TT earthing

TT earthing, also called a TT system, is an earthing arrangement where the installation uses its own earth electrode instead of relying on a TN earthing connection from the distributor. IET guidance explains that TT systems may be used where the distributor does not provide a TN earthing system or where a TN system cannot be used, with the first T referring to the distributor transformer being earthed and the second T to the earth electrode at the consumer's installation. IET model electrical forms list TT alongside TN-S, TN-C-S and IT earthing arrangements, so the label can appear in certificates, inspection reports and home-energy electrical paperwork.