TT EARTHING WIRING MATTERS

A good intro.

Possibly strange use of ‘ADS’. I consider that an RCD also automatically disconnects the supply, just not from measuring the live current alone as fuse or MCB would. 

I'd have probably said ‘over current protection’  or even "fuse/mcb" to make it totally  clear.

Missing items. 

1) Insulating the top foot or so of  an electrode by boxing in the top,  greatly reduces the step voltage risk, as the peak potential on the surface is then reduced, and also slightly current limited,  by the volume of earth in series with the bare foot even standing pretty much right on top of it. For valuable livestock this is worth considering.

2) It is a good idea (mandated in many parts of the planet) for  grid or tape electrodes, where there are buried joints that cannot be seen, to attach two wire tails and not  in the same place. A ring round continuity test between the two points of connection  can then be performed at the surface to verify the underground joints are not rotting off.

3) The DNO electrode resistance may not be that great - if your electrodes are lower impedance than theirs, then during faults there is potential to lift the substation neutral some way off true ground.

4) Higher touch voltages possible than for TN, is the reason for shorter ADS times.

Mike.

A good intro.

Possibly strange use of ‘ADS’. I consider that an RCD also automatically disconnects the supply, just not from measuring the live current alone as fuse or MCB would. 

I'd have probably said ‘over current protection’  or even "fuse/mcb" to make it totally  clear.

Missing items. 

1) Insulating the top foot or so of  an electrode by boxing in the top,  greatly reduces the step voltage risk, as the peak potential on the surface is then reduced, and also slightly current limited,  by the volume of earth in series with the bare foot even standing pretty much right on top of it. For valuable livestock this is worth considering.

2) It is a good idea (mandated in many parts of the planet) for  grid or tape electrodes, where there are buried joints that cannot be seen, to attach two wire tails and not  in the same place. A ring round continuity test between the two points of connection  can then be performed at the surface to verify the underground joints are not rotting off.

3) The DNO electrode resistance may not be that great - if your electrodes are lower impedance than theirs, then during faults there is potential to lift the substation neutral some way off true ground.

4) Higher touch voltages possible than for TN, is the reason for shorter ADS times.

Mike.