Contracted Power in Spain: How Many kW Do You Need?
How Spain's contracted power charge works, why tripping your breaker means you're undersized, and how to size it right without overpaying.
The charge you pay whether you use it or not
A Spanish electricity bill has two halves that work completely differently. The energy term is what most people think of as "the bill": price per kWh times what you actually consumed. The power term is different — it is a flat daily charge based purely on the kW you have contracted, and you pay it every single day of the year whether you draw that power or not. Contract more than you need and you are paying rent on capacity that sits idle; contract less than you need and your breaker will tell you about it, usually at the worst possible moment.
Contracted power in Spain is set in standard steps rather than any number you like — typically 2.30, 3.45, 4.60, 5.75, 6.90, 9.20 kW and up. Your retailer can only offer you one of these tranches, so "the right amount" really means picking the lowest tranche that comfortably covers your real peak demand.
What actually happens when you trip the ICP
The ICP (interruptor de control de potencia) is the switch that enforces your contracted limit. It has nothing to do with a short circuit or a safety fault — it simply adds up the power every running appliance is drawing at that instant, and if the total goes over your contracted kW, it cuts the supply. No warning, no beep, just the lights going out until you go to the fuse box, switch something off, and flip it back on.
The classic trigger is a coincidence, not any single appliance: an electric oven preheating, a washing machine mid-heat cycle, and a kettle going on at the same time can easily add up to 5–6 kW on their own, even though none of them alone would trip a 4.6 kW contract. This is why the practical fix is often about timing as much as about the contract itself — running the highest-draw appliances one at a time rather than in parallel.
Working out the kW you actually need
The reliable way to size a contract is to think in terms of your worst realistic combination, not your average day. List the appliances most likely to run at the same time and add their power:
| Scenario | Appliances running together | Approx. combined power |
|---|---|---|
| Small flat, no electric heating | Fridge + oven + microwave briefly overlapping | ~3–3.5 kW |
| Typical flat | Fridge + washing machine (heating water) + a few lights and devices | ~4–4.5 kW |
| House with electric water heater | Water heater + oven + fridge + general electronics | ~5.5–6.5 kW |
| House with AC or induction hob | Air conditioner + induction hob + water heater overlapping | ~7–9 kW |
Add roughly 10–20% headroom to whatever number you land on — appliance nameplate power is usually higher than steady-state draw, but startup surges (a compressor kicking in, an induction ring at full power) are real and worth a buffer. Then round up to the nearest standard tranche your retailer offers. Rounding down to save a few cents a day on the power term is the single most common cause of an ICP that trips every few weeks.
The electricity cost calculator and the whole-home estimator on this site both work from an appliance's wattage — the same numbers you'd use here. If you want to check a specific appliance's typical draw before adding it to your worst-case list, the appliance pages give a typical wattage for 30 common devices.
Signs you have the wrong contract
- The ICP trips more than once or twice a year: you're almost certainly undersized — move up one tranche.
- You've never had it trip, ever, and you run AC or an induction hob: you might be oversized, especially if the contract predates buying a power-hungry appliance you no longer worry about combining with others.
- You added air conditioning, an EV charger or an induction hob recently: that's exactly the moment to recheck the sizing — a contract that was right for the old appliance mix often isn't right for the new one.
Changing it costs less than living with the wrong number
Most Spanish retailers allow a free change of contracted power once a year, with further changes possible for a small fee. Given that the power term is billed daily for the full year regardless of use, a contract that's one tranche too high can easily cost more over twelve months than the fee for an extra change would — so if you're not sure which side of the line you're on, checking is close to risk-free. Your retailer can usually tell you your actual peak demand from smart-meter data going back a year, which is a more reliable guide than any rule of thumb, including the one above.
Frequently asked questions
What happens if I set my contracted power too low?
Your main breaker (ICP) trips whenever demand exceeds it — lights out, no warning, until you switch something off and reset it. It's inconvenient, not dangerous, but it tends to happen at the worst moment.
What happens if I contract too much power?
Nothing trips, but you pay the power term every single day of the year for capacity you don't use. Spain's power charge is flat, calculated on the kW contracted, not on what you actually consume.
Can I change my contracted power without penalty?
Yes — Spanish retailers must allow one free change of contracted power per year, with unlimited changes at extra cost. If you've never checked, it's the one free lever on a bill that hasn't been touched in years.