What "Grid CT Lost" means
If you've seen a Grid CT Lost notification on your zappi, eddi or libbi, it means the device has temporarily lost its wireless connection to the harvi. When this happens, charging or diverting pauses until the connection is restored.
In the vast majority of cases, nothing is wrong with your equipment. Both devices are working correctly, and the connection re-establishes on its own within moments. If the notification keeps appearing, it's usually a sign the harvi could be positioned better relative to the device it talks to. The rest of this article explains why it happens and how to improve it.
Why it happens
The harvi communicates with your zappi, eddi or libbi (the "controller device") over radio frequency (RF), not Wi-Fi. This is a deliberate design choice: because it doesn't rely on your home network, the harvi keeps talking to your devices even if your Wi-Fi changes, drops out, or fails altogether.
Because it works wirelessly, where you place the harvi has a big impact on how reliably everything works. In ideal conditions with clear line of sight, the harvi can reach up to around 30m — but that's the very top of its range, not a target to aim for. For a dependable connection, install the harvi as close to the controller device as possible. As a rule of thumb, we don't recommend more than 20m, and in most installations it should sit under 15m. The closer it is, the more reliable the connection.
Certain materials can weaken the signal even at shorter distances: stone or metal walls, foil-backed insulation, metal enclosures and other devices communicating on a similar frequency. These interfere with the wireless signal and can affect both the connection quality and the accuracy of the data your harvi reports.
Improving your connection
Most harvi connection issues come down to placement. To improve things, try:
- Change the radio channel to see if the connection improves — see Checking & Changing the radio communications channel
- Mount the harvi as high as possible - with harvi mounted vertically (not horizontally)
- Relocate the harvi to another location where the signal is better
- Swap the controller device — if more than one unit is fitted (e.g. zappi, eddi or libbi), set the other as the controller and monitor for signal improvement (see Pairing Devices). Because eddi and libbi have external radio antennas, they may connect more reliably — so where you have the choice, they make a stronger controller
- Upgrade the antenna — the external RF antenna on eddi and libbi can be replaced with a third-party high-gain antenna to extend range and improve signal strength
- Installers only: extend the CT clamp cable using twisted pairs, up to 100m, to allow the harvi to be relocated within a reliable range to the controller device.
A note on firmware version 5
If you've had your harvi for a while and recently updated to firmware version 5, you may notice it now reports brief connection drops that it didn't flag before, particularly when the harvi is connected to your grid CT clamp. This is expected, and it doesn't mean anything has gone wrong with your setup.
The reason is a change in how the harvi responds to short interruptions. On version 4 and earlier, if the connection briefly dropped, the device would carry on charging or diverting for up to an hour and only show an error if the link didn't come back — so momentary drops usually went unnoticed. A UK regulation for wirelessly connected CT clamps (Engineering Recommendation G100 Issue 2, 2022 Amendment 2) now requires a faster response. From version 5 onwards, if the connection is lost for 30 seconds, a Grid CT Lost notification appears and charging or diverting pauses until the link is restored.
If you experience issues after updating your device from version 4 firmware, follow the steps listed above.