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TX to switchboard cable sizing

danny wells

Hi all, new to the forum 

hoping for some help with my following questions.

I have been asked to take on a project that has had a new 800kva transformer installed by northern power grid and the supply conductors have been installed from the new switchboard underground in 2x sets of 400mm AWA per phase, 1 x 400mm AWA neutral and 240mm cpc. The sets of phase conductors are installed in 2 x 4m of ducting in trefoil along with neutral conductor in single duct between the above two ducts and cpc in separate duct. 
the sizing of the conductors appear to have been sized for an 800amp 3phase fused supply from the transformer although I have asked for 500amp fuses as at present 800 amps is not required and I believe it was to allow for future development of the site. The site is going to house 120 residential park homes with ev charger on all homes.

my question is will the neutral need to be larger size for future expansion to allow for an 800 amp supply and should the cpc be larger than 240mm.

From my calculations the phase conductors are fine but correct me if I am wrong just trying to make sure all is correct before I take on the project.

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  • 0

    Hi all

    Have found out today that the reason for the future upgrade in the supply was that only 78 homes have been planned but may increase to 120 in the future. All homes will have gas heating and hobs direct feeds from main gas network, the original contractor who for some reason cannot now take on the installation of the park form the switchboard had calculated 468KVA  supply with diversity and allowed for all EV chargers to be no more than 16 amps. I have done my own calculations and fusing at 500 amp per phase in my opinion should be fine but happy to take on others opinions and calculations.

    There will be no other common facilities on site and street lighting appears to be 36 x 7w LED bollard lights.

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  • 0

    Hi all

    Have found out today that the reason for the future upgrade in the supply was that only 78 homes have been planned but may increase to 120 in the future. All homes will have gas heating and hobs direct feeds from main gas network, the original contractor who for some reason cannot now take on the installation of the park form the switchboard had calculated 468KVA  supply with diversity and allowed for all EV chargers to be no more than 16 amps. I have done my own calculations and fusing at 500 amp per phase in my opinion should be fine but happy to take on others opinions and calculations.

    There will be no other common facilities on site and street lighting appears to be 36 x 7w LED bollard lights.

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