Advice Wanted - VERY High Earth Resistance Problem

[UKMeterman]

Hi,
This link might give some ideas. https://www.wbdg.org/FFC/NAVFAC/DMMHNAV/hdbk419a_vol1.pdf

 

[mhar]

Hi,
This link might give some ideas. https://www.wbdg.org/FFC/NAVFAC/DMMHNAV/hdbk419a_vol1.pdf

Got to page 403 then gave up

 

[johnduffell]

I’d look at burying tape rather than rods and create an Earth nest.

I got a c asking Ra last week even with all the sun we’ve had.

0.74ohms can't be going through the earth surely, did you touch the water supply pipe on the way down and are going back to the network via someone else's bonding?

 

[Strima]

0.74ohms can't be going through the earth surely, did you touch the water supply pipe on the way down and are going back to the network via someone else's bonding?

I didn't install it, only tested it, it's been in the ground 15 years.

I reckon it's hit another service on its way down, according to the paperwork the rod is 5/8" and 3m long so not a twig by any means.

 

[davesparks]

0.74ohms can't be going through the earth surely, did you touch the water supply pipe on the way down and are going back to the network via someone else's bonding?

Why can’t that be going through the earth? The DNOs regularly achieve Ra lower than that for substations

 

[johnduffell]

Why can’t that be going through the earth? The DNOs regularly achieve Ra lower than that for substations

I assumed he wasn't t testing a substation just a normal rod, but i did add a "surely", to account for the fact that it could be some crazy setup for amateur radio or something

 

[Gavin John Hyde]

Need to borrow neighbours dogs and encourage them to cock there legs on the top of the rod! will help get a better reading, failing that a bit of marconite could do the trick.

 

[static zap]

Got to page 403 then gave up

Fore warned ..403 Went straight to appendix-es ..
Now getting bored with list .

EARTH ELECTRODE SUBSYSTEMS -- 11, 24, 25, 31, 33, 44, 51, 52, 63, 64, 65, 66, 70, 7 1 , 85, 86, 87, 8 9 , 101,
107, 120, 131, 137, 138, 145, 148, 170, 187, 190, 196, 205, 212, 213.

213 ..FAIL ..mostly surface corrosion /good connection (+ RF Impedance)

.... Then got side tracked with memories "Things wrapped in Brown wax paper ,in heat sealed polythene bags..."
( may see if my -Inner lucky stumble , is working later )

 

[Axnfell]

Managed to get it down to 112 Ohms, after paying out a small fortune, 3 earth rods later all connected with flat copper tape (25mm x 3mm x 25m) dug into the ground about 12” deep, couldn’t get any deeper due to roots and rock. Thanks guys for the advice

 

[Strima]

Managed to get it down to 112 Ohms, after paying out a small fortune, 3 earth rods later all connected with flat copper tape (25mm x 3mm x 25m) dug into the ground about 12” deep, couldn’t get any deeper due to roots and rock. Thanks guys for the advice

Cool, go back when you've had a couple of days rain and test again, just out of curiosity.

Personally I wouldn't have bothered with rods and gone solely for tape.

 

[Deleted account]

Ive been getting some higher than normal earth resistance reads due to the dry wether, however no where near as high as yours. What reads do you normally get when we have a normal wet summer?

 

[Spud28]

Am I missing something ? Why the need for such low readings, gn3 anything under 250 ohms is acceptable but in theory fine up to 1667 book not to hand so may be wrong?

 

[telectrix]

Am I missing something ? Why the need for such low readings, gn3 anything under 250 ohms is acceptable but in theory fine up to 1667 book not to hand so may be wrong?

1667 is only relevant to circuit/s downstream of RCD/s.

 

[Spud28]

Yes so protection using ads is a given for tt. On submains and final circuits.

 

[Deleted account]

Am I missing something ? Why the need for such low readings, gn3 anything under 250 ohms is acceptable but in theory fine up to 1667 book not to hand so may be wrong?

Agree with you the 1667, but if over 200ohms it is deemed unstable or words to that effect.
I haven't got my book to hand,but I'm not to sure about your 250 figure.

I had a 207 ohm Ze last week but let it go due to extremely dry whether. It had the additional protection of 30 ma rcd so in theory yes the 1667 would have been ok.

 

[Axnfell]

Stima, the main reasons for the extra earth rods were to fix the ends of the tape to them, mainly for testing, I just wanted to have each end of the triangle that I have made a testable point, just for my own peace of mind, the highest vale tested was what I recorded nearest the property anyway and it’s much lower away from the property when tested at the other two earth rods, it’s a tad over kill I know but much better now than the 1.8k that I could not get lower reading off and wanted a true reading to be as low as possible without having to water the rods which I feel is not really a true reading as no one will be watering the earth rods on a daily basis and wanted the readings to stand up on dry, hot days like we have now.

 

[Nigel]

Earth Rods are being hit in to their entire length, approx 1m deep, cannot get much deeper as we are hitting bedrook, have tested using |KEW-5105A and then tried removing the earth rood and testing again 1 meter further away from the property and so on, but cannot get the reading to get any lower. The soil is not the best, looks as though its had about 100 years of tiles, bricks and plaster pored into it.

Sounds to me you are doing loop testing not Ra testing(?)

 

[HandySparks]

Sounds to me you are doing loop testing not Ra testing(?)

In a case like this, the readings will be identical for all practical purposes.

 

[Nigel]

In a case like this, the readings will be identical for all practical purposes.

Can you really say that? Ra testing would only be between the rod he has installed which he said was 1M down and 10 meters away while the loop test will be the Ra plus the full loop.

An Ra test is a dead test and a loop test is a live one.

 

[HandySparks]

Can you really say that? Ra testing would only be between the rod he has installed which he said was 1M down and 10 meters away while the loop test will be the Ra plus the full loop.

An Ra test is a dead test and a loop test is a live one.

But in this case (and most others), the rest of the earth fault loop will add very little impedance on top of that provided by the interface between the rod and the bulk of the earth. So the difference between Ra and Ze will, in most cases, be negligibly small.