Connection capacity is the maximum amount of energy (electricity or gas) that can be delivered to a building through its utility connection. It indicates how much power can be drawn simultaneously and is expressed in kilowatts (kW) for electricity or cubic metres per hour (m3/h) for gas.
Why is connection capacity important?
The connection capacity determines how many appliances and systems can run at full power at the same time. If the capacity is too low, circuit breakers trip or the gas supply is insufficient. If it is too high, you pay unnecessary standing charges for capacity you do not use.
- Too low — breakers trip under peak load, insufficient heat from a gas boiler
- Too high — unnecessary costs for an oversized connection
- Correctly sized — enough capacity for all appliances with a safety margin
Electricity
For residential buildings, common connection capacities include:
| Connection | Capacity | Suitable for |
|---|---|---|
| Single phase 25 A | 5.75 kW | Small flat, few heavy appliances |
| Single phase 35 A | 8.05 kW | Average home, standard usage |
| Three phase 25 A | 17.25 kW | Larger home, electric hob, heat pump |
| Three phase 35 A | 24.15 kW | Large home, multiple heavy appliances |
For new builds or major renovations, the required connection capacity must be determined at the design stage. This takes into account the simultaneous use of appliances such as a cooker, heat pump, hot water cylinder, tumble dryer, and EV charger.
Gas
The gas connection capacity is determined by the output of the boiler and any gas hobs. In new-build projects, gas-free solutions are increasingly common, meaning a gas connection may not be required at all.
Application in construction and renovation
1. New build — the connection capacity is determined during the design phase and applied for with the network operator
2. Renovation — when installing heavy-draw appliances (heat pump, EV charger), check whether the existing connection capacity is sufficient
3. Upgrading — if the capacity is too low, it can be upgraded through the network operator, which requires work on the consumer unit
4. Building drawings — the connection capacity is often noted on the electrical services drawing
Related terms
- Consumer unit
- Circuit breaker
- Heat pump
- Electrical installation
- Insulation
- Building services
Learn more about building terms in our knowledge base at fredsdiyplans.com.