If you’ve ever asked a landlord, agent or the network operator how much power a building has, you’ve probably been given a number in kVA. It’s the figure everything else hangs off, but hardly anyone explains it. Here’s what it actually means for your business.
kVA, kW and amps: three ways of describing power
Amps are the current flowing through your cables. Your main fuse and switchgear are rated in amps, for example 100A per phase.
kVA (kilovolt-amps) is the “apparent power” your supply can deliver. It’s what the network operator sizes your connection by, and it’s the figure on many business electricity bills as your agreed or authorised capacity.
kW (kilowatts) is the useful power your equipment turns into work, heat or light. Because of power factor, kW is usually a bit lower than kVA. A site drawing 90kVA at a power factor of 0.9 is using about 81kW of real power.
How to turn amps into kVA
You can get a rough figure from the rating of your main fuse:
- Single phase: 230V × amps ÷ 1,000. A 100A single-phase supply is about 23kVA.
- Three phase: 400V × amps × 1.732 ÷ 1,000. A 100A three-phase supply is about 69kVA, and 200A is about 139kVA.
That tells you the most the supply can physically carry. It doesn’t tell you how much of it you’re already using, and that’s the number that matters when you’re planning new equipment.
Supply size is not the same as what you use
Most sites never get near their supply rating, and some are running much closer to it than anyone realises. Nameplate ratings on equipment don’t help much either, because machines don’t all run flat out at the same time. The only reliable way to know your real maximum demand is to measure it.
That’s what a power load survey does. We connect a logger at your incoming supply and record what the site draws over a normal working period, so you can see your peak demand in kVA, when it happens and how much headroom you’ve got left.
Why it matters
- Adding EV chargers, air conditioning, heat pumps or new machinery
- Moving into a new unit and comparing it with what you use now
- Asking the network operator for an upgrade (too small costs you later, too big costs you now)
- Tracking down nuisance tripping or blown fuses
Want to know your real kVA figure?
We use our own loggers and give you a plain-English report with the numbers you need. See how our power load surveys work, ask for a quote or call 01525 582582.
