Plug-in Electricity or Power Consumption Meters

Old page, much too complex

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 provide values also to a smartphone, making data logging entirely possible. However, as with features, the cost steeply rises and not all of them are worth the expense.

The most important information provided by a meter is instant power load, total electricity consumption and line voltage. The instant power load is essential as it shows as plainly as possible what amount of energy is required by a device, no matter how large or small, depending on how it is operated. As this value is clearly shown on the LCD of the meter, any doubt about the impact of device is cleared.

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 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 daily consumption	Comments
Air conditioning unit (on cooling)	5 minutes	5 W (standby), 60 W (high fan), 1060W (powered on)	5-10 kWh	Full power load reached in 5 minutes
Refrigerator (Freezer set at -18 Degrees Celsius)	5 minutes	5 W (standby), 60 W (high fan), 1060W (powered on)	5-10 kWh	Temperature lowered from normal to trigger start compressor
Cooking machine	5 minutes	1 W (standby), 40 W (high fan), 2000W (oven), 1500W (grill), 1000W (large/fast burner), 800W (medium burner), 600W (small burner)	5-10 kWh	No comment
Classic small oven	1 minute	0 W (standby), 1500W (powered on)	5-10 kWh	No comment
Microwave oven	1 minute	1 W (standby), 1000W (on), 1200W (grill)	5-10 kWh	No comment
Grill	>70	1 minute	2000W (powered on)	5-10 kWh	No standby load since no electronic control
Toaster	>70	1 minute	600W (low), 1200W (high)	5-10 kWh	No standby load since no electronic control
Electric Kettle	1 minute	1800W (powered on)	5-10 kWh	No standby load since no electronic control
Desktop computer	3 minutes	8W (standby), 40W (idle), 100W (full load)	5-10 kWh	Display measured separately
32 inch TV	3 minutes	4W (standby), 40W (low brightness), 60W (high brightness)	5-10 kWh	Older TVs do not control LCD backlight
Laptop	3 minutes	8W (standby), 40W (idle), 100W (full load)	5-10 kWh	Display measured separately
Washing machine	1 hour	8W (standby), 40W (idle), 100W (full load)	5-10 kWh
Compact hairdrier	less than 1 minute	serious issues for health and goods
Vacuum cleaner	less than 1 minute	serious issues for health and goods
LED desk lamp	less than 1 minute	serious issues for health and goods

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.

[[Standby or powered-off load

Most devices use some power even when turned off. This value may be small, reaching just a couple of watts. Newer and more efficient devices may require just 1 Watt while in this state while older or more inefficient ones may be using more energy. The standby power load is important as the device may be plugged on all day or even year round, which means that even small values have an impact. A 1 watt power permanent load year-round ends up to around 9 kWh.

Low power load

Using a device with only some of its capabilities will require less energy than a normal one. For instance, air conditioning devices, dehumidifiers and other appliances may have a fan that can be operated at variable speed. The fan itself may create a power load of only 60 watts while the whole device may require 1000 watts in operation. This is important as it shows that some situations do not require a lot of energy but have a large impact on end results as increasing fan speeds speeds up a typical result you may want.

Another typical low power load situation is with computers, laptops or any data processing unit. Simply powering them and leaving them running will typically result in idling, which requires much less electrical energy than when a data intensive process such as rendering, database operation or another service is required. The same goes for gaming, in the case of home users. With the exceptions of these scenarios, the idle load has a very low impact on energy consumption.

Of course, more modern computers, appliances and devices have a reduced amount of power while not running intensive tasks.

Typical power load

Operating a device as required generates a specific power load. Configuring the device may prove that there are some settings which affect quality or performance, while others do not. This matters particularly when a large number of similar devices are used. Computers, laptops, TVs, displays, can be configured in a very effective way.

Large appliances such as refrigerators, cooking machines, ovens, air conditioning, heating and cooling devices are highly sensitive to temperature or time settings. Requiring fast results or large temperature differences compared with the typical interior temperature has a major impact on consumption. Many times, a particular temperature is required for a particular process or storage situations but small optimizations can be done if the process is well monitored for end product or process result.

Maximum power load

It is highly unlikely that most devices will be used at this power range but knowing how much the consumption can increase from typical power load upto maximum power load can be a very important information. Knowing how consumption can scale means that you can better adapt the way in which you use the device to cater to your needs.

An equipment or appliance that is frequently used at typical power loads and quite frequently near the maximum power load may also be less efficient and could have a premature breakdown due to stress so understanding its use is highly valuable. Also, intense usage may also be stressful as it releases more heat or other process byproducts that have to coped with inside the building, which also reduces comfort and the availability to cope with other requirements.

Many devices or appliances never reach the stated maximum power load that may be present in documentations or product labels since such an ussage may be dangerous, annoying or simply not possible. This is why determining a likely maximum power load offers a much better assessment of capabilities.

In the end, maximum power load is also important to assess the potential load on a specific circuit or branch of the electrical installation, avoiding potential shortcomings or dangerous situations. This matters a lot for home and small business users as this information can be a very good assessment of an energy audit for the current electrical installation. While it does not replace professional advisory, it can significantly improve it since the end user also has a much better current situation awareness.

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.

The all important 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.