Garage Supply / PME

[besenzig]

Hi

I want to run a supply to the detached garage which is only a couple of meters away from the main building, my question is do I still need to treat this as an outbuilding?

My main supply is PME, i understand that you are not allowed to export the earth from a PME supply to an out building but make the outbuilding a TT. Is this still the case even though its only a couple of meters away?. There are no extraneous conductive parts (ie.water pipes) in the outbuilding.

I'm puzzled as to the best way to do this, any help would be appreciated.

 

[securespark]

"outbuilding":

a building subordinate to but separate from a main building; outhouse.

As I understand it, there is only a need to avoid exporting PME where extraneous conductive parts are not present.

 

[sparkyspike]

Is there any exposed structural steel in the garage? Or any other metalwork which could be extraneous?

If you do need to provide an earth, you can use an earth cable which is the same size as the bonding cable you already have in the main house - 10mm usually. This means you don't need to TT the garage.

You can do this by using 10mm multicore SWA, or by running a seperate 10mm earth cable to the garage.

 

[besenzig]

Is there any exposed structural steel in the garage? Or any other metalwork which could be extraneous?

If you do need to provide an earth, you can use an earth cable which is the same size as the bonding cable you already have in the main house - 10mm usually. This means you don't need to TT the garage.

You can do this by using 10mm multicore SWA, or by running a seperate 10mm earth cable to the garage.

The only exposed structural steel is the garage door, is this classed as extraneous conductive part? The meter tails are 25mm and I think the main earth is 16mm, do not really want to run a 16mmearth to the garage.

 

[sparkyspike]

I doubt your door would be classed as extraneous. It's unlikely to be introducing an earth potential into the garage. So you don't to need to run a seperate earth. Even if you did, you wouldn't run the main earth in, but the main bonding (which connects your water and gas etc to earth), which would be 10mm.

 

[besenzig]

I doubt your door would be classed as extraneous. It's unlikely to be introducing an earth potential into the garage. So you don't to need to run a seperate earth. Even if you did, you wouldn't run the main earth in, but the main bonding (which connects your water and gas etc to earth), which would be 10mm.

Thanks for the prompt reply, I think I will go for the 10mm earth and avoid a TT system in the garage.

Always wondered how people are able to give such prompt replies. Are you at home stuck in front of a Computer. In any case the advice is appreciated.

Thanks

 

[ricicle]

As I understand it, there is only a need to avoid exporting PME where extraneous conductive parts are not present.

You understand wrong Mr S

 

[ColJack]

go on....

never had to wire an outbuilding / shed yet, and the college sort of glossed over it.. please do continue..

 

[RF Lighting]

As I understand it, there is only a need to avoid exporting PME where extraneous conductive parts are not present.

You understand wrong Mr S

I think ricicle is referring to the double negative in Simon's post, which I expect was done in error

 

[Spark123]

As I understand it where there are extraneous conductive parts the bonding has to comply with the requirements of 54.8 (once verified with the DNO), the submain also has to meet this requirement if the bonding is to be taken from a "Building Earth Martialing Terminal". Failing that, a Main protective bond can be taken from the Main Earthing Terminal to the extraneous conductive part.
Resistance back to the MET should also be kept to a minimum - 0.05 to extraneous conductive parts.
An alternative to doing the above is to make the outbuilding TT, the building can have it's own MET and then the extraneous conductive parts only need to be bonded to that in TT sizes.
If there are no extraneous conductive parts then there is no reason not to export TN-CS as no protective bonding is required hence only the bog standard circuit calcs need to be done for CPC sizes.
The only places I am aware of that TN-CS is not allowed is for a caravan, a boat or a petrol station.

 

[RF Lighting]

Farms

 

[Spark123]

I don't think they are actually banned on farms
You certainly need to be a bit more carefull.

 

[sparkyspike]

I think I will go for the 10mm earth and avoid a TT system in the garage.

What will you be attaching the 10mm cable to in the garage? I'm not sure you need it at all. To be sure, you can measure any metalwork you suspect as being extraneous, if you can get hold of an insulation resistance tester set at 250v. Someone will be along in a minute to tell you the minimum resistance required for exposed metalwork, but I think it's something like 22,000 ohms. Can't remember right now.

 

[besenzig]

I think I will go for the 10mm earth and avoid a TT system in the garage.

What will you be attaching the 10mm cable to in the garage? I'm not sure you need it at all. To be sure, you can measure any metalwork you suspect as being extraneous, if you can get hold of an insulation resistance tester set at 250v. Someone will be along in a minute to tell you the minimum resistance required for exposed metalwork, but I think it's something like 22,000 ohms. Can't remember right now.

Your're right no extraneous conductive parts hence nothing to connect to the 10mm earth. Looks like I cam export the PME earth after all.....unless someone knows different.