Electrical power



The electrical power is the speed with which a device consumes electrical energy. A device with a lot of power will consume a lot of energy in an hour. A device with little power will consume little energy in an hour.

All electrical devices have the obligation to report their power consumption on a label.

Electric power formula

Another way to know the power consumption of a device is to calculate it by multiplying the voltage by the current that feeds an electrical device. The formula is the following:

P = V \cdot I

Being the magnitudes and units the following:

P = Power in watts [W]

V = Electrical voltage in volts [V]

I = Current intensity in amperes [A]

This formula is only valid for direct current or for alternating current of devices based on resistances. For devices powered with alternating current that are electronic, motors, fluorescent, etc. it is necessary to take into account that they will have reactive power and the previous formula will not be valid.

Active and reactive power

When we talk about the power consumed by a device, we refer to the active power, that is, the power that consumes energy.

In alternating current, which is the current that reaches our homes to the plugs, there is also reactive power that does not consume energy. This power appears when there are capacitors or coils in the devices. These components store energy from the grid and return it back several times per second. The end result is that they do not consume power, but increase the electrical current through the wires.

Many devices connected to alternating current have this behavior, so that the previous formula stops working.

For example, a low consumption light bulb has a label with the following values:

Power 12W [1]

Intensity 102mA

230V voltage

If we multiply the intensity by the voltage the result is 23.46 watts (0.102A * 230V = 23.46W) which is much higher than the 12 watts of active power declared. This is because the bulb "consumes" a reactive power of 20 watts.

The reactive power is not paid for in the electricity bill, but it increases the current consumption of the cables and can cause the Power Control Switch to disconnect the installation.

Power consumption

Below is a table with electrical power consumption of common household devices. The higher the power of an device, the more energy it will consume every hour it is on and the more it will cost on the electric bill.

These power consumptions are indicative and may vary from one device to another.

Device Power
Energy saving light bulb 12W
Laptop 30W
Desktop computer 80W
Gaming computer 300W
Microwave oven 900W
Heat zone of a ceramic hob 500 W to 2500 W depending on size
Air heater 2000W
Hair dryer 2000W
Drill 100W to 500W
40 inch LED television 80W
Fridge 150W
Cold washing machine 100W
Washing machine with hot water 1000W
Electric iron 800W
Phone charger 5W to 20W
Vacuum cleaner 1000W
Air-conditioning 1000W
Electric oven 2000W

Motors are a special case within the consumption of electrical devices. Other devices consume a fixed amount of power, but motors can consume more or less power depending on the mechanical load they are moving. For example, an electric car that has a 85,000 watt motor will actually only consume about 10,000 watts at a speed of 100 km/h on a flat road. This power will increase if the car goes up a hill or while the driver is accelerating.

Blenders with 1000-watt motors can be easily found on the market. In reality, these mixers will barely use 100 or 200 watts when they are blending a liquid or a puree.

Power Control Switch

The IPC or Power Control Switch is a control device, mandatory in all electrical installations. Its function is to disconnect the electrical installation if the total consumption of all the devices is greater than the contracted power.

The maximum standard powers that can be contracted in homes are the following:

Maximum contractable power limit (at 230V voltage)
Power Limiter Monthly cost (approx.)
2300 W 10 A 6 €/month
3450 W 15 A 9 €/month
4600 W 20 A 12 €/month
5750 W 25 A 15 €/month
6900 W 30 A 18 €/month
8050 W 35 A 21 €/month
9200 W 40 A 24 €/month
10350 W 45 A 27 €/month
11500 W 50 A 30 €/month

The higher the contracted power, the more the fixed term charged by the electric company will cost monthly. For this reason it is advisable to hire the least amount of power that we can.

On the other hand, if we are going to connect high-power devices simultaneously, it is advisable to increase the power limit so that the control switch does not continuously cut off the electrical connection due to high consumption.

[1]The power on the labels of electrical devices is measured in watts [W] and always refers to the active power, that is, the power that consumes energy.