Rank: Forum user 
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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.
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Rank: Super forum user 
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Where the cabin comes with an "installed" ring-main etc., it would seem inevitable that the system requires a T-T earth system to enable on-site certification of a safe and compliant temporary installation?
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Rank: Super forum user
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Yes TT system. 17th Ed BS7671 Special locations. Tested every 12 weeks
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Rank: Forum user
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Thanks guys, last one was certified without earth spike, electrcian said it didn't need it!
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Rank: Super forum user 
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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.
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Rank: Super forum user
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As Paul says, quite rightly, there are a few small exceptions such as generators etc but for the most part if you us a TT system with RCDs and a rod you'll be fine. More detail would be cool. Pop it over if you like and I'll take a peep for you.
Good to see you're still about Paul :-)
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Rank: Super forum user
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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
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Rank: Super forum user
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For the benefit of those of us inclined to wonder if there's any faintly tenuous link with motorbike races on the Isle of Man, please can someone explain what TT means in its electrical context?
As an aside about earthing my first car was an elderly VW Beetle for which its previous owner gave to me a detailed maintenance manual. I was initially puzzled by the references to "ground" in the electrical chapter until I realised that the manual had evidently been translated direct from the original German version in which "grund" was presumably the word for earth.
p.s. After buying the car I couldn't find anywhere in the engine compartment to top up the coolant system with water and antifreeze, so subsequently didn't bother trying to do so! Anyhow, the car always started first time even during prolonged spells of severe freezing weather when I lived and worked in Northern Scotland. :-)
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Rank: Super forum user
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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.
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Rank: Super forum user
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Graham,
Forgot IIRC the old Beetle was air cooled, well the ones I worked on were anyway!
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Rank: Super forum user
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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.
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Rank: Super forum user 
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paul.skyrme wrote: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 - Thanks for the above post. This takes me back almost 40 years when did a number of City & Guilds electricalinstallation courses. I am going to hang on to your reply and place it in my reference folder so that I can at least pretend to understand what project managers or sparkies are talking about!!
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Rank: Super forum user 
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paul.skyrme wrote:Graham,
Forgot IIRC the old Beetle was air cooled, well the ones I worked on were anyway! And the 'really' old ones were 6v! I am showing my age now
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Rank: Super forum user
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I would have gone into the full lecture mode had I thought the need :-) but the answer I gave was all that was required to answer the post given the detail to hand at the time.
TN-C-S or pme is IMHO a dangerous system if not understood correctly. If you think about it is the inherent danger in presents that bans it for marinas, caravan parks and construction sites etc. If anyone would care for the reasons behind this then please give me a call.
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Rank: Forum user
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Thanks for all the info.
I'll have a good look at the certificate next time I visit that site.
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Rank: Forum user
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Depends if your exporting a suppliers earth ?
Depends on your earthing arrangements
Is it on a construction site?
An office at the construction site but not part of construction?
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