Farm Buildings ( Barn)

[Deleted member 14631]

Hi hope this makes sense.

Been asked to look at the electrics in a large Barn Complex. Three Metal constructed Barns joined to each other ( Used for Animals, storage etc). I know there is a section in BRB about this, but does not answer my question. Inclined to turn the job down as I do not have enough experience of this type of building.

But any way here goes. It is all about the earthing on this Barn set up.

At the minute ther is a Domestic Distro situated about 5 metres from the main Incoming Meter Box, feeds various Lights and sockets etc.

From this distro a 6sqm Twin and Earth protected by 32a MCB has been taken to feed another Domestic Distro about 30meters away in another Part of the Barn complex again feeding lights and sockets.

Ignoring the Loading requirements etc on this lot which I am happy to check out my, question how should this lot be earthed.

EG how many earthbonds, what Sizes etc should be done to the metal work of say three Barns that are attached to each other and to which Distro or MET. should they be run.

Also I am inclined to recomend that the second Distro be taken straight from a switched fuse instead of a Distro. I would recomend them to upgrade to an SWA as the existing cable is wired in a vunerable loaction for machinery.

Any Comments appreciatted

 

[IQ Electrical]

What is the earthing system?

 

[Guest123]

There are so many variables and factors to this querey that need to be ascertained first, it's almost impossible for me to help you.

Do you have access to Guidance note 8 by the IEE, this will provide you with all the answers you need.

 

[IQ Electrical]

Guidance Note 7 too, good explanations and diagrams.

 

[Deleted member 14631]

Thanks for this.

It is a PME system and I know it should really be a TN-S I believe for this sort of building.

Will see if I can get my Hands on Guidance Notes 7 and 8

 

[malcolmsanford]

That is interesting I read the OP and was about to say no your right you can't use a TNC-S but regulation 705.411.4 just says you can't use a TN-C which is totally different from a TNC-S learn something everyday

 

[IQ Electrical]

That is interesting I read the OP and was about to say no your right you can't use a TNC-S but regulation 705.411.4 just says you can't use a TN-C which is totally different from a TNC-S learn something everyday

The TN-C-S 'rule' came from the DNO's and in turn from the ESQCR 2002 regulations where it was stated "it may prove difficult to attach and maintain all the necessary equipotential bonding connections for a PME supply."

TN-C-S is generally not recommended if there is no metal floor grid present-regulation 705.415.2.1 refers to Figure 705 which details a suitable grid.

 

[malcolmsanford]

Thanks for that IQ not done a great deal of Agi work so as always a learning curve.

 

[IQ Electrical]

Thanks for that IQ not done a great deal of Agi work so as always a learning curve.

No prob's, all the best too!

 

[malcolmsanford]

I'm such a sad person lol ............last day with the fmaily and just been over to my mate who as the 17th edition as mine is in Saudi.

I thought I was right, well in a way. Marinas. exhibitions caravans and such all highlight in the regs that TNC-S can not be used and even point to the ESQCR but Agi don't just as I thought mentioned TN-C.

So I'm assuming IQ providing the DNO give permission you can use TNC-S in it?

 

[IQ Electrical]

Exactly, it's down to the DNO at the end of the day.

I still prefer TT in that situation though, for obvious reasons but that's preference!

 

[malcolmsanford]

Yes I have always used TT and in my ignorance always thought that was the only way to do an Agi install ........other than TN-S. Well thanks mate as I said never to late to learn something. Have a great New Year and as mr Spcok say live long and prosper.

 

[IQ Electrical]

Yes I have always used TT and in my ignorance always thought that was the only way to do an Agi install ........other than TN-S. Well thanks mate as I said never to late to learn something. Have a great New Year and as mr Spcok say live long and prosper.

Just going back to what I wrote regarding the metallic grid, there is actually a note at the end of 705.414.2.1 saying "where a metal grid is not laid in the floor a TN-C-S supply is not recommended"

 

[Deleted member 14631]

Thanks for all this.

I am going to do another quick check on the buildings when that way in a few days time, and going to re-read regs with regards to the supply for this complex.

It definitly does not have any metal grids in place which i know are comon in cattle sheds for the waste disposal.

Which leads to bonding on the frames. Lord knows if the slabs have any re-inforcement in them which in theory need bonding (Guidance note 7 and 8 for all this).

Just left to see if the second Distribution board should be a TT or not and how this would be earthed in relation to Frame and equipotential bonding.

Apologise in advance if I dont resppond to this thread I started, as will be off line as taking a new year holiday in a day