Efergy CT Sensor XL with Jackplug Fitting suitable for most Efergy Elite, E2 and Ecotouch Electricity Monitors as well as the Efergy Engage Internet Hubs The large sensor is required for use on cables that are larger 12mm and up to 19mm diameter. They are also suitable for more powerful electrical installation up to 200 amps per phase. How it Works Efergy transmitters come with three spaces for sensors. Just look on the underside of the transmitter, take out the rubber cover of one of the spare spaces and plug in your additional sensor. Then attach it the same way as the previous one. IMPORTANT! Please Check Connection Type: If you are purchasing a sensor for a monitor that you already own, PLEASE check the connection type between the sensor and transmitter before ordering, to ensure you receive the correct product. Efergy have used 2 types of connectors for their Energy Monitors. This sensor is the type used on recent models and has a small "Jackplug" similar to the small jackplug used to connect headphones to an ipod or mp3 player. Older models use a 3.5mm DC connector similar to the connector found on many household transformers. if you are uncertain which type of connector you require, please contact us and we can supply more details by email