long, long run.....

[FAA Greenie]

Hi Guys,

Quick one for you all. A client i am currently working for has asked me to quote him for supplying a wooden workshop he is planning on building in his (very large) garden. The problem is he plans on placing it 200 meters away. He only wants enough capacity to operate light stuff such as drills and a kettle etc so i have allowed for 2.5Kw (kettle plus a bit of extra). Obviously the limiting factor here is voltage drop and my calculations say i need a 10mm 3 core SWA which alone comes in at near enough £900. If he can come down to 150M i reckon 6mm or 4mm at 100M. Am i missing any tricks to get this price down? (I'm happy to export the earth etc, he is on a TNC-S system), but would it be any cheaper to use two core SWA and sink a good thick Earth rod in? He lives at the bottom of a valley and the ground is always nice and damp apparently. Any thoughts or similar installs?

 

[morph]

you need to brush up on your knowledge if you are happy to export the earth

 

[londonlec]

I wouldn't go any smaller than 10mm, and would probably run in a large duct too. If he can afford a garden that large, then he can afford 200m of armoured!

As above, reconsider the CPC.

Edit: spelling

 

[paturback]

you need to brush up on your knowledge if you are happy to export the earth

Care to expand morph?

 

[Graeme Harrold]

TT the shed would be my answer................

 

[morph]

expand
exporting the earth on a TNC-S system is not permitted.

 

[IQ Electrical]

expand
exporting the earth on a TNC-S system is not permitted.

Who told you this morph? Have you ever researched it or read any of the massive threads on this very subject?

There is nothing preventing you from 'exporting' the earth on a TN-C-S system so long as main protective bonding requirements for this system are met.

In this particular case, economics will dictate the use of an earth electrode at the remote end.

Have a read of this: http://www.electriciansforums.net/e...159-good-guide-exported-pme-outbuildings.html

 

[morph]

not read any of the threads no
thanks for the link,i do remember reading it some time ago think it may have been in wiring matters or something like that, at the time i was converted having been one of the older sparks who was always taught not to export earths , for reasons such as broken neutrals and out side of equipotential etc etc , taps being one of the main focus points ( still would want to see a plastic coupler before tap pipe work leaves building)
any way i digress with taps and what not
then a few years back i was talking to an engineer from the DNO in this region and he was still adament that we should not export, so kinda base my reasons on that, its similar i suppose to 16mm earth because its TNC-S even if adiabatic equation proves otherwise

thanks

 

[IQ Electrical]

not read any of the threads no
thanks for the link,i do remember reading it some time ago think it may have been in wiring matters or something like that, at the time i was converted having been one of the older sparks who was always taught not to export earths , for reasons such as broken neutrals and out side of equipotential etc etc , taps being one of the main focus points ( still would want to see a plastic coupler before tap pipe work leaves building)
any way i digress with taps and what not
then a few years back i was talking to an engineer from the DNO in this region and he was still adament that we should not export, so kinda base my reasons on that, its similar i suppose to 16mm earth because its TNC-S even if adiabatic equation proves otherwise

thanks

Yes but the adiabatic does not apply to TN-C-S earthing/bonding calculations.

 

[morph]

yes i know , thats my meaning , poor example maybe,
i am not an old git who wont change thats why i run neutrals in to switches
many grey areas exist as we know , i only base my feelings on the advice of a dno engineer, i have swung one way to the other and may do again, have you ever found any other credible info on the matter ?
thanks

 

[IQ Electrical]

yes i know , thats my meaning , poor example maybe,
i am not an old git who wont change thats why i run neutrals in to switches
many grey areas exist as we know , i only base my feelings on the advice of a dno engineer, i have swung one way to the other and may do again, have you ever found any other credible info on the matter ?
thanks

Absolutely, Guidance Note 8 has some good examples and diagrams.

 

[morph]

dont have GN8
does it actually say its ok , or does it just give an example similar to the pdf you supplied, i will be very interested to see the info, feel a purchase coming on

thanks

 

[SMB]

Yes, GN8 is a publication which I don't have and really should.

£25 I think.

 

[SMB]

I think its going to be ammended this year though?

 

[IQ Electrical]

I think its going to be ammended this year though?

It's due next year but I don't know what month.

 

[SMB]

Thanks IQ.

 

[FAA Greenie]

Thanks for your replies gents. Glad it didn't turn into a huge debate that this subject often does!! Yeah, i agree, pure economics is pointing to the TT but if he is happy to pay the extra i would rather keep a guaranteed, year round earth for the guy. He has no plans for any other services up there, ie water so the arrangements will be pretty easy to keep within the requirements for equipotential etc. Just be such a shame to run 10mm cable up there and put a 10A mcb on the end of it!!

 

[VoltzElectrical]

Yes but the adiabatic does not apply to TN-C-S earthing/bonding calculations.

I am not disagreeing with you, I would like to read it in full. Can you tell me where it says this please. I just read chapter 54 and couldn't really find it. I have a few more questions too, but in due course.

CXheers

 

[IQ Electrical]

I'm 'out and about' at the moment but I think 544.1.1 is the regulation, I'll check when I get back to the office.

It refers to table 54.8 'where PME conditions apply' and references the suppliers neutral conductor CSA.

Remember that on PME systems, the earthing conductor also serves as a main protective bonding conductor and must be sized accordingly.

 

[VoltzElectrical]

I read the table before i originally posted, and noted the 'where pme' conditions apply. having re-read it, i understand it that the bonding conductor to gas/ water etc.. in pme installations is sized according the the size of the neutral.

And where not pme, then it is sized in relation to the size of the earthing conductor.