Electrical Connection from House to Garage

paul8f

Hi all,

I have a handy bit of electrical experience, but I need some advice
on how to connect my new garage to the house's CU (Consumer Unit).

The electrical load will be reasonably light, and the garage is only
a few meters from the house, so I'm running 6mm squared twin and
earth STW (Steel Wire Armour) cable through an underground pipe. The
house has a modern style (module type) CU with spare slots available...


In the garage itself, there will only be a light, a washing machine,
a tumble drier, and an IP55 external socket for the lawnmower. I've
purchased a mini consumer unit (4 slots), a 25A MCB (Mini Circuit
Breaker), a 10A MCB for the lights, and a 63A/30mA RCD (Residual Current Device).

(1) The first problem is that I'm not sure where to put the RCD.
Should this go on the house fuse board, or on the new mini board in
the garage.

(2) The second issue is that I don't know what kind of earthing
system I should use? ---- Should I sink a new earthrod, or should I
use the earth wire in the T&E to tie up with the Earth Rail back in
the CU of the house. (The house was built in the late '70s, but I
don't know what type of Earthing system it has).

Any help greatly appreciated !
Paul

Cerbera

Pay someone to do it for you.

It's obvious from your post that you are tempting fate if you do this yourself.

Sorry to burst your bubble but that's just the way it is.

Avns1s

I would connect the SWA to a 32A breaker in your Consumer Unit in the house.

Run the SWA to the mini box in the garage. Use the RCD to protect the sockets for the Washing Machine and Dryer and the Lawnmower via the 25A breaker and connect these using 2.5sq T+E NYM Cable. Don't forget to use a proper gland on the IP55 socket.

Connect the light via a 10A breaker not on the RCD, and on 1.5 sq. NYM Cable.

Finally, you should connect the earth wire of the SWA to the earth block of your consumer unit in the house as well as the block in your mini box. I would also install a new earth rod and connect the earth block in your mini box to this via a bit of 10 sq. earth cable using the proper box and clamp.

Hope this helps.

enmac

see attached article - should be helpful - no need for earth rod , especially if its only a few metres away - terminate the SWA correctly using glands and ensure the armouring is earthed. Do all the outside work first and it may be a good idea to put a temporary plug on the house end of the SWA and test th enew circuit it by plugging it into a socket before you start connecting it to the distribution board

bertie1

He has no space in his enclosure for a switch fuse to isolate the garage

paul8f

Thanks for all the help!

- At first I thought that sinking an earth rod was a bit 'over the top', but that Electrical Installations PDF file showed that the copper pipes must be bonded. So now I am considering installing an earth rod for the garage. Anybody have any more advice on this ???

- Am I definatly to ground the armouring in the cable as well? (on pg 3 of the PDF file, the last few lines of the TT SYSTEM paragraph, is says NOT to connect the armour.

- A 32A MCB placed in the house's CU also seems a good idea, as it covers overcurrent on the whole garage installation.

- I'll put the RCD in the garage's CU. (This RCD will feed the 25A MCB, that will protect the double socket and the IP55 single socket).

- I'm thinking of using a 6A instead of a 10A MCB for the lights. (___I will only be putting up a 100W ceiling rose, a single florescent strip light, and a smoke alarm.... so 6 Amp protection is plenty here___).

enmac

not too sure what bertie is on about - switchfuse ??

anyway - i would go along with your proposal of mcb in main board feeding the RCD and MCBs in the garage.

I would avoid the TT system - bring out a separate 10mm earth cable from the main distribution board and use this for bonding any metallic pipes etc.
Do connect the armouring to earth at both ends using a swa gland - this is in addition to the actual earth wire within the SWA cable.

i assume the pipes supplying the garage are copper pipes - if there is just a single hydrodare pipe running to the garage then you won't require the 10mm bonding cable

Steve

paul8f wrote: »

- Am I definatly to ground the armouring in the cable as well? (on pg 3 of the PDF file, the last few lines of the TT SYSTEM paragraph, is says NOT to connect the armour.

You must earth the shield on the SWA and you shouldn't use a separate earth rod.

The Irish grid is TN-C, not TT.

This is probably more suited to the electrical forum.

paul8f

To 'enmac':
The pipe in the garage is copper, but just noticed that the feed to the garage is actually Qualpex. I wont bond it now... even though I think the regulations still say you should...:D

To 'SteveC':
I always thought that the TT earthing system was where the Earth connection was independent of the local transformer.. i.e an Earth rod is to be provided on the customer's site (which is independent to the Earth connection at the generating station or transformer).

Is it possible to move or copy this thread to the Electrical Forum?
Thanks.

Steve

paul8f wrote: »

To 'SteveC':
I always thought that the TT earthing system was where the Earth connection was independent of the local transformer.. i.e an Earth rod is to be provided on the customer's site (which is independent to the Earth connection at the generating station or transformer).

That is correct but it's highly unlikely you have a TT system - it's more likely you have a neutralised system. That PDF was from the IEE and is based on UK regs which are not the same as here.
The ESB don't allow the consumer to chose the earthing they use, it must tie in with the local grid. The safest thing to do is bond everything back to the main earth rail in your consumer unit as this will cover you either way.

Some wiki info here:

Earthing/Grounding System

• TN-C-S is preferred. This is referred to in Ireland as a "Neutralised" supply. Most homes and businesses are connected to such a system.
  Where this system is used, all metal pipe work must be bonded i.e. connected to the system's earth/ground creating an equipotential zone.

In such an installation earth straps and yellow & green earth wires can be seen connected to pipework under sinks, in heating systems etc.

• TT system is used where TN-C-S earthing is not possible due to the design of the local distribution network, or the geology. This system is referred to as 'unnutralised' or 'not neutralised'.

Where a TT network connection is used, the entire supply must be protected by an RCD
Converting a TT supply to a TN-C supply "Neutralisation" may only be carried out by an ESB engineer with the approval of ESB Networks. Under no circumstances should a home owner, or an electrical contractor make any connection between the Earth/Ground and Neutral. To do so inappropriately could expose people to a risk of serious shock or electrocution.

paul8f

Thanks for clearing that one up! You learn something new every day.

I think I'm finally ready to do some wiring

paul8f

I bought all the material in Dwyers Electrical, Forge Hill, Cork. I’ve been told that they are ok on receiving back unwanted items, so I shouldn’t have any problems returning the earth rod, earth clamp, earth inspection pit cover and the denso tape.

I will post back here again when the job’s completed to say how it all went

Steve

Great, hope it goes well!

paul8f

It all panned out fine....

Working with Steel wire armour is like wrestling a python snake. Connecting it up is nearly harder!

Other than that no real issues. Everything's wired up and working properly. Didn't have to sink a 2nd earth rod, and I connected up the protective steel wire to earth terminals.