Exporting PME to garage

[peteelecs]

Please canyou help I am a bit confused about the earthing to a shed if the house is PME can I just run an earth from the MET to the shed or can I only do this if house is TNS.How do i get earth to shed if its PME hope this doesnt sound to confusing any suggestions would be appreciated

 

[pushrod]

cant see the relevance.....the 'added' extraneous conductive part would need bonding even if it was TT....just the method of bonding would be different.

Easier to do with a TT though as quite likely that the distribution cable has been buried and cheaper too.

 

[kung]

A garage will prob have a concrete floor then an issue is that the garage may be damp, have incoming services etc.
In which case you would not export a PME/TN-C-S house earth from the house, you would make the garage a TT install with earth rod

 

[IQ Electrical]

Is this a garage or a shed?
Are there other services in there?
What is the construction of the garage/shed?

The answers to these questions are rather important here.

 

[kung]

It is confusing as the op would suggest a shed made of wood but the heading is Exporting PME to garage

 

[Hawk81]

I know theres no requirements of TT in the brb its what i always do as said its personal pref only although the DNO might have a different view !

The DNO do not actually care if you export a PME to a shed or garage or whatever. All they say is that they prefer you dont.

 

[SimpleSimon]

Why's that I wonder? Couldn't it be run with swa and use an earth from that and TT it at the end?

 

[SimpleSimon]

For the Zillionth trillionth time there are no regulations preventing the TNCS earthing system being used for an outbuilding.If there are extraneous conductive parts in the outbuilding requiring main bonding then you must run that bonding back to the MET,which means a TT is more sense....if there are no parts requiring main bonding then use the TNCS earth as for any other install....or if you prefer waste your time and money providing a totally unecessary separated earth.

It's late and I'm tired. Wirepuller could you explain to me how you mean by saying you can use the TNCS install? Does this mean you. Would use the main MET?
Sorry for being dense.

 

[pushrod]

I think with all of these things you want to do what complies with BS7671 and is the most economical. If you have a tn-c-s earthing arrangement at the main DB you can most economically just export the earth to an outbuilding. However if , for whatever reason, there is main bonding required in the outbuilding, then you will have to run a 10mm cable back to the MET. If the outbuilding is any distance from the main DB then it rapidly becomes more economical to bang in an earth rod (£10ish) to save the long run of the main protective bond (£1.50+/meter).

 

[trebor]

Exactly as i said wirepuller, if it can be bonded safely bond it and use pme, if it doesnt need bonding use pme , it does not matter whether its attached or not bearing in mind that megas of new properties have the tn-c-s service and main bonding in the garage anyway

I would suggest that anyone wanting to beef up on this subject and earthing in general buys a copy of Gudance Notes 8 from the IET.

 

[Deleted member 9648]

It's late and I'm tired. Wirepuller could you explain to me how you mean by saying you can use the TNCS install? Does this mean you. Would use the main MET?
Sorry for being dense.

Yes,as long as there is nothing in the outbuilding requiring main bonding it is acceptable and more economical to use the earthing system from the MET.

 

[Deleted member 9648]

A garage will prob have a concrete floor then an issue is that the garage may be damp, have incoming services etc.
In which case you would not export a PME/TN-C-S house earth from the house, you would make the garage a TT install with earth rod

I presume then that every external light/socket etc which is derived from a TNCS source and is subject to damp you install a separate rod for then?

 

[SimpleSimon]

Yes,as long as there is nothing in the outbuilding requiring main bonding it is acceptable and more economical to use the earthing system from the MET.

I get ya. And if bonding is required best install a separate rod ane MET in the shed and use an earth from swa cable to provide an earth return path to the main MET?

 

[kung]

I presume then that every external light/socket etc which is derived from a TNCS source and is subject to damp you install a separate rod for then?

Good point ! my last post was a copy that i forgot to edit the you and replace with i ! what i am saying is if its a detached garage from the house with a tncs/pme earthing i always tt it as it is easier and cheap and just as safe ! i did also acknowledge the fact that there is no requirements in bs7671 that doesnt permit a pme being used ! as also said its personal pref ONLY

Houses usually (although not always) have insulating floors etc which mean that main bonding can establish a reasonably equipotential zone, so even if the electrical system's earth is at some higher voltage (e.g. PME with a broken CNE) it would be difficult to get a shock while inside the house. Go outside, or in an outbuilding with a damp concrete floor (no damp proof membrane) and voltage differences can rocket!

 

[pushrod]

I get ya. And if bonding is required best install a separate rod ane MET in the shed and use an earth from swa cable to provide an earth return path to the main MET?

If the outbuilding is very close though it may still be more economical and/or convenient to just run your bonding back to the MET

 

[telectrix]

dunno about exporting earths. my missus says if i spend all day on this forum, she will export me and the PC to the garage!