export pme or tt for garage.

[Fezzie]

I am running a distribution circuit for a pre-fabricated steel garage and

workshop. Its going to be run in armoured.

my mate, who i sub for (on occasion) always exports an earth (even on farms),

this is residential but i'm more of a 2core and tt man.

is there a compelling argument for one or t'other.

 

[Spark123]

Either way is acceptable however the thought of having a big lump of metal attached to the neutral conductor outdoors imo is a bad idea.
If you do choose to go the TN-CS method then the supply earthing conductor needs to be sized large enough to be a main protective bonding conductor or run separate main protective bonding conductors from the MET.

 

[ericmark]

In wiring matters Electrical installations outdoors: a supply to a detached outbuilding this is referred to and it is by no means plain.

I would look at how close the house is to garage and what else surrounds it.

In general where surrounded by premises with PME then to export PME is likely best idea as there is a risk of items plugged into either the garage or house being used near to the other and the two earths therefore want to be the same.

However for a single house in the country the garage may have quite a voltage ramp as one leaves the area local to the house so in that case one would want a local earth.

There is also a consideration with the garage metalwork forming a good earth even without any rods or imported earth and often one needs at least 6mm SWA to have a large enough earth to be able to export the PME to the garage safely without the problem that under fault conditions at the house or supply the earth cable could be overloaded.

So sorry not a simple answer.