Earth Rod - DIY

[ban-all-sheds]

I'd love an excuse to use a thermite welding kit.

 

[dunny]

I cant easily get to an outside location as the CU etc is in the middle of the house, hence one of my first questions was could I have the rods inside. Under the living room floor is the most convenient location otherwise it is either break a concrete floor up or go through 2 rooms and an outside wall. I have 2 x 4 foot rods that I was planning to use to whack into the subsoil; we are on clay here with a high water table so hopefully this would be suitable. I suppose if it fails the sparks test I would have no choice but to think again.

 

[ericmark]

Because I had zero potential I was given the job of installing earth rods on a gas receiving plant, in the main each rod needed to be 8Ω and it required between 4 and 8 rods of 1.2 meters each screwed together to get this reading, at the incoming sub-station we had 4 x 8Ω rods in a pit with bare copper connecting them which was all back filled.

However the worry was the current in the earth provided by the DNO and the site earth, so there was a box about the size of a transit van which held a massive resistor, this was to limit the current under fault conditions.

Now in a domestic a single earth rod will likely only be around 80Ω so not much current will flow, however where an earth pit is dug then consideration must be given as to how much current will flow with a 400 volt supply through the earth cable.

I have seen the result when a radio amateur fitted a massive earth pit to assist his transmitter, when the electrician bonded the earth bar with 4 mm² cable to the DNO TN-C-S supply and road workers caused the neutral/earth to be lost. By time I arrived that 4 mm² cable was just a load of copper balls on the ground. The poor guy had seen the plastic melting and had switched off the whole supply to the house, however that made no difference the cable just got hotter and hotter until it melted, lucky it was not where it could do much damage.

Since he had turned off all the power he only lost the earth cable, most other houses in the street had loads of equipment fail.

So there has to be both a upper and lower limit to earth rods when connected to the DNO earth, well they are not under 17th even called earth rods, the are simply classed the same as water pipes, gas pipes and re-bar.

I am sure if an earth is required as well as the DNO earth then there will be either resistors or limits to how good the earth can be, it will I hope not be just left without some protection included in case the DNO lose their earth, he was lucky the wall it ran along was not likely to go up in flames, and he was throwing water on the wires where they went into his shack.

 

[JohnW2]

I cant easily get to an outside location as the CU etc is in the middle of the house, hence one of my first questions was could I have the rods inside. Under the living room floor is the most convenient location otherwise it is either break a concrete floor up or go through 2 rooms and an outside wall.

Could you not go above the ceiling (below the floor above) to get to an outside wall.

I have 2 x 4 foot rods that I was planning to use to whack into the subsoil; we are on clay here with a high water table so hopefully this would be suitable. I suppose if it fails the sparks test I would have no choice but to think again.

You might get away with it, but one problem is that, without repeated re-testing, you would not know whether the earth had become inadequate (hence potentially dangerous) due to drying out. I also have heavy clay soil with a high water table but, even with my outside rod, its resistance can double during long dry periods.

Kind Regards, John

 

[dunny]

Could you not go above the ceiling (below the floor above) to get to an outside wall.

I could but this would be a lot of disruption and I also dont want the wire to run down the outside wall. I would have to take the floor up on a landing and possibly 2 bedrooms and then come down a wall inside before getting to the outside.

I will however have a further ponder today.

 

[ban-all-sheds]

By the sounds of it you have a suspended floor downstairs - is there no way to run an earth conductor under that to a rod outside?

 

[Adam_151]

As no one seems to have mentioned it yet, if stacking rods on top of each other, fit a coupler and a driving stud (effectivly just a big bolt that threads into the other end of the coupler) onto the rod you are knocking in first, otherwise it'll be difficult to fit the coupler after you have beaten 7 bells out of the thread with the hammer.....

 

[ban-all-sheds]

Can you get corkscrew-like rods? Could be easier to install, and would give a larger contact area per unit of depth.

 

[dunny]

By the sounds of it you have a suspended floor downstairs - is there no way to run an earth conductor under that to a rod outside?

Yes, latest plan, under the living room floor and out of the wall through an airbrick, Th reason for going through the airbrick is the whole of the front of the house is sat on a sandstone plinth and the wall is about 18 inches thick. There are 2 airbricks for the living room subfloor and each has a brick box built around them with a second airbrick in. I can put the rods in there?

 

[bernardgreen]

Driving the ground rod into ground onto which a roof drains will go some way in keeping the soil damp and hence the resistance of the rod low enough to meet regulations and ( more important ) ensure the safe operation of protective devices ( RCD ) should a fault occur.

 

[ban-all-sheds]

I can put the rods in there?

As Bernard said, rod(s) outside, not within any bounds of a building.