Ufer Earthing
A Ufer Earth is a type of local earth with very low impedance, which can improve the safety of TT earthing systems.
A Ufer Earth consists of a connection to steel mesh reinforcement in a building's concrete ground slab, with the sheets of mesh being tied with wire before the slab is poured. It can therefore only be fitted at new build time, it is not usually practical to retrofit.
A Ufer Earth is not used alone, a conventional earth rod is still needed as usual.
Ufer Earthing explained. Note that the site also discusses standard US grounding practices, which are not identical to ours.
Advantages
Using Ufer Earthing in conjunction with the standard earth rod brings 3 main advantages:
- Much lower TT earth resistance makes the house earthing system safer and more effective.
- Ufer earthing equipotentially bonds a house's concrete slab floor to the electrical earthing system, eliminating the risk of shock from the CPC or equipotential bonding to floor. This risk exists with TT systems where a floor slab is damp, and to a lesser extent with PME supplies.
- Lastly a Ufer earth means the house has 2 earths, and loss of a connection to either one does not leave the building with no working earth, which can happen with standard TT systems, and which is a dangerous fault.
It is not standard practice to include it in domestic build, but it does improve the electrical safety of TT earthed installations. The cost of adding Ufer earthing during construction is trivial when a reinforced slab is being laid. Ufer earthing is mostly used by radio hams.
Disadvantages
- Separate rod earthing is still legally required
- Can't be retrofitted