Plastic water incomer-

[Dave 85]

Hi lads.
Doin a new build log holiday home. Water main is plastic into the cabin then goes Into a bit of surface copper round the tank then back to plastic for all hidden pipe work. Do I need a main bond?

 

[sparc]

No, it would be entirely pointless bonding this pipe.

Of course, you should still try to bond anything else relevant - including structure steel, etc

 

[Strima]

Put 100mm of copper into the incoming water supply and bond to that. I have heard an LABC inspector want that before... :lol:

 

[sedgy34]

Hi lads.
Doin a new build log holiday home. Water main is plastic into the cabin then goes Into a bit of surface copper round the tank then back to plastic for all hidden pipe work. Do I need a main bond?

main bond above main tap on the surface copper you mentioned

 

[mdelect]

Had a similar conversation with the NICEIC. The outcome was that if the plastic pipe rises from the ground by at least a meter then it is highly unlikely to be a extraneous conductive part, so will not need bonding. You can always test it by measuring the insulation resistance from the MET to the nearest piece of copper to confirm. If it is above 250 Mega Ohms its not a extraneous conductive part.

 

[brman]

Had a similar conversation with the NICEIC. The outcome was that if the plastic pipe rises from the ground by at least a meter then it is highly unlikely to be a extraneous conductive part, so will not need bonding. You can always test it by measuring the insulation resistance from the MET to the nearest piece of copper to confirm. If it is above 250 Mega Ohms its not a extraneous conductive part.

22k ohms I think. A lot of the circuits I have tested don't have 250M ohms between live and earth

 

[Smudge]

personally, depending how far the bit of copper is from the main stop cock, if it were very close to it, i would earth it. Then a big tick can go on the test sheet. But that is purely down to my opinion rather than facts or regs about it.

 

[IQ Electrical]

How could that piece of copper introduce a potential into the installation?
As brman states, if an insulation resistance test between MET and the pipe in question reads greater than 22k Ohms then the part is not defined as an extraneous-conductive part and should not be bonded.

The 'if in doubt, bond it' brigade do not understand the principles behind bonding (they often refer to it as earthing) and the possible dangers of distributed fault voltages on non-extraneous conductive parts that have been bonded unnecessarily.

 

[Smudge]

^^^^^^^^it can't. But on the SELECT test sheets we use at work, there is tick boxes for bonded at main water, gas and steel, so if it has a bit of copper reasonably close to where its meant to be bonded, i would bond it. It is a lot easier explaining to an inspector why it is there, rather than why it is not. It isn't doing any harm being there and if you were to get someone a#sy inspecting, it could make it a un needed headache. But as i said above, that is purely my opinion, and not based on regs/fact etc.

question that will obviously annoy you (really not intended!!) why the reference to bonding and earthing? is the point of both not to get to the same potential as earth? please be gentle...i'm only wee...

 

[Silly Sausage]

main bond above main tap on the surface copper you mentioned

Eh?

In another thread you say that you wouldn't bond an incoming lead water pipe, yet here, you'd bond a length of copper on an incoming plastic water pipe...

Confused!!! :confused5: :crazy:

 

[IQ Electrical]

^^^^^^^^it can't. But on the SELECT test sheets we use at work, there is tick boxes for bonded at main water, gas and steel, so if it has a bit of copper reasonably close to where its meant to be bonded, i would bond it. It is a lot easier explaining to an inspector why it is there, rather than why it is not. It isn't doing any harm being there and if you were to get someone a#sy inspecting, it could make it a un needed headache. But as i said above, that is purely my opinion, and not based on regs/fact etc.

question that will obviously annoy you (really not intended!!) why the reference to bonding and earthing? is the point of both not to get to the same potential as earth? please be gentle...i'm only wee...

Hi Smudge
If there is no extraneous-conductive part to bond then you don't bond it and enter 'N/A' in the appropriate box, knowing that you've complied with BS7671:2008 (2011) and can explain that to anyone who might not understand the principles of bonding.

The idea of earthing is to connect exposed-conductive parts of an installation to the main earth terminal so that in the event of a fault, sufficient fault current flows to operate whatever protective device is in use.

The idea of protective bonding is to further reduce the touch voltage between exposed-conductive parts and extraneous-conductive parts in the event of a fault or an open circuit PEN on a PME supply.

Bonding items that do not meet the definition of an extraneous-conductive part means that those items (at one stage in the 15th edition this included handrails, window frames, ceiling grids etc.) are subjected to fault voltages until the protective device operates.

The 22k Ohm test is no big secret and any assessor worth his salt should commend you on having the knowledge to decide whether to bond or not to bond rather than just the 'if in doubt bond it' mindset.

 

[Smudge]

Hi Smudge
If there is no extraneous-conductive part to bond then you don't bond it and enter 'N/A' in the appropriate box, knowing that you've complied with BS7671:2008 (2011) and can explain that to anyone who might not understand the principles of bonding.

The idea of earthing is to connect exposed-conductive parts of an installation to the main earth terminal so that in the event of a fault, sufficient fault current flows to operate whatever protective device is in use.

The idea of protective bonding is to further reduce the touch voltage between exposed-conductive parts and extraneous-conductive parts in the event of a fault or an open circuit PEN on a PME supply.

Bonding items that do not meet the definition of an extraneous-conductive part means that those items (at one stage in the 15th edition this included handrails, window frames, ceiling grids etc.) are subjected to fault voltages until the protective device operates.

The 22k Ohm test is no big secret and any assessor worth his salt should commend you on having the knowledge to decide whether to bond or not to bond rather than just the 'if in doubt bond it' mindset.

ok, i shall change my rule...'if in doubt...ask IQelectrical'... ;-)

thanks

 

[brman]

ok, i shall change my rule...'if in doubt...ask IQelectrical'... ;-)

thanks

You make a good point about being picked up on it buy an inspector. Or possibly more likely some spark in the future who likes his bonding and wants to moan you haven't done your job properly!

I guess it would do harm to spell it out in the "comments on existing installation" box. eg. "Plastic water incomer and internal pipework measured at >22kohm" or something like that?

 

[kingeri]

At the end of the day if everything's put in to comply with BS7671 and is properly documented as such....then bring on the inspectors I say.

 

[Amp David]

The nightmare kitchen job i posted about the other week was just as this. 6 meters of plastic, a short length of copper so they could fit a stop tap, then back to plastic all the wall upstairs to the airing cupboard.

Had previously been bonded, so took a reading to check and got 2.25 Mohms, so this time it was left without.

Will be mentioning this one during this years site visit and see what Mr Elecsa reckons.