Determine True String VOC

True String VOC Test Overview

The following procedure closes the MCIs (also referred to as bypassing the MCIs) to check the Voc of the string, confirming that the string has been wired correctly.

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Note
Perform this testing after wires have been pulled through but before they have been landed at the Powerwall+ / Tesla Solar Inverter.
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Note
This test must be completed on PV strings before they are to be combined (paralleled).

Required Tools:
  • Insulation Resistance Tester in 1000V test mode (Tesla recommends Klein ET600)
Figure 1. Klein ET600 Tester in 1000V Mode for True String VOC Test
  1. Safely shut the system down:
    1. Initiate Rapid Shutdown:
      • For Powerwall+, push the System Shutdown Switch if one is present, then turn the Enable switch OFF.
      • For Tesla Solar Inverter, turn the AC disconnect OFF if one is present, then open the Solar Inverter circuit breaker.
    2. Open the Powerwall+ / Tesla Solar Inverter circuit breaker (turn OFF) if not already done.
    3. Remove the DC Isolator connector.
      Figure 2. Tesla Solar Inverter DC Isolator
    4. Wait 30 seconds before proceeding with any work.
      Warning IconA warning icon, calling your attention to a possibly risky situation
      Warning
      Confirm Powerwall+ / Tesla Solar Inverter is de-energized before proceeding. Confirm the breaker is open (OFF) and solar production is disabled in Tesla One.
  2. Plug the positive and negative meter tester leads into the meter. For combination insulation resistance and multimeter testers, insert the test leads into the designated insulation testing ports.
  3. Set the tester to 1000V mode.
  4. Disconnect both (positive and negative) conductors to test a string. The conductors can be disconnected from the inverter (on the ground) or on the roof.
    Informational PurposesAn informational icon, calling your attention
    Note
    Paralleled strings must be tested independently. This must be done on the roof, and can be done by undoing Y-connectors or removing jumpers inside the combiner box.
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    Note
    For very short strings of two modules, test the short string together with a string that passes the test. Short strings may not be able to be tested by themselves.
  5. Connect the positive tester lead (red) to the positive conductor.
  6. Connect the negative tester lead (black) to the negative conductor.
    Figure 3. Testing Conductors on the Ground (at Inverter)
    Figure 4. Testing Conductors on the Roof
  7. 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.
  8. If any string does not display the expected string voltage (see planset), inspect the wiring on the roof to ensure it matches the design.
  9. If all wiring has been performed correctly, look for evidence of damage that may be causing the string to under perform:
    • Inspect where the wires exit conduit, as nicked wires may occur here
    • Check for wires pinched by mounting hardware
    • Look for evidence of damaged modules:
      • Microcracks
      • Signs of water intrusion
      • Module leads are bent at sharp angles