Advice Wanted - VERY High Earth Resistance Problem

[Axnfell]

I have been doing some tests around our property here and I cannot get the earth resistance test to get anywhere lower than 1.86k, even started tested now up to 30 meters away from the property and still cannot get any lower readings.

Any advice would be greatful.

Kind Regards

James

 

[telectrix]

pleas explain what you're trying to do. are you looking to get a Ra?

 

[Axnfell]

Hi, Yes trying to test 'Ra', Here on the Isle of Man most of the Island is TT based Earthing.

 

[telectrix]

are you banging in a decent sized rod?

 

[SJD]

How exactly are you testing, and what depth of earth rod?

Round here I can almost get a few kOhm by just dipping the end of my test probe in the soil!

 

[Axnfell]

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.

 

[Octopus]

Try watering the ground

 

[telectrix]

hire one of these beasties. maybe HSS do them:

 

[Strima]

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.

 

[telectrix]

1553 and Wiha screwdrivers.... copycat. .

 

[Strima]

1553 and Wiha screwdrivers.... copycat. .

1552, I’m not as much of a tool tart as you...

 

[telectrix]

1552 and 1553 best MFTs ever. just had mine calibrated for 4th time since buying 2nd hand from MDJ, 5 years ago.

all the 1553 has over the 152 is bluetoth which i never use.

1. i don't need it.
2.i don't undersatand it anyway.

 

[Strima]

Had to get mine repaired, the test lead sockets fell to bits, apart from that I’ve never had a problem with it.

 

[SJD]

A depth of 1m is not that deep, I normally drill the first 1m with an extra long bit first. But if it really is solid rock after 1m then I appreciate going deeper could be tricky, unless you can find some super-long drill bits. Possibly burying tape, or an array of rods spaced out might be worth trying.

What about neighbours, assuming there are any, what sort of values do they have?

 

[telectrix]

Had to get mine repaired, the test lead sockets fell to bits, apart from that I’ve never had a problem with it.

could have done that yoursen.

 

[davesparks]

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.

1m is not deep enough to get an Ra which is stable long-term.
And using just one rod is not a very good plan either.
You need to go deeper or else find another method of installing an earth electrode

 

[Yozza19]

900x900 earth mat on bed of marconite about 3 m deep

 

[Axnfell]

They kind of live in the middle of woodland, on a hill that seems to be basically baserock with a light covering off soil and roots, all looks lovely but a real pain at the moment, I have not tried Tape yet, I was kind of hoping that this would be a simple fix somewhere along the line, Will have to pop to Yesss on Monday to see if they have any tape in stock, Thanks guys for the help, Very much appreciated.

 

[jamie-spark]

Do you have access to another test instrument to make sure your meter/ leads are not faulty.

If the ground is hard you need an sds max gun with an attachment to make easy work of it, I’ve done an install at Loch Lomond where the ground was full of rocks, it can make a lot of difference if you sharpen the end of the first rod to a point as this can break small rocks or help deflect the electrode when going down. As others have said you’ll need more than just one electrode for stability , I usually go for a minimum of 3 1.2 m you may also need multiple electrode sites. The above job I mentioned we hade 5 electrode pits with 4 electrodes deep as the soil resitivity was poor although we were looking to achieve an Ra of under 10 ohms

 

[westward10]

Stick the rod into a tree.

 

[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.