Outbuilding supply TNC-S to TT - Oil heating system

[robo83]

Hi,

I have looked at a job where the house is TN-C-S and it is heated via oil from a tank in the outbuilding. I can see the pipe feeding the house from the outbuilding oil take is metal and runs underground.

The customer wants an electrical supply in the outbuilding where the tank is, he wants a changeover switch so that he can also run a generator when loss of power.

Am i understanding this correctly?

Convert the outbuilding to TT, running a 10mm SWA 2 core from an isolator in the house to the outbuilding Consumer unit. Then from the outbuilding MET bond the oil tank 10mm, run 16mm to an earth rod.

Then within the house which is TN-C-S bond the incoming oil pipe with 10mm?

 

[Pete999]

Hi,

I have looked at a job where the house is TN-C-S and it is heated via oil from a tank in the outbuilding. I can see the pipe feeding the house from the outbuilding oil take is metal and runs underground.

The customer wants an electrical supply in the outbuilding where the tank is, he wants a changeover switch so that he can also run a generator when loss of power.

Am i understanding this correctly?

Convert the outbuilding to TT, running a 10mm SWA 2 core from an isolator in the house to the outbuilding Consumer unit. Then from the outbuilding MET bond the oil tank 10mm, run 16mm to an earth rod.

Then within the house which is TN-C-S bond the incoming oil pipe with 10mm?

 

[Midwest]

From Table 54.1, I see that it gives guidance om minimum csa for buried earthing conductors.
As regards, the re-emerging metallic pipework, my (NICEIC) snags & solutions, earthing & bonding booklet suggest (as you are), bonding of the oil line at both ends.
I suppose consideration could be given (with a larger 3c swa) to extend the PME, but then other factors would need to be considered.
I'm sure the more learned will clarify.

 

[Nigel]

If the oil tank building is metal then I would donas you suggest. However if it is non-metallic then you can run an earth from the main house without a problem. You would be ‘extending’ the EBZ as opposed to ‘exporting’ it.

You would need to do your calculations to prove that your cable sizes are correct but I would certainly bond both the tank and the pipework within the outbuilding.

 

[robo83]

Thanks Pete 99, I will read once off site with a hot cuppa.

The outbuilding is brick.

I was considering a 3core SWA and EBZ but I how would this fall with the backup generator. That will needs its own TT system, so I was thinking converting the out building to TT, utilising this for both the outbuilding and generator?

Thanks for the quick replies.

 

[Nigel]

You will need to check the Regs but I would probably utilise the existing TN-C-S earth provided by the DNO and then install an earth electrode as a ‘back-up’ it the neutral were to be disconnected by the DNO.

Trouble is you would then need to change the whole installation and design to the TT earthing arrangement.

 

[Midwest]

Trouble is you would then need to change the whole installation and design to the TT earthing arrangement.

Why you need to do that? The IET are only considering to add an earth rod to all TN supplies.

 

[Devonchris]

I would be more concerned about the oil tank within the building first. This is a fire risk and could dictate what type of installation, if any, is required.

Is there a risk of vapour? What ventilation is available? Is zoning required ? Should any installation be intrinsically safe.

I would check this one with Building Control first. It could be an expensive install.

 

[Nigel]

Why you need to do that? The IET are only considering to add an earth rod to all TN supplies.

That is not in yet and if you are putting an earth electrode in surely you are expecting it to be used?

So where is your fault protection when the earth electrode is used as the sole earth?

 

[Midwest]

That is not in yet and if you are putting an earth electrode in surely you are expecting it to be used?

So where is your fault protection when the earth electrode is used as the sole earth?

Sorry I was just getting confused, with you saying use the DNO's earth (PME), add an earth rod at other end, but having to turn the whole installation to TT?