1. Check home run wires (from PV modules to combiner box) at DC string combiner box to ensure there is no voltage on them.
2. Recheck that fuses are removed and all switches are open.
3. Connect the home run wires to the DC string combiner box terminals in the proper order and make sure labeling is clearly visible.
4. Check open-circuit voltage of each of the panels in the string being wired to verify that it provides the manufacturer’s specified voltage in full sun. (Panels under the same sunlight conditions should have similar voltages–beware of a 20 Volt or more shift under the same sunlight conditions.)
5. Verify that the both the positive and negative string connectors are identified properly with permanent wire marking.
6. Repeat this sequence for all source circuit strings.
7. Recheck that DC Disconnect switch is open and tag is still intact.
8. Box (place common lead on the negative grounding block and the positive on each string connection-pay particular attention to make sure there is NEVER a negative measurement). Verify open-circuit voltage is within proper range according to manufacturer’s installation manual and number each string and note string position on as- built drawing. (Voltages should match closely if sunlight is consistent.)
9. Retighten all terminals in the DC String Combiner Box.
10. Verify that the only place where the AC neutral is grounded is at the main service panel.
11. Check the AC line voltage at main AC disconnect is within proper limits (220-240 Volts AC ).
12. If installation contains additional AC disconnect switches repeat the step 11 voltage check on each switch working from the main service entrance to the inverter AC disconnect switch closing each switch after the test is made except for the final switch before the inverter (it is possible that
the system only has a single AC switch).