Confusion over earthing arrangements for Garages and sheds

[Tony Way]

Speccing a re-wire in bungalow with separate garage (1m from house) and a new shed/workshop to be 5m from house.

Bungalow on TT rod - no option for TNS orTNCS conversion

Now back in my learning days, I am sure that I was told that any separate building must have its own earthig arrangement ie rod.

I have been told recently that it is fine to export the main bonding via SWA third core and/or sheeth to a separate building. Although not sure that is correct.

Also if I use a separate earth for each building, I should not RCD the distribution circuit as each shed/garage should have CU and RCDs - therefore no discrimination between RCDs in series. But if I don't RCD the distribution circuit only protection for SWA would be MCB. - Is this enough?

Confused of ********** would appreciate any assistance.

Many thanks

 

[davelerave]

don't work in UK but the sub-main will need ADS via 'main rcd' and mcb(tt)

the additional 30ma protection shouldn't be needed for a swa submain-if i'm understanding the uk rules correctly

 

[pennywise]

Had the exact same situation on friday bungalow on a TT with a shed/out building.The NIC basically said no need to put another rod in for the shed you can utilise the houses rod. As for the submain It needs protecting with a 100mA time delay RCD. then you get discrimination between the submain protection and the garage boards 30mA RCD. The shed supply I put in was protected with a 30mA RCBO at the consumer unit in the house as the customer didn't want a garage 2 way unit to save money, It does the power and lighting. The NIC didn't really think it was worth trying to discriminate between the power and lighting as it wasn't an inhabitable room. Every circuit on a TT system has to have RCD protection.

 

[davelerave]

so is that the existing 100mA main rcd that protects the new sub-main? -obviously it must be

sorry i'm not very familiar with tt

(don't want to hijack the post-may help though)

 

[pennywise]

so is that the existing 100mA rcd that protects the new sub-main?

Yep the 100mA RCD protects the submain but is has to be an S type time delay one, so a fault in the garage doesn't take out the submain protection.

 

[Spudnik]

Any circuit on a TT must have RCD protection because of disconnection times.

Therefore there is no need for a rod in the garage or an RCD in the sub board.

 

[davelerave]

Any circuit on a TT must have RCD protection because of disconnection times.

Therefore there is no need for a rod in the garage or an RCD in the sub board.

i thought the 100 mA 'main rcd' was enough for the sub-main here and then additional 30ma's in shed

 

[pennywise]

i thought the 100 mA 'main rcd' was enough for the sub-main here and then additional 30ma's in shed

It would have to be time delayed or you would lose both the garge 30mA and the 100mA RCD in the consumer unit in the house. Far easier putting the submain on the 30mA side of the house consumer unit and use that as the protection for the garage then you don't need to spend out for RCD board in the garage It's just a bit of a nusainace if the garage starts tripping the RCD in the house CU.

 

[davelerave]

ya time delayed upstream-i get it anyway

i would have the garage separate-to avoid the nuisance

 

[Tony Way]

Thanks guys. Much appreciated