If you try to apply power from the Trex unit when the device is externally-powered, the Loop Diagnostics application prevents the Trex unit from supplying power. This protects the Trex unit from damage.
CAUTION:
Remove the USB cable from the Trex
unit before connecting to a device.
CAUTION:
Do not add any external power to
the device when the Trex unit is powering the device. This can blow a fuse
inside the Trex unit. The repair/replacement will need to be completed at an
authorized service center. Ensure the device is disconnected from the
loop/segment and no other wires are connected to the device before providing
power from the Trex unit.