Earth rod

[mickys86]

Hi guys. I've been reading a few posts about earth rods. What's the preferred way to join them, and also when installing a few of them what is the preferred way to link them? I've read some posts that says when installing them next to each other you should spread them apart the same distance as you go down. But none to answer my above question. Cheers

 

[Engineer54]

But this assumes that anything approaching 200 ohms IS going to be unstable...the fact is it isn't....why should 200 ohms be any more unstable than 30 ohms?
As I've stated on here before I've tested and installed many 'useless twigs' in my area over many years and typically get readings of between 100 and 150 ohms summer and winter.Some have been on installs which have had regular updates and alterations over long periods and so have had regular Ra tests,if I have found dangerously unstable Ra readings believe me I would be doing something about it.....but I haven't. And many of the "it's got to be 20-30 ohms" brigade seem to forget that 30 ohms or 200 ohms they are still totally reliant on an RCD to meet disconnection times
Of course if in your ground you cant get a stable Ra with a 'twig' then don't use one....but to state across the board that standard UK rods are never going to be adequate or stable is wrong.

I am plainly stating that a single twig sized so-called earth rod, is basically useless, no matter what the inital Ra value is, i'll stand by that statement come what may!! I honestly can't see how your not seeing seasonal differences with such twig's, i would go as far as saying it would be almost impossible Not to see drastic seasonal differences... Not only that, a TT system should be suitable for a 30 year life span, but most will still be in service 50 or 60 years. Anyone that thinks these twigs are suitable or i suspect even designed for such durations are only fooling themselves. The only use i can see for these twigs, is for a very temporay install, or as re-usable test rods for an earth tester!!

Any domestic TT system should minimally consist of at least 2 X 5/8'' rods coupled together wherever it's possible to drive them. On commercial and/or industrial installations of any size, a far more concerted effort should be made to get a good working TT system. I will agree, that there are certain times that due to the ground conditions you can be hard pushed to better a stable 200 ohm value with driven rods. Depending on the installations requirements, even these TT systems can be substantually improved. I'm not saying this would make sound economic sense on a domestic installation, but it can for other installations...

Perhaps if these short rods of any size were never brought on to the market and you were still using the older 6 and 10 foot rods, we wouldn't be having these debates!! As in those day's 10 ohms was what the electricians were looking for, certainly not 200 ohms or anywhere close. What's more, in my old county of Essex you would feel unlucky if you saw an Ra 10 ohms, it was generally much lower!! And here you are telling us all, of the benifits using these 3'8'' twigs and of drawing the line at 200 ohms or so. Thank god that most water/gas services are still metallic and can give much needed support to these numbty twigs and values that you can't see any problem with....

 

[mickys86]

So what advice do you give to someone on paye who has been given 1 earth rod to put in and only having a mft to test with. I tested Ze (my next question soon will be what's Ra) and the value I got was 179ohms. When I told my boss he said its below 200 so it's allowed......

When you join the rods do they clamp together or screw into each other? Because the rod that is in is just 1m copper rod. I need sound advice so I can learn something and also do the job right.

So what action do you suggest I take.... I already have a 'twig' in the ground and my boss has told me its ok. I know the depth that it's in so I could put another rod that same distance away from the first rod. Or could I get an extension (as in post 12) for the 'twig' that is already in?
Or do I bite my tongue, say nothing, as someone else said earlier.... It's not my name on the certificate?

 

[richy3333]

mickys86 - you're clearly not happy and have a conscience. It sounds as though you work for a company so your obligation would be to report matters to your boss unless you have the latitude to stick another rod in yourself without asking? Those stick thin rods that can't be extended are useless as others have already said.

 

[mickys86]

I done another Ze reading today (With
My mft) and it's been peeing down all day and yet I have 246 ohms. Not good.
The rod that I have put in the ground I think I'm going to disconnect from that, get 3 rods that you join together and put them in.
You telling the boss or shall I?? Haha

 

[johnboy6083]

Bear in mind Micky, that over time the ground will consolidate around the rods, and the readings will improve. This doesn't mean that you shouldn't strive for decent Ra values, but it may put your mind at ease. If you've got another rod and coupler, then bang another one on top.

 

[Engineer54]

I done another Ze reading today (With
My mft) and it's been peeing down all day and yet I have 246 ohms. Not good.
The rod that I have put in the ground I think I'm going to disconnect from that, get 3 rods that you join together and put them in.
You telling the boss or shall I?? Haha

As i've stated those twigs are about as good as a bad joke!! lol!!

As has been previously suggested, bring 3 X 5/8'' extendable rods to the job, drive in 2 of them and see what Ra you have. If you think it's worth improving then use the third rod. One thing you will definitely achieve is the rods stability.

Whatever final reading you obtain, it will improve over time as the soil around the rods consolidates. This is especially so, where couplers have been used, as these have a slightly larger circumference than the rods. Depending on the soil, expect a good 10+ to 15+% improvement on your final reading...

Don't forget to fit a flush earth rod pit over the finished rod, it'll protect the cable to rod connection, and be a visible location finder for the future....

 

[Sparky 7]

Generally to confirm the effectiveness of your electrode reading you perform the calculation found in regulation 411.5.3 of BS 7671 which is a basic ohms law calculation

Assuming you have a 30mA RCD fitted to your installation with a recorded value of 179ohms = 179 x 0.03 = 5.37V which is less than the maximum permitted (50V) so therfore your reading of 179 ohms is satisfactory in this application, providing that the reading can be trusted to remain stable, as other posts have pointed out rod type and ground conditions have a bearing on the stability of the electrode resistance.

 

[Engineer54]

Generally to confirm the effectiveness of your electrode reading you perform the calculation found in regulation 411.5.3 of BS 7671 which is a basic ohms law calculation

Assuming you have a 30mA RCD fitted to your installation with a recorded value of 179ohms = 179 x 0.03 = 5.37V which is less than the maximum permitted (50V) so therfore your reading of 179 ohms is satisfactory in this application, providing that the reading can be trusted to remain stable, as other posts have pointed out rod type and ground conditions have a bearing on the stability of the electrode resistance.

Not much good though, if and when that RCD goes belly up!! lol!!

 

[Guest111]

All advice is good, trouble being paye for so long is when your chucked a twig and a clamp you just do it, also not being a domsetic godess does not help matters ,no company i have ever worked have so much as owned any kit for testing rods.

Now being the boss of myself i find lots of very helpfull advice thanks guys

on a lighter note unless you are sure she cannot get on here stop lying,unless you are happily single no doubt your boss will be lurking somewhere, you may think you,re the boss but do you have your wifes permission to say so? if not you are an exceedingly brave man lol:89:

 

[Deleted member 9648]

Generally to confirm the effectiveness of your electrode reading you perform the calculation found in regulation 411.5.3 of BS 7671 which is a basic ohms law calculation

Assuming you have a 30mA RCD fitted to your installation with a recorded value of 179ohms = 179 x 0.03 = 5.37V which is less than the maximum permitted (50V) so therfore your reading of 179 ohms is satisfactory in this application, providing that the reading can be trusted to remain stable, as other posts have pointed out rod type and ground conditions have a bearing on the stability of the electrode resistance.

Not much good though, if and when that RCD goes belly up!! lol!!

Neithers 20-30 ohms mate....

 

[Engineer54]

Neithers 20-30 ohms mate....

Agree to a point, ...well as far as domestic applications go anyway!! Which is why we both agree that on domestic TT installations it's prudent to also include an up-front S type RCD, to cover such failures.

But then, if i had driven two of these 1.2m rods in the ground and got a 20 or even a 30 ohm reading, i'd be inclined to go with a third rod, ...that's going to get me pretty close to those TN values (even if i have to wait for soil consolidation) that you think aren't worth going for!! ...Got to be cheaper than providing an S type RCD!! ...lol!!

 

[GLENNSPARK]

Agree to a point, ...well as far as domestic applications go anyway!! Which is why we both agree that on domestic TT installations it's prudent to also include an up-front S type RCD, to cover such failures.

But then, if i had driven two of these 1.2m rods in the ground and got a 20 or even a 30 ohm reading, i'd be inclined to go with a third rod, ...that's going to get me pretty close to those TN values (even if i have to wait for soil consolidation) that you think aren't worth going for!! ...Got to be cheaper than providing an S type RCD!! ...lol!!

absolutely eng at £80 odd a throw....lol...