Steel Bath how to earth.

[JohnW2]

But even where an RCD is present, I would never take that as an excuse for not taking some other precaution which I would take if that RCD were not present. In other words, if I wouldn't omit some particular bonding between two pieces of equipment if the RCD were not there, I'm not going to omit it just because an RCD has been added to the design.

I agree totally. Indeed, even if an RCD were (if it functioned correctly) the panacea that some seem to think, there would still be the possibility that it would fail to function when it should - so, like you, I would generally not omit any safety measures which would be required in the absence of an RCD simply because I knew an RCD was present.

The matter of supplementary bonding in bathrooms which is being discussed in this thread is potentially a complicated question and my inclination would be to apply what I regarded as common sense on an individual-casis basis.

There is one bathroom situation, which I imagine is pretty common (and certainly applies to some in my house), which we haven't really discussed. If there are no exposed conductive parts in the room (and, indeed, nothing 'electrical' other than ceiling mounted light fittings and pull-switches), and if all pipes etc. are splidly connected to MPB via metal pipework, then I don't see any real point in supplementary bonding (with or without an RCD), even if someone brings the hypothetical vacuum cleaner with a frayed lead into the room, and can even imagine that some people might call it 'meddlesome'. What do you think?

Kind Regards, John.

 

[EFLImpudence]

I don't see any real point in supplementary bonding (with or without an RCD), even if someone brings the hypothetical vacuum cleaner with a frayed lead into the room, and can even imagine that some people might call it 'meddlesome'. What do you think?

Hello, it is I with the tatty vacuum.

That was a different argument when you were arguing for supplementary earthing to non-extraneous-parts.

 

[JohnW2]

I don't see any real point in supplementary bonding (with or without an RCD), even if someone brings the hypothetical vacuum cleaner with a frayed lead into the room, and can even imagine that some people might call it 'meddlesome'. What do you think?

Hello, it is I with the tatty vacuum. That was a different argument when you were arguing for supplementary earthing to non-extraneous-parts.

Yes, I know it was. I only mentioned the tatty vacuum because I thought that someone (maybe you) might otherwise wheel it out as a means of introducing electricity into an essentially 'electricity-free' bathroom It's not otherwise relevant to what I was saying.

Anyway, what about my question - what are your thoughts/feelings about locally joining metalwork (all of which is connected to MPB via metal pipework) in an essentially 'electricity-free' bathroom to the installation's CPC (in the absence of an RCD)? It's perhaps difficult to see what harm it could do (except in rather bizarre hypothetical situations), but I'm not sure I can see what good it could do, either (except for providing a 'supplementary CPC' for whatever it was connected to in the installation!).

Kind Regards, John.

 

[EFLImpudence]

Well, I think we're back to the regulation which says that supplementary bonding is not needed when conditions do not require it.

 

[JohnW2]

Well, I think we're back to the regulation which says that supplementary bonding is not needed when conditions do not require it.

This is a genuine, not 'funny', 'clever' or rhetorical, question .... which regulation says that? 701.451.2 appears to require supplementary bonding in a bathroom, unless (and only unless) (iv), (v) and (vi) of that section are all satisfied (which they would not be in the absence of an RCD), even if the only 'electrics' in the room are a a light fitting (even a Class 2 one!) and maybe a pull-switch on the ceiling - which is the situation I was describing.

Kind Regards, John.

 

[bernardgreen]

Going at a tangent.

What use is an RCD if there is no CPC involved in the fault ?.

For example when the lead of a double insulated hedge trimmer is cut ?

Or rather what use is there in specifying a maximum impedance for the CPC when it is not and cannot be involved in the hedge trimmer scenario.

 

[JohnW2]

Going at a tangent. What use is an RCD if there is no CPC involved in the fault ?.

Well, the simple answer to that general question is obviously that an RCD will operate if any significant amount of current finds a return path other than the neutral conductor - that alternative path can theoretically be one to earth which does not involve a CPC.

For example when the lead of a double insulated hedge trimmer is cut ?

I'm sure you know the answer to that one as well as I do - that, in the absence of other factors you're not mentioning, an RCD will be of no use in that situation (assuming the cable is only 2-core!). However, if,despite being Class 2, any exposed metalwork of a hedge trimmer (or whatever) becomes live, then the RCD would obviously become of considerable value, given the ready paths to earth which exist in a garden.

Or rather what use is there in specifying a maximum impedance for the CPC when it is not and cannot be involved in the hedge trimmer scenario.

I'm not quite sure what CPC you're talking about here. If you're talking about the fixed wiring to the socket then, as you say, the CPC of that cannot possibly be relevant to RCD function if something with a 2-core lead is plugged into the socket - but the nature of sockets is that anything could be plugged into them, hence the need for a low enough impedance for RCD function (almost impossible not to achieve!) if a 3-core lead is plugged in.

Kind Regards, John.

 

[securespark]

Going at a tangent.

What use is an RCD if there is no CPC involved in the fault ?.

For example when the lead of a double insulated hedge trimmer is cut ?

I have (unintentionally, I might add) personally tested an RCD in a similar situation.

I cut the 2 core cord of a lawnmower protected by RCD. Somehow, the RCD did not trip until I (stupidly) picked up the sliced end lying in the damp grass.

Whereupon I received a short burst of something my kids call "ouchy", then the RCD dropped out.

My point being that an RCD protecting a Class II appliance is still useful.

 

[ebee]

exactly,
whether the appliance require a cpc or not, anyone touching a phase conductor who is capable of getting a shock to earth is capable of tripping the RCD. If you get a phase to purely N on its own then an RCD will not protect you. So a two core flex connected to mains voltage should still be RCD protected.

Infact, if you had a faulty install, say Ph & N connected to a socket but no E connection, and a RCD protecting that socket then you would have protection from earth faults for anything you plugged in (say a metal cased electric fire with broken element). Note I am not advocating doing away with any earth connection on RCD protected circuits but just pointing out that luckily a RCD would mitigate this problem

 

[sparkticus]

exactly,
whether the appliance require a cpc or not, anyone touching a phase conductor who is capable of getting a shock to earth is capable of tripping the RCD. If you get a phase to purely N on its own then an RCD will not protect you. So a two core flex connected to mains voltage should still be RCD protected.

Yes, actually the RCD concept is quite clever isn't it. The idea of detecting a differential current between the phase and neutral is much better than some device which might try to detect a specific current flowing in a protective conductor (if you had a protective conductor which you don't in a two core flex) Some of the old voltage operated ELCBs had the main earth in series with the earth rod so that it could detect a PD across the two ends (installation VS earth rod)

 

[sparkticus]

if I wouldn't omit some particular bonding between two pieces of equipment if the RCD were not there, I'm not going to omit it just because an RCD has been added to the design.

Yes that's the philosophy that I have adopted regarding RCDs. I factor the disconnection time potentially afforded by them but I certainly don't count on it.

 

[bernardgreen]

Some of the old voltage operated ELCBs had the main earth in series with the earth rod so that it could detect a PD across the two ends (installation VS earth rod)

Which was a very good, near perfect way to detect the majority of live to exposed metal faults provided the safety green wire ( aka the CPC "earth" wire ) was connected to the exposed metal work. Unfortunately the arrival of immersion heaters and similar equipment meant the safety green wire was connected via pipe work to true ground thus by passing the coil in the ELCB.

This was still safe as the exposed metal had a better ground connection and if the fault current was very high metal work then would not get higher than 50 volts as the ELCB would then react.

Then plastic service pipes arrived and the ELCB was no longer by-passed.

Then the sensitive differential RCD was developed into a unit that provided a cost effective method that could be used in domestic situations.

 

[ban-all-sheds]

My point being that an RCD protecting a Class II appliance is still useful.

Even more useful for things like mowers, strimmers, hedgetrimmers etc is to use a 3-core flex - just leave the cpc unconnected at the appliance end.

Whereupon I received a short burst of something my kids call "ouchy", then the RCD dropped out.

Is that as in "If you don't behave Mr Ouchy will come and get you"?