Installing an earth rod

[nmilner]

Hi,

While getting my electrical installation in the garage tidied up I want to run a length (60m) of armoured cable from my garage to my shed at the end of the garden. I will be using an RCD MCB in the garage consumer unit to supply the armoured cable. My question is regarding earthing. It has been suggested that I should provide a seperate earth (via an earth rod) for the consumer unit in the shed rather than rely on the earth via the armoured cable to the garage. It think this makes sense but I was wondering how I install an earth rod. I realise you hammer the rod into the ground but is there a certain distance from the shed I should install it?

Also, I have noticed that newer earth rod installations have a cover over the rod and the earth rod clamp. Is this now mandatory?

Thanks

Nick

 

[mapj1]

What is the earthing at the house end (TT/PME/ TN-s) ?
this affects what you should do.. then we can come back with more detail.
M.

 

[nmilner]

Hi,

I believe it is TN-s.

Nick

 

[ban-all-sheds]

If that's the case then you should not need a rod. Use large SWA cable (10mm² minimum), 3-core so you aren't relying on the armour for the earth (but do still earth the armour at each end to protect the cable).

What loads will there be at the garage, and what size/type of fuse/MCB will there be at the house end for the cable?

 

[nmilner]

I will be using a 32A MCB (in the RCD side of my split load consumer unit). I am concerned that it is a long run to the shed and would feel happier with an earth rod.

Nick

 

[ban-all-sheds]

Well, R1+R2 for 60m of 10mm² is 0.22 ohms. So assuming a Ze of 0.8 ohms, you're looking at a Zs of just over 1 ohm. You'd never get anywhere near that with a rod.

As a second verification, for a 32A Type B the OSG lists the maximum length for a 10mm² radial as 69m, but bear in mind that's for T/E,where the cpc is 4mm², not 10mm² as it would be with SWA.

I really can't see the need for an earth rod.