Tag Archives: Kill A Watt

Measuring power use on 240V appliances

In the USA large appliances like clothes dryers or electric car chargers are built for 240V. I happily have used the Kill-A-Watt EZ for simple measurements, but 240V appliances can’t be measured through it. The TED5000 I have measure whole-house electricity usage, but I wanted to update my chart of where power goes in my house (electric power, that is). I want to get an updated picture of what % goes to heating, fridges, etc.

The TED5000 could be a great option but having to install a new MTU and CTs seemed complex, especially once it comes to aggregating the data into only one gateway. I thought splitting the 240V lines and feeding one live/neutral pair in a Kill-A-Watt… but not knowing more about the internals of the Kill-A-Watt I felt I may introduce unnecessary safety risks.

Instead, I built my own portable 240 Volt power meter:


  • Get a Dryer cable (there are differrent models, older 3-prong and newer 4-prong plugs with separate ground and neutral connections. I got the type of cable I needed). Example
  • Get a surface-mount receptacle for the same type of cable you have. Example
  • Get a EKM DIN-Mount power meter

With these elements in hands I assembled a simple 240V “extension cord” that has a remote display to measure the power going through it. The remoteness of the display (a design idea from the Belkin Conserve meter that is otherwise useless) is useful especially with 240V appliances where the outlets are inaccessible, behind heavy stuff, plugs are huge and hard to maneuver in cramped conditions, and you generally don’t want to be messing around with them.

 The assembly was simple. I got lucky since the CT of the EKM device fit nicely in the surface mount box with no stress to case or cable.

Since it measures current going only through one live lead, the actual power is twice the displayed value in the meter. Unlike many other countries where the use of 2 out of 3 phases at 120deg phase is common, in the USA higher-voltage appliances are powered with two counter-phase live lines of 120V each, so getting the real power used is a simple matter of multiplying by 2 instead of by square root of 3.

This meter is handling 240V with high currents so it is important to do a careful job if you decide to build your own. Doing 240 V in Canada is illegal if you are not an electrician and you can void your house insurance. You can hurt your loved ones, yourself, or your property if you don’t know what you are doing (this is true for everything in life, however).

The EKM meter gets the current reading from the ring ammeter in the outlet, and reads the voltage through a couple of extra cables.

Here is the end layout before getting the EKM meter and cable into casing and protective stuff:

DIY 240 V power meter

The meter reads cumulative kWh so you need to keep a logbook of when you started and stopped measuring what. It tracks kWh to 2 decimal places so it’s more than precise enough for the use we are giving it.

Portable vs Breaker Panel metering?

I like the meter I built, for its portability, simplicity, and that I can lend it to friends.

But after getting some basic measurements I am considering installing the EKM as an add-on to my breaker panel. This will allow me to periodically re-wire the CT onto different circuits. I may decide to invest in a better meter – EKM has a very compelling product line– , but I have pushed my electricity consumption so low already that I would need to expect to discover significant in the data obtained in order to recover the cost. After all, the basics save most of the money.

But if you are starting the process I went through improving your house’s electricity efficiency from the beginning, or you want to discriminate between appliances such as electric cars, and you care about measuring stuff, I would highly recommend installing one of EKM’s smarter meters near the breaker box and investing in a couple of clamp-on CTs. If you don’t care about fine-grained measurement just follow the main improvements and use your bill to track improvement.

Feel free to leave comments & questions below!

Measuring Energy used with TED 5000 and Kill-A-Watt

You can improve a lot of things about your energy consumption by following a few rules of thumb, but at one point or another you’ll need to measure your use to know where to place your efforts. Your utility bill is a great tool, and it gives you a high-level overview of trends, but it won’t help you change your behavior in real-time, pinpoint problem areas, or dispel assumptions.

By tracking things better you can also decide where it may be worth it to install some smart control (a timed switch or outlet, a presence sensor, etc), or if upgrading an appliance is worth it energetically. In this post I will share some some of the approaches to measurement I’ve taken for electricity use.

  • TED 5000 for house-level usage and overall patterns
  • Kill-a-watt EZ for appliance and outlet-level analysis.

TED 5000

The TED 5000 (http://www.theenergydetective.com/)is a small simple device that installs in your main electricity junction box and measures current and voltage in real-time. This allows it to compute power used and keep track of it over time.

You install the measurement unit (which they call “MTU”) in the junction box, and then it sends out the measured data to a box plugged elsewhere in the house which is called a “Gateway”. This gateway has a network cable interface and you can plug it into your ethernet. The Gateway exposes a web page which you can see in your browser, which shows real-time and aggregate information.

The TED 5000 Dashboard, accessible by browsing to your TED Gateway’s IP Address

I have found TED 5000 (TED is an acronym for “The Energy Detective” and a not-subtle resemblance to the TED talks logo) to be useful for:

  • Real-time checking of how much appliances are using when they are on or an average over time.
  • Good for real-time tracking that allows me to hunt down phantom/vampire/leech devices that eat up more energy than I thought
  • Seeing how my hourly & weekly electricity usage patterns can be changed.
  • Getting really annoyed at appliances that I can’t turn off e.g. refrigerator.

I have not found it useful for:

  • An appliance-by-appliance analysis of my usage, because of the way it measures and tracks electricity, and also because it’s appliance “Load Profile” scheme seems to mix up my house appliances a lot.
  • Everyday behavior adjustment based on usage and projections – I am finding external apps are more likely to do this for me.
The TED 5000

Mobile Apps for the TED 5000

The information can be seen in a bunch of mobile apps which connect directly to your TED 5000 Gateway, amongst which Mirawatt T5K (http://ted.mirawatt.com/)is the one I liked the most (I use an iPhone, there are similar apps for Android and possibly Windows Phones). It is only worth the $4.99 price because it has no competition as far as user experience goes. (It is not spectacular, however. It is just the least bad of the bunch). Others I didn’t like as much were TED-O-Meter or iTED. These are free, so yay & kudos for the efforts to those developers. To access the information outside your home via your mobile network you will need to configure your internet router to expose the TED Gateway IP address directly on the internet.

Cloud Services & Mobile Apps

PeoplePower (http://peoplepowerco.com/)is a relatively new effort that provides an internet service and a mobile app to access your data. The TED 5000 Gateway stores some usage data, but PeoplePower promises to save your data for a longer time on a real server and its mobile app has more features around projecting and setting goals for your electricity use. It’s headed in a promising direction, and they are also making some steps in gameifying environmental behaviors.

You configure the service by telling your TED device to “post” data to their website. Just follow the instructions you get when you sign up. If you run into any issues or the TED configuration is acting up on you, just email them- I can attest their technical support is excellent.

Kill-A-Watt EZ

The Kill-A-Watt EZ is a great little device. It tracks the energy usage over time and displays real-time or accumulated information. It can show Watts, KWH, or $ (you have too tell it your electricity rates).

I have found it useful for:

  • Measuring the overall electricity used of a device that has complicated use patterns (e.g. my workstation, where I have multiple monitors, and I use it more of it some days than others)
  • Keeping ongoing track of devices that have “spikes” of use. For example, knowing how many watts my microwave oven uses when it’s on is less interesting than knowing how much energy I am using in it over a month.
  • Measuring specific outlets I want to track for other purposes like the charger outlet to the battery of my car, which runs off a standard 120V outlet. I want to track if my battery recharging becomes less efficient over time, and have concrete data for EV naysayers who say it uses more electricity than it’s worth it in gas.

I have tried other devices like the “Belkin Conserve Insight Energy-Use monitor”. It has a nicer physical design but it’s almost a waste of money when it comes to measurements, because of the way Belkin chose to aggregate and display the data. I’ll stick with the Kill-a-watt.

I have a couple of Kill-A-Watt unit (one fixed for the car charger and one that ‘roams’ around the house as I make week-long measurements). The next obvious evolution is to have these meters transmit data via wireless to services such as PeoplePower’s. I’m sure an enterprising soul with a Kill-A-Watt, some micro controller  knowledge or a new ElectricImp and time to invest in a cool project could take the output of the former and beam it via wireless provided by the latter. Sounds worthy of a Maker Faire project.

Note that none of the above help measure electricity used by built-in lamps or lighting systems that you turn on and off via a wall switch (unless you wire things yourself). Maybe one day soon light switches and outlets that automatically measure, store , and forward usage patterns will become economically viable. Some smart digesting of the ensuing data deluge could provide actionable and personalized tips to do more with less.