Design calculations
Maximum demand & diversity (domestic)
List every circuit or fixed appliance in the dwelling, pick its category, and the calculator applies the correct On-Site Guide Table A1 diversity rule to each group — then totals the assessed maximum demand and compares it against the service fuse and cut-out rating. Enter loads in amps or kilowatts; kW is converted at the working voltage.
Calculator inputs & results
| Group | Connected | After diversity |
|---|---|---|
| Lighting66% of total demand. | 7.00 A | 4.62 A |
| Cooking appliancesFirst 10 A + 30% of the balance (+5 A if the cooker unit has a socket). | 43.48 A | 20.04 A |
| Instantaneous water heaters / showers100% of largest + 100% of second largest + 25% of the rest. | 41.30 A | 41.30 A |
| Thermostatic water heaters (immersion)No diversity allowable. | 13.04 A | 13.04 A |
| Socket-outlet circuits & stationary equipment100% of largest circuit + 40% of every other circuit. | 64.00 A | 44.80 A |
Results
Assessed demand exceeds the cut-out rating — reduce load, apply load management, or ask the DNO about a supply upgrade before proceeding.
Above 60 A — inform the DNO. With the assessed maximum demand now exceeding 60 A, the DNO must be informed before the work proceeds to ensure compliance with their connection arrangements. This includes where load limiting is to be used: load curtailment must be agreed with the DNO under an ENA G100 arrangement, not fitted unilaterally.