Water pipe bonding

[bernardgreen]

You were the one who mentioned a hot tap earthed by the immersion or boiler and the cold not

Yes I did, that is "normal" for the vast majority of houses, so if the cold tap was accidently made live by a fault there would be a difference in potential between the taps with a good low impedance "earth" ( neutral ) on the hot tap. A bond between taps would allow earth leakage currents to flow and trip the RCD as soon as the fault developed which would be before anyone discovered it by getting a shock.

Alternatively a fault in an immersion heater that was not earthed could lift the hot tap to a potential somewhere between Neutral and Live. Touching that hot tap and something earthed would produce a shock.

 

[PBC_1966]

You are, of course, entirely free to earth all the pipes in your house and then hope the more likely danger never happens - especially to another member of your family.

They are already earthed throughout - The NEC still requires the bonding of internal metallic water systems to ground/supply neutral.

The risk of being involved in a accident where the seat belt is necesary is very small.

And in more minor accidents the belt can actually result in severe damage to the body which without it would not have occurred.

Sometimes when extracting people from a crashed vehicle the seat belt delays the extraction.

And on occasions has resulted in somebody being unable to escape from the vehicle at all before being drowned, burned to death, or crushed by some other consequence of the accident.

Well "may be" simply isn't good enough.

It's good enough for the metal casing of a class I appliance to be earthed these days. But speaking of things in general (leave aside specific things like heating elements on a stove which we know tend to go leaky over time), just how much more common is a fault to the casing of such apparatus than a fault to exposed pipework, radiators, sink tops, etc?

 

[EFLImpudence]

Yes I did, that is "normal" for the vast majority of houses,

No, it isn't.
How does the cold water get to the heating appliance to which the hot is connected and so earthed?

Anyway:

so if the cold tap was accidently made live by a fault there would be a difference in potential between the taps with a good low impedance "earth" ( neutral ) on the hot tap.

Do you mean by way of an exposed-c-p or your mythical wandering pipe-attacking live conductors.

But - Yes, until the OPD operates.

A bond between taps would allow earth leakage currents to flow and trip the RCD as soon as the fault developed which would be before anyone discovered it by getting a shock.

Now you've introduced RCDs which allow omission of supplementary bonding altogether.
But - It would, but as I keep trying to explain, that scenario is far, far less likely than a person receiving a shock from frayed flex or faulty appliance.
It depends against which types of shock you wish to protect. You can't guard against all so we cover the most likely which aren't yours.

Alternatively a fault in an immersion heater that was not earthed could lift the hot tap to a potential somewhere between Neutral and Live. Touching that hot tap and something earthed would produce a shock.

So, don't earth what you don't need to.
But - Yes, but now you are getting into the realms of your one-off incident which negates ALL the safety measures we try to achieve.

 

[EFLImpudence]

They are already earthed throughout - The NEC still requires the bonding of internal metallic water systems to ground/supply neutral.

Do they mean earthing?

And in more minor accidents the belt can actually result in severe damage to the body which without it would not have occurred.
And on occasions has resulted in somebody being unable to escape from the vehicle at all before being drowned, burned to death, or crushed by some other consequence of the accident.

If that is your thinking and reasoning then you don't understand probability so there is little point trying to explain further.

It's good enough for the metal casing of a class I appliance to be earthed these days.

It's not 'good enough'; it's a necessary safety measure.
It would be better if it were not needed - double insulated washing machines etc.

But speaking of things in general (leave aside specific things like heating elements on a stove which we know tend to go leaky over time), just how much more common is a fault to the casing of such apparatus than a fault to exposed pipework, radiators, sink tops, etc?

I'm not sure of the purpose nor reasoning of that question after your arguments nor do I have figures but -

I would say infinitely more common; hence the requirements (over here).

 

[ban-all-sheds]

... if the cold tap was accidently made live by a fault ...

Is the cold tap likely to be made live by a fault? Yes or no?

Is the cold tap inclined to be made live by a fault? Yes or no?

Do cold taps tend to be made live by faults? Yes or no?

Is the cold tap disposed to be made live by a fault? Yes or no?

Is the cold tap apt to be made live by a fault? Yes or no?

Is the cold tap predisposed to be made live by a fault? Yes or no?

Is the cold tap prone to being made live by faults? Yes or no?

Is the cold tap given to being made live by faults? Yes or no?

YES OR NO, BERNARD.

Stop with all this b******s about what "might happen", and answer the questions relevant to whether the tap is or is not an extraneous-conductive-part

 

[PBC_1966]

Do they mean earthing?

250.104 Bonding of Piping Systems and Exposed Structural Steel.

(A) Metal Water Piping. The metal water piping system shall be bonded as required in (A)(1), (A)(2), or (A)(3) of this section. {.....}

(1) General. Metal water piping system(s) installed in or attached to a building or structure shall be bonded to the service equipment enclosure, the grounded conductor at the service, the grounding electrode conductor where of sufficient size, or to the one or more grounding electrodes used. {.....}

It's not 'good enough'; it's a necessary safety measure.

Yes, I know it's a requirement. I meant that if it's "good enough" to have earthed metalwork on, say, a electric wall heater which could provide a path to earth for shock, then why not an earthed tap or hot-water radiator?

 

[bernardgreen]

Stop with all this b******s about what "might happen", and answer the questions relevant to whether the tap is or is not an extraneous-conductive-part

The tap is not an extraneous-conductive-part most of the time if the plumber and electricans did all the right things.

The tap is an extraneous-conductive-part when a fault or spilt water creates a path between Live wires and the copper pipe to the un-bonded tap.

 

[bernardgreen]

Bonding is not straight forward, the basic set of rules do not cover all eventualities.

For what it is worth

The water supply to my cottage surfaces in my outside toilet room ( I have an indoor one as well ) and this pipe work is bonded to the MET. There is also a metal water pipe going from the toilet room that takes water to my neighbour's property ( a shop so very little water useage but still metered ). This pipe would appear to be an extraneous-conductive-part and should therefor be bonded. It is not bonded and the instruction from the DNO when they installed my new supply , was that it must NOT be bonded. The reason it must not be bonded is that the shop is a TT supply with a ground rod. ( the shop and cottage were originally one property with the electric supply from the shop ). If at a later date the shop supply is up graded to a PME system it would not be from the same street cable ( my supply comes from the cable in a side street ) and thus bonding in the toilet room would be linking the Neutral in two different supply cables to two different areas of the village.

There is a 2 metre length of plastic pipe in the run to the shop to galvanically separate shop and cottage plumbing. The advice was that the metal pipe on the shop side of that isolation gap should be boxed in and labelled as being connected to a ground rod. It was pointed out that my washing machine is close enough to shop side plumbing for a person to touch both at the same time. The DNO informally mentioned that during a network fault this close proximity could present a shock hazard. A similar close proximity had to be considered when installing power cables in my second bedroom half of which is above the shop and its electrical system. The simple and acceptable solution was to restrict my wiring to the area of the bed room that was not above the shop.

 

[ban-all-sheds]

The tap is not an extraneous-conductive-part most of the time if the plumber and electricans did all the right things.

The tap is an extraneous-conductive-part when a fault or spilt water creates a path between Live wires and the copper pipe to the un-bonded tap.

No no no no no.

Is the cold tap likely to be made live by such an event? Likely, Bernard, LIKELY. Yes or no?

Is the cold tap inclined to be made live by such an event? Inclined , Bernard, INCLINED. Yes or no?

Do cold taps tend to be made live by such events? Tend, Bernard, TEND. Yes or no?

Is the cold tap disposed to be made live by such an event? Disposed, Bernard, DISPOSED. Yes or no?

Is the cold tap apt to be made live by such an event? Apt, Bernard, APT. Yes or no?

Is the cold tap predisposed to be made live by such an event? Predisposed, Bernard, PREDISPOSED. Yes or no?

Is the cold tap prone to being made live by such events? Prone, Bernard, PRONE. Yes or no?

Is the cold tap given to being made live by such events? Given, Bernard, GIVEN. Yes or no?​

(Apologies to those who don't like the use of large letters and different colours, but it seems as though Bernard is having problems seeing these words)

 

[bernardgreen]

I can see them, I am ignoring them.

To get a serious electric shock the person has to be touching two different items and there has to be a voltage difference between those two items. So ( but do NOT try this ) it is possible to hold a live wire and not get a shock PROVIDED that NO other part of the body is touching anything that is in any way conductive. Birds can perch on 11,000 volt cables.

BAS is concerned that someone who is holdning an appliance that has a live metal case will also touch a water tap. It is true that if the water tap has no connection to any potential such as Ground, Earth or Neutral then the person is most un-likely to get a severe shock. BAS is correct that if this is the scenario then connecting ( bonding ) the tap to anything that is earthed will increase the severity of the shock.

So there BAS, the question is :- Is it likely that some one holding a live metal object would also touch a tap ? ( I won't repeat the question using the alternatives for likely ).

If they did and the tap was total isolated from any other potential they might not feel anything. If the tap has water in the pipe then it is not totally isolated and the person will feel a tingle. If the pipe to the tap runs close to other pipes or cables then capacitive coupling comes into the equation and the tingle might be quite strong and could in some people be hazardous to health 10 milliamps across the chest for several seconds can damage to vital organs. But 10 milliamps will not trip any safety devices ( RCDs used in domestic installations require a nominal 30 milliamps to trip, few will trip below 15 milliamps ).

If the tap was bonded to an earth potential then the intensity of the shock would be much higher but the current would almost certainly be enough to trip the RCD thus limiting the duration of the shock to less than 1/10 of a second. In the majority of cases a short duration shock does far less harm to a person than a lower current shock of lower duration.

A severe short duration shock will stun the heart and stop it, then as soon as the shock ceases the heart will self start. This is how defibrillators work. A longer duration shock will cause damage (*) to the heart muscle and nerves and as a result the heart may not be able to restart when the shock ceases.

(*) eletrochemical damage and while the heart is stunned it is not pumping blood thus the body's vital organs, in particular the heart muscles and brain, are deprived of oxygen.

 

[EFLImpudence]

250.104 Bonding of Piping Systems and Exposed Structural Steel.

Does the term 'bonding' have a specific meaning as it does here or does it just mean connected in the US?

Yes, I know it's a requirement. I meant that if it's "good enough" to have earthed metalwork on, say, a electric wall heater which could provide a path to earth for shock,

It's not 'good enough'; it is a necessary evil to achieve disconnection.
It would be better if nothing required earthing.

then why not an earthed tap or hot-water radiator?

Because it is not necessary for the above reason as it does not contain electrical parts but introduces a hazard which was not there before.
(Obviously, an electric radiator does and will be DI or require earthing)

 

[ban-all-sheds]

I can see them, I am ignoring them.

You may not.

And this discussion is getting no further, and I am not going to bother to read a single thing you write on the topic until you stop ignoring them, and tell us whether these bits of metal you are so concerned about are, or are not, extraneous-conductive parts.

 

[EFLImpudence]

From the Colonies:
I don't know, obviously, how authoritative the site is, but they do seem confused.

They are talking about the introduction of plastic piping.

"At what point is the water piping system not considered to be metal and thus not required to be bonded? The answer to this question is not as clear as the one for the grounding electrode. An assessment must be made regarding the amount of metal in the system and whether this metal pipe and any metal support for the metal piping may become energized. It is also important to determine if a difference of potential could exist between the metal piping in the water system and an electrical circuit located in proximity to the water pipe.

Could the electrical system energize the metal piping in the predominantly nonmetallic water piping system? If the answer is no, or unlikely, then the metal piping would not be required to be bonded. If the answer is yes, then the metal water piping must be bonded in accordance with 250.104(A)."

http://www.ecmag.com/section/systems/bonding-water-piping

 

[333rocky333]

sorry to dig up this post but was there ever an agreement.

I was asked about a 5 year old water instalation and whether I felt it needs bonding, there is 150 mm of galv pipe out the concrete floor then a brass stopcock.

From the stopcock is a further 150mm of copper then a PLASTIC push fit elbow followed by a further 2 metres of copper followed by another PLASTIC push fit coupler.

It then distributes round the premises all in copper but with all PLASTIC elbows etc.
The system includes a electic water heater too.

I myself, feel that after the first PLASTIC elbow that its no longer an Extraneus conductive part.

However 544.1.2 states, bond near point of entry and goes on to say "Where there is an insulating section or insert at that point, the connection shall be made to the consumers hard metal pipework"

I further read, that IN the Guidance book that I dont possess , you do a test and if below a certain figure, then a non Extraneous part should be classed as if it was an Extraneous part.

I am a bit confused now, I was mainly with bans aproach that its ok not to be bonded, yet across the net, it seems conflicting even on this site.
Even if It was bonded after the first elbow, its only gonna bond the 2metre length up to the 2nd elbow anyway.
Help apreciated from my learned friends.

 

[EFLImpudence]

The pipe which emerges from the ground will need main bonding.

The stopcock and what happens in the premises, as long as none goes underground again, are irrelevant.
Ignore the bit about insulating sections and consumer side; it is WRONG and you are correct with your doubts.
The only extraneous-conductive-part is the pipe in the ground.

The measurement you mention is an IR test between emerging pipe and MET.
If over 24kΩ it is regarded as NOT extraneous.
To be clear it won't come down to 23999 or 24001. It will be a few ohms or Mega ohms. 24kΩ is just the threshold for 10mA at 240V.