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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.

Parents
  • 0

    With gas heating and cooking, I would expect that 12.5 amps per home, average after diversity would be fine. Marginal without gas but fine with gas in my view.

    Modern practice is generally towards full size neutrals in DNO street mains, and in those parts of a private network that serve a similar purpose to street mains.

    Between transformer and switchgear, half size neutrals remain more popular.

Reply
  • 0

    With gas heating and cooking, I would expect that 12.5 amps per home, average after diversity would be fine. Marginal without gas but fine with gas in my view.

    Modern practice is generally towards full size neutrals in DNO street mains, and in those parts of a private network that serve a similar purpose to street mains.

    Between transformer and switchgear, half size neutrals remain more popular.

Children
  • 0 in reply to broadgage

    I think folk have temporarily forgotten that at least until the next U turns, from 2025 new homes are not supposed to be heated by gas, and from circa 2035, neither are pre-existing ones. Now it may not come to pass, but in terms of sizing such things as street cables and transformers, that have lives of well over 50 years, by which time the gas will have run out and such pre-emptive govt policy will be moot,  it seems foolish not to allow for the inevitable load creep of all-electric heat, as well as more houses.

    Mike.

    Mike.

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