MLPE string safety voltage check

This check measures the DC voltage of a string built with module-level power electronics while the inverter is off or disconnected. In that state each optimizer or rapid shutdown device outputs only a small safety voltage instead of the full module voltage. For SolarEdge optimizers the string should read about 1 V for each optimizer in series. Other devices have different standby values, for example 0.6 V per TS4-F unit, about 1 V per JMS-F device, and roughly 0.6 to 0.7 V per APS device. Measure each string on its own before connecting it to other strings or to the inverter. Use a voltmeter accurate to at least 0.1 V, check polarity at the same time, and make sure the modules are in sunlight so the optimizers switch on. A string voltage that is too high points to wiring errors, such as an extra optimizer in the string or a module connected without an optimizer, and means the installation may not have a safe low voltage. To find a power optimizer failure, disconnect the string and measure each optimizer to locate the one without its safety voltage. To find a rapid shutdown device failure, keep halving the string until the faulty unit turns up. A correct safety voltage does not prove every device works. Devices stuck in bypass may only show up as a low operating voltage once the system is running, so also compare the voltage with the system active. Only qualified electrical workers should do this check. Strings can carry lethal voltage in sunlight, so wear protective equipment and confirm cables are dead before you touch them.

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• sentence 7: support check: partial - Passages cover qualified persons, lethal voltage in sunlight, PPE, and checking cables voltage-free, but the qualified-persons warning comes from a different procedure and not this check specifically. -->