Main Bonding, plastic pipes.

[Damocles]

Now heres one I havn't seen exactly.

House has plastic water main running to copper stop tap in kitchen, outside tap and copper pipe to sink. Then plastic main disappears off into house to become metal after the plastic water tank.

Where to put the main water supply bonding?

 

[Lectrician]

where you usually would

 

[ban-all-sheds]

OSG, he say if incoming gas and water services are of plastic, main bonding conections are to be made to metal installation pipes only.

But why? If the incoming water main is plastic, then the water pipes are no more "earthy" than the door handles or metal shelf brackets in the house.

How is a piece of metal, not liable to introduce any potential 'cos it's insulated from earth, an extraneous conductive part?

 

[biblio]

In the case of copper or steel water (filled) pipes though, wouldn't the water itself act as a good earth source – as long as the water is not drained out or air-locked.

 

[ban-all-sheds]

No - tap water in a 15mm pipe has a resistance of 115 k ohms per metre, and 20mm is 65k per m.

If the incoming pipe is plastic, then it's probably plastic for some distance underground too.

It would be really interesting, in Damocles' case, to bang in an earth rod or two, and see what the resistance is from the metal part of the pipes in the house to actual earth. I'd bet it's enormous...

I sometimes think people go "ooh - plumbing - better earth it" without giving any thought to what's going on electrically.

 

[Damocles]

Hard to say what the impedance is, but the eart to the copper gas pipe which is connected to the metal boiler where the water ends up, probably brings it down a bit.

So the man he say 'connect bonding to metal installation pipes only'.

The question is which set, the small set at the sink, or the big set starting from the cold water tank?

Just connecting an earth at the incoming supply point is a bit of a cop out. It conveniently ignores that breaks in the cinductive parts of the pipework are quite likely.

Now of course, shouldn't the metal drain pipe from the sink also be earthed..... and what if it only nips through the wall and discharges into a drain?

 

[ban-all-sheds]

Hard to say what the impedance is, but the eart to the copper gas pipe which is connected to the metal boiler where the water ends up, probably brings it down a bit.

Now that's true. In my defence, you didn't mention the gas, but in my plea-bargain I will admit that it was an oversight not to think of it. But what if the incoming gas pipe was plastic, what would you do then?

Now of course, shouldn't the metal drain pipe from the sink also be earthed..... and what if it only nips through the wall and discharges into a drain?

You have to go back to basics, and consider the definition of an extraneous-conductive-part. A length of copper pipe in a house, which is not buried in the ground at one end is no more an e-c-p than a brass curtain track. If you don't earth it, then it has no involvement whatsoever with the electrical installation in the house, and it is no more likely to become live than the curtain track is.

Complications:

Immersion heaters. CH boilers. Electric showers. Washing machines. Dishwashers.

 

[kai]

I actually ran a 10.0.sq.mm. (TEN-mm) earthing bond cable between the immersion and my main earthing terminal in the fusebox for safety's sake. (Eight metres long run).

 

[Damocles]

On which grounds Kai?

yeah, I don't mean coffee. I mean, what was the safety reasoning for doing it?

So BAS, you would argue that if a plastic gas pipe comes into the house, then I do not need to bond the metal part which starts just inside the wall.
Nor do I need to bond the cold water supply which turns into copper just inside the wall, then runs all over the house? Admittedly a bit large for curtain tracks, but otherwise essentially the same?

 

[ban-all-sheds]

That would be my starting point. If it comes in on plastic, then it does not meet the definition of an extraneous-conductive-part.

But there are appliance fault conditions to consider - if any of the metal pipes are connected to the cases of Class I appliances, then you should bond.

D/W, W/M etc will be connected via rubber hoses, so they're OK. With incoming services done in plastic, I'd be sorely tempted to put plastic runs into the pipes supplying the hot water tank, shower (or pump), boiler etc, and be done with the need for any bonding.

 

[Damocles]

Ok, to be clear, what you are saying is that bonding of incoming supplies is not always necessary to satisfy either safety considerations, or regulations? So we are getting to the point where we can forget about all that nonsense of running thick green and yellow cables all round the house connecting the incoming supplies?

 

[Damocles]

And to get back to my original point, the sink and associated metal pipework from cold tap to stopcock and outside tap does not need earth bonding? (because supply entering building is plastic, and further run to plastic cistern is also plastic, remainder of house plumbing copper)

Nor does the remainder of the plumbing system?

Earth tag to gas pipe can be removed because supply pipe to meter is plastic, or must be retained because a short piece of copper comes through wall from outside meter in box?

(assuming cross bonding in bathroom)

 

[securespark]

As I understood it from the IEE (after another long philosophical conversation with Paul Cook), I was given to understand that if the incoming water main was plastic, I should carry out the main bonding where it changed to copper.

 

[ban-all-sheds]

Ok, to be clear, what you are saying is that bonding of incoming supplies is not always necessary to satisfy either safety considerations, or regulations? So we are getting to the point where we can forget about all that nonsense of running thick green and yellow cables all round the house connecting the incoming supplies?

FFS don't introduce the regs into this - they often do not intersect with reality. Take a deep breath and repeat after me:

I will not look for logic, consistency or reason in the wiring regulations. That way lies madness.
I will not look for logic, consistency or reason in the wiring regulations. That way lies madness.
I will not look for logic, consistency or reason in the wiring regulations. That way lies madness.
I will not look for logic, consistency or reason in the wiring regulations. That way lies madness.
I will not look for logic, consistency or reason in the wiring regulations. That way lies madness.
I will not look for logic, consistency or reason in the wiring regulations. That way lies madness.
I will not look for logic, consistency or reason in the wiring regulations. That way lies madness.
I will not look for logic, consistency or reason in the wiring regulations. That way lies madness.
I will not look for logic, consistency or reason in the wiring regulations. That way lies madness.
I will not look for logic, consistency or reason in the wiring regulations. That way lies madness.
I will not look for logic, consistency or reason in the wiring regulations. That way lies madness.
I will not look for logic, consistency or reason in the wiring regulations. That way lies madness.


But seriously, if the regs are based on the definition of an extraneous-conductive-part, then IMHO they should not require you to carry out main bonding on services which are plastic where they enter the house.

Earth tag to gas pipe can be removed because supply pipe to meter is plastic, or must be retained because a short piece of copper comes through wall from outside meter in box?

But this is where it starts to get less cut and dried. You have a piece of metal coming from outside the house to inside. Is this piece of pipe in general contact with the mass of the earth? No. Can you be sure that dampness in or on the wall, or in the cavity, or in the meter box won't give you a connection to earth? Probably not.

 

[ban-all-sheds]

As I understood it from the IEE (after another long philosophical conversation with Paul Cook), I was given to understand that if the incoming water main was plastic, I should carry out the main bonding where it changed to copper.

For what purpose?

Another quote from Mr Cook, he of the "don't bond plastic pipes" paper (but from his book, not that paper), with my emphasis:

An extraneous-conductive-part is a conductive part liable to introduce a potential, generally earth potential, and not forming part of the electrical installation. The essence of an extraneous-conductive-part is that it is likely to introduce earth potential into a building. Examples include metal service pipes, gas, water, fuel oil, metal waste pipes and building metalwork in general contact with the earth. The essential requirement is that extraneous-conductive-parts be exposed, conductive, and in general contact with the mass of the earth.

So I wonder why he told you what he did. Was it recent?