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Supply to Outbuilding with Extraneous Pipework

statter
Hello

Situation is an outbuilding (1)  housing gas meter and longish length of exposed steel gas pipe (not plastic covered).

Power is used for internal lighting and external lights and socket for internal and external use and is being supplied via a 16A MCB from another outbuilding (2) which has a TT supply with 30mA RCD.  The exported TT earth is not connected in outbuilding 1.


The TT supply for outbuilding 2 comes via overhead L+N conductors from a house which has a TNC-S supply.  The arrangements in outbuilding 2 all look and test fine.


The gas pipe on the customer side of the meter goes underground from outbuilding 1 to this house and is steel throughout. 


Gas pipework is bonded to the BMET in outbuilding 1. There is also a 10mm2 G/Y earth cable from the BMET in outbuilding 1 to the MET at the source in the house. There is separate bonding of the gas pipe to the house MET where it enters the house.

So the outbuilding 1 supply effectively is TNC-S but the earthing is odd to say the least as it is separated from the supply.

The power requirements are low so 10mm2 should be quite adequate and the circuits have 30mA RCD overall.

This all feels quite unconventional but I cant see that it breaches any regulation?  There is a diagram by the intake showing the arrangement.

Long term the plan is to tidy this up which will not be simple but meanwhile what am I missing?


Peter
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  • 0
    Whilst this may appear slightly odd, it sounds OK. The gas pipe and 10mm provide a positive TNC-S Earth (with a reasonable local connection to the ground I expect from the pipe) and the fact this is a different route from the L&N is not a particular problem. You say building 2 is TT, I presume it has an Earth electrode which is satisfactory? As there are no exposed conductive parts connected to the building 1 Earth, it sounds safe enough, and both buildings have 30 mA RCD protection which is basically suitable as both additional protection (building 1) and Earth and additional protection (building 2). There is nothing here which contravenes the regulations directly but as you say is a little unusual. I think I would prefer building 2 to be connected to the TNC-S Earth as well as the electrode so that an extension from building 1 is not connected to a different Earthing system, but that is all. It is all as safe as you can make it with the gas pipe present.
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  • 0
    Whilst this may appear slightly odd, it sounds OK. The gas pipe and 10mm provide a positive TNC-S Earth (with a reasonable local connection to the ground I expect from the pipe) and the fact this is a different route from the L&N is not a particular problem. You say building 2 is TT, I presume it has an Earth electrode which is satisfactory? As there are no exposed conductive parts connected to the building 1 Earth, it sounds safe enough, and both buildings have 30 mA RCD protection which is basically suitable as both additional protection (building 1) and Earth and additional protection (building 2). There is nothing here which contravenes the regulations directly but as you say is a little unusual. I think I would prefer building 2 to be connected to the TNC-S Earth as well as the electrode so that an extension from building 1 is not connected to a different Earthing system, but that is all. It is all as safe as you can make it with the gas pipe present.
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