Three-phase electricity upgrade cost
A three-phase upgrade quoted by the DNO for a rural barn conversion ranges from £8,000 (short cable run, existing three-phase nearby) to £40,000+ (long run, new transformer). Lead time from DNO assessment to energisation typically 12-26 weeks.
When you need it
A typical 200 m² conversion with single-phase 100A supply is fine for one heat pump, EV charger and domestic load. Three-phase becomes necessary when you add a second EV charger above 7 kW, a large GSHP (over 12 kW), or a workshop with high inrush motor loads.
Contestable vs non-contestable works
The DNO must do the non-contestable works (connection to the network, metering). Contestable works (the cable run from the connection point to the property) can be done by an independent connections provider, typically 20% to 35% cheaper. Ofgem guidance covers the split.
Lead time
Formal quote within 60 working days. From acceptance, design and consenting runs 4 to 8 weeks; construction 4 to 12 weeks; commissioning and meter swap 1 to 4 weeks. Plan around it; a barn conversion timed for September completion needs the DNO order in by March.