Help,main water after a stop cock plastic

[arturas]

Hi there, i have been trying to find an answer everywhere but i couldn't.. so that's my problem, there is a stop cock which is about 300mm from a floor level, and after stop cock is plastic pipe connected which goes straight to boiler. Now the gas is coper and has been earthed within 600mm after stopcock and goes to boiler as well. Now is it enough to do a cross bonding under the boiler on all boiler incoming and outgoing coper pipes?or should i get new 10mm earth cable to boiler and then do cross bonding?should i bond the metal part of the incoming water before stop cock?thank you.

 

[needasparks]

I'm sure someone will come up with a different answer but i had same problem a couple of times, On a job a few years ago the water from the stopcock was plastic upto the downstairs WC and the rest of the house was a mixture of pastic and copper so i run a bond to the first bit of copper it past through which IMO was the first accessable place to bond and marked it on the cert and why and also i crossed all pipework at the boiler and under the sink, I brought it up with my NIC inspector on the next visit and he was fine with it, He did mention that i should have asked for a small piece of copper say 100mm to be installed at the stop just to bond to but was happy on that occasion that i had made an effort to make sure it was done but i do get on with my inspector and i wonder if other ones may have different views.

 

[arturas]

But then in my case the nearest metalic pipe is under the boiler,all house has been done in plastic ,exept a little bits for comnections for rads and under boiler,so should i run lets say 10mm earth from CU to one of coper pipes under the boiler and then cross connect all of them with 6mm?

 

[malcolmsanford]

The best way to check this is with a wander lead attached to the MET of the installation go around and do an IR test on all the pipework that is metal and that your concerned about, if you get results of over 23Kohm then the metalwork is not classed as an extraneous conductive part and does not need bonding.

I would be amazed if your cold water feed to the boiler which is PVC will be able to produce a potential back to your metallic stop cock.

 

[Engineer54]

IF, ...you have a section of copper water pipe entering the building is it always better to bond it. In your case if the gas main bond is anywhere in the same proximity then just extent that bonding cable to that short section of copper water pipe. There shouldn't be any need to cross bond the boiler piping....

 

[IQ Electrical]

Just to clarify, that value is actually 22K Ohm for the extraneous-conductive part test, it comes from 10mA being the 'let-go' threshold but allows a resistance of 1000 Ohms for hand-to-hand contact of the human body.

I've just sent a mail to Professional Electrician magazine concerning this as they had the 22K Ohm figure correctly stated but then went on to say that values below this WOULD NOT need bonding!
They also mentioned disconnecting 'the main earth' for the test and using a test voltage of 5000 Volts.....

 

[malcolmsanford]

The best way to check this is with a wander lead attached to the MET of the installation go around and do an IR test on all the pipework that is metal and that your concerned about, if you get results of over 23Kohm then the metalwork is not classed as an extraneous conductive part and does not need bonding.

I would be amazed if your cold water feed to the boiler which is PVC will be able to produce a potential back to your metallic stop cock.

Just to clarify, that value is actually 22K Ohm for the extraneous-conductive part test, it comes from 10mA being the 'let-go' threshold but allows a resistance of 1000 Ohms for hand-to-hand contact of the human body.

I've just sent a mail to Professional Electrician magazine concerning this as they had the 22K Ohm figure correctly stated but then went on to say that values below this WOULD NOT need bonding!
They also mentioned disconnecting 'the main earth' for the test and using a test voltage of 5000 Volts.....

See what happens when a) fat fingers b) don't re read c) don't know what your talking about ...............

Thanks IQ rightly as you say 22 kohm though at 10mA and the NICEIC that as this wonderful 6667ohms (not to be confused with 1667ohms) for 30mA.

I only put the last part in to show that my error wasn't c) lol

 

[IQ Electrical]

See what happens when a) fat fingers b) don't re read c) don't know what your talking about ...............

Thanks IQ rightly as you say 22 kohm though at 10mA and the NICEIC that as this wonderful 6667ohms (not to be confused with 1667ohms) for 30mA.

I only put the last part in to show that my error wasn't c) lol

Well if you don't know what you're talking about, there's no hope for any of us!

 

[arturas]

So if i'll go with wonder lead to each radiator and do IR tests with main earthing conductor,so i should get less then 0.22 megaohms then i would not need to bond it?what voltage should i use?50, 250, 500 or 1000?it's maximum on my fluke 1653

 

[malcolmsanford]

I would do it 250v

Rcp is the resistance between the conductive part and the MET in ohms

Uo is the nominal voltage to Earth in volts

Ib is the 30mA of the RCD

Ztl is the impedance of the human body in ohms. The value suggested in DD IEC/TS 60479 is 1000 ohms where Uo is 230 V (50 Hz) under dry or wet conditions.
Taking Ib as 30 mA and Ztl as 1000 ohms (as suggested above where the disconnection times in the installation are 0.4 s or less and Uo is 230 V), the limiting value of Rcp is given by:

Rcp > (230/0.03) - 1000
Rcp > 6667ohms

This though is some schemes take on things and in a way it is correct because 30mA is the protection device. I was always taught that you err on the side of caution and use the value 10Ma as this value can often cause defibrillation of the heart and so it would then be

Rcp>(230/0.01) - 1000
Rcp > 22 000ohms

 

[Deleted member 9648]

So if i'll go with wonder lead to each radiator and do IR tests with main earthing conductor,so i should get less then 0.22 megaohms then i would not need to bond it?what voltage should i use?50, 250, 500 or 1000?it's maximum on my fluke 1653

You should get more than 22k if bonding not required....in practice this test can be misleading as you can pick up parallel paths through conductive parts joined to or in contact with the pipework. Also you are not looking for continuity on all your pipework...the only bit you are concerned with for the purpose of main bonding is the first bit of copper after the stopcock....the rest of the system is irrelevant.

 

[arturas]

Allright,so if the rest of the house has been done in plastic pipes should i be worried about rads and sinks?

 

[malcolmsanford]

How many rads are there in the bathroom? doubt it is Rads, you are now going in to supplementary Bonding and then your only concerns in this case is the bathroom, unless the house have other special locations, that are recognized in the Regs.

WP just noted the only place your worried about is the copper at the stopcock and if your really worried the metal work in the bathroom, though I doubt as I said in my earlier post you do have anything to worry about if it is plastic going to the boiler.

 

[Deleted member 9648]

How many rads are there in the bathroom? doubt it is Rads, you are now going in to supplementary Bonding and then your only concerns in this case is the bathroom, unless the house have other special locations, that are recognized in the Regs.

WP just noted the only place your worried about is the copper at the stopcock and if your really worried the metal work in the bathroom, though I doubt as I said in my earlier post you do have anything to worry about if it is plastic going to the boiler.

Assumed the query was regarding main bonding Malc....as you stated anything else is supplementary.

 

[telectrix]

which raise a point. suppose that the installation had wet underfloor heating, piped in copper. could this, being buried in a concrete floor, introduce an earth potential to the radiators?