I am currently running a new circuit to an outbuilding in SWA. Incoming supply to property is TNCS and I was going to TT the outbuilding. The property has oil fired heating and the feed pipe inside is bonded at the boiler to the TNCS system, I was going to bond the oil tank/outlet pipe in the outbuilding to my TT system but I am now beginiing to think I should just leave it connected at the house end, any thoughts?
Earthing and bonding question.
- Thread starter LearningSpark
- Start date
Sponsored Links
If using the TN-C-S earth, the extraneous-conductive-parts in the outbuilding must be bonded to the supply MET with a minimum 10mm² copper conductor or the equivalent.
This is usually the deciding factor on whether to use TT or not at the outbuilding.
This is usually the deciding factor on whether to use TT or not at the outbuilding.
Thanks for the reply EFLI, yes I am planning on TT ing it at the outbuilding but not sure whether I should bond the tank in the outbuilding as in theory it is already bonded to the MET in the main property.
You can't do both.
If you TT it then nothing should be connected to the house MET.
Does the oil pipe run to the house as well?
Is there a metal water pipe from the house to the outbuilding?
If you TT it then nothing should be connected to the house MET.
Does the oil pipe run to the house as well?
Is there a metal water pipe from the house to the outbuilding?
Sponsored Links
Thats where I was getting confused.
Oil pipe runs from out building to house and is bonded as it enters the boiler in the property with 10mm² to MET.
No water pipe between house and outbuilding, no other extraneous conductive parts in the outbuilding.
Oil pipe runs from out building to house and is bonded as it enters the boiler in the property with 10mm² to MET.
No water pipe between house and outbuilding, no other extraneous conductive parts in the outbuilding.
Then you will have to use the supply earth through the armour - and third core if there is one.
What csa is the swa?
Bond the oil pipe in the outbuilding with 10mm² and the pipe itself can and will be used as the bonding conductor to the supply MET.
What csa is the swa?
Bond the oil pipe in the outbuilding with 10mm² and the pipe itself can and will be used as the bonding conductor to the supply MET.
It does seem that the OP has a bit of a problem. If the metal oil pipe is (as it must be, if it's an extraneous-c-p to the property) bonded to the TN-C-S earth in the house, then, if it also travels into the outbuilding, it would certainly be 'liable to introduce a potential' into that outbuilding, and therefore would needed to be bonded to whatever earthing system trhe outbuilding had.
I haven't thought this through too deeply, but is this perhaps an (unusual) case in which TTing an outbuilding might cause more problems than it solves?
Kind Regards, John
Test the resistance of the oil pipe outbuilding to house to ensure it is satisfactory.
I don't think it is a problem. There is no point TTing it.
Did you see my latest reply yet?
SWA is 6mm² and 3 core so yes I can use armour and 3rd core as you suggest.
Thanks for your help EFLI, that makes perfect sense now. I was beginning to doubt myself earlier hence my question as I have never come across anything like this before.
Thanks for your help EFLI, that makes perfect sense now. I was beginning to doubt myself earlier hence my question as I have never come across anything like this before.
I will test oil pipe tomorrow when I return to connect up just to ensure it is connected as I assume it is.
Ah, just noticed that.
It should of course be bonded to the MET from where it enters the premises.
It won't make any difference but that is the regulation.
If the pipe to the outbuilding travels underground, I suppose the outbuilding will already be effectively "TTd", whether one likes/wants it or not!
About the pipe resistance? If so, yes. I would have thought that (in the absence of any 'insulating sections'!) it would be very unlikley that the resistance of the pipe would be greater than that of any conductor which might be contemplated.
Kind Regards, John
No, sorry the one before - about not TTing it.
Pipe goes under ground and the first place I can see it appear is behind the floor mounted boiler so in theory I guess that is where it enters the property.
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
