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Voltage selection when a PoE power supply is installed
When a PoE power supply is hotswapped into the chassis, the system automatically adjusts the voltage
to match that of the PoE power supply or supplies that are currently installed in the chassis.
The following examples describe how the voltage is selected when a PoE power supply is installed:
• If a 54 volt-capable power supply is installed in a chassis that is operating with 52 volt-capable power
supplies, the newly installed power supply is set to operate at 52 volts.
• If a 54 volt-capable power supply is installed in a chassis that is operating with 54 volt-capable power
supplies, the newly installed power supply is set to operate at 54 volts.
• If a 52 volt-capable power supply is installed in a chassis that is operating with 54 volt-capable power
supplies that are actively providing power, the system rejects the newly installed power supply since
it cannot safely operate with the 54 volt-capable power supplies. In this case, the 52-volt power
supply is powered OFF, and an error message similar to the following is displayed on the console.
device(config)#
Power supply 1 (from left when facing front side) detected.
Power supply 1 (from left when facing front side) is up.
Shutting down power supply in slot 1 because it is not compatible with the existing
PoE power supplies. Please remove and replace.
When the system is next reloaded, the power supply voltage will be selected as described in the section
Voltage selection during bootup on page 344.
• If a 52 volt-capable power supply is installed in a chassis that is operating with 54 volt-capable power
supplies that are not actively providing power, the system configures the power supplies to operate at
52 volts. In this case, the newly installed 52-volt power supply is not powered OFF, and a message
similar to the following is displayed on the console.
NOTE: Automatically downgraded all PoE power supplies to 52V.
Voltage selection when a PoE power supply is removed
If a 52 volt PoE power supply is removed from the chassis, the system surveys the remaining power
supplies to determine if they are 54 volts-capable. If the remaining supplies are 54 volts-capable and
the system is not currently providing power to any PDs, the software upgrades the voltage of all
supplies to 54 volts. The system displays and log a message similar to the following:
NOTE: Automatically upgraded all PoE power supplies to 54V.
However, if the system is currently providing power to one or more PDs, the system does not upgrade
the voltage level. When the system is next reloaded, the power supply voltage is selected as described
in the section
Voltage selection during bootup on page 344.
Power over Ethernet cabling requirements
The 802.3af and 802.3at standards currently support PoE and PoE+ on 10/100/1000-Mbps Ethernet
ports operating over standard Category 5 unshielded twisted pair (UTP) cable or better. If your network
uses cabling categories less than Category 5, you cannot implement PoE without first upgrading your
cables to Category 5 UTP cable or better. PoH has the following cabling requirements based on
distance:
• Cat 5e - 25 meters
• Cat 6/6a - 55 meters
• Cat 7 - 100 meters.
Voltage selection when a PoE power supply is installed
FastIron Ethernet Switch Administration Guide 345
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