HP Integrity NonStop X NS7 Planning Manual page 92

Once the downstream UPS is in this state, it still might not immediately perceive stable input
power. The downstream UPS is thus compromised until it achieves a lock on stable input power
and is able to recharge its batteries.
Such problems are very difficult to predict. Their occurrence is a function of the output
characteristics of the primary UPS, the input characteristics of the downstream UPS, and the
load characteristics of the other devices deriving power from the upstream UPS. Factors can
include the other types of loads which are driven by the upstream UPS. Some non-linear loads
such as lighting or larger motors are more likely to distort the upstream UPS output than other
electronic equipment.
The occurrence of these problems is unpredictable and has affected NonStop customers. There
is currently no known method to analytically predict the occurrence of such instability. To ensure
correct UPS function, Hewlett Packard Enterprise recommends that you conduct on-site system
testing and that you try to use the supported UPS configurations described in this appendix.
92 UPS and Data Center Power Configurations