Earthing Problems

[Onoff]

Referring back to my UN post, you could backfill with charcoal and salt.

An interesting idea and I've read up on it a little. I wonder how much it would cost?

Edit: About £500 I reckon! Looks like it'll be multiple rods if the plate doesn't work then!

 

[Farside]

An interesting idea and I've read up on it a little. I wonder how much it would cost?

Edit: About £500 I reckon! Looks like it'll be multiple rods if the plate doesn't work then!

Money's no obstacle if other people are paying, as you know.
Anyway, I was referring to your small hole, not a metre cubed.

 

[Onoff]

Anyway, I was referring to your small hole

Oi, mods!!!

 

[Blue Chips]

I think any of these earth-enhancing materials could be of interest. Per my earlier post, I used a similar product that drastically improved ground/earth rod conduction. It's the easiest solution that I can think of:

https://www.powerandcables.com/product/earth-tapes-rods-bars-copper/marconite/

https://www.an-wallis.co.uk/product...ing-compound/low-resistance-earthing-compound

https://www.jointingtech.co.uk/Download/Furse Conductive Aggregate.pdf

 

[Turbo]

Don't know why you need to clean the plate, a few months buried in wet soil it will turn green anyway!

 

[Onoff]

Update...

I've now got rod/plate/rod. Tidied all the connections up, new crimps and dipped in ACF-50. Printed a couple of TPU grommets to go in the bottom of the earthing box and over the rod.

The original rod position:

https://flic.kr/p/2opHrhW

https://flic.kr/p/2opL9ty

https://flic.kr/p/2opMvwr

Then it goes to the plate, then to the second rod.

I might put the 16mm2 cable in flexible conduit if I can find the glands!

As it stands the earth loop impedance is in fact worse than when I had 3 rods in. I haven't fully buried the plate yet.

Testing and I'm seeing an earth loop impedance of 21.5 ohms. So a pfc of 11A.

View from upstairs, boards over the trench I'm gradually filling by hand:

That's a lot of flints!

 

[brightspark]

the reason been is if u cant get the impedance down the rods need to be at 1 meter apart minimum spacing a large one in one spot makes no diffrence

 

[Guineafowl]

21.5 ohms is a great improvement on >200, or am I missing something?

 

[Onoff]

the reason been is if u cant get the impedance down the rods need to be at 1 meter apart minimum spacing a large one in one spot makes no diffrence

They are over a metre apart.

 

[Onoff]

21.5 ohms is a great improvement on >200, or am I missing something?

I really don't believe it was ever over 200 ohms tbh. Don't think he wanted to do the job.

 

[Guineafowl]

I really don't believe it was ever over 200 ohms tbh. Don't think he wanted to do the job.

Under 100 is pretty good, though. I doubt you’ll get it much better.

 

[Onoff]

Under 100 is pretty good, though. I doubt you’ll get it much better.

Just watch! I'm on a mission!

30m of 9x1mm tape next just for a laugh.

 

[500e]

Had mats on radio towers on Bodmin, more than 5mtr sq mainly to cut rf noise off tower 50 x 3mm of each leg to mat.
Bodmin has poor earth properties thin soil and rock.
Can't remember the figures but even with all that not Stella

 

[brightspark]

Q & A of the Day – What reading should I be getting when using earth rods on a construction site?

James asks this question, which is about what the maximum measured values for earth rods in a TT system should be. It has been answered by the NICEIC (Theme – Distribution Equipment including Cable Management):

www.voltimum.co.uk

a lot of electrical information on this site for anyone interested

 

[Dave-sparks]

As it stands the earth loop impedance is in fact worse than when I had 3 rods in. I haven't fully buried the plate yet.

Give it time, it needs to bed in a bit and the soil consolidate around it.

 

[Onoff]

Give it time, it needs to bed in a bit and the soil consolidate around it.

Yep, figured that. Going to sling a couple of bags of kitty litter clay in just to see what it does.

 

[Dave-sparks]

They are over a metre apart.

They need to be separated by at least the length of the longest rod, ideally further.

Earth rods have a 'sphere of influence' around them. When these spheres of influence intersect it reduces the overall combined effectiveness of the rods.

So if you have 2 rods, each 8' long and with a resistance to earth of 20ohms, if you put them 4'apart they will likely combine to around 18 ohms whereas at 16' apart they will likely combine to 10ohms.

 

[Onoff]

They need to be separated by at least the length of the longest rod, ideally further.

Earth rods have a 'sphere of influence' around them. When these spheres of influence intersect it reduces the overall combined effectiveness of the rods.

So if you have 2 rods, each 8' long and with a resistance to earth of 20ohms, if you put them 4'apart they will likely combine to around 18 ohms whereas at 16' apart they will likely combine to 10ohms.

Yep, aware & what I did, 1st 4' rod banged in. Second rod put in over 4' away from the first. 3rd rod over 4' from the second. Rods only go in 4' here anyway.

Not sure on zones of influence for a plate...

 

[Dave-sparks]

Yep, aware & what I did, 1st 4' rod banged in. Second rod put in over 4' away from the first. 3rd rod over 4' from the second. Rods only go in 4' here anyway.

Years ago it was, and possibly still is, standard practice in HV and substation earthing design to use 5 rods in a crows foot pattern. I can't remember what the reasoning for that pattern was now though,

Not sure on zones of influence for a plate...

I've got an incredibly tedious book somewhere that covers earthing and earthing design somewhere, I'll see if I can dig it out. But I think for a plate it's just an elongated sphere.

 

[Onoff]

Well that's me flummoxed!

With my old meter, uncalibrated I get a consistent 21 ohms (11A to earth give or take). Tbh I thought that pretty good. The max I think for a TT in the OSG iirc is 20 + 1 "for the rod"?

I then tested using work's new MFT, calibrated etc. Got a well low reading:

Trouble is it's not repeatable, all over the shop on successive tests:

Loose connection maybe? Think I've some dead test results for that ring somewhere...