2nd Earth Rod on TT System

[Eric1066]

Hi all,
My electrical installantion here in Cyprus is TT.

As some are aware I have a metal framed shed outside and I wired it up for lights and sockets etc... it's earthed by adding a strap to the frame..

However, I have been thinking about ramming an earth rod near by and strapping a thick earth cable to the frame. Lightning strikes are a thing here.

Any ideas on that?

any help is greatly appreciated.

 

[MikeJhn]

Your title says second earth rod, if that is so the zone of influence comes into play from the original rod.

How is the power supplied to the shed, Armoured cable?

 

[Eric1066]

There's a 4mm armoured cable coming from a 32a RCBO from within the house.

Goes into a CU in the shed for a 32a ring and 6a lights.

The 2nd earth rod is simply going to be hammered in to the ground and strapped to the frame.

I know an earth rod can support a TN system, but not sure how that relates to a TT system and I'm not sure I should be taking this back to the shed's CU and terminate in to the earth block?!? Or just leave it strapped to the frame only.

 

[MikeJhn]

Is the Armoured cable earthed both ends or just the house end?

Earth rod should be taken into the CU in the shed onto the earth block, with a suitably sized cable, I would use 10/16mm.

 

[Eric1066]

Hi,
The armoured cable is earthed in the house, and is connected to the earth block in the shed.

Earth rod should be taken into the CU in the shed onto the earth block, with a suitably sized cable, I would use 10/16mm.

Then by doing this , I have effectively connected the 2 rods together. The one the house has, and runs through the armoured cable etc... and this new one by the shed. That's ok, yes?

 

[Sharpend]

It’s the same earthing systems at both ends so no problem ie TT at both.

 

[Eric1066]

Thank you all so much!!
Greatly appreciated!!

 

[MikeJhn]

There is a school of thought that says the armoured cable should only be earthed at the hose not the shed if you make the shed a separate TT, having the armoured earthed at both ends an earth problem in the shed could trip the main CU in the house, that's if you have RCD or RCBO's protection in parallel, but does not seem to make much difference to the operation only the convenience factor of knowing where the fault is.

 

[Murdoch]

There is a school of thought that says the armoured cable should only be earthed at the hose not the shed if you make the shed a separate TT, having the armoured earthed at both ends an earth problem in the shed could trip the main CU in the house, that's if you have RCD or RCBO's protection in parallel, but does not seem to make much difference to the operation only the convenience factor of knowing where the fault is.

disagree with this. The more TT stakes the better

 

[UNG]

disagree with this. The more TT stakes the better

While I agree with you on one part on the other if they are not correctly installed they can end up offering little benefit for the cost involved

 

[MikeJhn]

Each earth rod should be outside the Zone of influence of another or there is no benefit, it comes down to how deep each rod is.

 

[Eric1066]

How do I figure out the zone of influence?

 

[Sharpend]

Sorry if it’s just me, but surely anyone installing earth rods should be competent enough to know if it’s installed on both the correct vicinity and correctly?
Or at least capable enough to ask?

 

[Eric1066]

Sorry if it’s just me, but surely anyone installing earth rods should be competent enough to know if it’s installed on both the correct vicinity and correctly?
Or at least capable enough to ask?

Hi,
You are quite right, but I think and hope this DIY section (which itself denotes a non-professional) of this forum is for numpties like me who are going to take matters in to our own hands regardless, and you professionals are willing to advise us numpties, as we're going to attempt it anyways no matter what, so such numpties like me don't kill ourselves. And for this I am greatly appreciative!!

 

[Sharpend]

But there are some things that you can do and other things that you really should get someone in who knows!
Have you the correct test equipment?

 

[Eric1066]

Of course not

However, the 2 rods which are 4ft are at least 10m apart... and I'm working on the premise that 2 is better than 1.

What do I need and is it expensive?

 

[MikeJhn]

The zone of influence is generally regarded as equal to the length of the rod as a diameter around the rod, In short a 2M rod should not have another rod within 4M of it, but the length of the rod is according to the ground conditions and the readings obtained when testing.

Sorry should have said radius not diameter.

 

[UNG]

Sorry if it’s just me, but surely anyone installing earth rods should be competent enough to know if it’s installed on both the correct vicinity and correctly?
Or at least capable enough to ask?

Having seen the lightning conductor report for the local church produced by lightning conductor specialists and then seen the recommended remedial work by the same which included sinking another earth rod it would appear the so called professionals don't know what they are doing
Without knowing how deep the original rod is the new rod was sunk 450 - 600mm away from the original, it would have been very easy to have put the new rod 2 or 3 times that distance away from original add to that the new rod and it's tape connection have been tarmaced over rather than install a proper access pit to further complicate future testing
So even the supposed professionals clearly are not upto speed

 

[MikeJhn]

I don't know enough about lightning conductor requirements to comment, but there can be a requirement for multi earth rods inside their own zone of influence if something like base rock does not allow the sinking of a single sufficient length rod and insufficient land area is available to meet the zone of influence spread requirements to meet the readings required.

 

[binky]

Having seen the lightning conductor report for the local church produced by lightning conductor specialists and then seen the recommended remedial work by the same which included sinking another earth rod it would appear the so called professionals don't know what they are doing
Without knowing how deep the original rod is the new rod was sunk 450 - 600mm away from the original, it would have been very easy to have put the new rod 2 or 3 times that distance away from original add to that the new rod and it's tape connection have been tarmaced over rather than install a proper access pit to further complicate future testing
So even the supposed professionals clearly are not upto speed

Lightning conductors are a whole different ball game and a very specialist field of work.