You can monitor electrical power consumption at a remote property using our new Sensor-S module. It's easy to use ... but it's still worth reading though the guide below. 


The black box in the photo is the Sensor-S module, which you connect to a free Quatropus port (see How MaxMon works). The blue component (actual product colour may vary) is a current transformer. Clip this around ONE of the main current-carrying wires entering your property. The easiest place to do this is usually at your property's electricity meter.


Important things to note about installing the current transformer:

  • Do NOT cut cables or insulation or use with non-insulated cables. Contact a qualified electrician if you are in any doubt. Mains voltage can cause serious injury or death.
  • Installed as shown the current transformer is completely electrically isolated from the mains cables. It senses a small 'induced' secondary current, not the much larger primary current flowing through the thick cables.
  • It should not matter whether you clip the transformer around the LIVE or NEUTRAL cable (brown or blue respectively in the UK) but you must clip it around one or the other. If you clip it around a cable carrying current in both directions (e.g. a typical mains wire with live and neutral cores) the 'induced' currents cancel and the sensor will read zero! This is why the meter box is the best place to install the transformer, as most cables elsewhere are multi-core.
  • Clipping the transformer around an EARTH or GROUND cable will have no effect (unless you actually want to measure earth leakage current).
  • Orientation (direction of current flow) is not important, just ensure that the cable is as central as possible in the transformer and that the transformer is closed.
  • Don't forget to plug the transformer into the Sensor-S module. Depending on where this is located you will likely need to purchase a Sensor-S extension cable.


The Sensor_S appears as a typical MaxMon sensor:

  • It will be included in MaxMon reports and alerts (for help configuring sensor alert thresholds and alert actions - see Help: Sensors and Help: Alerts).
  • By default it measures cumulative electrical power consumption in kWh (kilowatt-hours, the same units used on your electricity bill).
  • Cumulative power consumption as reported by MaxMon needs a little interpretation. If your sensor log interval (see General settings) is 10 minutes then a reported reading of 1.4 kWh means that 1.4 kWh of power was consumed in the previous 10 minutes. If that power consumption continued unchanged then in an hour 6 x 1.4 or 8.4 kWh would be consumed. So as a rule of thumb (for a 10 minute log interval) multiply a kWh reading by 6 to estimate the instantaneous power consumption. The spikes in the graph above are an electrical vehicle being recharged at about 32A/240V (or 7.7 kW).
  • The MaxMon reports include cumulative totals for the report period, so you can see daily or weekly power consumption. This is a great way to detect excessive power consumption or unauthorised occupancy at a rental property without invading tenants' privacy.
  • You can switch the sensor to show instantaneous power consumption in kW (see the "Mode" setting in Help: Numeric sensor).
  • You can calibrate the sensor for more accurate readings. Perhaps the easiest way to calibrate it is to leave it in its default cumulative power mode and to note the electricity meter reading (in kWh) at the start and end of a daily reporting period (by default 7am). Then compare that value with the total power consumed in the MaxMon report 24 hours later. if the meter says 42.0 kWh have been consumed and MaxMon says 43.4 then simply calibrate the sensor to read 42.0 when it wants to read 43.4 (see the "Calibration" setting in Help: Numeric sensor).