HP Array Controller HSG V8.7 Software - Manual (Page 73)

Environmental Monitoring Unit
UltraSCSI RAID Enclosure 3–17
Monitoring Power Supply Operations
Even with four operational power supplies, it is possible that a power
supply problem might cause one or both of the dc voltages to be too
low. Both the PVA and EMU monitor power supply operations to
ensure that dc voltages are within a specified range (see Table 3–6).
At least four operational power supplies are required to maintain the
minimum voltage requirements shown in Table 3–6. With less than
four operational power supplies, the EMU notifies the array
controllers of a fault condition. The array controllers shut down and
then the EMU initiates standby power mode.
Caution
Some array controllers bypass the standby power mode
functionality from the PVA standby power switch. Refer to
the array controller documentation for availability of this
feature.
Note
Only the EMU monitors the I/O module +5 V dc
TERMPOWER. The PVA does not monitor this voltage.
Table 3–6 DC Voltage Ranges
Nominal Voltage +5 V dc +12 V dc
Minimum Voltage +4.7 V dc +11.4 V dc