What do you need?

What you need depends on what you want to measure, and what type of power system you have.  From time to time there will be various packages of items available for particular use, but the basic installation requires, at a minimum:

  • IoTaWatt base unit
  • USB power supply
  • AC Voltage reference transformer
  • One or more current transformers

Currently, accessories are only being sold for North American 120/240 Volt split-phase power systems. (Basically the US and Canada residential/light commercial)

Current transformers are used to measure the usage of individual circuits.  In a US residential setting, there are a few different categories:

  1. Mains - These are the two conductors that feed everything else in the home.  They are connected to two large circuit breakers. Typically these are rated at 200 Amps. Measuring consumption on the mains gives the whole house picture, and should match the consumption recorded by your meter.
    Consideration in selecting the CTs for these is both the size of the cable and the maximum current expected through the conductor.  Typically, a 200Amp split-core CT like the ECS24-200 or ECS25200-C2 is used for this.
  2. Solar - Renewable energy systems such as rooftop-solar are typically connected through the household electric panel and many export power through various "net metering" arrangements.  IoTaWatt can measure this energy production and also monitor the net usage including imported and exported power.  Typical rooftop solar systems of 10kW or less will only require a 50 amp current transformer that can fit on one of the conductors from the inverter.  The ECS10-50 has a 10mm (about 3/8") opening and works well.  If the conductor is larger than 10mm, the ECS16-100 will work fine as well.
  3. 120V Branch Circuits - These are typically plugs and lighting. They are usually protected by 15 or 20 Amp circuit breakers and are #12 wire. The 50 Amp current transformers can be used here, and in fact the conductors of several branch circuits can be passed through one ECS10-50 or ECOL09 to effectively monitor the total of several circuits as one.  There are also other ways of monitoring multiple circuits with several current transformers using just ine input on the IoTaWatt.  That is covered in the Wiki.
  4. 240V Circuits - Large appliances and branch panels typically are wired with a double breaker for 240V operation.  The appropriate CT for each of these depends on the particular load and the maximum current that will be measured. For some 240 volt devices, you only need to measure one conductor and double the result.  ECS10-50 is usually fine for that. 
    For others, both conductors need to be measured.  There are a variety of ways to do this, but it boils down to three choices:  one ECS10-50, two ECS10-50, or one ECS16-100. The various ways these can be installed is covered in the documentation.