MCI and PV String Issues

Table 1. Overview of Common MCI and PV String Troubleshooting Tests
Test	When to Perform	Required Tools	Pass	Fail
Insulation Resistance (Megger) Test	Isolation Self-Test Failure	Klein ET600 Tester in 1000V mode	Impedance reading (top value) ≥ 1 MΩ	Impedance reading < 1 MΩ
String True VOC	Powerwall+ / Tesla Solar Inverter displaying 0A for connected string Powerwall+ / Tesla Solar Inverter is under producing Arc Fault lockout	Klein ET600 Tester in 1000V mode	String voltage (bottom value) matches expected voltage on planset	Figure 1. Lower Voltage than Expected (Likely Wiring Error) Figure 2. Higher Voltage than Expected (Likely Open Circuit)
String Continuity	Powerwall+ / Tesla Solar Inverter displaying negative voltage for connected string	Insulation Resistance Tester in DC test mode Examples: Klein CL800 Klein ET600 Tester	Single strings: voltage between 10V and 30V	Voltage < 10 V (includes decimal or negative values)
String Continuity			Combined strings: voltage between 31V and 60V	Voltage < 10 V (includes decimal or negative values)
MCI Diode Test	Powerwall+ / Tesla Solar Inverter displaying 0A for connected string Powerwall+ / Tesla Solar Inverter is under producing MCI Self-Test failure Isolation Self-Test Failure Arc Fault lockout	Insulation Resistance Tester in Diode test mode Examples: Klein CL800 Klein ET600 Tester	0.25V ≤ Reading ≤ 0.5V	Reading < 0.25V or > 0.5V
MCI Resistance Test		Insulation Resistance Tester in Resistance test mode Examples: Klein CL800 Klein ET600 Tester	Reading of "OL" or > 1 MΩ	Reading < 1 MΩ