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 3.
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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 1000 V test mode (Tesla recommends Klein ET600)
Figure 1. Klein ET600 Tester in 1000 V Mode for True String VOC Test
  1. Safely shut the system down:
    1. Push the System Shutdown Switch if one is present, then turn the Enable switch OFF.
    2. Open the Powerwall 3 circuit breaker (turn OFF).
    3. Wait 30 seconds before proceeding with any work.
      Warning IconA warning icon, calling your attention to a possibly risky situation
      Warning
      Confirm Powerwall 3 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 1000 V 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 2. Testing Conductors on the Ground (at Inverter)
    Figure 3. 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 of the entire array to ensure it matches the design:
    • Confirm that all wiring has been connected correctly
    • Confirm that no connections have been missed
    • Confirm that each home run has been properly labeled based on its source (for instance, string 1 on the planset is labeled correctly as string 1 on the roof and at the inverter)
    • Confirm the crimp made on each MC4 head was done correctly (see Stäubli MC4 and MC4-Evo 2 assembly tutorial)
    • Confirm that any MC4 connections that were added (due to breaks or extensions) are tied to the correct home run or panel lead
    • If PV jumpers were used, confirm they are wired correctly. For example:
      • One string includes two arrays on two separate mounting planes. Confirm the positive from the MP1 array has been landed at the negative from the MP2 array
      • A common error in this scenario is to land positive to positive and negative to negative, which is incorrect when manually installing MC4 heads
    • If a junction box is present, double check all internal connections
    • Test VOC before making any parallel connections
      • The VOC should match across strings before they are combined
      • If the voltage of one string is lower than the string it will be combined with, the VOC of the combined string will be the lower output
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        Note
        It is possible to misinterpret this test result, obtained with the tester in 1 kV mode, as being the result of the PV strings being mixed up. To avoid this confusion, test VOC before combining strings.