There arethree main earthing systems found in homes throughout the United Kingdom, these are TN-S, TN-C-S and TT system. If you are having your house rewired or earthing updated by J R Electrical, your main earth conductor and bonding to your gas and water pipes will be upgraded to the current 17th Edition Wiring Regulations (dependant on what system you have installed). It is possible for us to upgrade the earthing without changing your fuse board if cost is an issue, it can be a good way to bring a old system up to a much more safer standard. The electricity company isolator shown in the three photos is not always fitted by the electric distributor.
The TN-S system features a separate metallic sheath (usually lead) on the incoming supply cable. The 16mm earth connection shown going to the main cable is not quite like this in real life. The Electricity company will usually fit either a soldered wiped joint or a braided earth strap that wraps around the lead sheath inside the supply head to make an earth connection. the other end of the braid will then usually be fitted to the main earth terminal. A 16mm earth conductor is then run to the consumer unit from the main earth terminal. Main gas and water pipes are then bonded with a 10mm earth conductor using earth clamps. these gas and water bonds should be made on the consumer side rather than the supply pipe from road.
The TN-C-S system is similar to the TN-S setup except that the incoming cable does not have a separate lead sheath for the means of earth. The main 16mm earth conductor is connected to a terminal on the cut out, this terminal is connected to the neutral conductor of the supply cable inside the cut out. Most new properties will have this type. It is sometimes labelled as a PME supply (Protective Multiple Earthing). A 16mm earth conductor is then run to the consumer unit from the main earth terminal. Main gas and water pipes are then bonded with a 10mm earth conductor using earth clamps. these gas and water bonds should be made on the consumer side rather than the supply pipe from road.
The TT system differs from the other systems in that there is no physical connection made to the main supply cable or cut out for the means of earthing. Instead an earth electrode is fitted into the ground outside, this should be fitted in an accessible inspection pit. An RCD should always be used as the main earth impedance will be higher than the other systems due to the fault current having to flow through the general mass of the earth. If an RCD is not used the fuses will not be able to reach there respective disconnection times set by the regs, so not giving the safety/protection that is needed. TT system is usually found in more rural areas, usually where the supply comes in overhead, however it is not limited to these areas. there are many houses in the UK that do not have an earth terminal provided by the electric company.
If you have this problem in your property its always a good idea to see if the electric company can provide you with a means of earthing by providing a main earth terminal. If it is not possible for the company to do this, which is often the case, it is recommended to turn these setup into a TT system. J R Electrical can do this for you.