So I have been asked to look at a job which includes providing 2 submains (one for a small dwelling, the other for a small workshop/garage). The supply at the farm is PME/TNCS from a pole mounted transformer.
The back story; whilst waiting for planning permission for a dwelling the customer decided to place a static caravan at his father-in-laws farm and requested a 100A single phase supply to an external block built meter cupboard (a couple of metres from the static caravan). The 100A supply was planned to be used in the dwelling which would be built adjacent.
Three years has passed now, and the plans changed considerably. The dwelling is now much smaller, and it's power consumption likely to be significantly lower (biomass heating, LED lighting only, smaller and less final ring circuits, etc.) The customer has now also converted one of the barns/pig houses in to a small office/workshop/garage to basically look after the farm machinery (it's currently powered off a 2.5mm T&E from the original farmhouse- typical farm!!) The customer also wants to keep the static caravan as guest accommodation now that the proposed new farmhouse is smaller). Both the new farmhouse and the workshop are approximately 100metres away from the cutout and joined by a party wall.
Despite what seems like a significant load, looking at the current overload protection/current consumption characteristics, I think the 100a fuse might just work. I propose on using 25mm SWA as the submain to the workshop where I will terminate it in a locked cupboard with tails out to the workshop CU, before continuing the 25mm submain to the new farmhouse CU (when constructed).
I'm trying to thrust bore the SWA under the other barns/sheds on the farm, but I'm not sure it will be possible. Therefore it would have to run 20m underground ducted, 60m through 3 of these buildings (clipped direct) and 20m underground again. My question is, would I be best using the PME to protect the SWA (isolating it from the workshop/house CU) and using electrodes to provide TT at the house and workshop as it is a farm with livestock? I will leave the TT installation at the caravan of course. I believe I will also need to protect the submain with a 300ma RCD for fire protection due to it running through farm buildings, despite the supply not being strictly, "agricultural". I will of course protect the submain from overcurrent with a FSU adjacent to the meter cutout.
The back story; whilst waiting for planning permission for a dwelling the customer decided to place a static caravan at his father-in-laws farm and requested a 100A single phase supply to an external block built meter cupboard (a couple of metres from the static caravan). The 100A supply was planned to be used in the dwelling which would be built adjacent.
Three years has passed now, and the plans changed considerably. The dwelling is now much smaller, and it's power consumption likely to be significantly lower (biomass heating, LED lighting only, smaller and less final ring circuits, etc.) The customer has now also converted one of the barns/pig houses in to a small office/workshop/garage to basically look after the farm machinery (it's currently powered off a 2.5mm T&E from the original farmhouse- typical farm!!) The customer also wants to keep the static caravan as guest accommodation now that the proposed new farmhouse is smaller). Both the new farmhouse and the workshop are approximately 100metres away from the cutout and joined by a party wall.
Despite what seems like a significant load, looking at the current overload protection/current consumption characteristics, I think the 100a fuse might just work. I propose on using 25mm SWA as the submain to the workshop where I will terminate it in a locked cupboard with tails out to the workshop CU, before continuing the 25mm submain to the new farmhouse CU (when constructed).
I'm trying to thrust bore the SWA under the other barns/sheds on the farm, but I'm not sure it will be possible. Therefore it would have to run 20m underground ducted, 60m through 3 of these buildings (clipped direct) and 20m underground again. My question is, would I be best using the PME to protect the SWA (isolating it from the workshop/house CU) and using electrodes to provide TT at the house and workshop as it is a farm with livestock? I will leave the TT installation at the caravan of course. I believe I will also need to protect the submain with a 300ma RCD for fire protection due to it running through farm buildings, despite the supply not being strictly, "agricultural". I will of course protect the submain from overcurrent with a FSU adjacent to the meter cutout.
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