earthing

[Unfinished]

how about this scenario.

Extended CH system - and to get around a particularly tricky section used plastic pipes - then back to copper. Does the new copper extension need bonding?


MOD

moved as posted in wrong forum

 

[mapj1]

If the radiators or attached extended pipework enter a room with a bath or shower yes. Otherwise, not particularly, although it is unlikely to do any harm.
regards M.

 

[ban-all-sheds]

How long are the runs of plastic?

 

[Unfinished]

How long are the runs of plastic?

2m long only. Just enough to allow me to feed it round some awkward bends.

 

[ban-all-sheds]

2m is long enough to effectively isolate what's beyond it, stopping it from being an extraneous-conductive-part, so even if it goes on to supply a bathroom there is no need for supplementary equipotential bonding.

 

[Damocles]

I think strictly there is Bas. If the piece going through the bathroom wall is metal then it has the ability to introduce a voltage into the bathroom. From the point of view of the bathroom rather than the house any such metal pipe going through the bathroom walls would still be an extraneous conductive part.

 

[Big_Spark]

BAS...I hate to disagree with you, but the pipework MUST be supplementary bonded as the water within the pipes can carry a current, but it's resistance is such that this current could be dangerous, hence the need to Earth.

It is only when the entire CH system is in plastic that you can, in some instances, get away without supp bonding.

 

[ban-all-sheds]

any such metal pipe going through the bathroom walls would still be an extraneous conductive part.

How does passing through a wall make a pipe an e-c-p?

the water within the pipes can carry a current

<5mA.

 

[breezer]

sorry to say this but you can not g'tee it will carry lesss than 5mA, so if its earthed its safer

 

[ban-all-sheds]

2m of water?

 

[Damocles]

Extraneous means outside? well ok, I think it was a made-up word, but the question must be whether the connection is extraneous to the bathroom, not whether it is extraneous to the house. If I can ignore a metal pipe running into the bathroom then surely I can ignore one running into the house. Which I can't.

If it is safe to assume that all metalwork within the house has been 'neutralised' by the main bonding process, then what is the point of bathroom bonding at all?

But I agree with you about the plastic. Water is an insulator. Remember that folks. IEE research says a 15mm pipe full of water typically has resitance 20-100 k ohm per metre. Depending on impurities.

 

[ban-all-sheds]

Extraneous means outside? well ok, I think it was a made-up word,

The dictionary definition of extraneous is of external origin, foreign to or no belonging to.

The definition of an extraneous-conductive-part in the wiring regs is

‘Extraneous-conductive-part. A conductive part liable to introduce a potential, generally earth potential, and not forming part of the electrical installation.’

but the question must be whether the connection is extraneous to the bathroom, not whether it is extraneous to the house.

No - the question is can it introduce a potential.

If I can ignore a metal pipe running into the bathroom then surely I can ignore one running into the house. Which I can't.

But we're talking here about a metal pipe which at some point is attached to a plastic pipe, and so is electrically insulated from the general mass of the earth.

If it is safe to assume that all metalwork within the house has been 'neutralised' by the main bonding process, then what is the point of bathroom bonding at all?

It's precisely because it is not safe to regard all the pipes as having been "neutralised that we have supplementary equipotential bonding.

Supplementary because it supplements the main bonding, and equipotential because its purpose is to ensure that all the extraneous-conductive-parts in the bathroom are at the same potential. What you don't want is poor connections somewhere resulting in a PD between the chrome plated shaver socket faceplate which has just become live and the towel rail, because if you then complete the circuit, current will flow through you, and current flowing through the human body is a Bad Thing™. So everything is connected together, and to the cpc of all circuits supplying equipment in the bathroom.

However, the safest environment is one which is earth free. With no possibility of being connected to earth, you could grab hold of a live wire in absolute safety.

But I agree with you about the plastic. Water is an insulator. Remember that folks.

I do remember that, and if you do also I'm puzzled at your insistence on bonding in this situation..

IEE research says a 15mm pipe full of water typically has resitance 20-100 k ohm per metre. Depending on impurities.

So 40 - 200kohm for a 2m run, i.e. at 230V the possibility of a 1.15 - 5.75mA current, marginally less considering the resistance of the human body as well. (Apologies, BTW, should have written "<6mA" above...)