Mitsubishi Electric MELSEC iQ-R Series User Manual page 224

The OVERCURRENT LED is ON or flashing
Check item
Is the amount of the current consumption of the peripheral devices connected
to a USB port large?
32 TROUBLESHOOTING
222
32.1 Checking Errors with LEDs
Corrective action
Check the specifications (current consumption value) of the peripheral
devices to make sure that the devices can be connected to this product. If the
specification exceeds the allowable current consumption of this product,
review the devices being used (such as self-powered devices), or change the
configuration so that a self-powered USB hub is used.
Clear an error after reviewing the configuration.
(Page 60 Calculation for the current consumption value of a USB device)