Physical installation of earth electrode

The biggest risks from rods with exposed tops is probably from falling over them, or damage to the wiring.  If the TT installation has working RCDs as has been noted the dangerous time before the ADS kicks in is quite short, and as we all know, I hope, shorter than half a heartbeat is what the turning point on the graphs of permissible shock voltages versus duration. There will be odd cases of stuck RCDs or badly maintained systems where the fault is persistent and not realised.  In such a case making the electrodes and anything connected to them inaccessible or hostile to bare feet is worthwhile.

In the same way that a short length of plastic pipe in the feed to any outside taps or other plumbing limits the shock current, nothing beats having some extra R between you and it.

A lot of townie sparks are not very  familiar with TT, and tend to worry unduly, done well it is an excellent system with limited fault currents and less risk of tingles than PME. It is of course sometimes not done well -but that is true of all systems.

There are some funnies worth looking for e.g. metal gates and bars in milking parlours that are not licked and rubbed smooth by the cows as they queue up may be an indicator of poor earthing and leakage into ground causing voltage gradients.

If the transformer is small and serves only a few properties, it is possible that the customers earth is lower Z than the one(s) at the transformer neutral and then a fault to earth may not pull up the voltage of the customers earth, but rather depress the live, and in doing so push the neutral to earth voltage well off centre. Such faults on overhead lines can cause great consternation, and is the reason that double pole isolation is required for front end ADS and safe working.

Mike

The biggest risks from rods with exposed tops is probably from falling over them, or damage to the wiring.  If the TT installation has working RCDs as has been noted the dangerous time before the ADS kicks in is quite short, and as we all know, I hope, shorter than half a heartbeat is what the turning point on the graphs of permissible shock voltages versus duration. There will be odd cases of stuck RCDs or badly maintained systems where the fault is persistent and not realised.  In such a case making the electrodes and anything connected to them inaccessible or hostile to bare feet is worthwhile.

In the same way that a short length of plastic pipe in the feed to any outside taps or other plumbing limits the shock current, nothing beats having some extra R between you and it.

A lot of townie sparks are not very  familiar with TT, and tend to worry unduly, done well it is an excellent system with limited fault currents and less risk of tingles than PME. It is of course sometimes not done well -but that is true of all systems.

There are some funnies worth looking for e.g. metal gates and bars in milking parlours that are not licked and rubbed smooth by the cows as they queue up may be an indicator of poor earthing and leakage into ground causing voltage gradients.

If the transformer is small and serves only a few properties, it is possible that the customers earth is lower Z than the one(s) at the transformer neutral and then a fault to earth may not pull up the voltage of the customers earth, but rather depress the live, and in doing so push the neutral to earth voltage well off centre. Such faults on overhead lines can cause great consternation, and is the reason that double pole isolation is required for front end ADS and safe working.

Mike

I recently visited a thatched house in The Norfolk Broads area with a large detached garage. The garage supply was from the house with P.M.E. earthing. In the garage there is a split load consumer unit. The sockets are 30mA R.C.D. protected, but the light circuits are just protected by a B6 M.C.B. The garage earthing is TT.

So, the metal fluorescent lights and outside are just protected by a B6 M.C.B. with no R.C.D. protection.

The earth rod is outside with its top buried. I had no chance to test the resistance of the rod. But the water table was about 3 to 4 feet below ground level, so the rod soil will not dry out presumably.

My concern was that a fault with a resistance may liven up the rod top and surrounding soil without tripping off a M.C.B. for an extended period of time.

Z.

Thanks Mike.

If a rod is sticking above the ground, could this be an insurance claim - assuming that there is a yellow warning notice isn’t nearby.

yet another warning notice .

Exposed earth rod tops can be covered with temporary things like large upturned flower pots, a traffic cone, old bike or deceased pet. Some people build a small wall around the earth rod top with a few decorative stones or house bricks with no mortar. 

Z.