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	Insulation Resistance Tester in 1000V test mode Tesla recommends: Klein ET600	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	Insulation Resistance Tester in 1000V test mode Tesla recommends: Klein ET600	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)
DC Voltage Test (Completed String and Polarity)	Powerwall+ / Tesla Solar Inverter displaying negative voltage for connected string	Insulation Resistance Tester or Multimeter in DC test mode Tesla recommends: Klein ET600 Klein CL800	Single strings: voltage between 13V and 30V	Voltage < 13 V (includes decimal or negative values)
DC Voltage Test (Completed String and Polarity)			Combined strings: voltage between 30 and 60V	Voltage < 13 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	Multimeter in Diode test mode Tesla recommends: Klein CL800	0.25V ≤ Reading ≤ 0.5V	Reading < 0.25V or > 0.5V
MCI Resistance Test		Insulation Resistance Tester or Multimeter in Resistance test mode Tesla recommends: Klein CL800 Klein ET600	Reading > 1 MΩ	Reading < 1 MΩ