There are two numbers that describe how much power a commercial building can have, and people mix them up all the time. One is the physical size of the supply. The other is what the network operator has agreed you can take. Knowing the difference can save you a nasty surprise.
Supply size: what the cables and fuse can carry
This is the physical connection: the cable, the cut-out and the main fuse, rated in amps. A 200A three-phase supply can physically carry about 139kVA.
Agreed supply capacity: what you are allowed to take
The agreed or authorised supply capacity (often shown as ASC or “available capacity” on half-hourly metered bills) is the amount in kVA that the network operator has agreed to provide to that site. It’s part of your connection agreement, and it can be well below what the cable and fuse could physically handle.
If your demand goes over the agreed capacity, many suppliers add excess capacity charges, and the network operator can ask you to apply for a formal increase.
Why the difference matters
- Moving premises: a unit with a big main fuse may still have a low agreed capacity. Ask for both figures.
- Adding load: EV chargers or new machinery might fit the cables but push you over your agreed capacity.
- Paying too much: some sites pay capacity charges for far more than they ever use. Measured demand gives you evidence to ask for a lower figure.
Where to find each figure
The agreed capacity is usually on your electricity bill or available from your supplier. The physical supply size is on the main fuse or cut-out, or we can check it on site. Your actual demand is the third piece of the puzzle, and the only way to know it for certain is a power load survey.
Not sure which figure you are working with?
We can check your supply, measure your real demand and tell you how it compares with your agreed capacity. See how our power load surveys work, ask for a quote or call 01525 582582.
