Installing an Earthing Rod

[Munroast]

Need to instal an Earth Rod so as I can use the EPS (Emergency Power supply) from my solar battery set up

What do I need to know about earthing rods, it will probably be the solar company installing it (they have to configure the inverter with their password access) and I want to understand Earthing rods before i am sold a load of stuff i don't need

 

[ericmark]

NOTE 2:* The resistance of the installation earth electrode should be as low as practicable. A value exceeding 200 ohms may not be stable. So that's your upper limit. Assuming using a RCD.

The rod should not be so you can touch the rod, if your supply is TN-C-S then with a loss of PEN the house earth could get to 230 volts above true earth, unlikely as you have an earth rod, but should that happen, clearly you would not want to touch the rod, this would stop you getting too close, but this with a slab on top of it is all I have, the paving slab means you are reasonably safe.

With 6 mm² cable you want the current not to melt the insulation so assuming it can carry 40 amps, 230/40 = 5.75Ω so really don't want the resistance less than 6Ω or with loss of PEN it could melt.

Since the inverter will likely with loss of power connect the earth and neutral together, your supply will be TN-S not TT, at least that is how mine works.

There are two methods to measure the resistance of an earth rod, one is you have two probes and a special meter and you have to put them in around 50 meters from the earth rod, and with most properties you can't get in the ground at the required distance, so second method compares it to the DNO earth, basic idea is you measure the resistance of both the DNO and your earth, and assume the DNO earth is very low, so you can ignore that, and assume the earth loop impedance is the resistance of your rod.

 

[Mottie]

When I had a separate electricity supply installed to our workshop in around 1988, the LEB dropped me down a piece of bent plastic pipe and an earth rod about a metre in length. I had to dig my own hole from inside the premises, underneath the footings of the outer wall and drive this earth spike into the ground. I did that and then a mate that worked for the LEB at the time came and tested the spike. According to him it wasn’t good enough so he got me an internally threaded connecting piece and another earth rod. I screwed that onto the newly driven earth rod, screwed the earth rod extension onto that and drove that into the ground. He said it was just about alright!

 

[ericmark]

I was required to get 8Ω for each earth rod, and in the sandy soil at point of Ayr gas terminal I needed 3 to 8 rods at 1.2 meters each, and needed a paddies motorcycle to knock them in.

But in most cases one earth rod will show around 60Ω which is well within what is required.

 

[morqthana]

OOI, has anybody ever tried the installation technique of driving a length of steel conduit into the ground, then using a water jet to remove the soil inside the conduit (and if necessary allowing it to be driven deeper,) then dropping the rod in and removing the conduit?

 

[mikehammer69]

That makes no sense to me as an installation method

 

[ericmark]

A conductive medium is formed over time, so a 5-year-old earth stake is better than a new one, but also the electrochemical series can cause an earth rod to be eroded and so it needs testing at regular intervals.