Socket behind dishwasher pt.2 - are we being had?

[JohnW2]

Then all the refuseniks would simply add sockets "one at a time", and there would never be more than 1 new socket at any point.

Yes, that's the problem, so what I suggested would probably not be particularly workable. However, the same people would quite probably often claim that the new sockets were not new (if they 'looked newer' than others, they would probably say that they had simply replaced old, existing, sockets - which I don't think triggers the need for RCD protection, does it?).

If they wanted such a regulation, it probably would have made more sense to require that the entire circuit be RCD-protected if new sockets were added - but, again, some would undoubtedly deny that they had added any sockets.

Kind Regards, John

 

[EFLImpudence]

What criteria do you think should be used to determine if an RCD should be installed?

Where there is a specific hazard. Not just ALL sockets for the sake of it.

What voltage would you be happy to see exposed conductive parts reach because of slightly worn elements?

More than causes what could be a 16mA RCD to operate.

 

[JohnW2]

More than causes what could be a 16mA RCD to operate.

[I presume you mean a 16A MCB !!]
However, I agree - as I recently wrote/implied, given a typical EFLI (assuming TN), the circuit's OPD should operate at touch voltages less than would be 'worrying'.

Kind Regards, John

 

[EFLImpudence]

No, I meant 16mA.

I.e. an element fault to earth of 15kΩ.

Or, more likely 26mA with 9.23kΩ

 

[ban-all-sheds]

Where there is a specific hazard. Not just ALL sockets for the sake of it.

What about concealed cables?

 

[JohnW2]

No, I meant 16mA. I.e. an element fault to earth of 15kΩ.

Oh, I'm a bit confused then. With, say, an earth component of the EFLI of 1Ω, 16mA would only produce a touch voltage of 16 mV - is that what you meant?

Kind Regards, John

 

[JohnW2]

What about concealed cables?

That also gets a bit odd in the 'transitional' situation if one uses mechanical protection (or earthed shield, or whatever), rather than an RCD covering the whole circuit, to protect a small piece of new buried cable. One then could end up with 5% of the circuit's buried cable 'protected' and 95% of it non-protected - and the person with a drill in his hand would not know which, if any, he was about to try to drill into!

Kind Regards, John

 

[ban-all-sheds]

So don't do it that way, then.

 

[JohnW2]

So don't do it that way, then.

I wouldn't (not that I have any non-RCD-protected circuits, anyway). However, the point is that it would be re-compliant.

Kind Regards, John

 

[EFLImpudence]

Oh, I'm a bit confused then. With, say, an earth component of the EFLI of 1Ω, 16mA would only produce a touch voltage of 16 mV - is that what you meant?

Well, in away.
I suppose 50V could be considered the limit for touch voltage but that isn't likely to occur, is it?

I just don't want the RCD to disconnect the supply and render the appliance unusable because of an insignificant earth fault.

 

[ban-all-sheds]

the person with a drill in his hand would not know which, if any, he was about to try to drill into!

Who decides that it's OK for them to drill into a cable because it's RCD protected?

 

[JohnW2]

Well, in away. I suppose 50V could be considered the limit for touch voltage but that isn't likely to occur, is it? I just don't want the RCD to disconnect the supply and render the appliance unusable because of an insignificant earth fault.

OK, I think I'm coming to understand what you were saying. I was approaching the issue from another angle.

If I now understand correctly, you are saying that you don't want to have an RCD which (with a path to earth of, say, 1Ω) would trip with a touch voltage of only 16mV (or 26mV) (or some equally trivial voltage) - and I would definitely agree with that.

I was thinking more of a much lower resistance L-E fault (approaching a 'dead short') which did have the potential to cause a dangerous touch voltage - but was pointing out that, in most situations, the circuit's OPD would immediately clear such a fault, even in the absence of an RCD. Is my reasoning not correct? (and that' a question as much for BAS as for you)

In other words, in response to BAS's question, I was essentially agreeing with you that one does not usually need an RCD to clear a fault which could result in a dangerous touch voltage.

Kind Regards, John

 

[JohnW2]

Who decides that it's OK for them to drill into a cable because it's RCD protected?

No-one says that it is "OK" !! However, that is the presumably the eventuality which the reg seeks to address.

Kind Regards, John

 

[Risteard]

Whatever one thinks about RCDs, it is seemingly a bit odd to require RCD protection of just one (new) socket on a circuit, whilst all the others on the same circuit remain without such protection.

It's a matter of opinion. I note, for example, that Mark Coles wrote the following a number of years ago in the IET Wiring Matters publication:

"Some installers are of the opinion that when adding to an existing circuit, provided that the existing circuit meets the requirements of BS 7671:2001(2004), i.e. the 16th Edition, then the 17th Edition simply applies to the new addition. This article shows that in all cases, the 17th Edition is to be applied to the entire circuit worked on."

 

[EFLImpudence]

Is that confirmed by a regulation or is it merely Mr.Coles' opinion?

"No less safe" springs to mind for some reason.