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Very long run of LV Cabling

fiftyhertz

Hi all,

 

im looking at a project where the landlords LV cut out is approx 850 metres from the proposed tenants installation. The earthing arrangement is TT and protected by a time delayed 300ma RCD and a 63A MCCB.

 

The landlords sub main is going to be 2 x 4C 95mm2 in parallel buried in the ground to supply 20KVA worth of power. This achieved a volt drop of 1.6% which leaves 1.9% VD for lighting. From my Amtech calcs I also get about 1ka at the load Dis board (Phase fault)

 

im not worried about Earth Loop because of the RCD, but i am thinking about the adibatic of the phase conductors. If the tenant puts a long run of cabling in, this will comply from a Zs perspective, but could there be issues with the line under a phase to neutral /phase to phase fault as the cable could slowly cook under a lowish load without tripping the breaker. Is this a valid concern? Amtech isn’t throwing up any faults, but just wanted your thoughts.

 

thanks in advance

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    The cheapest option is 2km of DNO overhead line.

    But check options with your DNO - my local one seems to have a policy of all new HV lines being underground - and only allow overheads if it's not physically possible to trench (e.g. crossing waterways). Oddly new pole mounted transformers are still done, fed from underground cables. Underground is likely to be significantly more expensive than overhead would have been.

       - Andy. 

     

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  • 0

    The cheapest option is 2km of DNO overhead line.

    But check options with your DNO - my local one seems to have a policy of all new HV lines being underground - and only allow overheads if it's not physically possible to trench (e.g. crossing waterways). Oddly new pole mounted transformers are still done, fed from underground cables. Underground is likely to be significantly more expensive than overhead would have been.

       - Andy. 

     

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