Power Rating of Common Appliances: Everything You Need to Know
Have you ever wondered where the utility company gets the figures that go into your electricity bill? Okay, you know those numbers reflect the electric power usage of your home’s various electronics and appliances. But how does the electrical energy from the grid go into those electronics? And how can you determine how much power they consume?
Let’s discuss those details to give you an idea of the electric power consumption of all those devices in your home and the meaning behind the power rating of each appliance.
What is Power Rating?
Power rating describes the total electrical power an appliance requires for its normal operation. It defines how much energy is being transferred from the grid to power the instrument or device. Usually, this figure can be found in the manual that comes with the electrical device or appliance. The power rating also indicates the maximum power at which the unit can safely operate.
For example, most phone chargers have a power rating ranging between 5 and 25 watts. That means the devices draw a maximum power of 25 watts or 25 joules-per-second from the mains electricity supply. Meanwhile, a typical electric kettle has a power rating of 3 kilowatts (kW) or 3000 joules per second. This is 120 times more than the power consumed by a phone charger.
Power Rating Formula
Electronic and electrical devices come with a power rating on their nameplate. Other information includes the maximum power rating at which the appliance or device can safely operate, along with the cable and plug specifications that can handle the electric power going into the unit. The information can help you compute how much energy is transferred in a circuit.
There are two formulas you can use to determine the power rating of an appliance or device. The first one goes like this:
P = VI
In words, this means
Power = Electric Potential x Current
In this method, P is the power, which is expressed in watts (W), V is the potential difference in volts (V) between the points of energy transfer, and the current is in amperes (A). As such, 1 watt of electric power can be defined as the energy transferred when a current of 1 ampere (A) flows through a potential difference of 1 volt (V).
The other formula used in defining the power rating of an appliance uses the work done or energy transferred by a piece of electrical equipment in a given amount of time.
P = W (or E) / T
In words, this means
Power = work done/time taken
In this method, W is the work done or E, which is the energy transferred in joules, and t is the time in seconds. Watts is the unit used in the power rating. For electrical devices or appliances that have higher power consumption values, you can use kilowatts or megawatts.
Here’s the formula for that.
Efficiency = useful work output / total input energy transfer
In calculating efficiency, you’ll get a decimal value less than or equal to one. Using a percentage is an excellent way to represent this value. Multiply the efficiency by 100% to get what’s called the percentage efficiency.
A device that converts all the supplied power into usable power has 100% efficiency. Meanwhile, a percentage efficiency of 30% means that the device only converts 30% of the supplied power into usable energy or work.
An excellent example of an inefficient device is the traditional filament light bulb. The electric filament bulb is designed to produce light, but 95% of the energy that goes into the device is converted (and wasted) into heat energy.
Power Rating Calculation
Let’s see how the power rating formula applies to specific appliances or devices. For this purpose, we’ll use the examples we mentioned at the start of the article. These are the mobile phone charger and electric kettle.
By using the formula in calculating power rating, we’ll determine how it would take a 3-watt phone charger to transfer the same amount of energy as a 3000-watt kettle if the kettle can boil a liter of water in 5 minutes.
Step 1: Look for the given values
P(kettle) = 3000 W
T (kettle) = 5 minutes
P (charger) = 3 W
Step 2: Convert the values
Time = 5 minutes = 5 x 60 = 300 seconds
Step 3: Calculate the energy transferred to the kettle by rearranging the equation for power
P = E/t
E (kettle) = P (kettle) x t
E (kettle) = 3000 W x 300 seconds = 900,000 joules = 900 kilojoules (kJ)
Step 4: Calculate the time it takes for a phone charger to transfer the same energy as the kettle
P = E/t
T (charger) = E (charger)/ P (charger)
T (charger) = (900 x 103 joules) / 3 watts = 300,000 seconds
Step 5: Convert the time from seconds into minutes
300,000 seconds / 60 seconds/minute = 5,000 minutes
This power rating calculation shows that it will take the phone charger 5,000 minutes to transfer the same amount of energy that a kettle can transfer in 5 minutes.
Efficiency Labels of Appliances
You probably noticed the multi-colored stickers with the letters stuck on the front of all new appliances. These are called efficiency labels, and they indicate how energy efficient the said appliance is with regard to its power consumption. Energy-efficient appliances use less electric power to achieve the same level of performance as models with the same size or capacity. This means it costs less to run.
The power rating on the energy efficiency labels ranges from A+++ to D, with A+++ being the best and D being the poorest. They are defined for each type of appliance using several tests and criteria. As such, the ratings can be used to compare the same kind of appliance.
The power rating of each appliance or electronics can be found on the unit itself (on the nameplate) or in the manual. However, although this information indicates how much electric power the unit draws from the grid, keep in mind that not all of the power consumed by the electronics or appliance is converted into useful work. Sometimes, it gets dissipated as heat energy.
Looking at the efficiency label lets you easily compare the power consumed by the same type and model of appliance you intend to purchase. In the US, Energy Star-rated models are considered the most energy-efficient.
Power Ratings of Common Appliances
The energy consumed by an appliance is directly proportional to its power rating, whose unit is expressed in watts (W). For example, an appliance with a power rating of 2000 W will consume 2000 joules per second.
That’s why you can use the power rating of your electronics and electrical devices to help you determine the watt hours your appliances and devices consume. If you intend to install solar panels, you’ll need the information to estimate the size of your solar energy system or how much power it should generate per day.
You can find the power rating of most devices and appliances in the manual or on the appliance itself. Find its rated power to calculate its watt-hour usage. However, keep in mind that not all appliances run 24/7. Some operate for only a few minutes a day. For example, you use garage openers for only a tiny fraction of an hour. The power consumed by a 500-watt lawn mower may seem significant, but running it for only one hour a week translates to 71 Watt-hours per day.
Moreover, some appliances, such as refrigerators, seem to run all day. In reality, they operate for only 12 to 15 hours daily (they turn on and off as needed). The same goes for air conditioning units. Thus, they don’t use the maximum amount of energy all the time.
Also, be aware of phantom loads. Otherwise known as ghost loads or vampire power, phantom loads refer to the energy consumed by devices that remain plugged in. The current drawn by these appliances or devices is typically small, often less than 1 watt. However, since they’re running 24 hours a day, that amount adds up, sometimes by as much as 100 watt-hours in one day. Examples of appliances that consume energy even when not in use include microwaves, printers, and TVs.
Let’s look at the power rating of common appliances, devices, and equipment.
|Appliance/Equipment||Watts (Power rating)|
|Freezer (Upright – 15 cu. ft.)||1240 W (whole day)|
|Freezer ( Chest – 15 cu. ft.)||1080 W (whole day)|
|Refrigerator ( 20 cu. ft.)||1411 W (whole day)|
|Refrigerator (16 cu. ft.)||1200 W (whole day)|
|Air conditioner (room)||1000 W (continuous operation)|
|Air conditioner (central)||2000 to 5000 W (continuous operation)|
|Fan (box)||200 W|
|Fan (ceiling)||120 W|
|Fan (table)||10 to 25 W|
|Laptop computer||20 to 75 W|
|Desktop PC||80 to 200 W|
|LCD monitor||100 W|
|Heater (engine block)||150 to 1000 W|
|Heater (portable)||1200 W|
|Heater (stock tank)||100 W|
|Heater (waterbed)||400 W|
|Coffee machine||1000 W|
|Dishwasher||1200 to 1500 W|
|Electric kettle||1200 W|
|Microwave||600 to 1500 W|
|Electric oven||1200 W|
|Hot plate||1200 W|
|Toaster||800 to 1500 W|
|Clothes dryer (electric)||4000 W|
|Clothes dryer (gas heated)||300 to 400 W|
|Clothes washer||800 W|
|TV (LCD)||150 W|
|TV (plasma)||200 W|
|Stereo||10 to 30 W|
|Vacuum cleaner (upright)||200 to 700 W|
|Vacuum cleaner (portable)||150 W|
|CFL bulb (40 watt equivalent)||11 W|
|CFL bulb (60 watt equivalent)||18 W|
|CFL bulb (75 watt equivalent)||20 W|
|CFL bulb (100 watt equivalent)||30 W|
|LED bulb (40 watt equivalent)||10 W|
|LED bulb (60 watt equivalent)||13 W|
|LED bulb (75 watt equivalent)||18 W|
|LED bulb (100 watt equivalent)||23 W|
|Band saw (14 inches)||1100 W|
|Belt sander (3 inches)||1000 W|
|Drill (¼ inch)||250 W|
|Drill (½ inch)||750 W|
|Drill (1 inch)||1000 W|
|Weed Eater||500 W|
|Hedge trimmer||450 W|
What is the Power Rating of a Motor?
The power rating for electrical equipment and devices specifies the required supplied voltage for their smooth operation. It also defines the maximum amount of current that can safely flow through the equipment or appliance. If the current drawn by the equipment exceeds its power rating, it could lead to a breakdown.
Why is Power Rating Important?
The power rating indicates the maximum power input that can flow through a given piece of electrical equipment. Exceeding that capacity increases the chances that the machine or equipment will break down since it is not equipped to operate beyond the given parameters.
What Does a Power Rating of 100W Mean?
The power rating of 100 W means that the power consumed by an appliance or device is 100 joules per second (where 1 watt-hour equals 3600 joules). But if you’re computing your electricity usage, you’ll need to determine the equivalent of 100 watts in kilowatt-hour. A kilowatt-hour is 1000 watts used for an hour. For example, the power consumed by a 100-watt light bulb operating for ten hours is 1 kilowatt-hour.
How is Motor Power Rating Determined?
You can determine the power rating of a motor by multiplying its voltage by the full load current. You’ll get a result in watts. Divide the watts by 1000 to get the motor’s power rating in kilowatts (because 1000 watts is equal to 1 kilowatt).
The power rating of a machine, appliance, or device tells you several things. One is the maximum amount of power that can flow through it. It also lets you determine how much energy it consumes.
If you’re shopping for new appliances or devices, you can compare each one’s power rating. You can also look for their efficiency labels. These two pieces of information will help you choose the one that won’t significantly impact your energy bills.