One of strings showing voltage but not pulling full amperage when connected to combiner

[NomNomCameron]

I have 300 watt pannels connected 4 in series per string going to a combiner which feeds an EPEver 100 amp 200v charge controller. I started connected the strings today, first 2 went off without a hitch, showing 20 amps @ ~150v, when I connected the third string the amperage did not increase on the charge controller and when I check the current around that string (where it connects to the combiner) the amperage is showing opposite polarity of the other 2 strings? This third string in question shows ~150v when probed with the same polarity as the other 2 strings and I have triple-checked that all strings are wired in series correctly all the way to the combiner. I connected another string the same way, without an issue so this problem seems to be isolated to this string. Could one of the panels be bad or could I have done something wrong??

I've never run into this issue before with new or used panels (these have never been used, purchased at a liquidation auction).

Any help on this would be greatly appreciated!

 

[MichaelK]

Have you verified the voltage, or negative voltage idependently with a volt meter? I would think it rare, but the MC4 connectors could have been reversed at the factory?

 

[NomNomCameron]

Have you verified the voltage, or negative voltage idependently with a volt meter? I would think it rare, but the MC4 connectors could have been reversed at the factory?

I have not checked that, I figured since I get positive voltage at the end of the leads when the panels are in series that couldn't be the case. I'll check each panel's voltage next time I'm out there

 

[Jim Burrow]

If you have negative voltage on one of your strings, I agree with Michaelk in that the one string probably has the wiring in the MC4 connector reversed. That is easy to do. I screwed up once and reversed the wires in one of my MC4 connector.