Why does my inverter show two input voltages when there is only one solar string?

Most solar inverters have two separate inputs, or MPPTs as they're often known.

These discrete channels allow the inverter to measure the connected panels and extract the maximum yield from the given amount of sun available at any moment, hence the Australian developed technology called Maximum Power Point Tracking or MPPT.

Many newer units have three or even four input channels. This should not to be confused with pairs of plugs connected to two input channels, they've been available for years, and there should really be blanking plugs on the unused jacks if your inverter has them.

Some systems are configured with just one DC circuit or string of panels though, offering higher voltage and greater efficiency.

Some inverters have the ability to program out the second input and render it redundant but many don't and this is a cause of unnecessary worry.

If you have a inverter that displays for instance 400volts DC and 12amps on channel #1, then it also displays 150volts DC and zero amps on channel 2, this is normal.

As a solid state device there can either be some "leakage" inside the inverter that provides a measurable but otherwise phantom voltage, or there can be magnetic or capacitive coupling, again inside the machine and still nothing to worry about.