Discuss Farm outbuilding supply in the Electrical Wiring, Theories and Regulations area at ElectriciansForums.net

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Hi

Il try and keep this a simple as possible..

Been to look at a job today which started off as 'install a supply from the house to a static caravan in the garden' simple enough, when i arrived the house was a farmhouse which had recently been rewired in places and a new 17th split load board installed.
Its a small holding comprising of farmhouse and a few outbuildings which house a few chickens and ducks, only small scale.

Supply to the house is overhead TT.
The house DB is supplied from the external meter box wired in 16mm2 T+E approx 7m away with no up-front RCD.

The DNO fuse is rated at 80A, there is an isolator in the external meter box straight after the meter, then a double pole henley block which the 16mm2 T&E is connected into, aswell as another feed for an outbuilding wired in SWA. (SWA to galv box then tails to the henley)

Im wanting to install another supply from the meter position to an outbuilding with no current electricity supply, where i will install a consumer unit to supply the static caravan and also be of use in the future for lighting and small power in the outbuilding.

To power the caravan hes currently using extension leads (multiple) and complaining about tripping when using the 2Kw heater at the same time as switching on the kettle :mad2:


I understand that any submain from a TT supply needs RCD protection whether SWA or not, so am i better trying to squeeze in a 100mA S type in the meter box to cover the entire installation?
I plan to install an earth rod at the new outbuilding DB and also at the caravan. Can these locations (mains intake, outbuilding and caravan) have the earths linked as to provide a lower Ra or does the caravan need to be isolated from the TT at the origin.
 
Hi

Il try and keep this a simple as possible..

Been to look at a job today which started off as 'install a supply from the house to a static caravan in the garden' simple enough, when i arrived the house was a farmhouse which had recently been rewired in places and a new 17th split load board installed.
Its a small holding comprising of farmhouse and a few outbuildings which house a few chickens and ducks, only small scale.

Supply to the house is overhead TT.
The house DB is supplied from the external meter box wired in 16mm2 T+E approx 7m away with no up-front RCD.

The DNO fuse is rated at 80A, there is an isolator in the external meter box straight after the meter, then a double pole henley block which the 16mm2 T&E is connected into, aswell as another feed for an outbuilding wired in SWA. (SWA to galv box then tails to the henley)

Im wanting to install another supply from the meter position to an outbuilding with no current electricity supply, where i will install a consumer unit to supply the static caravan and also be of use in the future for lighting and small power in the outbuilding.

To power the caravan hes currently using extension leads (multiple) and complaining about tripping when using the 2Kw heater at the same time as switching on the kettle :mad2:


I understand that any submain from a TT supply needs RCD protection whether SWA or not,so am i better trying to squeeze in a 100mA S type in the meter box to cover the entire installation?
I plan to install an earth rod at the new outbuilding DB and also at the caravan. Can these locations (mains intake, outbuilding and caravan) have the earths linked as to provide a lower Ra or does the caravan need to be isolated from the TT at the origin.

Have a read of section 705 and 411.5.1
 
Thanks, so if im reading this right then if i can provide a low Zs then i dont need an RCD - 411.5.2
How can you guarantee its reliability?
 
Yes you can link the earth rods at each location, assuming you have a suitably sized cpc between them. Doing do will give you a better overall Ra than trying to get a low value at each point.
 
100mA time delayed the best option then? Didnt like the galv box inside the meter box and the single insulated conductors entering it or the henley block being protected by only the 80A fuse.
 
Is this your first experience of working on a TT system?? If so there are a a multitude of previous threads on the subject that may help you. Some can be found at the bottom of this page. One golden rule to remember ''Do Not'' use the non extendible 1.2m 3/8'' twigs use at least 2 X 1.2m X 5/8'' rods with a threaded rod coupler for each earth rod location.

It is Always better to link multiple earth rod positions with a suitably sized copper conductor, either directly or via CU/DBS EMT. It will give the overall installation a far lower and stable Ra value. A good reason for using 3 core SWA cable rather than 2 core for sub-main supplies. I have never and would never use T&E cable for supply tails, especially if cable is also going to be run underground whether direct buried or run in underground duct.
 
Last edited by a moderator:
Thanks Eng, I do have some experience of TT systems but mainly DB changes etc.. I did plan to use the larger rods that can be screwed together to get about 8ft in the ground.
Thanks
 

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