Earth rod

[Carlosfandango]

This might sound like a daft question to some of you guys. I've never had to work with TT systems before and I'm wondering how you go about getting a spike into rocky ground? The job I've been to look at has a spike in just now but the Ze at the mains is 107 ohms. I need to get this to an acceptable reading. I'm led to believe the area is build on bedrock! Any advice?

 

[Andy78]

I can't help as I have never had to TT into rock.. but someone will surely be along soon....
I'm guessing this is going to be a 5 page thread at least

 

[telectrix]

1m long 15mm drill. then bang a rod or 2 in. keep away from building walls.

 

[Carlosfandango]

That was my thinking. Can multiple rods be used at various points as the cable leaves the main isolator, comes up into an old electric board pillar (don't ask!!) then carries on to another isolator. The sub mains set up is a shambles but I'm trying to sort out the individual chalets then get a plan sorted for the supplies.

 

[telectrix]

nowt wrong with multiple rods. how do you think DNO create TNC-S?

 

[Carlosfandango]

Good point!

 

[shanky887614]

nowt wrong with multiple rods. how do you think DNO create TNC-S?

I remember a post a little while ago with some interesting information on this about dno earth nests

have a quick search

 

[GLENNSPARK]

Tapes, mat or grid may be the way forward here...

its about getting the surface contact area up....

you may have a stability problem though if theres no depth so another way would be to build an earth nest....go for the parrallel paths....

 

[shanky887614]

Tapes, mat or grid may be the way forward here...

its about getting the surface contact area up....

you may have a stability problem though if theres no depth so another way would be to build an earth nest....go for the parrallel paths....

This thread will be interesting where tony talks about earth nests

3 phase 70 KVA generator

 

[GLENNSPARK]

This thread will be interesting where tony talks about earth nests

3 phase 70 KVA generator

i`m sure he`l show up..

what you have to look for when constructing a nest is what we call `spheres of influence`....

you site the rods near enough to each other so the spheres contact.....but dont overlap so as to get the maximum benefit from whatever earth electrodes you install....

 

[GLENNSPARK]

youd have to remember as well that the ground area around the earth electrode could rise in potential when under fault conditions....so consideration would have to be paid to this as well....

step voltage....

 

[shanky887614]

youd have to remember as well that the ground area around the earth electrode could rise in potential when under fault conditions....so consideration would have to be paid to this as well....

step voltage....

If my memory is correct isnt there a set distance apart based on rod length or is that more to do with testing?

A figure of 1.8 keeps popping into my head, im going to have a quick flick through osg

Edit:

Dont know where I got 1.8 from.

It recomends a testing distance of 10x the length of the rods but that seems impractical

 

[GLENNSPARK]

to be honest i`d have to look for it myself but yep...there is a distance based on depth of rod/s...

 

[shanky887614]

to be honest i`d have to look for it myself but yep...there is a distance based on depth of rod/s...

10x.

If you dig them as deep as some members here you would be a couple fields over lol

 

[Carlosfandango]

Is there any regs on how far from the install the rods need to be? Could I run a suitably sized earthwire to a position where I can get a rod in?