But before the installation, a logical question arises: what do I have to do to keep everything running like clockwork without the bill skyrocketing? Having an electric vehicle charger at home is one of the smartest decisions for your finances, especially with the right power capacity, tariff, and setup.

The short answer: you don't always need to increase your power capacity

When buying an electric vehicle, it is common to think that the first mandatory step is to call your electricity company to increase your contracted power capacity, which entails an associated cost.

However, in most cases, having extra kilowatts is unnecessary. Many Spanish households contract from 3.5 kW, a figure that can be sufficient if you are going to charge it slowly at night.

Furthermore, there are solutions such as load balancing, which allow you to manage the available energy smartly without needing to increase your electricity contract.

Contracted power capacity and consumption: why they are not the same

To better manage your new home 'charging station', you need a good understanding of what you pay for on your bill. Your bill is primarily divided into two concepts that are often confused, but which have very different functions:

• Contracted power capacity (kW): This is the fixed cost you pay for the maximum amount of energy your home can draw from the grid at the same time. Imagine it like the flow of a tap; the wider it is, the more water (energy) can flow out at once.
• Energy consumption (kWh): This is a variable cost that depends on the total amount of electricity you have used during the month. Following the previous example, this would be the total amount of water that has come out of the tap.

Adjusting the power capacity correctly is important because the more kilowatts you contract, the higher the cost on your bill. But how many kW does an electric car charger need?

How many kW an electric car charger needs at home

The standard recommendation is 7.4 kW for single-phase installations, which are the most common in most homes. However, this does not mean that the charger will necessarily draw that entire amount.

Your charging speed will depend on your contracted power capacity and what the rest of your household appliances are consuming at that moment. If you have a low contracted power capacity, the car will simply charge more slowly, but it will charge. Therefore, the ideal power capacity will actually depend on your daily mileage and how long you can keep the car plugged in.

What changes if you install a 7.4 kW Waybox

Installing a 7.4 kW electric car charger would make your daily routine significantly more convenient. With this power capacity, you can fully recharge the majority of batteries on the market in a single night. It is the recommended option if you drive many kilometres a day or if you need the car ready in a few hours.

However, when installing a unit with this power capacity, you must bear in mind that if you run it at full capacity while using other powerful appliances at home, you could exceed your contract limit. This is where protection systems come into play, or you can decide whether to increase the power capacity so you do not have to worry about which appliances you turn on.

Load balancing: how to charge without tripping the fuse box

To avoid tripping the fuse box, the best solution for your electric car is to have a charger with load balancing. This smart system monitors how much your home is consuming in real time and automatically adjusts the car's charging speed.

For example, if you have 6 kW contracted and your house is consuming 1 kW at that moment, the charger will use the remaining 5 kW for the car, utilising the maximum available power. If you suddenly turn on the oven, the charger will detect the increase in domestic consumption and lower the vehicle's charging power so as not to exceed the contracted limit.

At Endesa, our Waybox Unifamiliar Plus and Waybox Comunitaria chargers include this feature.

Dual power capacity: when it is advisable to contract more power at night

A very interesting option is the possibility of contracting two different power capacities for different times of the day. This makes complete sense for an electric car user:

1. Choose a lower, more tailored power capacity during the day (peak/shoulder hours) to save on the fixed charge.
2. Set a higher power capacity during the night, weekends, and public holidays (off-peak hours), when energy is much cheaper, to charge the car faster without fear of tripping the safety switch.

Indicative table: recommended power capacity based on your car use

To give you an idea of what you might need, here is a reference estimate based on various usage profiles:

Remember that with a load-balancing charger, these figures could be reduced considerably; but before making a decision, it is worth calculating the power capacity you would need at home.

How to calculate if your current power capacity is sufficient

There are primarily two methods to calculate the power capacity your home needs:

• Traditional method: Turn on the appliances you usually use at the same time alongside the charger. If the safety switch doesn't trip, you have enough margin.
• Digital check: If you get your electricity from Endesa, log into your Customer Area. From there, you will be able to see a history of the maximum power demand, hour by hour, over the last year. If your peaks never approach your contracted power, you are overpaying.

Common mistakes when contracting power capacity for charging an electric car

A very common mistake is contracting too much power capacity 'just in case'. As we have seen, having extra kilowatts unnecessarily increases your bill every month.

Another mistake is failing to take into account the condition of your installation. If your electrical installation certificate (CIE) is more than 20 years old or if the new power capacity you are requesting exceeds what is certified, the distribution company will require you to renew it, which would entail an extra cost.

It is also a mistake to ignore the benefits of load balancing. Sometimes, investing slightly more in a smart charger with load balancing saves you much more money by avoiding the need to permanently increase your contracted power capacity.

Once you are clear on the power capacity you need in your home, we have solved 50% of the puzzle. At this point, all that remains is to find the best tariff for charging your car at home.

Endesa's Recarga en Casa Tariff: for charging without keeping an eye on the clock

If you are looking for peace of mind and not having to watch the clock to plug in the car, our Recarga en Casa Tariff is for you.

Unlike a time-of-use tariff (which would 'force' you to charge the car from 00:00 to 08:00 to save money), our electric car tariff offers a fixed monthly fee.

For just €24.65 a month, up to 216.99 kWh per billing cycle is included. This is equivalent to driving about 1,250 km a month or up to 20,000 km a year.

Furthermore, if you install the Waybox charger with us, you get an indefinite 30% discount on your monthly fee.

At Endesa, we have the ideal solution for those seeking the peace of mind of a known expense without time restrictions.

Checklist before increasing your power capacity or installing a charger

Before making any decisions, review these points:

1. How many actual kilometres do you do on average each month?
2. Does your charger allow time scheduling or load balancing?
3. Check your maximum power demand in the Customer Area.
4. Check the age of your electrical installation certificate.
5. Analyse whether the freedom of a fixed fee like that of Recarga en Casa is worth it for you.

Frequently asked questions about power capacity, electric cars, and home charging

Can I charge an electric car with 3.45 kW or 4.6 kW?

Yes, it is perfectly possible. Most homes with these power capacities can charge their cars overnight without any problems, although the charging speed will be slower.

What happens if I charge the car and put the oven on at the same time?

If you don't have load balancing and the sum of both consumptions exceeds your contract, the main breaker (ICP) will trip and the power will go out. With a smart charger, like those offered by Waybox, the car will charge more slowly while the oven is on to avoid a power cut.

Is Endesa's Recarga Tariff only for the car or for the whole house?

The kWh included in the Recarga en Casa Tariff fee cover the total consumption of your home, including that of your electric car. If you exceed 216.99 kWh per month, the additional consumption will be billed at €0.124571/kWh (price valid in August 2026, with a 20% discount during the first year).

How long does it take to charge a car depending on the power capacity?

It depends entirely on the capacity of your battery and the available power. At 7.4 kW you will charge much faster than at 3.7 kW.

How much does it cost to increase power capacity?

Increasing your power capacity costs approximately €46 for each kW you add, which you will pay to the distribution company on your next bill. Conversely, reducing it only costs around €9 as a connection fee.