Tncs Or Tt

[maffematics]

Hi all

I have just finished installing power to a barn via a switched fuse connecting directly to the incoming suppy. The house is a TNCS system which I have used to earth the switched fuse and the armouring of the swa I have used. As I have used metal clad sockets and switches I have put a rod in to make the barn a TT system but on the cert which earthing arrangement do I use and also which loop and PSC reading do I use hope this makes sense Matt

 

[mk1rob]

I would put TNCS for the supply characteristics section with the Ze/PFC etc readings at the switch fuse. On the NAPIT certificates theres a section on the test schedule form to fill in the characteristics of your new board if its not connected directly to the origin of the installation. This is where id put the TT and sub main details. Hope that helps

 

[maffematics]

Yes that's great. I was using niceic certs and that had the same info on them I am now using easy cert which doesn't give that option thanks again

 

[maffematics]

I have used an insulated consumer unit so swa is not connected to the TT system and tested it all correctly

Thanks for the help

 

[NozSpark]

So how have you brought the SWA into the insulated board??

 

[SLIPSHOD & SLAPDASH]

Yes that's great. I was using niceic certs and that had the same info on them I am now using easy cert which doesn't give that option thanks again

Easycert has that option in  boxes on page 4 & 5

 

[batty]

In the old days electric boards would check you had not taken the PME earth outside the equipotential zone nowadays nobody seems to worry.

 

[maffematics]

Noz spark

I used a swa gland

Slipshod

Thanks I will have a look

 

[NozSpark]

So you have 2 different earth potentials in a single enclosure.....

 

[maffematics]

I have not connected the the swa to the earth bar in the barn consumer so the 2 earthing systems are not connected together I am also using rcbos for the outgoing circuits

 

[NozSpark]

So you have an extraneous earth potential within the consumer unit that you're not going to bond then??

The proper way to do this would be to bring the SWA in through an adaptable box or to measure and cut it carefully, heatshrink the end and bring it in through a large enough PVC gland

 

[Adrian]

You are spot on Noz there are a lot of electricians who don't realise that 

 

[maffematics]

So to make this right I would need to re gland the swa into a plastic box below consumer unit and just bring the 2 conductors into the consumer unit. Thanks for the info Noz

 

[NozSpark]

Yep,,, but just make sure you don't have unsheathed conductors between the enclosures

 

[maffematics]

Would I need to do this for all earthing systems or just TNCS? and also if I used all plastic accessories would I be able to use the TNCS earth or still install a rod? on the job in question I will do as Noz recommends but wanted to know for future installations thanks for your input Matt

I will fit directly underneath thanks Noz

 

[sprocketflup]

Good on yer for doing and wanting to do it right Maffematics scoobed

Do you understand why there is or could be 2 different earth potentials? If yes, then that answers your question.

 

[NozSpark]

If this is a barn then it could be classed as an agricultural installation (a farm)??

You are not allowed to use TNCS earthing on a farm

As for the enclosures,,, some adaptable boxes won't but right up to another enclosure and leave a gap of a mil or two, this gap would be classed as outside of an enclosure and as we know you shouldn't be able to see any basic insulation outside of an enclosure

HTH

 

[NozSpark]

That poses an interesting question - will the DNO give TNCS on a Farm ?

I didn't think that they should

 

[NozSpark]

Ahh,,, when is a farm not a farm????

Well you have livestock farms, arable farms and then you have horticultural enterprises.... All of which shouldn't be supplied by TNCS

 

[Steve3948]

A bit like Petrol Filling Stations should not be TNCS but a lot are.

TNC not allowed but is TNCS, if supplementary bonding is carried out and installation is RCD/RCBO, is there really an issue.