Earthing Steel Bath

[EFLImpudence]

Precisely..... and when is the measurement of the 23 K ohms made ? Very unlikely that it will be made when someone is in the bath or efven shortly after the person gets out of the bath so the decision to bond or not to bond is not made on data from the main use of the bathroom.

That is true but, as I keep saying -

The figure of 23kΩ is merely a number derived from 10mA @ 230V and not actually a likely result from testing.
As mentioned earlier 24.5kΩ is a more realistic value.

You may apply another current value you consider safe if you wish balanced with the preferred situation of not earthing unnecessarily.

I use the term 'earthing' here because wrongly applied 'bonding' is not bonding but earthing.

RCDs save a lot of uncertainty.

Only if the total impedance of the circuit that includes the human body is low enough to allow 30 mA of earth current to flow.

My point was that with RCDs (and the accompanying conditions) no supplementary bonding is required so rendering any discussion redundant.

You are still free to apply supplementary bonding if you wish.

 

[viewer]

EFLI; I think you took a couple of my "posers" as statements. I meant to suggest that even if the electrician worked to the best possible guidelines and science the effort could be nullified by changes in the plumbing. I can imagine copper being repaired using plastic, but not the other way around, thus creating an isolation which had not thereto existed. No criticism and many thanks for taking the trouble to go through the points. Most grateful.

 

[EFLImpudence]

EFLI; I think you took a couple of my "posers" as statements.

I didn't mean to. Did that affect the answer?

I meant to suggest that even if the electrician worked to the best possible guidelines and science the effort could be nullified by changes in the plumbing.

Well, yes, obviously anything can be changed.

The main problem with a plastic water supply is the loss of a good earth but
insulating sections isolating the majority of domestic pipework would be a good thing.

I can imagine copper being repaired using plastic, but not the other way around, thus creating an isolation which had not thereto existed.

True - but isolation is good.

 

[JohnW2]

The main problem with a plastic water supply is the loss of a good earth but insulating sections isolating the majority of domestic pipework would be a good thing.

Inserting insulating sections where pipework entered a property would certainly prevent them 'introducing a potential', and therefore would get rid of most of the concerns. However, if that were done, if taken literally the regs would appear (at least to my reading) to still require main bonding of the pipework on the consumer's side of that insulating section, even though that pipework is not (any longer) an extraneous-conductive-part. What are your views on that?

Kind Regards, John

 

[EFLImpudence]

Yes, I think that is the correct interpretation if the supply has an insulating section only at the origin.

However, my suggestion was more a methodical and systematic planned isolation of as much of the pipework as possible, hence majority.

Parts would still be earthed and it can't be done to the gas pipe.

 

[JohnW2]

Yes, I think that is the correct interpretation if the supply has an insulating section only at the origin. However, my suggestion was more a methodical and systematic planned isolation of as much of the pipework as possible, hence majority. Parts would still be earthed ...

Yes, I realised that - but (in terms of electrical common sense, rather than the regs) an insulating section at the origin should remove the need for any 'main bonding'. As you say, there would probably still be need for earthing of parts of the pipework, and maybe supplementary bonding (indeed, more so in the absence of 'main bonding'), but there is no rational reason I can think of why there should be a need for any 'main bonding'.

.... and it can't be done to the gas pipe.

That's true. However, I wonder (have no idea!) whether modern gas meters are still metal (or, at least, have electrical contuinuity across them?) If not, and if they were 'external', then the pipe entering the premises probably wouldn't qualify as an extraneous-c-p. (requiring main bonding), would it?

Kind Regards, John

 

[viewer]

EFLI; I think you took a couple of my "posers" as statements.

I didn't mean to. Did that affect the answer?
No, just confused my little brain.

I meant to suggest that even if the electrician worked to the best possible guidelines and science the effort could be nullified by changes in the plumbing.

Well, yes, obviously anything can be changed.

The main problem with a plastic water supply is the loss of a good earth but
insulating sections isolating the majority of domestic pipework would be a good thing.

I can imagine copper being repaired using plastic, but not the other way around, thus creating an isolation which had not thereto existed.

True - but isolation is good.

I know I'm being a bit perverse and this is a thought experiment, but my thinking is this; suppose that we have 2 taps and an electric shower. A common situation. The pipework is copper and is bonded. The CPC to the shower may also be joined to the copper pipe because this bonds the pipe at both ends to MET potential (the incoming pipe being bonded). The insertion of a plastic piece upstream now means that the pipes are not tied to MET but the bath is. Using the mythical hair dryer fault, the user would be safer if the bonding between bath and pipe/shower CPC had been removed. OK I've no idea how much safer, but I think that we agree that the situation would never arise if all the pipework had been isolated by design and construction, i.e. no metal pipes connected to bath.
Apologies for rambling.

 

[EFLImpudence]

I know I'm being a bit perverse and this is a thought experiment, but my thinking is this; suppose that we have 2 taps and an electric shower. A common situation. The pipework is copper and is bonded.

Right.

The CPC to the shower may also be joined to the copper pipe because this bonds the pipe at both ends to MET potential (the incoming pipe being bonded).

The cpc of the shower will go to the MET but the supplementary bonding only joins parts and CPCs in the location.
It will indeed be connected to the MET by the pipes and main bonding but the SB is only to equalise potential in the location.
It does not go anywhere else.

The insertion of a plastic piece upstream now means that the pipes are not tied to MET but the bath is.

Ah. but the bonding downstream of the inserts will have to be removed thus 'unbonding' the now isolated pipes, taps and bath.

Using the mythical hair dryer fault, the user would be safer if the bonding between bath and pipe/shower CPC had been removed.

Yes.

OK I've no idea how much safer,

It is not now a danger

but I think that we agree that the situation would never arise if all the pipework had been isolated by design and construction, i.e. no metal pipes connected to bath.

It would but pipes could still be connected to the bath if they were isolated elsewhere - as long as they have NO connection by any route to the MET, i.e. above the 23kΩ - preferably infinite.

 

[viewer]

"
Quote:
The CPC to the shower may also be joined to the copper pipe because this bonds the pipe at both ends to MET potential (the incoming pipe being bonded).

The cpc of the shower will go to the MET but the supplementary bonding only joins parts and CPCs in the location.
It will indeed be connected to the MET by the pipes and main bonding but the SB is only to equalise potential in the location.
It does not go anywhere else.

Quote:
The insertion of a plastic piece upstream now means that the pipes are not tied to MET but the bath is.

Ah. but the bonding downstream of the inserts will have to be removed thus 'unbonding' the now isolated pipes, taps and bath. "

This was the point I was trying to make.
Before insertion of our plastic joint the SB to the bathroom pipework tied all the pipes at equal potential, but because the shower CPC was linked into the bonding, this was in physical and electrical terms linked to the MET. So bath and local connectors were all at MET potential.
Now insert the plastic joint. The connections of the 'local' SB are still connected to the MET via the shower CPC and, as you say, the bonding needs removing in order to isolate the bath. In real life, however, it is highly unlikely that this will be done.
The conclusion must be that it is better to isolate the bath and taps by design of the plumbing than try to overcome the need for ensuring equal potentials using SB. From this my original suggestion was that advice to DIY or bathroom fitters should include the use of isolating connections (e.g. plastic or flexible rubber) to the tap work and not bonding the bath.
Thanks for help.

 

[bernardgreen]

If the bath is isolated ( or more than 23 k ohms from earth ) and pipes bonded what will happen when a double insulated electrical appliance falls into a bath of water.

NOTHING, the RCD will not trip as there is no earth current.

But the bath is now at about 120 volts AC above ground so the potential for severe shock exists for anyone in the bath touching any earthed pipework.

If there is no RCD then the duration of that severe shock will not be limited.

Of course no one with common sense will put electrical equipment in a bath but safety precautions have to cater for people with no common sense.

 

[A1Dan]

Right, er, well glad to have prompted such enthusiastic debate!

To be honest the last couple of pages have gone way over my head, but as far as I can see they seem to be related to a hypothetical bath, rather thant eh one I will be soaking msyelf in, so that's OK.

Going back to mine, and some of the questions on page one... there is no elevtrical side to it, such as whirlpool bath, electric shower etc, it's just a plain old bath. As mentioned, the nearest electrical thing at all is a shaver point, a couple of meters away, or maybe the lights.

So, from what I can gather the answer is no, don't earth, right?

I can see how that makes sense, as there's no reason at all the bath should have an electrical potential, whereas connecting it to anything else that comes into the room gives the possibility of it being live.

 

[JohnW2]

Going back to mine, .... it's just a plain old bath. So, from what I can gather the answer is no, don't earth, right?

I think it's probably fair to say that most people would say that. However, as you've seen, the situation is not totally black and white , and a few would say the opposite (see most recent post from Bernard).

The point is that there are (incredibly small) theoretical hazards introduced by connecting, or by not connecting, the bath to earth (or earthed things). One's opinion is therefore dependent upon which of two types of incredibly unlikley incident one feels is the more likely.

[ the two types of 'incident' can be exemplified by (a) dropping a live hairdrying into the bath full of water you were sitting in and then touching something earthed and (b) being in contact with live electricity due to using a faulty vacuum cleaner in the bathroom and then also touching the bath. In the former case it would be safer if the bath were connected to earth, in the latter case it would be safe if the bath wasn't connected to earth]

Kind Regards, John

 

[A1Dan]

Cheers John.

To be honest I'm going to try not to do either of those things. The latter seems marginally more likely, and given that not connecting the bath to earth is clearly the easier option, I think I'll go with that!

 

[JohnW2]

Cheers John. To be honest I'm going to try not to do either of those things. The latter seems marginally more likely, and given that not connecting the bath to earth is clearly the easier option, I think I'll go with that!

Exactly. I don't think you'd need many fingers to count how many people had done either of those things (or equivalents) in the last 50 years, so the discussion is really pretty hypothetical. For what it's worth, I would personally take the same view as you.

Kind Regards, John

 

[EFLImpudence]

These discussions remind me of the unfortunate MP's daughter who was electrocuted by touching a cutlery hook on the wall while her leg was touching the washing machine.

The hook was live because the fixing screw was screwed into a cable and making contact with the line conductor.

In this case it would have been better had the hook been earthed (opd would have tripped) and/or
the washing machine carcass not been earthed (no (or greatly reduced) path to earth through her body).

As you can see, there is always a very unlikely scenario why the situation would be better had it been done differently.

However, I don't think anyone would advocate earthing a metal hook and leaving the washing machine unearthed 'just in case'.

The safety of electrical installations is a compromise based on the likeliest hazard.