Hitachi WJ200-001S Quick Reference Manual page 101

Inverter doesn't block the current flowing into itself when it is not powered. This may
cause the closed circuit when two or more inverters are connected to common I/O
wiring as shown below to result in unexpected turning the on the input. This may lead
to dangerous situation. To avoid this closed circuit, please put the diode
(rated:50V/0.1A) in the path as described below.
IF the protection diodes used when the units are in wired parallel are only single diodes
then their condition would be checked as part of the proof test.
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