Electrical power¶
Note
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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:
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:
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:
| 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. |