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.

 

[driverman]

Yes your right.....as far as I know building sites to be TT. Also re containers building site or not TT also.

 

[Deleted member 9648]

Yes your right.....as far as I know building sites to be TT. Also re containers building site or not TT also.

Well it is permitted in both situations but there are conditions as stated in the OP, I'm just not sure whether those conditions are met in this case.

 

[driverman]

Getting late, tired. Worked for a DNO and anything that was "portable" like porta cabins etc, PME would not be provided. The same with any steel enclosures even thought fixed, PME would not be provided.

 

[ipf]

I wouldn't class it as fixed, personally, being fed via 32amp inlet sockets and plugs. I'd go with the recommended (717) as a result.

However, if the condition of the installation is good, I wouldn't worry, it being extremely unlikely that problems will ensue and having only carried out a MW. Grey area, I agree, but you've stated your asumption re the original installer.

 

[Guest77]

If it is a building site then TNS or TT is acceptable to the sockets, remember as it is a building site it will want a EICR carried out and a copy of the report handed to the site manager/foreman every 3 months, PME/TNCS is an absolute no-no on a construction site for temporary buildings, I would drop the earth off into a wago or connector at the sockets and drive a 5ft rod in to the ground under the sockets and TT them there.

 

[ipf]

If it is a building site then TNS or TT is acceptable to the sockets, remember as it is a building site it will want a EICR carried out and a copy of the report handed to the site manager/foreman every 3 months, PME/TNCS is an absolute no-no on a construction site for temporary buildings, I would drop the earth off into a wago or connector at the sockets and drive a 5ft rod in to the ground under the sockets and TT them there.

Agreed but I think Wirepuller knows the score. He's only done a small addition and made his thoughts and observations known.

 

[topquark]

Should really be flagged before hand. Same category as main bonding for any prework survey ie suitability and provision of earthing system. Talk to the site super and ask if he wants it sorted? Any provision for lightning protection?

 

[Guest77]

Agreed but I think Wirepuller knows the score. He's only done a small addition and made his thoughts and observations known.

He is very knowlegable without doubt, however he dropped a clanger on this occassion, he shouldn't have done any work under those circumstances.

 

[Chr!s]

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.

You need to work to the general requirements of BS7671 and section 704 in conjunction with BS7375. Now its clear that canteens, toilets and administrative units fall outside of 704, so general requirements apply.

Chris

 

[Deleted member 9648]

If it is a building site then TNS or TT is acceptable to the sockets, remember as it is a building site it will want a EICR carried out and a copy of the report handed to the site manager/foreman every 3 months, PME/TNCS is an absolute no-no on a construction site for temporary buildings, I would drop the earth off into a wago or connector at the sockets and drive a 5ft rod in to the ground under the sockets and TT them there.

According to section 704 TNCS is allowable to fixed buildings on a construction site,so the question really is whether a transportable unit which is going nowhere for the duration of the site work meets this requirement

He is very knowlegable without doubt, however he dropped a clanger on this occassion, he shouldn't have done any work under those circumstances.

Again...the area of concern is administrative,if you read through section 704 and 717 there is no cast iron TNCS not permitted regulation,it is open to interpretation. I may have dropped a clanger...or I may not. But certainly if I was doing the original install I would not have used the TNCS earth system.

You need to work to the general requirements of BS7671 and section 704 in conjunction with BS7375. Now its clear that canteens, toilets and administrative units fall outside of 704, so general requirements apply.

Chris

Indeed,possibly.....but that still leaves section 717.

Thanks for all the replies guys....much appreciated. I still feel by noting it on the MW cert I completed and stating that the responsibility for assessing the suitability of that means of earthing lies with the original installer I have covered my ---....(hopefully)

 

[Guest77]

Not trying to be difficult fella, far from it, just saying it as I see it, I just don't agree with your interpetation of it, no offence to you intended.

 

[topquark]

You're assuming they've used 717.411.4(ii) before they've connected, not sure I'd want to argue from that pos though

 

[Chr!s]

According to section 704 TNCS is allowable to fixed buildings on a construction site,so the question really is whether a transportable unit which is going nowhere for the duration of the site work meets this requirement


Again...the area of concern is administrative,if you read through section 704 and 717 there is no cast iron TNCS not permitted regulation,it is open to interpretation. I may have dropped a clanger...or I may not. But certainly if I was doing the original install I would not have used the TNCS earth system.



Indeed,possibly.....but that still leaves section 717.

Thanks for all the replies guys....much appreciated. I still feel by noting it on the MW cert I completed and stating that the responsibility for assessing the suitability of that means of earthing lies with the original installer I have covered my ---....(hopefully)

717 isn't really appropriate with regards construction site, there are subtle differences. These issues are dealt with within 704 and BS7375.

Chris

 

[jamie-spark]

Slightly if topic

There used to be a guidance on the industry section , on the electrical safety website , that if mobile or transportable units were connected by swa. They were no longer classes as mobile or transportable and general rules applied.

Like that made it any safer :-/

 

[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.