Physical installation of earth electrode

During fault the to of the rod and the ground around it become live relative to the rest of the ground further away and there is a touch and step shock hazard if the area is likely to be accessible

To that end insulating the top of the rod is a good idea, so that the full mains voltage only starts below ground, and by the time it reaches the surface the available shock current is limited by the resistance of some inches of earth and maybe some  free draining gravel or paving as well.

But joints below ground corrode and need to be accessible for inspection. A wire and clamp up in the air can be seen if it is failing but equally it can be hit by a lawnmower and forgotten in long grass...

Personally I think the access pit method is best, but it is dearer.

The nice way to verify fully buried electrodes is to make two connections in not quite the same place so that you can ring round with a meter on the low ohms range and verify that clamps have not rotted off, but as it uses twice as much material and is not mandated in the UK, it tends not to be done.

Mike.

Thanks Mike. I consider that the pit would have an inspection cover to gain access to the connection. I believe that animals are at risk from a voltage difference if standing on the ground across area up to 2.5 meters.

The pit method is not in the regs ( though it may be in the British Standards)

surprised that the regs and on-site guide don’t even cover protection needed.

Thanks Mike. I consider that the pit would have an inspection cover to gain access to the connection. I believe that animals are at risk from a voltage difference if standing on the ground across area up to 2.5 meters.

The pit method is not in the regs ( though it may be in the British Standards)

surprised that the regs and on-site guide don’t even cover protection needed.

the safe distance relates to the step voltage during fault, and is particularly a problem for longer baseline animals like cows and horses,where the front feet may be near the rod at more than 200V and the back feet may be  further away on a bit of ground only a few volts above the voltage of the plate at the end of the universe. For barefoot humans the step distance is taken to be 1m, and then calculate how far away you have to go to get to two voltage rings 50V apart at that separation. Chickens have small dry feet close together and do not straddle significant voltage drops.

(imagine the voltage on the surface during faults to be more or less the shape of a fried egg, with a 'yolk' of the ground near the electrode more or less at electrode voltage, and then current spreading and getting thinner so less steep voltage drops with distance, falling to non at all far away, but with odd ripples in ir depending on the varying composition of the ground beneath.)

As a quick rule of thumb more than half the voltage has gone from around a rod electrode by a rod length away. Only true for sensible sized rods in sensibly uniform soil free of buried metal, conductive salt deposits etc.

If need be, fencing off an area around the electrode, or something like gravel hostile to bare feet and a poor electrical conductor as a surface finish  can help reduce the hazards.

M,

Thanks for this .