Detached garage

[diditrain]

A colleague has asked me if I would carry out the electrical installation for the detached garage that he has just had built.
The supply in his house is TN-C-S and his gas and water services are correctly bonded.
The garage is constructed out of steel stanchions buried in the ground with blockwork in-between, a metallic roof and then rendered on the outside.
He has already buried a 6mm² csa xlpe in-between the house and garage.
He is planning on having a radiator in there supplied from the house using copper pipework buried underground.
My concern is the two different potentials in the garage from the steel stanchions and the copper pipework which is already bonded back at the house.
I am thinking that there should be an additional 10mm² csa MEB ran in from the house to the garage, linking the steel stanchions and the radiator pipework where it enters the garage.

Does this sound ok?

 

[ian.settle1]

A colleague has asked me if I would carry out the electrical installation for the detached garage that he has just had built.
The supply in his house is TN-C-S and his gas and water services are correctly bonded.
The garage is constructed out of steel stanchions buried in the ground with blockwork in-between, a metallic roof and then rendered on the outside.
He has already buried a 6mm² csa xlpe in-between the house and garage.
He is planning on having a radiator in there supplied from the house using copper pipework buried underground.
My concern is the two different potentials in the garage from the steel stanchions and the copper pipework which is already bonded back at the house.
I am thinking that there should be an additional 10mm² csa MEB ran in from the house to the garage, linking the steel stanchions and the radiator pipework where it enters the garage.

Does this sound ok?

New one on me never heard off a roof being rendered before:rolleyes4:

Sounds a really bad idea taking 2 pipes to the garage to heat it, how is he going to insulate them as they will lose most off their heat by the time they get to the garage. Suggest that if he wants to heat the garage to lokk at putting in a couple of electric heaters

 

[diditrain]

Sorry, just meant that the walls had been rendered.
He is a heating engineer so i am not concerned with heat loss on his pipes etc. Just concerned with the electrical side

 

[telectrix]

you may need to bond the steelwork to the pipes. make a EMT in the garage.. a 10mm back to the MET is not needed as your copper pipes are bonded back to the MET anyway.a rod added at the garage might be advantageous. ( i'm not 100% on this, and so stand to be corrected by E54 or someone. )

 

[yellowvanman]

you may need to bond the steelwork to the pipes. make a EMT in the garage.. a 10mm back to the MET is not needed as your copper pipes are bonded back to the MET anyway.a rod added at the garage might be advantageous. ( i'm not 100% on this, and so stand to be corrected by E54 or someone. )

In theory you can use copper pipes as a bonding conductor, if you bond them to the steelwork then that acts as a rod anyway! Although you may want to test the Ze of the metalwork to make sure.

 

[decolad69]

New one on me never heard off a roof being rendered before:rolleyes4:

Sounds a really bad idea taking 2 pipes to the garage to heat it, how is he going to insulate them as they will lose most off their heat by the time they get to the garage. Suggest that if he wants to heat the garage to lokk at putting in a couple of electric heaters

Sorry, I agree with you, what a mad idea! The worms will love it :jester:

 

[itselectric]

Personally I would bond all metal parts as they enter the garage. Being a plumber, your mate will probably run his heating pipes in plastic anyway. If you equipotential bond in the garage then there will be no potential difference.

 

[Guitarist]

10mm bonding between main and garage cu, then bond this to the steelwork and pipework in 10mm inside the garage. For all you know, there may be a plastic coupling in the heating run, then your pipework will just become an ECP, along with the steelwork. Never rely on anything which could be removed at a later date to be your bonding.

 

[diditrain]

So many different opinions, great stuff and thank`s for taking the time to reply.

 

[ajelec10]

Think you will find you can't export the earth from the main building as it TN-C-S you will have to only bring out the line and neutral from house, make the detached garage a tt system, then bond all extraneous parts to you new tt main earthing terminal. Ie structural steel and heating pipes. Job done!

 

[Guitarist]

Think you will find you can't export the earth from the main building as it TN-C-S you will have to only bring out the line and neutral from house, make the detached garage a tt system, then bond all extraneous parts to you new tt main earthing terminal. Ie structural steel and heating pipes. Job done!

Here we go again.....

 

[imago]

Check the resistance between the steel uprights in the garage and the MET. As the stanchions are into the ground you may find that you have a ready made 'rod' with the garage steelwork which gives a good reading.

There is a term for it, but the word escapes me E54 or Tony will know I'm sure.

 

[imago]

Think you will find you can't export the earth from the main building as it TN-C-S you will have to only bring out the line and neutral from house, make the detached garage a tt system, then bond all extraneous parts to you new tt main earthing terminal. Ie structural steel and heating pipes. Job done!

Anyone for pop-corn?

 

[colshaws]

try this http://www.electriciansforums.net/a...ted-pme-outbuildings-garage-shed-supplies.pdf

 

[ajelec10]

Good link!

 

[Heisenberg]

And have a read of the article in here...

View attachment 2005_16_autumn_wiring_matters__complete_no_adverts (1).pdf

 

[Sintra]

Think you will find you can't export the earth from the main building as it TN-C-S you will have to only bring out the line and neutral from house, make the detached garage a tt system, then bond all extraneous parts to you new tt main earthing terminal. Ie structural steel and heating pipes. Job done!

Think you will find that who ever told you that is an obsessive compulsive liar. :lol:

 

[telectrix]

Think you will find that who ever told you that is an obsessive compulsive liar. :lol:

you must be referring to niceic, then. or a politician.

 

[Sintra]

you must be referring to niceic, then. or a politician.

Well if the cap fits................

 

[Guitarist]

It's in the old ESQCR. Many lecturers still state what aj did.
Funny how this topic keeps raising its head

 

[Sintra]

As I see it the correct word in this situation would be EXTEND rather than EXPORT.

 

[Engineer54]

As it's a separate building and with a PME service at the head, you will need the separate 10mm bonding conductor between the MET and garage EMT in this garage to connect to the steel frame and to the daft copper heating pipes etc, if your intending on extending the house PME equipotential zone!! What sort of distances are we talking about here??

 

[diditrain]

The detached garage is no more than 5 metre`s from the house.

 

[telectrix]

if the 6mm SWA is already in place and a 10mm bonding conductor would be a pain to fit, then TT the garage. bloody big rod and the steelwork should give a decent Ra. LOL.

 

[diditrain]

Yeah it`s already in situ, beneath a block paved yard. His garage is still under construction but he is putting insulated plasterboard on the walls, tinted windows etc. Should be nice and snug when complete

 

[telectrix]

Yeah it`s already in situ, beneath a block paved yard. His garage is still under construction but he is putting insulated plasterboard on the walls, tinted windows etc. Should be nice and snug when complete

a good argument for putting the cable in ducting. could have pulled a 10mm bonding in retrospectively. now he's fooked.

 

[diditrain]

Totally agree, I will probably just tell him to run one in himself. Give him the hassle

 

[Engineer54]

Yeah it`s already in situ, beneath a block paved yard. His garage is still under construction but he is putting insulated plasterboard on the walls, tinted windows etc. Should be nice and snug when complete

Sounds more like a very comfortable naughty boy's room, where your mate goes for a beer and to watch the footie in peace!! lol!!

 

[diditrain]

Yeah, i believe it is his place to go and hide. Then again they say that every man should have one

 

[Guest55]

Think you will find you can't export the earth from the main building as it TN-C-S

..........

 

[diditrain]

Hi telectrix, if i was to TT the garage, there would still be a path back into the house via the bonded central heating pipework.

 

[Engineer54]

The detached garage is no more than 5 metre`s from the house.

No problem then!! Should of asked you to advise in the first place, ...that or run the existing cable in a duct as Tel suggested!! lol!! Try conducting a sheath test on that cable your mate has installed, ...what's the betting it fails?? lol!!

 

[diditrain]

Yes, that could be interesting, to say the least.
Am i right in saying that the copper equivalent for the armoured is 7.39?

 

[Guitarist]

Hi telectrix, if i was to TT the garage, there would still be a path back into the house via the bonded central heating pipework.

Because of this, it is unlikely that you will be able to isolate the garage from the house (unless plastic is used in the pipework). 10mm bonding cable is the way to go imo.
To put your mind at rest, why not speak to your scheme provider

 

[Engineer54]

Yes, that could be interesting, to say the least.
Am i right in saying that the copper equivalent for the armoured is 7.39?

Let's put it in these terms, ...there is no way the existing 6mm SWA cables armour is going to provide your bonding requirements, so it's either changing existing cable for a 3 core 10mm SWA, (whose armour Still wouldn't comply for bonding purposes) or run in a separate 10mm bonding conductor!! lol!!

Steel requires about approx 8 times the CSA of a complying copper conductor, for it to be equivalent/suitable for bonding purposes!!

 

[diditrain]

Thank`s for all of the replies guys, been very informative.