The old 'to TT or not to TT a shed' debate

[The Dentist]

Hi Folks

I have read loads of threads here about outbuildings and earthing arrangements, and when to export and when to TT, but I still cant quite get my head around exactly which scenario fits which situation best?

Surely a 'fix-all' would be to export the earth AND a rod at the outbuilding, with bonding to any exposed metal shed structure? Surely this way all earths are at equal potential?

Please can someone give a definitive and in depth answer to this long-debated question, just to settle my curiosity, I just cant sleep at night anylonger

Thanks

 

[flameport]

For TN systems (i.e. most of them):

1. For outbuildings which have no extraneous conductive parts, then install the circuit as normal, using whatever size cable is suitable.

2. If there are extraneous conductive parts, these would need to be bonded to the main installation earth. This usually means a 10mm wire from the main building to the shed/garage or whatever.
An easy method of acheiving this in most normal situations is to use 10mm 3 core SWA.

TT would be used if it is the ONLY possible option, such as where the main building is TT.
In the majority of installations, it is not the only option, and therefore would not be used.

 

[holmslaw]

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