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HP ProCurve 2520 Planning And Implementation Manual: Poe/poe+ Power Supplies; Why Mixing Power Supplies Is Not Supported

Procurve power over ethernet (poe/poe+).
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Introduction
PoE Capabilities of the Products
The 12V system power is used to operate the internal components of the
switch. The 50V PoE or 54V PoE/PoE+ power is used to power the PoE devices
connected to the modules.
It is important to provide a secondary power supply for redundancy purposes
for both the 12V and 50V or 54V circuits. The internal power supply in these
switches provides both the 12V (system) and 50V (PoE) or 54V (PoE+)
circuits. If the 12V (system) power fails the switch will shut down. If the 50V
or 54V fails, all PDs would lose power. Therefore, to keep the switch running
should one power supply, or either power source fail, you should install a
second power supply.
The 5406zl/8206zl chassis can hold two internal power supplies and the
5412zl/8212zl chassis can hold four internal power supplies.

PoE/PoE+ Power Supplies

Why Mixing Power Supplies is NOT Supported
Using a combination of zl PoE power supplies J8712A and J8713A and a J9306A
zl power supply in PoE/PoE+ systems is NOT supported. Use the J9306A zl
power supply for systems providing PoE and PoE+ power.
The reason the power supplies should not be mixed is because the J8712A and
J8713A power supplies provide PoE power at 50 volts (273 watts for J8712A
and 900 watts for J8713A). The J9306A zl power supply provides PoE/PoE+
power at 54 volts (300 watts at 110 volts and 900 watts at 220 volts). If you
install a J8712A or J8713A with a J9306A power supply, they do voltage sharing.
This means that the 54 volts of the J9306A zl power supply will supersede the
50 volts of the J8712A or J8713A power supplies. Only the J9306A will provide
PoE/PoE+ power.
For example, if an HP ProCurve 5406zl switch on a 110 volt circuit has a J8712A
installed, and then a J9306A is inserted, the switch only provides 300 watts of
power, not 573 watts (273 watts + 300 watts). Only the J9306A provides PoE/
PoE+ power, which is 300 watts.
In another example, if an HP ProCurve 8212zl switch on a 220 volt circuit has
three J8713A power supplies installed, and then a J9306A is inserted, the
switch only provides 900 watts of PoE/PoE+ power, not 3600 watts (2700 watts
from the three J8713A power supplies and 900 watts from the J9306A power
supply). Only the J9306A will provide PoE/PoE+ power.
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