Delta RT Series User Manual page 31

If you connect the Delta external battery pack(s) to the UPS:
Verify if the UPS's input cord meets with N, L & G of the wall socket and the utility AC power
works normally.
Check the '+'and '-' poles of the Delta external battery pack(s) and ensure that wiring is
correct.
Connect the Delta external battery pack(s) to the UPS.
Plug the UPS's input cord into the wall socket.
Press and hold the ON/ OFF button (
beep. After the UPS performs self-diagnosis, the UPS will run in ON-LINE mode.
) for 3 seconds and release it after you hear one
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