Earth rod query

[Engineer54]

And you keep banging on like you always do without knowing what i do!

Or knowing what your doing!!

 

[Top Cat]

Or knowing what your doing!!

You can put clairvoyant on your CV now then!

 

[Engineer54]

You can put clairvoyant on your CV now then!

Best stick to your Meow jokes/humour...

 

[Top Cat]

Best stick to your Meow jokes/humour...

OK, i thought i was the catty one, meow!

 

[IQ Electrical]

OK, i thought i was the catty one, meow!

And you can install a purrrrrrfectly good earth rod?

 

[Deleted member 9648]

I go back to my original question... What is the point? There's no difference between 200 and 1000 ohms when it comes to an earth rods effectiveness??? This is the part I struggle to understand.

I've been ploughing a relatively lone furrow on exactly this point on here for ages....and taken a lot of flack for it.
The logic of those who scoff at the Bs recommended max of 200 ohms,and then smugly state they wont settle for anything over ...say...40 ohms has always defeated me.
I would also point out that I have never accepted the single RCD on a TT....there should be a requirement for a 'master' 100ma T/D alongside the 30ma device unless it can be proved that an Ra value low enough to operate an OCPD can be maintained.
Bear in mind as well that most of the TT queries on this forum concern small installs....(not the kind of big stuff E54 deals with)....for which multiple super rods are overkill IMO

 

[Engineer54]

I've been ploughing a relatively lone furrow on exactly this point on here for ages....and taken a lot of flack for it.
The logic of those who scoff at the Bs recommended max of 200 ohms,and then smugly state they wont settle for anything over ...say...40 ohms has always defeated me.
I would also point out that I have never accepted the single RCD on a TT....there should be a requirement for a 'master' 100ma T/D alongside the 30ma device unless it can be proved that an Ra value low enough to operate an OCPD can be maintained.
Bear in mind as well that most of the TT queries on this forum concern small installs....(not the kind of big stuff E54 deals with)....for which multiple super rods are overkill IMO

The flack came and rightly so, from you advising junior members to bung a twig in the ground and if you saw 200 ohms or less, that's all you needed for a TT system, and not bothering any further...

I think that i have stated many times now that as far as domestic installations go, a couple of coupled 5/8'' rods (coupled) should be the standard installation, coupled with an up-front S type RCD device. Do you really think that's over the top, considering that the TT installation you have installed should be robust enough to last a min of 30 to 40+ years??

Now let's say that driving 2 rods in the ground on a domestic installation gave you an Ra value of say 10 ohms. You know that in all probability, the stability is going to be present. Would you approach the client and give them a choice of adding another rod, thus getting down, pretty much close to the 1 ohm mark (after settlement) or not?? Which is the other point i've been trying to make over the many threads on this subject... Wherever or whenever possible, go that extra distance to get the desired results, and not just rely on what it says in the Reg's...

As for commercial and industrial installations that have a number of employee's etc why wouldn't you be trying to aim for TN values?? A 200 ohm's max in such circumstances, is complete tosh!! Oh, ...and what you call ''Super Rods'' were once the standard sized rods used in the UK and everywhere else and STILL ARE, in most of the countries i've ever been.... I actually saw for the first time, a 1m 5/8'' rod while in an electrical wholesalers in Cyprus while i was home a short time ago. I asked if that was the standard size they were using now in Cyprus. ...What i got was a blank look, he then disappeared out back and came back with a what looked like a 2.4m rod, ''first one of these, ...then one of these'', pointing to the 1m rods!!! So even in Cyprus the one metre rod is classed as no more than an extension piece!! lol!!!

 

[Engineer54]

And you can install a purrrrrrfectly good earth rod?

How do YOU know?? lol!!!

 

[Top Cat]

How do YOU know?? lol!!!

Maybe he's clairvoyant the same as you!

 

[Engineer54]

Maybe he's clairvoyant the same as you!

Yep, ...must be!! lol!!

 

[Deleted member 9648]

The flack came and rightly so, from you advising junior members to bung a twig in the ground and if you saw 200 ohms or less, that's all you needed for a TT system, and not bothering any further...

I think that i have stated many times now that as far as domestic installations go, a couple of coupled 5/8'' rods (coupled) should be the standard installation, coupled with an up-front S type RCD device. Do you really think that's over the top, considering that the TT installation you have installed should be robust enough to last a min of 30 to 40+ years??

Now let's say that driving 2 rods in the ground on a domestic installation gave you an Ra value of say 10 ohms. You know that in all probability, the stability is going to be present. Would you approach the client and give them a choice of adding another rod, thus getting down, pretty much close to the 1 ohm mark (after settlement) or not?? Which is the other point i've been trying to make over the many threads on this subject... Wherever or whenever possible, go that extra distance to get the desired results, and not just rely on what it says in the Reg's...

As for commercial and industrial installations that have a number of employee's etc why wouldn't you be trying to aim for TN values?? A 200 ohm's max in such circumstances, is complete tosh!! Oh, ...and what you call ''Super Rods'' were once the standard sized rods used in the UK and everywhere else and STILL ARE, in most of the countries i've ever been.... I actually saw for the first time, a 1m 5/8'' rod while in an electrical wholesalers in Cyprus while i was home a short time ago. I asked if that was the standard size they were using now in Cyprus. ...What i got was a blank look, he then disappeared out back and came back with a what looked like a 2.4m rod, ''first one of these, ...then one of these'', pointing to the 1m rods!!! So even in Cyprus the one metre rod is classed as no more than an extension piece!! lol!!!

The thing is E54 I have seen many TT installs in my area which are 20+years old with a single 'twig' which are perfectly satisfactory today,and will be for another 20 I've no doubt...I base my opinions on that.
My only argument is with those who turn up their noses at 200 ohms...and yet seem to think they are the dogs danglies with 40 ohms.....I just cant see the logic.....If the installer insists the Bs value is not acceptable then he should get a stable TN value....I have no dispute with that at all.

 

[spark 68]

I was just looking through the 1995 16th ed.amd.1 OSG, and this recommends the earth electrode should not exceed 220 ohms, and does not appear to be mentioned at all in the same edition of the regs.
There is also no mention of it in the 2004 16th ed.amd.2 regs either

So this looks to have been lowered slightly to 200 ohms in the 17th.

 

[Engineer54]

The thing is E54 I have seen many TT installs in my area which are 20+years old with a single 'twig' which are perfectly satisfactory today,and will be for another 20 I've no doubt...I base my opinions on that.
My only argument is with those who turn up their noses at 200 ohms...and yet seem to think they are the dogs danglies with 40 ohms.....I just cant see the logic.....If the installer insists the Bs value is not acceptable then he should get a stable TN value....I have no dispute with that at all.

Have these twigs been the norm there for 20 years now then?? Wow!! If so, are you pulling these rods up to look then, or just relying on the high Ra value, that you blindly accept as being fine cause it says so in 7671??

If nothing else, those that put a little extra effort in and gets anything from 50 ohm or lower (which would be about the norm for 2.4m's of 5/8'' rod) stable installation IS the dog's dangles compared with those that just bang a twig willy nilly in the ground and think they have actually achieved a TT system. That logic, i will never understand. I'm not however implying that a domestic TT installation should cost mega bucks, it shouldn't. But using the right materials and quantity with a little care, is how i would want any electrician to perform on a standard TT job that i (and i suspect customers) employed him for....

Sorry, but apart from anything else, a stable 1m twig ain't gonna happen...

Finally, why is it that a Standard rod size that had in the past almost always delivered the goods in both stability and Ra values, be superseded by a twig that ''almost always'' (i'm being kind here), will never be able to deliver either??

 

[Deleted member 9648]

I think I'll change my user name to twiggy.....or twiglet perhaps?

 

[Top Cat]

I think I'll change my user name to twiggy.....or twiglet perhaps?

Maybe smear your rod in E45 then everyone is happy!

 

[Silly Sausage]

or E54 changes his name to 'twigpuller'

 

[Top Cat]

or E54 changes his name to 'twigpuller'

Wish there was a "like a lot button"!

 

[IQ Electrical]

Maybe smear your rod in E45 then everyone is happy!

E54 surely?

 

[Richard Burns]

Maybe smear your rod in E45 then everyone is happy!

E45 sends a very different message compared to E54 and unfortunately gives an insght into TC's mind!!:cheesy:

 

[La Poste]

All this talk about earth rods and I have one query.

When measuring an earth rod resistance and trying to get it down to 10 ohms are we talking about the rod resistance itself or are we talking about the EFLI?

If we are talking about the rod resistance being ten ohms then what about the impedance of the transformer rod which could be twenty ohms itself so no matter how low we get our earth rod resistance we are never going to get lower than the impedance of the transformer rod.

Admittedly there will be parallel paths involved through other peoples bonding etc but when talking about a low Ra are we talking just about the earth rod or are we talking about the total earth fault loop?

Thanks.