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Volt drop % - Private Supply Def

Peter Hartley

Good day everyone 

Public supply Volt drop 3% Lighting 5% Power.

Private supply Volt drop 5% Lighting 8% Power.

Define private supply?

Option 1 - HV public grid supply to privately owned transformer. Is LV supply private?

Option 2 - Main source of supply is from Privately owned source of generation such as PV, diesel/gas/nuclear generator?

Why is this not defined in BS7671?

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    In what situations would voltage drop be less relevant than energy efficiency? 

    In the general situation too - 5% v.d. represents a 5% loss in energy too - so and increase in consumption to have the same effect.  Say you had a constant 1kW load - 5%  would mean a loss of a 438kWh a year - or say £131.40 at 30p/kWh - over say a 30 year installation lifetime that's £3,942 - which could justify going up a cable size or three if you could reduce the losses by a few percent. Similar reckoning for say 3kW for 8 hrs/day (heat pump) or 7kW for 4hrs/day (EV).

       - Andy.

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  • 0

    In what situations would voltage drop be less relevant than energy efficiency? 

    In the general situation too - 5% v.d. represents a 5% loss in energy too - so and increase in consumption to have the same effect.  Say you had a constant 1kW load - 5%  would mean a loss of a 438kWh a year - or say £131.40 at 30p/kWh - over say a 30 year installation lifetime that's £3,942 - which could justify going up a cable size or three if you could reduce the losses by a few percent. Similar reckoning for say 3kW for 8 hrs/day (heat pump) or 7kW for 4hrs/day (EV).

       - Andy.

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