Why does a Smart-UPS turn off when a standard serial cable is attached?

Issue:
Why does a Smart-UPS turn off when a  standard serial cable is attached?

Product Line:
Smart-UPS

Environment:
All SU, SUA, SURT, and SUM  models, All Serial Numbers

Cause:
A Smart-UPS may turn off if a standard serial cable is connected. This is due to the proprietary pinout of APC Smart-UPS serial cables.

Resolution:
Always make sure a proper APC Serial Cable such as the 940-0024, 940-1524, or 940-0020 is being used. APC Serial Cables will always have part number clearly marked on the connector end of the cable. 
SMT, SMX, SMC, and SRT models use a new Keyed RJ45 to DB9 cable to further differentiate between the APC cable and a standard serial cable.