Why Use an Earth Rod when a Disc will do?

The greater surface area of the disc would be an advantage - but I'd not be happy about shallow burial. Both drying and freezing can increase the resistance of soil very considerably. How deep you need to go to get to a layer that's consistently damp and never freezes will depends a lot of the location. In general you'd probably have to be at least 0.5 deep to avoid freezing - probably more like 0.75m in some areas (the water regs require a minimum depth of 750mm for water pipes in the UK to avoid freezing). Damp is trickier as it depends a lot more on the kind of soil (sand on a hilltop rather than peaty clay in a valley bottom) - but them that know seem to suggest that if you hit a layer that offers a resistance of 200Ω or less you're likely (in the UK) to have it a layer that'll be reasonably stable over the seasons.


The idea of a "flat" electrode rather than a rod isn't new - I'm sure I've seen a recommendation from years ago that suggested using a buried "plate" as an electrode - positioning it 'on edge' as it were rather than flat, so it wouldn't shelter the soil below it from moisture.


There's also the issue with close-to-surface electrodes of significant voltages being imposed on the surface - which can of themselves be hazardous (especially to those with bare feet or 'long wheelbase' animals.)


So while this disc seems a good idea in principle, to make an adequately robust installation I think you'd have to dig a reasonably deep hole for it - at which point you might as well drop a rod into the bottom (like the DNOs do).


   - Andy.

The greater surface area of the disc would be an advantage - but I'd not be happy about shallow burial. Both drying and freezing can increase the resistance of soil very considerably. How deep you need to go to get to a layer that's consistently damp and never freezes will depends a lot of the location. In general you'd probably have to be at least 0.5 deep to avoid freezing - probably more like 0.75m in some areas (the water regs require a minimum depth of 750mm for water pipes in the UK to avoid freezing). Damp is trickier as it depends a lot more on the kind of soil (sand on a hilltop rather than peaty clay in a valley bottom) - but them that know seem to suggest that if you hit a layer that offers a resistance of 200Ω or less you're likely (in the UK) to have it a layer that'll be reasonably stable over the seasons.


The idea of a "flat" electrode rather than a rod isn't new - I'm sure I've seen a recommendation from years ago that suggested using a buried "plate" as an electrode - positioning it 'on edge' as it were rather than flat, so it wouldn't shelter the soil below it from moisture.


There's also the issue with close-to-surface electrodes of significant voltages being imposed on the surface - which can of themselves be hazardous (especially to those with bare feet or 'long wheelbase' animals.)


So while this disc seems a good idea in principle, to make an adequately robust installation I think you'd have to dig a reasonably deep hole for it - at which point you might as well drop a rod into the bottom (like the DNOs do).


   - Andy.