I’m a bit confused about part p

[dingbat]

There is a lot wrong with over-bonding.

By bonding otherwise isolated parts you create paths to earth that did not exist previously. You cause parts that would otherwise have no involvement in the electrical system to become live in the event of a fault. More seriously, you increase the opportunity for the unskilled/unwary to have direct contact with a live part whilst in contact with an extraneous conductive part... which would not have been an extraneous conductive part had you not bonded it. (EEBAD[o/S] will not disconnect a lethal quarter-ampere flowing through you.)

Always think before you bond.

 

[ColJack]

by your definition then, if I had plastic pipes entering my house carrying the gas and water, and no central heating or shower to potentially connect live to the copper pipes, then I don't need to bond them at all since they are not earthed into the ground an are not likely to become live in the event of a fault?



if there is a shower, and a boiler then the copper pipes need bonding since they can become live in the event of a fault..

cross bonding at taps is ok since it is possible that with plastic seals and the like that there is no electrically conductive connection between hot and cold pipes..

cross bonding at every set of taps is not nescesarily needed providing that the resistances back to the nearst point of cross bonding do not create the posibility of a PD between taps in the event of a fault..

 

[Pensdown]

I think you're getting confused between the reasons for bonding incoming metallic services, cross bonding in a bathroom and maintaining an earth connection across trunking/conduit joints.

Three different types of earthing/bonding for three totally different reasons.

 

[dingbat]

by your definition then, if I had plastic pipes entering my house carrying the gas and water, and no central heating or shower to potentially connect live to the copper pipes, then I don't need to bond them at all since they are not earthed into the ground an are not likely to become live in the event of a fault?

Correct

if there is a shower, and a boiler then the copper pipes need bonding since they can become live in the event of a fault..

No. Extraneous conductive parts (by definition) cannot become live in the event of a fault on the electrical system. IF they are bonded, however, as part of EEBAD, they will rise to the same potential (near enough) as exposed conductive parts that have become live in the event of a fault, so that no dangerous touch voltage appears between them in the time it takes the fault to clear.

If, by definition, conductive parts are not extraneous and you bond them you have done nothing useful and you have also created an additional path to earth, which could become dangerous in the event of direct contact.

Read Guidance Note 8.

 

[dx90]

I've done some continuity tests with the meters. The mains gas supply and the mains waters supply has both been bonded back to the CU. I took out all the old rapped around earth wire as it was not doing anything. The bathroom is directly above the CU and mains water supply.
I did the tests from the mains water supply bonding tab to all hot and cold water pipes and the radiator pies in the bathroom and got continuity on all. The electrician has passed it.

Is having just the gas and water supply bonding ok in this instance?

Thanks

 

[RF Lighting]

it depends what the resistance reading was when you carried out the continuity test between the pipes.

 

[dx90]

The beep was continuous on the multi meter, a dead short. Do you want me to take reading instead?

 

[RF Lighting]

You need to carry out cross bonding if the resistance between pipework etc. exceeds 0.05 ohms.

Dont forget to test to the hot pipe, coldpipe, lights, shower, radiator, metal waste pipes, heater supply etc

 

[ColJack]

you misunderstood me there dingbat..

if I have plastic incomming services, and a boiler or shower, then in the event of a fault inside these there is a posibility of the pipes then becoming live if they are not bonded since there would be no path to earth..

If the nearest cross bond between hot and cold pipes is 20 meters away ( along the pipe including drops etc.. ) then could the PD between the taps not rise to dangerous levels in the event of a fault due to the resistance of the pipes?

if for example a wire touches a hot pipe and eventually melts through at the hot tap end at the exact moment you have one hand on hot and cold taps filling the kitchen sink?

 

[dingbat]

if I have plastic incomming services, and a boiler or shower, then in the event of a fault inside these there is a posibility of the pipes then becoming live if they are not bonded since there would be no path to earth..

...if for example a wire touches a hot pipe and eventually melts through at the hot tap end at the exact moment you have one hand on hot and cold taps filling the kitchen sink?

You should not be designing an installation where this could ever happen. (Mutual detrimental influence). If you do, you should maybe consider this pipe as not an extraneous conductive part but an exposed conductive part and earth it as you would a CPC.

Protection from DIRECT contact is different from protection from INDIRECT contact. EXPOSED conductive parts are different from EXTRANEOUS conductive parts and are dealt with by EEBAD. EARTHING is different from BONDING.
When you fully understand the definitions and the techniques available you will be able to treat each case on its own merit. But, I repeat, it is not correct (and it is potentially dangerous) to bond everything conductive regardless of its actual status.

 

[Softus]

if for example a wire touches a hot pipe and eventually melts through at the hot tap end at the exact moment you have one hand on hot and cold taps filling the kitchen sink?

This is unlikely to happen, because the DHW inside a copper pipe would not be expected to be more than 60°C, and the melting point of PVC is at least 80°C.
__________________

Protection from DIRECT contact is different from protection from INDIRECT contact. EXPOSED conductive parts are different from EXTRANEOUS conductive parts and are dealt with by EEBAD. EARTHING is different from BONDING.
When you fully understand the definitions and the techniques available you will be able to treat each case on its own merit. But, I repeat, it is not correct (and it is potentially dangerous) to bond everything conductive regardless of its actual status.

dingbat, this paragraph (of yours) makes me realise that I don't understand the definitions and techniques. Do you have any recommended reading material that would help me overcome this shortfall?

 

[dingbat]

...I don't understand the definitions and techniques. Do you have any recommended reading material that would help me overcome this shortfall?

Part 2 of BS 7671, followed by GN5 and GN8.

 

[Softus]

Many thanks.

 

[ColJack]

that was a theoretical occurance to illustrate my thinking...

I was tought at college to cross bond between taps at sinks and baths, and to bond everything metal in the bathroom to the nearest available electrical earth...

is this not the way to do it..

( BTW I don't DO domestic, I'm an industrial / commercial sparky.. although I have subied on a large flat conversion.. )

 

[dingbat]

I was tought at college to cross bond between taps at sinks and baths, and to bond everything metal in the bathroom to the nearest available electrical earth...

Aaaaarrrrgghh!!!!!!!

is this not the way to do it..

Guess!