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 Klein ET600 Tester in 1000V mode
Impedance reading (top value) ≥ 1 MΩ
Impedance reading < 1 MΩ
String True VOC 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 3 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)
Combined strings: voltage between 31V and 60V
MCI Diode Test

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