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!