Negative multimeter voltage reading

A digital multimeter shows a minus sign when the voltage it measures is negative. When you check a string this way, the minus sign means the string is connected in reverse polarity. To take the reading, put the positive meter lead on the positive string cable and the negative lead on the negative string cable, then measure across the two. Check the polarity of every DC cable before any other test, and before closing switches or inserting string fuses or overcurrent devices. When you check many circuits, the minus sign is easy to miss. As an alternative, connect the strings to a shared negative bus and measure from positive to positive. A reversed string then reads about twice the system voltage instead of close to zero. When the inverter reports a reversed PV input, turn the DC switch off, open the fuse holders and use the meter to find which string is reversed, then correct its connection. DC inputs with the wrong polarity may damage the inverter. If a reversed string is found on a system that was already connected, check its modules and bypass diodes for damage.