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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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  • 0

    Thanks all for the contributions, to give more background. The site is due expansion in the next couple of years where a HV network will be integrated more readily, within 300 metres or so.

     I also have seen what Andy has mentioned on DNOs being overhead line averse especially with a recreational airfield and way leaves involved.

    This is the reason the Genset is my preffered option, at 50% load PRP rating the set only uses 2.5 l/h, I’ve proposed a 2000L above ground tank and based on 6 hours a day, and a business week where the user switches the generator on/off, you’ll be looking at under 20K over a 3 year period. (even with the red diesel ban in April) and maybe 10K in maintenance  over three years including a service for every 450 hours of work done, and maybe 30k for the installed equipment, this would then also facilitate a sensible LV DNO connection in the future.

    I still think the 850m of LV is viable, but defiantly on the extreme side from a cost perspectiv, with a potential risk of theft also

    thanks again all

     

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  • 0

    Thanks all for the contributions, to give more background. The site is due expansion in the next couple of years where a HV network will be integrated more readily, within 300 metres or so.

     I also have seen what Andy has mentioned on DNOs being overhead line averse especially with a recreational airfield and way leaves involved.

    This is the reason the Genset is my preffered option, at 50% load PRP rating the set only uses 2.5 l/h, I’ve proposed a 2000L above ground tank and based on 6 hours a day, and a business week where the user switches the generator on/off, you’ll be looking at under 20K over a 3 year period. (even with the red diesel ban in April) and maybe 10K in maintenance  over three years including a service for every 450 hours of work done, and maybe 30k for the installed equipment, this would then also facilitate a sensible LV DNO connection in the future.

    I still think the 850m of LV is viable, but defiantly on the extreme side from a cost perspectiv, with a potential risk of theft also

    thanks again all

     

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