TNCS construction site transportable unit

[Deleted member 9648]

Went to do a small addition on a construction site last week. The installation was installed and certed by others 6 months ago and consists of 3 transportable units (converted steel containers). They are fed by an SWA from a TNCS supply to a junction box,this then feeds the 3 units via 3x32a plugs into 32a inlet sockets on the outside wall of the units. Now bs 7671 prohibits the use of TNCS on a construction site except for fixed buildings,and section 717 prohibits it's use for transportable units unless under the supervision of an instructed person and the suitability of the means of earthing is confirmed before connection.
Firstly is a transportable administative building classed as 'fixed' for compliance with section 704 (construction sites).....and secondly is a recommended retest interval classed as 'under supervision of an instructed person' for compliance with 717...(transportable units) ?

This seems a grey area,I noted the TNCS supply on my MW cert for the job,and stated that it was assumed that the original installer had assessed the suitability of a TNCS supply at the time the EIC was provided. However I'm now wondering whether I should have flagged this up before carrying out any work.
Your thoughts please esteemed members.

 

[Deleted member 9648]

All views taken on board,but thinking about it the EIC provided by the original installer will be the one that gets scrutinized in the unlikely event of anything happening which is attributed to the earthing system. I have flagged it up in writing on my MW and verbally informed the site manager that there are special requirements if a TNCS earthing system is in place. I think I will leave it at that.

 

[ipf]

Should do the trick, in my opinion of course.

 

[Richard Burns]

You have certainly not made the installation any less safe and could have given the potential for there to be greater compliance with the regulations should the customer accept your information.
I would say that the original installer has made an interpretation of the regulations that I would not have liked to have made.
There would be a case for considering a stationary office building on a construction site as being permitted TNCS earthing, but I think that fact that it can be moved and is fairly clearly outlined as a transportable unit would trump this and require a TT / TNS system.

However if one were to arrive at this site then the hazards associated with an office building (albeit transportable) being on a TNCS system may be considered low and the additional cost to change the earthing system is probably not justified if one were to do a risk assessment of the existing installation, especially since it is a temporary arrangement only during construction.