Plug-in Electricity or Power Consumption Meters

What is a plug-in electricity meter?

Electricity meters come in many shapes and forms. The best known device is the electricity meter installed on the premise by the electricity provider or distributor. This equipment stands in a fixed position and monitors the entire consumption. Although it offers the most accurate information about energy use it is not able to show quick information about the current power load or estimate consumption based on the present situation.

A plug-in electricity meter is a compact device than can be inserted into a circuit, like an extension cord, to monitor the consumption of any particular electric or electronic device or equipment. The device typically has an LCD that shows instant values for voltage, current and power load, as well as the total energy consumed since the meter was turned on in a specific place.

Features

There are many varieties of plug-in meters. Some offer basic functionality while others include additional features such as cost estimations. The most advanced ones can also transmit readings to a smartphone, making data logging entirely possible. However, along with features, the cost steeply rises and not all of them are worth the expense.

While there are many brands and models, a good product should have the following capability: quickly display instant power load in watts, line voltage, total kWh consumption maximum and minimum wattage history shows device behaviour and power line impact does not require battery to operate even if running with it keeps last values (simple maintenance) able to withstand maximum socket current load (16 Amps for E.U. states) reflective LCD display (greyish-green when off) for good readout in low light the main unit has clock or timer display, to simplify consumption tracking power factor display shows poor device design that loads the power line more than necessary energy cost calculation may be useful but it is not mandatory graph showing electricity consumption variation over a day may be useful

Utility

Few devices provide any information about partial load or consumption in various states, in the manual or labels. A device's label may show the maximum power load of it, but this is likely to be only a momentary situation and may even not be ever reached in normal operation. Some devices may get to the maximum consumption only briefly in operation, such as the case of a washing machine or air conditioning device, while others draw some energy even when powered off or in standby.

All of the above means that determining the actual cost impact of using an electrical tool or appliance is very difficult. The energy meter installed on the premise will only show the total energy being consumed and you would have to turn off all devices but your equipment, and operate for possibly a few hours in that state, to collect reliable information. This is not practical.

Typical testing scenario

A plug-in meter can be quickly moved from one device to another, no matter how large or small, if it is provided with the typical wall plug. While this may be an issue with three-phased powered equipment, most consumer and small business devices are single-phase ones that plug using the typical end connector. Inserting the plug-in meter between the device and the wall plug is very simple.

Device	Minimum required testing time	Power load	Estimated monthly consumption	Comments
12000 BTU Air conditioning unit (on cooling)	5 minutes	5 W (standby), 60 W (high fan), 1060W (powered on)	100-300 kWh	Full power load reached in 5 minutes
300l Refrigerator (Freezer set at -18 Degrees Celsius)	5 minutes	<1 W (standby), 100-300 W (powered on)	36-72 kWh	Temperature must be lowered from normal to trigger start compressor
Cooking machine	5 minutes	<1 W (standby), 40 W (high fan), 2000 W (oven), 1500 W (grill), 1000 W (large/fast burner), 800 W (medium burner), 600 W (small burner)	10-70 kW/h	No comment
Classic small oven	1 minute	0 W (standby), 1500 W (powered on)	8-16 kW/h	No standby load due to no electronic control
Microwave oven	1 minute	1 W (standby), 1000 W (on), 1200 W (grill)	8-16 kW/h	No comment
Grill	1 minute	2000 W (powered on)	10-27 kW/h	No standby load, rarely any power control
Toaster	1 minute	600 W (low), 1200W (high)	3-6 kW/h	No standby load due to no electronic control
Electric Kettle	1 minute	1800-3100 W (powered on)	10-25 kW/h	No standby load, no power control
Desktop computer	3 minutes	8 W (standby), 40 W (idle), 100-400 W (full load)	10-24 kW/h	Display power load should be measured separately
50 inch TV	3 minutes	1 W (standby), 40 W (half brightness), 90 W (high brightness)	9-19 kW/h	Note that older TVs have no backlight control
Laptop	3 minutes	<5 W (standby), 40 W (idle), 100 W (full load)	5-7 kW/h	Power load slightly higher if battery recharges
Washing machine	1 hour	2-4 W (standby), 50-155 W (washing), 250 W (800rpm centrifugation), 1500 W (washing with heating)	11-18 kW/h	No comment
Compact (travel) hairdryer	less than 1 minute	560 W (half), 1100 W (full)	5-8 kW/h	No standby load
Older Vacuum cleaner	less than 1 minute	220 W (lowest), 1300 W (highest)	5-9 kW/h	Appliance has power control
Newer Vacuum cleaner	less than 1 minute	100 W (lowest), 600 W (highest)	2-4 kW/h	Appliance has power control
Iron	less than 1 minute	1600-2100 W (depending on product)	5-6 kW/h	No power control
LED desk lamp	less than 1 minute	2-10 W (typical)	1-2 kW/h	Some lamps have brightness control

All power load estimations are given according to European typical product ranges. Products for the American, Japanese or other markets may have highly different specifications.

The time consideration centers around the utility of first checking quickly consumption of various common devices and then chose which more frequently used one to monitor for an hour or a day. Note that consumption estimates can vary based on use. Some modern vacuum cleaners still may have no power control.

Monitoring time

Most devices can be easily tested for how much power they use, in different situations in less than 2 or 3 minutes. This may be enough for TVs, computers, laptops and various other products that respond instantly to various demands.

Cooling and heating devices, food preparation devices, various tools require hours to have a good determination of their consumption impact. Simply using them at a low and high power state is not relevant. Some devices require at least an hours until they reach the desired temperature, as is the case for space heaters and coolers

In the case of food preparation, the best assessment you can make is by focusing on the process time. This means that the amount of time required to prepare any meal has to be timed somewhat accurately and the whole power required for this process has to pass through the plug-in meter. Such a specific information shows the most accurate impact of energy consumption to reach a desired result.

When it is not possible, monitoring the highest impact device, such as a cooking machine, grill, oven, can show reliable information that can easily guide an improvement process.

Flexibility

Monitoring consumption in the same place for more than 1 day is generally not advised, as the monthly impact can be easily determined by analyzing the one of a typical day. Moreover, it is important to be aware that biggest feature of plug-in meters is flexibility, so not using them in as many places as possible and quickly extracting then analyzing such data is a missed opportunity.