OSG, bonding plastic pipes etc etc

[magnoliafan89]

Hi all

Having a thumb through the OSG and on section 4.5 Main protective bonding of plastic services, it says there is no need to bond an incoming service of the service pipe is plastic....thats kind of a given....my struggle lies on the next page;
"Where there is a plastic incoming service and a metal installation within the premises, main bonding is recommended unless it has been confirmed that anu metallic pipework within the building is not introducing Earth potential"

Is there a way of determining if there could be an earth potential?
I may be asking a really simple question and be mortified by stupidity but at this moment in time im lost. If a house is supplied with plastic services incoming but then throughot the dwelling it is metal pipes...whats the score with bonding?

Cheers in advance

 

[Richard Burns]

The plastic incoming service cannot introduce an earth potential but the metallic pipes within an installation may go underground or perhaps across to another building in an unsealed duct and the contact of the pipes with earth may permit them to introduce an earth potential, even a copper pipe firmly clamped to a very damp wall without a DPC might be able to do it.
Testing the resistance of the metal pipework to earth and ensuring it is above 22kohms, just as you would for a metal incoming service pipe. would test this (usually with an IR tester).

 

[Deleted member 9648]

In practice this test can be difficult to interpret due to parallel paths. Disconnect the means of earthing from the MET before testing or you may get a reading through water heaters/pumps/boilers etc. Even then a parallel path to the water service may exist through the gas/oil service to the boiler mechanically linked to water pipes. The gas/oil service will be separately bonded and will not affect the need or otherwise to bond the water service.
In practice I find a reading above 22K means I can ignore the water service, but a reading below does not necessarily confirm the water requires bonding. In that case a certain amount of visual verification is required and the application of professional judgement.

 

[Pete999]

In practice this test can be difficult to interpret due to parallel paths. Disconnect the means of earthing from the MET before testing or you may get a reading through water heaters/pumps/boilers etc. Even then a parallel path to the water service may exist through the gas/oil service to the boiler mechanically linked to water pipes. The gas/oil service will be separately bonded and will not affect the need or otherwise to bond the water service.
In practice I find a reading above 22K means I can ignore the water service, but a reading below does not necessarily confirm the water requires bonding. In that case a certain amount of visual verification is required and the application of professional judgement.

Just bond the pipe at the plastic/copper transition point.

 

[Midwest]

OP, I've asked a similar question a while back, can't find the thread now. As been said about testing to see if the pipework is extraneous. If you have a copy of GN8, it goes into a bit of detail in 6.1, with some example formulae & calculations.

 

[Rpa07]

The boiler manifold, having gas and water input with all feed pipes going their ways, will give connection to the Boiler circuit CPC as well which has given rise to the 18th edition dropping bonding on plastic water incoming services.

 

[Midwest]

That has somewhat confused me (the example boiler cpc thing). Size of bonding is selected to size of earthing conductor, to enable it to carry fault current in certain circumstances, i.e. larger csa than typical final circuit cpc. Therefore can't see how that's changed from the 17th to 18th?

 

[Richard Burns]

I too would like to have some clarification on post #6, background, references and reasoning for compliance.

 

[Pete999]

I watched a JW video on main bonding, now I'm the last person to say he is wrong knowing his track record, but despite my earlier post where I said bond it anyway, a sweeping statement you say, well JW made another statement plastic incomers with copper internal pipe work does not need bonding, no testing mentioned, so unless there is a definitive statement to "not bond" I'll stick to my guns and bond it anyway.

 

[magnoliafan89]

Thanks for all the replies guys

 

[suffolkspark]

The thing i think of if say in a loft or under the floor... A rat munches on a cable and it lays on a hot pipe... Perfectly reasonable scenario... Well if we all stop bonding the water at point of entry as seems to be the case, and more so with the 18th coming... Whats to protect us from the pipework becoming live in this situation

 

[telectrix]

but the hot pipe is bonded by way of the boiler , and hence the gas pipe,

 

[suffolkspark]

Yea guess thats true

 

[magnoliafan89]

So what youre saying is that because there is a cpc by means of the boiler supply that this can act as a bond?

 

[Pete999]

So what youre saying is that because there is a cpc by means of the boiler supply that this can act as a bond?

Think what Tel is saying is "the boiler will be bonded via the main Gas bond" Tel will rip me a new one if I have it wrong I'm sure.

 

[telectrix]

agree pete, if the gas is bonded, then the metal water pipes are also bonded, albeit not in accordance with 7671.

 

[Midwest]

I believe the draft 18th was suggesting amending reg 411.3.1.2 with 'Metallic pipes entering the building having an insulating section at their point of entry need not be connected to the protective equipotential bonding'. Whereas currently its sort of mentioned in reg 544.1.2 that the bonding should be made after said insert.

But that still doesn't change the fact that extraneous conductive parts shall be connected to the main earth, as required by 411.3.1.2.

The IET, wouldn't be winning prices with the Plain English Society

 

[Ian1981]

Despite this new regulation coming into play when the 18th edition comes into effect about plastic inserts , my company just had their annual NICEIC inspection.
A question I wanted asking by my QS to the NICEIC inspector was does this now clarify the fact that gas pipes for new builds do not require protective bonding as the pipe underground is in yellow plastic rising to a meter box on the side of the property.
From there a copper pipe exits from the consumer side of the gas meter through the wall in a plastic sleeve,then off into the house to wherever it needs to go.
The answer was it’s metallic in the house so requires bonding.
How if the supply is in plastic does it still require bonding?
So despite this new regulation coming it seems there’s still much confusion to what is and what isn’t an extraneous conductive part.
I’ve even tested it as a matter of interest in one of the plots I did.
15Mohms was the reading I got but I’m told it still requires bonding pfttt!!

 

[Midwest]

I was having a butchers round some new show homes recently. On the CU was a printed label, that said words to the effect, water service plastic, internals plastic, therefore water not bonded. Don't know why they chose to share that with everyone?

 

[Rpa07]

I think that this subject reference to the 18th omission of bonding where incomers are plastic rises from the fact that in the 18th all circuits are required to have RCD protection, Lighting included.
I can imagine that with so many homes going up that new house builders are required of these things and are able to omit these things (bonding) whereas the rest of us who deal in the real world who daily come across old installs in domestic that have no bonding or earthing and obviously are not RCD protected.
I found one on Thursday that requires massive updating to bring it up to even a safe state so I’m having to quote to TT an install after making my call to the DNO today.
We’ve all got stories.
As for @Richard Burns I heard this at the ELEX Elecsa talk to trade seminar referencing the 18th changes expected post the consultation.
There is a cinema event coming up at 40 cinemas over the country in The next month.
@camerabloke can bring his popcorn!