Harvi is designed to work by "harvesting" power from the connected current transformers (CT's). This means that if there is no power (current) flowing in the circuit being monitored then the harvi will go to sleep and will not transmit and data.
If this is a problem, then it is possible to use an external DC power supply to keep the harvi alive.
The external power supply should be connected to a spare CT input on the harvi.
The external DC power supply should have a voltage between 9V and 12V to ensure that the harvi wakes up and is not damaged by too high a voltage being connected.
On the Master device (eddi/zappi) the CT input that you have used for the external power supply should be set to "None"
As you will be using a spare CT input for the external power supply you cannot power the harvi if it's already got all three CT inputs connected (eg on a three phase system).