Test PV Strings with MCIs

The following tests are performed on each PV string to confirm the PV wiring has been installed correctly and the array is functioning as expected:
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Warning
Before connecting or disconnecting any PV strings:
  1. Ensure the Powerwall+ Enable switch is turned OFF.
  2. Ensure Powerwall+ is not connected to AC power.
  3. If an external PV disconnect means is available, open the external PV disconnect switch.
  4. Ensure that there is no voltage on the PV inputs of Powerwall+.
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Note
For each of the following tests, ensure the tester leads are connected to the correct conductor as described in the test instructions. If the polarity is swapped, for instance if the negative tester lead is connected to the positive conductor, the test results will be incorrect.

Required Tools

  • Standard DC voltage meter
  • Insulation resistance tester (Tesla recommends the Klein ET600 tester)

Verify PV String Polarity

Required Tools:
  • Standard DC voltage meter or Insulation resistance tester (Tesla recommends the Klein ET600 tester)

Testing Procedure:

  1. Set the voltage meter to DC test mode.
  2. Connect the voltage meter positive lead to the string's positive conductor.
  3. Connect the voltage meter negative lead to the string's negative conductor.
  4. Confirm the result is a positive number. If the number is negative, string polarity has been swapped.
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    Note
    The voltage meter test result will not reflect the actual expected string voltage because there are MCIs installed in the string.

In the following diagram, the top image displays a multimeter correctly connected to the positive and negative leads in the PV array, resulting in a positive voltage (though this is NOT the string voltage). The bottom image displays an array where the positive and negative PV leads are swapped, resulting in a negative voltage test result. Correct the meter probe polarity and test again.

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Note
The diagrams above illustrate example PV stringing configurations; the number of MCIs and where they are installed in the string varies by installation configuration.

Verify String Voltage

Required Tools:
  • Insulation resistance tester (Tesla recommends the Klein ET600 tester)

Testing Procedure:

  1. Set the insulation resistance tester to 1kV test mode.
  2. Connect the insulation resistance tester positive lead to the string's positive conductor.
  3. Connect the insulation resistance tester negative lead to the string's negative conductor.
  4. On the insulation resistance tester, push the TEST button.
  5. Confirm the DC voltage result is equal to (or nearly equal to) the expected voltage per the system planset (it may not be the exact voltage).
    • If the DC voltage is significantly lower than the expected voltage, there is likely a wiring error.
    • If the DC voltage is significantly higher than the expected voltage, there is likely an open circuit.
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Note
If the difference in DC voltage is an increment of the panel voltage, the string may be missing panels (voltage is too low) or have too many panels connected (voltage is too high). For instance, if the expected DC voltage for a system with 40V panels is 420V, but the test result is 380V, the string may be missing (1) PV panel.
Figure 1. Insulation Resistance Tester Displaying String Voltage (433V in this example)
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Note
The diagram above illustrates example PV stringing configurations; the number of MCIs and where they are installed in the string varies by installation configuration.

Perform Insulation Resistance Test

Required Tools:

Testing Procedure:

  1. Temporarily connect the (2) extra MCIs to the string to test for ground faults:
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    Note
    If possible, connect the extra MCIs at Powerwall 3 to test the entire string. The extra MCIs can be connected on the roof, but they will not test the wiring between the roof and Powerwall 3 in this configuration.
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    Note
    The extra MCIs are not required if the string already has an MCI at either end of the string.
    1. Create (4) jumpers, two for each MCI, by crimping MC4 connectors to short lengths of PV wire. Connect the jumpers to the extra MCIs.
    2. Connect the (2) extra MCIs to each end of the PV string.
  2. Set the insulation resistance tester to 1kV test mode.
  3. Test positive to Ground :
    1. Connect the insulation resistance tester positive lead to the string's positive conductor.
    2. Connect the insulation resistance tester negative lead to the string's equipment grounding conductor (EGC).
    3. Insulate and protect the string's negative conductor, as it is live and is not being tested during this step.
    4. Press and hold the TEST button to begin the test. Allow the reading to stabilize before recording the measurement (take the resistance value while STILL holding the TEST button).
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      Note
      Keep the test leads connected to the circuit until it is completely discharged, and the display shows near zero volts.
    5. Confirm the resistance value is greater than 1 MΩ. If the value is less than 1 MΩ, there is likely a damaged wire and/or ground fault in the system. Look for nicked or pinched wires, improper field-made connectors or improper crimps, or evidence of damaged modules that need to be replaced.
  4. Test negative to Ground :
    1. Connect the insulation resistance tester negative lead to the string's negative conductor.
    2. Connect the insulation resistance tester positive lead to the string's equipment grounding conductor (EGC).
    3. Insulate and protect the string's positive conductor, as it is live and is not being tested during this step.
    4. Press and hold the TEST button to begin the test. Allow the reading to stabilize before recording the measurement (take the resistance value while STILL holding the TEST button).
      Informational PurposesAn informational icon, calling your attention
      Note
      Keep the test leads connected to the circuit until it is completely discharged, and the display shows near zero volts.
    5. Confirm the resistance value is greater than 1 MΩ. If the value is less than 1 MΩ, there is likely a damaged wire and/or ground fault in the system. Look for nicked or pinched wires, improper field-made connectors or improper crimps, or evidence of damaged modules that need to be replaced.
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Note
The diagrams above illustrate example PV stringing configurations; the number of MCIs and where they are installed in the string varies by installation configuration.

Explanation for Testing with Temporary MCIs

The insulation resistance test outlined above uses a temporary MCI connected at either end of the PV string to mitigate the following scenario:
  • Panel(s) are present at the end of the string (between Powerwall 3 and the first MCI in the string)
  • A ground fault is present in the string upstream of the first MCI
  • Because of the ground fault, voltage is present on the string, meaning the insulation resistance test cannot be completed (the tester will display a failure due to presence of voltage)
    Figure 2. Failed Test Due to Missing Temporary MCIs

The addition of a temporary MCI at either end of the string ensures the insulation resistance test can be completed in this scenario. While it is possible to perform an insulation resistance test without connecting the temporary MCIs, and to simply add the MCIs if the test fails due to the presence of voltage, Tesla recommends starting with the temporary MCIs so that the test need only be completed once.

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Note
This scenario is not the only one which will result in an error on the insulation resistance tester, and the error(s) displayed depend on the tester being used. See MCI and PV String Issues in the Powerwall 3 Device Setup Guide for additional troubleshooting steps depending on the issue(s) observed.