Outside garage supply

[Jeremy Hale]

To supply power to new garage 20 meters at bottom of garden from main house.

Plan to run a three core 4mm SWA to garage, fit a metal clad two way dB with 30ma RCD in garage. Using one off the three cores together with the armour as cpc.

At the house end terminate swa in An adaptable box adjacent to house BD and use 6mm twin and earth to connect lives and earth to a 20A spare way of existing plastic board.
This incorporate an RCD covering whole installation. There is an earth rod so I assume this is a TT installation.

Assuming Zs at garage is ok. This is what I planed

However lots of talk about fitting an earth rod at garage end.
In your opinion should I also fit an earth rod at garage end and common back up earth. Also I think I could ask for supply co for a pms at this site there is a new cut out or would this be just complicating things

 

[Deleted member 105166]

This is notifiable work, you need to engage the services of a local electrician, who will specify and supply the circuit protective device, cable, earthing arrangements and terminations. If you want to save a few £££, you do the digging and back-filling, this will be a win-win for you both.

 

[Dustydazzler]

JH are you a new electrician or DIYer ?

Tin hat on but if you are a new electrician you could install the job and get a competent electrician to help test it with you

 

[Toneyz]

Unfortunately, there is no profile for the O.P. although Tony you say to engage the services of a local electrician the O.P. could be an electrician like myself that now does commercial work and is competent to do the work and has no need to belong to a scheme and is going through the local building control route. By the way, not a dig at you Tony just highlighting a common point.

 

[Bricktop]

Has the existing rod been tested lately and can you inspect it? Ie in an inspection chamber and not buried.

 

[Midwest]

Two RCD's in series won't be much use, unless the one 'covering the whole installation' is S Type?

I think I would try and convince the home owner to save up for a CU change, to improve things here, before spending money on providing power to garage. What will the garage be used for?

 

[gaz_sparky]

Hi, your plan sounds ok apart from the additional earth rod.
You can use an earth rod at the garage, but you must isolate it from the supply earth and treat the garage supply as a new TT system.
You need to do this to avoid parallel earth paths from the original installation.

 

[Jeremy Hale]

Hi, your plan sounds ok apart from the additional earth rod.
You can use an earth rod at the garage, but you must isolate it from the supply earth and treat the garage supply as a new TT system.
You need to do this to avoid parallel earth paths from the original installation.

Thank you for your reply as the house system is not PME and TT, also there are no extraneous parts in the garage. My thinking is that the additional earth rod located at the garage end would serve as a back up rod and may even reduce ZE, in common with house Rod. That said please let me know if I am Wong in relation to parallel earth paths from original installation.

 

[Midwest]

Thank you for your reply as the house system is not PME and TT, .

What supply is it then?

 

[Jeremy Hale]

What supply is it then?

Sorry Its a TT supply with earth rod at front of house

 

[Midwest]

Sorry Its a TT supply with earth rod at front of house

What is the house RCD?

 

[MJPD29]

RCDs in series bad idea, with all due respect it seems you are missing some fundamental knowledge here, if you do undertake this work yourself be wary it may be notifiable work and be careful.

 

[Jeremy Hale]

It may be that I install a 100ma rcd and 20a trip at house location protecting SWA and two way board in garage with 30ma RCD coving installation.
However my original question stands that is which would be the best, to connect earth rod at garage in common with the house rod/earth, or to isolated SWA earth / sheath from the garage installation, therefore creating a separate TT installation at garage. Note the house is not PME and no extraneous parts in garage.
My logic tells me to connect both rods together resulting in lower ZE and security. comments on this would be appreciated to assist

 

[westward10]

If the electrode at the origin is sufficient a secondary one is not required.

 

[Deleted account]

Agree not required, but no harm fitting one.

 

[gaz_sparky]

The image shows an example of the earthing and bonding arrangements where an installation in a house supplies an installation in a detached outbuilding, forming part of a TT system with its own installation earth electrode and MET. It is desirable for there to be no connection between the earthing and bonding arrangement of the installation in the outbuilding and that of the installation in the house (such as through a protective conductor or shared metallic pipeline), as shown.
Note: Although both options show an earthing facility provided by the distributor being used as the means of earthing (TN-S or TN-C-S system), the earthing conductor could be connected to an installation earth electrode instead (TT system).

 

[gaz_sparky]

Found this for you on Voltimum