Water pipe bonding

[JohnW2]

Im getting you all confused now

As I said, I think you are worrying unnecessarily.

The hot pipes are via a electric water heater and 70% of entire system is via metal pipes with just plastic elbows.

That doesn't alter what I've said. It sounds as if the hot water pipes are probably earthed via the heater, but that the cold ones are 'floating'. That's not really a problem.

regarding the EAWR i found this,not sure if its relevant.

It says ".... to prevent danger arising when any conductor (other than a circuit conductor) which may reasonably foreseeably become charged as a result of either the use of a system, or a fault in a system, becomes so charged ....", and I don't really see that it can be said to be 'reasonably foreseeable' that a short bit of floating pipe (floating because of the plastic elbows) could become 'charged' (which I presume meanss 'electrically live'). Even if you thought that was 'reasonably foreseeable' that regulation would require that you 'earth' it, which may or may not be satisfied by connecting it to the other (hot) pipe.

As I said, I think you should stop worrying!

Kind Regards, John

 

[333rocky333]

Thanks all, its not so much worrying, its that I need to go back with an answer and the reason and cost will be scrutinised.

Really fishing for regulations to justify it, which you have all helped with, thanks.
Im by no means unqualified, yet when so called more experienced staff at work are confused, then that gets me flustered.
in fact I trust your opinions more.

It all came about as another company said they are getting readings in excess of 999ohms between the MET and the pipework due to no Main water earth bond, however, if ive understood you correct, this will still be the case, except where some pipes pick up an earth via other means, even after they weigh out for us to install a Bond as per regulations.
Though I think we agree, that them unearthed pipes are not a risk, unless due to extreme unforeseen cicumstances.

My initial plan was to run 50 metres of 16mm from the Main earth bar mounted next to the head, to that short protruding extraneous waterpipe, BEFORE the first elbow, which i think we all agreed on.
followed by a report to get the installers back to rectify ther install error and fit soldered elbows as per there specification.
The existing supplementary bonds across hot and cold, installed by others I think I will leave in place, though I have no idea why.
Does that sound ok

 

[EFLImpudence]

It all came about as another company said they are getting readings in excess of 999ohms between the MET and the pipework due to no Main water earth bond,

Are you sure it wasn't 999 Mega ohms?
If it is, that will show that the pipe in question is totally isolated and should not be bonded.
If it is 'just' 999 ohms, that will probably be due to some of the plastic joints even if the main bonding is correct. They still don't need any more bonding.
If there is no main bonding then, obviously that should be rectified and the 999 will likely reduce.
However, they are not measuring at the right place.

My initial plan was to run 50 metres of 16mm from the Main earth bar mounted next to the head, to that short protruding extraneous waterpipe, BEFORE the first elbow, which i think we all agreed on.

Yes, although only 10mm² is required.

I think I will leave in place, though I have no idea why.

 

[333rocky333]

I thought they said ohms, i will check later, though before it gets to us, theres often typos (via indian helpdesk), i never tested any of it, just there to see if there was a main bond fitted.

I chose 16mm, its a 3ph 200 amp head, fuse size unknown first thought was 25mm but was told its 4 x 50mm cables to the distboard am i wrong

Apoligies but, Back to the elbows though, if theres barely 20 mm of plastic each one, would not the water bridge them gaps, so if the protruding section of extraneous pipe had some contact to earth, that would transfer through to the metal sections via the water, giving them some reading when they probe tested, therefore as you say once that extraneous bit is bonded any readings 999 ohms or Meg ohms should reduce drastically

when you say measuring at the wrong place, what did you mean by that, I think that they just go probing all metal points, mistakingly thinking they should all be earthed, rather than any official test like, Main bond continuity, or whatever the tests called.

 

[Risteard]

Are you sure it wasn't 999 Mega ohms?

Or even perhaps Megohms...

 

[JohnW2]

Or even perhaps Megohms...

Slow

Kind Regards, John

 

[EFLImpudence]

Rocky - sorry, didn't realise the size.

 

[EFLImpudence]

Or even perhaps Megohms...

If you omit the 'a'.

 

[EFLImpudence]

Google 'Meg'.

 

[333rocky333]

Rocky - sorry, didn't realise the size.

thats ok, I never said

 

[bernardgreen]

Double insulated is deemed safer than earthed exposed-conductive-parts.

Sorry but that is wrong...... Double insulated is only safer when the appliance cannot get water into it. Double insulated hedge trimmers where the motor brushes can be seen through the air vents are double insulated while dry, the insulation is by passed by any moisture that gets into the device.

The reason for not exporting the "earth" from the house to the metal case of an appliance in the garden is that the applaince is outside the equipotential zone and the person using it has direct connection to the Ground.

Put it another way. Would you connect the case of an appliance to the Neutral of the incoming supply. ?

What you say about the two scenarios is a little misleading, in that you fail to mention that an RCD, if present, will hopefully limit the effects of the shock in your first scenario.

If there was an RCD and the sink was earthed then the current through the body is more likely to be high enough to trip the RCD, severe but short duration shock, very painfull but not necessarily fatal

If there was an RCD and the sink was NOT earthed then the current through the body is NOT likely to be high enough to trip the RCD, mild but prolonged duration painfull and due to prolonged duration it could be more injurious and possibly fatal.

The short high current shock from a defibrillator stuns the heart and stops it.... the heart then re-starts by itself when the current ceases. It doe very little damage to the muscles of the heart. A weaker current for a prolonged period can cause irreversbile damage to the heart muscles ( and other muscles and organs ). Death may not be immediate.

 

[JohnW2]

Put it another way. Would you connect the case of an appliance to the Neutral of the incoming supply. ?

That is surely precisely what one does do with a Class I appliance supplied by a TN-C-S supply. So, IF EFLI has such a supply, then it is not only something that he "would" do, but probably something that he does do every day!

f there was an RCD and the sink was earthed then the current through the body is more likely to be high enough to trip the RCD ... If there was an RCD and the sink was NOT earthed then the current through the body is NOT likely to be high enough to trip the RCD...

Why on earth do you say that? You were postulating a (non-earthed) sink which became live by virtue of contact with a live conductor or faulty appliance sitting on it, with someone touching both it and something earthed. That is surely no different from the situation in which one touches a 'live' appliance and an earthed sink. In both cases, the current through the body could be very high, determined by the impedances of the 'contacts', the body and the fault 'loop'.

The short high current shock from a defibrillator stuns the heart and stops it.... the heart then re-starts by itself when the current ceases.

... or doesn't re-start (due to damage to the heart, oxygen deprivation or whatever) , as the case might be (and, of course, we're talking about a DC shock).

A weaker current for a prolonged period can cause irreversbile damage to the heart muscles ( and other muscles and organs ). Death may not be immediate.

It is extremely unusual for a survivable electric shock to be associated with significant damage to heart muscle. As you imply, by the time one gets to that stage, there is so much damage to other tissues and organs that the event is unlikely to be survivable.

Kind Regards, John

 

[bernardgreen]

(and, of course, we're talking about a DC shock).

Most defibs are bi-phasic
https://cardiophile.org/difference-between-a-monophasic-and-biphasic-defibrillator/

(due to damage to the heart, oxygen deprivation or whatever

which seldom occurs from a 230 volt shock that lasts for less than a second

The un-earthed sink cannot take much current from a hand when the other hand is in contact with 230 volts. The only paths to Ground from the sink are ( non conductive ? ) water ( plastic pipes or un-bonded copper ), capacitive coupling and possibly dampness in the wall. Almost always the impedance of the path to ground is high enough to prevent 30 mA flowing.

 

[JohnW2]

Most defibs are bi-phasic

I know, but you're quibbling. Apart from anything else, for decades we used monophasic ones (just the discharge of a capacitor). The biphasic ones now used deliver just one pulse in each direction. Call that 1 cycle of AC if you wish, but the important thing is that if one subjects the heart to AC of more than one cycle (i.e. more than just one pulse in each direction), that is more likely to cause than to terminate (potentially fatal) rhythm disturbances.

The un-earthed sink cannot take much current from a hand when the other hand is in contact with 230 volts. The only paths to Ground from the sink are ( non conductive ? ) water ( plastic pipes or un-bonded copper ), capacitive coupling and possibly dampness in the wall. Almost always the impedance of the path to ground is high enough to prevent 30 mA flowing.

That's obviously true. In fact, with an (essentially) unearthed sink, the current through the body will be zero, or near zero - no more than enough to perhaps produce a 'tingle' (which would cause the victim to 'withdraw'), and certainly not enough to cause any damage to the heart (or anything else) such as you suggested.

The other way around, with an unearthed sink which has 'become live', touched by someone who is also in good contact with something earthed, the current through their body could be very high, certainly usually enough to cause a 30 mA RCD to operate.

Kind Regards, John

 

[EFLImpudence]

Sorry but that is wrong......

By DI I meant Class 2; not sure if you think that the same.

It must be deemed safer than earthed metal case which may become live or provide a low impedance path to earth.

If not, why do they do it?

Double insulated is only safer when the appliance cannot get water into it.

Well, so is every other electrical appliance/accessory/anything.

The reason for not exporting the "earth" from the house to the metal case of an appliance in the garden is that the applaince is outside the equipotential zone and the person using it has direct connection to the Ground.

Is that the reason?
Why do they make Class 2 appliances for indoors?

Put it another way. Would you connect the case of an appliance to the Neutral of the incoming supply. ?

See above.

If there was an RCD and the sink was earthed then the current through the body is more likely to be high enough to trip the RCD, severe but short duration shock, very painfull but not necessarily fatal

If it wasn't earthed then it would present no hazard.

If there was an RCD and the sink was NOT earthed then the current through the body is NOT likely to be high enough to trip the RCD, mild but prolonged duration painfull and due to prolonged duration it could be more injurious and possibly fatal.

Best not earth it, then.

I don't follow the reasoning.