Earthing - Cautionary note

Nick,

The short answer is that i really don't know,but there are a couple of avenues to explore.

Seems that quite a lot has to do with the prevailing earth type in your area and property.

To my eyes and thoughts,the earth that i installed should have been pretty good,but the tests proved otherwise.

I would be tempted to increase the depth of the rods by connecting more together using the correct connectors (to help ensure maximum connectivity).

Tip time.....when you connect the rods and drive the collar of the connecting section,remember to "backfill" as you are driving down as the collar is bigger in diameter than the rod.

In more industrial regeons they seem to dig very large areas to some depth and sink a "grid" type arrangement. (Hi-Fi Earth extremus ?)

I suspect that I will end up driving a couple more rods in to dig down deeper till ii find something suitable......then add another....just to be sure...

I have no idea of the "numbers" for any given application,but I would suspect that the lower the number the better. ( you do need to be exact about the "regs" for any specific conditions).

Besides digging deeper,i would possibly be looking at increasing the guage of the wire connecting it all together ?

If you find a good method....let us know.

Regards

Chris

Interesting topic - especially at the moment when so many people are engaged in dedicated mains installations for HiFi equipment.

I have no experience of this topic - just done a bit of reading.

I would be very interested to hear how people have had the earth electrode resistance measured by their electricians.

My understanding is that there is only one viable method for smaller installations. This is called the 'fall of potential method' in which four interconnected earth spikes are used along with an instrument which is set up to measure various readings of current and voltage.

The two spikes 'at the extremities', one of which is the test rod, are placed a considerable distance apart (at least 10 times the length of the earthing rod under test). The other two spikes are placed at intermediate points. These are referred to as the 'potential electrodes' An applied voltage to the spikes at the extremities results in a current flow between these spikes. This is measured. The potential differences between the other 'potential electrodes' and the earthing rod under test are also measured. Standard Ohm's law R=V/I calculations provide the resistances at these two points. Take the average of the calculated R and that is the earth electrode resistance. This is acceptable as long as the difference between the calculated Rs is very small in comparison to the average R.

Still on the earth electrode issue I have noted that consideration should be given to the potential field that arises around the earth connection when a large fault current flows into it. It is thus seen to be beneficial to have the top of the earth rod well below ground level. An earhing rod inspection pit as part of the installation may thus also be beneficial. To have the top of the earthing rod above ground or even near to the surface may be dangerous under fault conditions.

I realise that most of us are considering earthing rods just for our HiFi systems - and that the earth provided is supplementary to but is bonded to the main earth in the house. This may be a further consideration/complication/ or ameliorating factor in the whole equation.

Can anyone provide real clarity? Does anyone have real expertise, practical experience and knowledge?

Terry

Anyone got anything to contribute?
Terry

Hi,
I have no idea whether any of this is relevant: When we moved to an isolated rural UK property. The electricity board insisted on replacing our transformer on a pole. They laid two massive braided copper cables. Each probably 30 metres long and at right angles to each other leading to the pole. It certainly stopped the lights fading when we put the kettle on.
When we moved to Denmark it was all unearthed 2-pin plugs. So I buried a length of old copper pipe under the lawn and soldered a braided wire to this. Then brought the other end back to the hifi earthing point. The earth leads on the 3 core equipment leads were simply taped back.
Later we had the electricians in, to install 3 pin plugs in the kitchen. Naturally one would think these should be earthed. But I had to insist on the sytem being earthed. This meant a trip to the shop to buy a 6' mains earthing rod and hammering it in myself. They then connected to "my" earthing rod! No measurement of any type were taken as far as I know.
While they were busy I fed a 2x2.5mm cable between my hifi and the fusebox and they happliy connected this (bypassing the RCD). I fitted 3-pin plugs to the few items of earthed equipment and plugged these into my newly earthed mains 3-pin sockets. I rely on the 10A fuse in the fusebox as Danish plugs are fuseless. When tempted to up the 10A fuse to 16A (the standard for 3 phase wiring (common in Danish homes for cookers and water heaters) I found the fuse was a different size and so I couldn't cheat. Probably just as well! MY copper pipe earth under the lawn continues to be my "system" earth.
Interestingly(?) I read somewhere. That having a seperate earth to anything attached to the mains. Is as good as flying a kite in a thunder storm on thick copper wire! It invites the lightning indoors. I wish I could remember where I read this.
I'd still like to know how one measures the earth rod resistance in everyday life? Between <what> and the earth rod? The mains earth and the rod? Then how do you measure the resistance of the mains earth alone? Does a "Megger" have an "artificial" earth to allow such measurements? I was hoping to use my ordinary digital multi-meter. But I know where there's a "Megger" for sale (cheaply) if it's worth buying.
My two earths are only 6 feet apart in permanently damp clay soil. Perhaps I should replace my copper pipe earth with a proper rod? They don't cost that much. Would it change anything? Should I move it further away from the mains earthing rod? Ignorance is bliss?

Nime

Nime
You will find lots of useful information here.
Terry

Terry....Nice one !

Chris

I'll third that. Thanks Terry. Just what I needed. Great stuff.

Nime

I installed a garden earth spike, but simply attached it to the lower ground ring main earth at the socket supplying my hi-fi. Was this pointless? It seemed to improve my connection to earth, without any additional risk.
malcolm