Does anyone know the definitive answer to whether we need earthing spikes for temporary cabins on site? There seems to be two opinions, but no definitive answer.

Yes TT system. 17th Ed BS7671 Special locations. Tested every 12 weeks

Yes as per Zimmy & generally TT. However, there are other means of earthing rather than an earth rod. Also, there can be exceptions, though these are rare. Without the installation details we cannot tell. If the incoming supply is TN-C-S (PME) then the cabin MUST be TT. If the supply is from a generator then there will need to be an independent means of earthing somewhere, e.g. a rod. Then it gets complicated. Without sight of the certs & the details of the install I cannot say any more.

Cerith #4 I'd like to see a copy of the certificate! Tested without a rod as it was not required? I need a giggle Rob

Graham, Totally from memory and in a rush, so there may be one or two slips! If anyone finds anything wrong, sorry, I'll get quotes from the regs & legislation. TT is a reference to Terra Terra. The supply system is directly earthed, that is the star point, or Neutral of the secondary, low voltage side of the local distribution transformer is directly connected to a means of earthing which is directly connected to the general mass of earth. The first T. The second T refers to the earthing of the installation at the consumers location also being connected directly to the general mass of earth. As opposed to TN systems where the supply is as above. Where as the consumers installation is earthed via either a separate earthing conductor connected back to the star point, TN-S, or using a combined neutral & earthing conductor, CNE, which is known as TN-C-S. TN-S refers to earth & neutral being fully separate throughout their length. TN-C-S refers to the neutral & earth being combined in the distributors network, but seperated in the consumers installation. TN-C-S is also colloquially known as PME, Protective Multiple Earthing, though this is not yet fully implemented throughout the UK AFAIK, though it should be soon. Even with a TN-S presentation at the consumers installation, the supply system may well still be utilising a CNE. Generally in the UK we do not allow TN-C systems within consumers premises connected to the public distribution system.

paul - many thanks for the prompt response to my query about TT. As for my quip about coolant for my Beetle, I suppose it would only amuse those who know that for decades Beetles had air-cooled engines. I could have added another quip about getting a fright on finding no engine at the front of the car and then being relieved to find one in the boot! By contrast I guess that modern Beetle-shaped VW cars have water-cooled engines at the front. On a seasonal note, I found that the Beetle with the weight of its rear-engine over the rear driven wheels gave good traction on snowy/icy roads driving, especially if I put a heavy bag or two of sand in the front boot to improve the traction of the front wheels.

And the 'really' old ones were 6v! I am showing my age now

Thanks for all the info. I'll have a good look at the certificate next time I visit that site.