High-gain mode is available on the EG4xxx hardware only. To enable high-gain mode, navigate to Settings -> Installation. Check the "Use high-gain mode" option just above the dropdown menus for CT selection.

High-gain mode selection box

High-gain mode amplifies the incoming signal from all CTs by a factor of ten. From a practical standpoint, this means a CT with a higher amperage rating can be used to measure much lower amperages. For example, with high-gain mode enabled a 100A CT could be used in place of a 10A CT. 

High-gain mode does not require any changes to standard installation or wiring procedure. When high-gain mode is enabled, the CT amperages displayed in the drop down menus will decrease by a factor of ten (for example, an 800A CT will be listed as an 80A CT). For the simplest configuration, it is recommended to set actual CT amperages first and then enable high-gain mode. Note that high-gain mode is a global setting - when enabled, it applies to all configured CTs. As with most other installation settings, enabling high-gain mode will only impact data recorded from that point moving forward.