Main bonding flow and return to oil boiler

[BLBelfast]

Hi this is pickling my head and any advice is appreciated. I have a TNCS system. I have an external oil boiler fed from the house in a detached garage. The main water in the house and the flow and return from the boiler are all bonded back to the house MET from within 600mm of where they enter the house.

Do they need bonded where they enter the garage aswell from the garage CU which will be a TT system due to extraneous conductive parts being present...IE water supply from house? The garage is around 3m from the house

 

[Leesparkykent]

Yes they will need bonding in the garage as well from the garage board that's TT.

 

[davesparks]

In my opinion it would be better to take a suitable bonding conductor to the outbuilding and have the outbuilding connected to the TNCS earth. This is assuming the heating flow and return are continuous metal pipes and so bonding them in the outbuilding will be effectively connecting it to the TNCS earth anyway.

I'm also wondering whether these pipes, if metal, could be used as the bonding conductor?

 

[Sylvia Namusisi]

In my opinion it would be better to take a suitable bonding conductor to the outbuilding and have the outbuilding connected to the TNCS earth. This is assuming the heating flow and return are continuous metal pipes and so bonding them in the outbuilding will be effectively connecting it to the TNCS earth anyway.

I'm also wondering whether these pipes, if metal, could be used as the bonding conductor?

I thought pipes are not allowed to be used for bonding conductors according to the regulations in the 17th edition.

 

[telectrix]

I thought pipes are not allowed to be used for bonding conductors according to the regulations in the 17th edition.

not sure. they're not allowed as earthing conductors. agree with dave, pipes will connect the outbuilding to the TNCS anyway, so add a decent rod as well. pre-empt the 18th.

 

[davesparks]

I thought pipes are not allowed to be used for bonding conductors according to the regulations in the 17th edition.

Which regulation number is that?

 

[davesparks]

not sure. they're not allowed as earthing conductors.

Which regulation is that then?

 

[Ian1981]

Oil Pipes and gas pipes can't be used as protective conductors regulation 543.2.3 I think it is, not sure about bonding conductors without looking it up

 

[telectrix]

Which regulation is that then?

sorry dave, i meant as a means of earthing.

 

[davesparks]

Oil Pipes and gas pipes can't be used as protective conductors regulation 543.2.3 I think it is, not sure about bonding conductors without looking it up

Yes they are the exception, any other pipe can be used as a protective conductor.

 

[davesparks]

sorry dave, i meant as a means of earthing.

No worries, though I am inclined to ask the same question again. Metal pipes can be used as a means of earthing if they are suitable (permission of the owner, size, reliability etc etc)

 

[telectrix]

No worries, though I am inclined to ask the same question again. Metal pipes can be used as a means of earthing if they are suitable (permission of the owner, size, reliability etc etc)

agreed. it's public service pipes that can't be used as they are liable to be replaced in plastic.

 

[BLBelfast]

Thanks for the advice. Embarrassing as this is as its a recent purchase i just realised its a TNS system. I dont know why I presumed it was TNCS :-(

My thinking now is simply leave the 10mm main bonding from the house MET to the flow and return entering the house. Export the TNS earth to garage, Likely a 6mm 3 core swa and bond from the garage CU to the pipes entering the garage again in 6mm. The oil line wont be touched. Does this sound reasonable? Do i even need to bond entering the garage as they are already connected to the TNS in the house which is a few feet away. They are also strung across on a bit of timber so they dont touch the ground.

It might seem daft to ask confirmation but I dont normally deal with domestic and its just its my own house or I wouldn't be doing it.

Any advice appreciated thanks

 

[davesparks]

The oil pipe would normally need to have a main bond too.

As it stands I don't see that the flow and return pipes would need additional bonding if one earthing system is in use, Especially considering that they are installed above ground

 

[Dave OCD]

And if the flow and return have their own main bond back to the MET as stated [Which is unusual] I'd be inclined to just cross bond from them to the oil feed near the boiler in 10mm.

 

[davesparks]

And if the flow and return have their own main bond back to the MET as stated [Which is unusual] I'd be inclined to just cross bond from them to the oil feed near the boiler in 10mm.

Not unusual in this situation where they are strictly speaking extraneous parts entering the installation.

I think to take the regulations absolutely literally they should be bonded as extraneous parts entering the outbuilding too, but since those very pipes can probably be used as a bonding conductor anyway it's fair to accept them as they they are.

 

[Dave OCD]

Yes they'll be at least 22mm pipes possible even bigger so between the two of them they'll have a lower resistance and a lot more csa than 10mm earth cable.

 

[BLBelfast]

Yeah the 10mm main bonding to the flow and return is definitely there as i wired it myself.

Thanks for taking the time and giving your advice. And i will bond to the incoming oil line in 10mm from the garage cu then though it also doesnt come into contact with the ground so not sure what the theory of this is. It's literally a 2m pipe from tank to boiler.

 

[davesparks]

Yeah the 10mm main bonding to the flow and return is definitely there as i wired it myself.

Thanks for taking the time and giving your advice. And i will bond to the incoming oil line in 10mm from the garage cu then though it also doesnt come into contact with the ground so not sure what the theory of this is. It's literally a 2m pipe from tank to boiler.

The most popular theory at the moment is to test it to establish whether or not is extraneous to establish whether or not main bonding is required.
Personally I interpret ten regulations slightly differently, but I'm in the minority with that opinion and am probably wrong.

 

[Wilko]

No worries, though I am inclined to ask the same question again. Metal pipes can be used as a means of earthing if they are suitable (permission of the owner, size, reliability etc etc)

Hi - just reading through 542.2.6 and it seems a gas or flammable liquid pipe should not be used as an earth electrode, but I may have misunderstood (?).

 

[davesparks]

Hi - just reading through 542.2.6 and it seems a gas or flammable liquid pipe should not be used as an earth electrode, but I may have misunderstood (?).

You're right, no gas or oil pipe can be used as a protective conductor or earth electrode.