Insulation Resistance Test Overview

Insulation resistance testing is performed by “injecting” potential onto the conductor in the form of DC voltage, with a second conductor or ground conductor as a reference point. Any “leakage" of the potential indicates a fault in the insulation.

Identify the Faulty String

Identify the Failure in the Faulty String

To find the failure, perform a close inspection of all the components in the faulty string:

• At the Powerwall+ / Tesla Solar Inverter, look for poor wire termination (wires not fully seated in terminals, wire strands are frayed)
• Inspect where the wires exit conduit, as nicked wires may occur here
• Check for wires pinched by mounting hardware
• For Solar Roof installations, check for wires damaged by screws (screws may be accidentally run through wires when installing the tiles)
• Check for improper field-made connectors or improper crimps
• Look for evidence of damaged modules:
  • Microcracks
  • Signs of water intrusion
  • Module leads are bent at sharp angles
• For the faulty string, try testing the string with the DC grounding conductor (EGC) removed from the inverter's ground terminal; if the string passes self-test with the grounding conductor removed, it is likely the string is faulting to ground somewhere

If any of the above issues are observed, repair or replace the equipment. For instance if the issue is caused by a nicked wire in the conduit body, cut out the damaged wire and splice the remaining segments together or replace the wire if splicing is not possible. If the issue is caused by a nicked wire in the middle of the array, cut the wire and crimp PV connector heads on either remaining segment, or replace the entire section of wire (whichever is easiest).

If none of the issues above are observed, see MCI Diode Test and Resistance Test (MCI Health Tests) to determine if a faulty MCI is causing the isolation failure.