, "there are so many possible situations").

Kind Regards, John

 

[flameport]

I wouldn't think any connected circuits or loads will stop the RCD working when tested,

Are you 100% sure about that?

On my C&G courses, we were all taught only to test RCDs in isolation.

That may have been correct decades ago when the only loads likely to be connected to an RCD were simple resistive items.
The 18th edition of GN3 still has that recommendation to test RCDs with loads disconnected.
GN3 is wrong.

There are many things which can cause incorrect operation of RCDs, and disconnecting everything before testing will remove all of those.

What would you suggest the correct procedure would be if you found the RCD to fail to complete the test process?

Find out why it's not working as intended and either fix the problem if there is one or replace with RCD with a type which is actually suitable for the installation.

 

[JohnW2]

Find out why it's not working as intended and either fix the problem if there is one or replace with RCD with a type which is actually suitable for the installation.

It's "that" topic again

I would be very interested to know how often (if ever) any electricians here have actually come across a situation in which an RCD in a domestic installation was not "working as intended" ('failed' an RCD test) but that "working as intended" was (or could have been) achieved by changing to a different Type of RCD.

Kind Regards, John

 

[BS3036]

How can you test the correct operating value of an RCD if there are a number of loads connected each leaking current to earth?

 

[EFLImpudence]

Are you 100% sure about that?

Does that mean, therefore, that the test button would not have been working anyway?

Not in reply to my post, but:

That may have been correct decades ago when the only loads likely to be connected to an RCD were simple resistive items.
The 18th edition of GN3 still has that recommendation to test RCDs with loads disconnected.
GN3 is wrong.

Or maybe not.

There are many things which can cause incorrect operation of RCDs, and disconnecting everything before testing will remove all of those.

Yet, it will confirm that the RCD is, itself, satisfactory.
That something else might be wrong is separate from testing the RCD.

Find out why it's not working as intended and either fix the problem if there is one or replace with RCD with a type which is actually suitable for the installation.

Why have all these LGBTQABF RCDs appeared since I retired?

 

[JohnW2]

How can you test the correct operating value of an RCD if there are a number of loads connected each leaking current to earth?

You obviously can't determine the actual trip threshold of the RCD, per se, if there are connected loads which are resulting in leakages to current.

However, particularly if they are loads which are usually/commonly connected to the circuit, what one can do is to determine what threshold of additional leakage current (e.g. due to a fault) would usually/commonly be needed to trip the RCD.

In any event, this is the 'least important' side of the equation (as far as safety is concerned). Having connected loads with earth leakage will reduce the apparent trip threshold (as measured by a ramp test), maybe even to the extent that it 'failed' the test because the trip threshold was too low (i.e. <0.5 x In) - but the worst consequence of that would be an increased risk of 'nuisance trips'.

The far more important situation would be if connected loads increased the trip threshold, maybe to the extent of preventing it tripping at all. Leakages to earth in connected loads would not cause that. The only thing of which I am aware of which could do this is this business about loads creating DC components of current which might impair the operation of a Type AC RCD - but I remain uncertain as to how commonly (if at all!)_ electricians actually experience that in domestic installations!

Kind Regards, John

 

[JohnW2]

Why have all these LGBTQABF RCDs appeared since I retired?

I would say probably at least partially because it has been possible to make them appear, and to (by regulations, propaganda or whatever) create a market for them

Kind Regards, John

 

[flameport]

I would be very interested to know how often (if ever) any electricians here have actually come across a situation in which an RCD in a domestic installation was not "working as intended"

That will be never.
Testing guidance and training for ever has been to test RCDs in isolation with everything disconnected and switched off. It still is.
End result - unless the RCD is actually broken, they all test perfectly every time, as anything that could affect their operation wasn't connected when the test was done.
That's not the only thing regarding testing that's outdated either.

Why have all these LGBTQABF RCDs appeared since I retired?

They have all existed for a long time.
Their apparent sudden appearance is due to the fact that the UK electrical industry is decades behind most other countries and only now is slowly starting to catch up.
Manufacturers of items like consumer units have been happy to turn out the same old outdated junk for the UK market despite it being banned in other countries long ago.

 

[JohnW2]

That will be never. Testing guidance and training for ever has been to test RCDs in isolation with everything disconnected and switched off. It still is.

If 'we' shared your view of this issue, would that not have changed?

They have all existed for a long time. ... Their apparent sudden appearance is due to the fact that the UK electrical industry is decades behind most other countries and only now is slowly starting to catch up.

As you will realise, I am not as easily 'pleased' (or 'convinced') as some people - which is why I continue to seek, so far essentially unsuccessfully, some actual concrete facts/evidence in relation to all this.

What, I wonder, have all these other countries actually achieved by being "decades ahead" of us? Do they actually (as a result) have significant lower numbers of injuries/deaths due to electric shocks and/or significantly less 'electrical fires' than we do in the UK?

Kind Regards, John

 

[JohnD]

That will be never.
Testing guidance and training for ever has been to test RCDs in isolation with everything disconnected and switched off. It still is.

And yet my RCD tester, and the one before that, came with an adaptor lead having a 13A plug on it, so you can plug it into a socket to test the "in service" trip.

 

[EFLImpudence]

I also have adaptors for other outlets as well.

They can also be used for other things apart from RCD tests.

 

[JohnW2]

What, I wonder, have all these other countries actually achieved by being "decades ahead" of us? Do they actually (as a result) have significant lower numbers of injuries/deaths due to electric shocks and/or significantly less 'electrical fires' than we do in the UK?

I haven't yet found figures for domestic electrical injuries, but I have found the following for work-related ones. These figures seem 'interesting', given that Germany is the country most often 'praised' for having been early in banning Type AC RCDs.

'

As for domestic electrical fires, they do seem a bit more common in UK (1,850 per million dwellings per year) than in Germany (1,444 per million dwellings per year), but not dramatically so. Goodness knows how accurate is the amazingly 'round' figure for Germany (60,000). I'm also not sure what a "not reported" electrical fire is

Kind Regards, John

 

[securespark]

Testing guidance and training for ever has been to test RCDs in isolation with everything disconnected and switched off. It still is.

So why were you so surprised at my stance of testing in isolation?