Earthing a water pipe??

[JohnW2]

Is anyone going to promote NOT earthing appliances as a desirable idea?

If you are thinking of what we would currently regard as Class I appliances, I think that could only be seriously considered as part of a package which included a requirement for earth-free environments - the practicalities of which don't bear thinking about. A (slightly!) more realistic alternative might be to insist that all appliances be Class II - but it would take a long time to 'phase in' such a change.

As things stand, with Class I appliances in existance and (other) earthed things around in a substantial proportion of buildings, I would think that the risk resulting from not earthing (Class I) appliances would be much greater than the risk resulting from earthing them.

Kind Regards, John

 

[JohnW2]

Well, one of those faults could exist for years without you knowing! The risk of you personally coming into contact with both in a metal free environment would be even lower ...

Yes, very little is impossible.

I might even get struck by lightning tomorrow.

Kind Regards, John

 

[John D v2.0]

If you are thinking of what we would currently regard as Class I appliances, I think that could only be seriously considered as part of a package which included a requirement for earth-free environments - the practicalities of which don't bear thinking about

Out of interest what would we need to do?
I'd imagine disconnect met from supplier earth/earth rod and everything else, insert insulating sections into the gas and water pipe, and hope that the floor is timber or modern solid floor and the building isn't steel framed.

 

[John D v2.0]

Yes, very little is impossible.

I might even get struck by lightning tomorrow.

Kind Regards, John

You should be wearing one of those chain mail suits I posted up the thread!

 

[EFLImpudence]

I think the live studwork came into contact with leaked water and the person leaning on the wet floor contacted earthed/bonded pipes with the other hand.

Edit - responding to John's not remembering the details.
I didn't realise there was another page.

 

[JohnW2]

I think the live studwork came into contact with leaked water and the person leaning on the wet floor contacted earthed/bonded pipes with the other hand.

Yes, that rings a bell. My point remains that, in a different situation, had that studwork been earthed (and not live), a shock could have resulted from simultaneous contact with that wet floor (earthed via studwork and water) and, say, an exposed L conductor in a damaged appliance flex.

As I've recently written (and I'll avoid the P-word, just for you!) I'm not sure which of those two incredibly unlikley scenarios is the more likely, so couldn't say whether, on balance, it would be better to earth or not earth the studwork.

Kind Regards, John

 

[EFLImpudence]

No, it depends which way the current is going to flow.

Some think one way is more likely despite the accepted reasoning being the other.

 

[aptsys]

No, it depends which way the current is going to flow.

In the circuits mentioned, current flows both ways, changing 50 times per second.

 

[winston1]

In the circuits mentioned, current flows both ways, changing 50 times per second.

100 times a second actually.

 

[JohnW2]

Out of interest what would we need to do? I'd imagine disconnect met from supplier earth/earth rod and everything else, insert insulating sections into the gas and water pipe, and hope that the floor is timber or modern solid floor and the building isn't steel framed.

Yes, I think those would be the main things (I'm not sure about telephone cables) plus, of course, 'structural steel'.

The main issue is presumably the gas/water pipes (and, in some cases, metal waste pipes). There are still an awful lot of metal gas/water pipes entering properties, so an awful lot of 'insulating sections' to install - complicated by the fact they would probably have to be inserted outside of the building in the case of gas.

If one wants to think laterally (and very hypothetically!), an alternative approach would be to leave consumer's installations as they are (but without any requirement for bonding or CPCs) but to require generators and DNOs to isolate their supplies from earth - but, as well as being a horrendous undertaking, that would also probably introduce new problems!

Kind Regards, John

 

[aptsys]

100 times a second actually.

Yep, brainfart moment.

 

[aptsys]

If one wants to think laterally (and very hypothetically!), an alternative approach would be to leave consumer's installations as they are (but without any requirement for bonding or CPCs) but to require generators and DNOs to isolate their supplies from earth - but, as well as being a horrendous undertaking, that would also probably introduce new problems!

That's the wrong solution, as then another customer could make the CPC live.

 

[bernardgreen]

Weak Earth or Strong Earth. and RCD operation

Weak = 10,000 ohms impedance from "earthed" metal to MET or the actual Ground ( via damp items for example )

Strong = very low impedance from "earthed" metal to MET or the actual Ground ( via a conducter be it CPC or a bonding conductor or a copper pipe )

A person touching both Live and a Strong Earth will take a severe shock, greater than 30 mA for less than 40 mSecs ( assuming RCD operates ). A severe but short duration shock is survivable. ( it is what defibrilators do, they stun the heart to stop an abnormal rhythm and then the heart can restart into a normal rhythm )

A person touching both Live and a Weak Earth will take a mild shock, less than 20 mA for an indefinate length of time ( assuming RCD does not operate on Δ20mA ).
A mild but prolonged duration shock can be fatal due to (1) the heart being stopped and not allowed to re-start and (2) non reversible tissue damage due to current and loss of blood circulation

 

[JohnW2]

No, it depends which way the current is going to flow. Some think one way is more likely despite the accepted reasoning being the other.

Quite apart from the technicality that has been mentioned by others, I'm not really sure what you are saying.

If current can flow through a path created by 'live' (not earthed) studwork ('live' by virtue of a screw penetrating a cable), water, a human body and an earthed pipe, then, if the studwork were earthed, the same current could flow through a path created by an exposed L conductor in an appliance flex, a human a body, water and the earthed studwork.

The question as to which of those scenarios is more likely to arise is essentially a non-electrical one, ro which I certainly don't know the answer.

Kind Regards, John

 

[JohnW2]

That's the wrong solution, as then another customer could make the CPC live.

What CPC?

As I said, such a hypothetical situation would remove the need for CPCs and, even if they still existed in an installation's wiring, they would not be connected to anything outside of the building.

Kind Regards, John