Driving in Earth Rod

[RickH]

Need to fit earth rod for a TT circuit.
The ground is very hard, is there any reason against pushing a 3’ long drill in first, give a chance on getting the whole 8’ rod in.
Ground is built up, clay & stone.
(Digging trench for cable was incredibly hard going)

 

[flameport]

Could be done, provided you are not drilling through pipes, cables or anything else that's concealed underground.

If the ground is that hard, rods are not likely to be particularly successful. There are many other options.

 

[sparkwright]

8 feet?

 

[ericmark]

We do it a lot, the ballast used around the railway means top bit of ground very hard, so SDS drill first, then knock in rod. The problem is getting the distance away from the rod to measure the resistance of the rod, 30 meters is a long way with domestic, and the deeper the rod the further distance to measure. Rods I used were 1.2 meters each, and lifting the paddies motorcycle up 1.2 meters to knock in next rod was not easy, with an 8 foot rod it would need scaffolding to reach top of rod. But have fitted 8 rods with connectors to get the 8Ω which plans required. So have fitted 9 meter rods in sections.

 

[RickH]

8 feet?

My fault was thinking of if I joined 2

 

[RickH]

We do it a lot, the ballast used around the railway means top bit of ground very hard, so SDS drill first, then knock in rod. The problem is getting the distance away from the rod to measure the resistance of the rod, 30 meters is a long way with domestic, and the deeper the rod the further distance to measure. Rods I used were 1.2 meters each, and lifting the paddies motorcycle up 1.2 meters to knock in next rod was not easy, with an 8 foot rod it would need scaffolding to reach top of rod. But have fitted 8 rods with connectors to get the 8Ω which plans required. So have fitted 9 meter rods in sections.

I have both issues, the site I’m on was built up about 30’ with a combination of stone from where they cut a dual carriageway through a hill .. plus a lot of slag from the steelworks.
then a railways sidings was put on top for a couple of decades …. So very firmly packed rubbish.
I have 2 other rods on site they work fine … the electrician just laid them in the trench (450mm). rather than drive down.
Trying to do this better …. The house is being converted to PME next month so those rods become redundant but this new circuit will remain.

 

[ericmark]

There are two ways to measure the earth rod, compare to the DNO supply, which clearly only works once there is a supply, and using a special meter and two test probes. The latter needs the equipment to test it which is not often included in the test kit normally used by electricians.

However to operate a 30 mA RCD it is considered you only need 200Ω higher than that would still work, but considered unstable, and in the main one rod at 1.2 meters will be enough.

The problem is the land dries and gets wet, so the resistance changes, and the soil normally slowly gets better over time, so return 6 months latter and normally the reading is better, but not always. But in the main by time the rod is low enough to fit the cover over it, as you want to stop anyone being able to touch it when in a fault condition, one rod is ample to make a RCD trip.

 

[JohnW2]

My fault was thinking of if I joined 2

Nothing wrong with that thinking - it's sometimes necessary (and is why the rods usually have the facility to be screwed together).

However, in answer to your original question, I see no reason why you couldn't first drill a 3' hole, but I very much doubt that would make much difference to how difficult it would be to hammer in the (last few feet of) an 8' rod.

Flameport's warning about underground pipes/cables etc. is obviously valid, but, given how hard you would have to be hammering the rod, I think you'd probably be almost as likely to damage any pipe/cable with the rod as with a drill!

I would personally first try with a 4' rod, and then (if that was not electrically satisfactory) with two or more 4' rods, before even thinking of an 8' one (which would probably be a challenge, certainly in localities such as mine (and, it sounds, also yours).

Kind Regards, John

 

[ericmark]

Last earth I fitted was for an aerial mast, it was a square of copper ½" pipe put under a meter of concrete poured to hold the mast, it was never tested, I am sure it works, but before concrete poured unlikely to have been a good earth, and after too late anyway. And to test, well next to 8 miles of railway track, so nearly impossible. Could not put probes in on our land without the rails affecting the reading.

 

[flameport]

The house is being converted to PME next month so those rods become redundant

They won't.

Supplementary earth electrodes are now recommended for PME supplies, and it's very likely they will be mandatory in the future.

 

[RickH]

Rod went in drill start then bit of sledging.

 

[JohnW2]

Rod went in drill start then bit of sledging.

4' or 8' ?

Kind Regards, John

 

[RickH]

4’ …. For now, will have that tested first... threaded end undamaged, so could extend if required.

Previously had clamps that screwed onto end on rod, then the clamp this time is as per pic.

Do you just strip end of earthing wire, an put it behind the rod (opposite side of screw) so no need to crimp on a Lug?
.

Ellen

 

[JohnW2]

4’ …. For now, will have that tested first... threaded end undamaged, so could extend if required.

Fair enough. Roughly what diameter hole did you drill? If 3' of the 4' rod is/was fairly loose in the drilled hole then you probably ought to do something to fill/compact the space around the rod, and certainly seriously 'water' it (particularly with everything as dry as it is at the moment) before you have it tested.

Previously had clamps that screwed onto end on rod, then the clamp this time is as per pic. ... Do you just strip end of earthing wire, an put it behind the rod (opposite side of screw) so no need to crimp on a Lug?

I would think you probably have no other option with a clamp of that type. Without a long screw and an additional nut on the clamp, I can't see how you could attach a lug to it (but maybe I'm missing something!).

Kindest Regards, John

 

[RickH]

Same thoughts on the clamp.

I used a 20mm drill, bottom of trench had a few mm of water that went in hole as well, so think all will consolidate around the rod … I will pack/whack ground around it before backfill.