How do I use the right Cisco (4500) switch power supply?

Do you wish to learn how to manage power on the Cisco Catalyst 4500 Series Switch? If yes, then continue reading this guide as, here, you will learn everything you need to know about Cisco switch power supply management with switch configuration.

 Which power supplies do Cisco Catalyst 4500 Series switches support with switch configuration?

Catalyst 4500 series switches support two types of power supply, which are as follows:

• Fixed Wattage – the power supply that delivers a fixed amount of inline and system power (1000 W AC or 2800 W AC)
• Variable Wattage – the power supply that adjusts the wattage automatically to fulfill inline and system power needs (1300 W AC or 1400 W AC)

When deploying fixed power supplies, you must choose a power supply that can support the switch configuration. On the other hand, when using variable power supplies, you must choose a power supply that can deliver enough power so that the chassis and PoE (inline power) requirements are less than the maximum power available for the chassis and PoE.

When a system boots, variable power supplies adjust the power resources automatically.

Important Note: You must not use the 1400 W AC Cisco Power Supply with any other power supply, not even for hot swaps or other short-term emergencies. Otherwise, it will damage your switch and you may not be able to use your switch further.

When you use different types of power supplies for your switch, the switch uses the only power supply in power supply bay 1 called PS1, and ignores the other power supply. When using different power wattages, there will be no issue of power redundancy.

Which power management modes do Cisco switches support?

Catalyst 4500 series switches support two types of power management modes, namely:

• Redundant mode
• Combined mode

1. Redundant Mode

The redundant mode uses only the primary power supply and keeps the secondary power supply as a backup. Thus, if the primary power supply fails, the secondary power supply fulfills the power requirements of your switch without disturbing your network.

What to Know About Redundant Mode Power Management

• It is a must for both power supplies to be of the same wattage.
• You need to ensure that a single power supply has enough power to support the switch configuration.
• This mode is the default power mode in the Catalyst 4500 series switch.
• In case you set redundant mode but install one power supply, then your switch will accept the configuration but it will operate without redundancy.
• To enjoy the reliability of redundant mode, it is better to install two power supplies (of the same wattage).

2. Combined Mode

The combined mode uses power from all power supplies installed to support your switch configuration. This mode has no power redundancy. Thus, if a power supply doesn’t function, it can lead to the shutdown of one or more modules.

What to Know About the Combined Mode Power Management

• This mode requires your switch to have two power supplies.
• The 1400 W AC Cisco switch power supply doesn’t support the combined mode. In case you set the power budget to 2, the switch will ignore this setting.
• The two power supplies are required to be the same type. If you use different types of power supplies or different wattages, the switch uses only one power supply.
• When using the combined mode, the total power available for switch configuration is not the mathematical sum of individual power supplies.
• Power supplies come with a predetermined current sharing ratio.

The total available power in the combined mode is:

P + (P * ratio)

Which power management mode should you use for your Cisco switch?

The choice of power supplies depends on your hardware switch configuration. For instance, if your switch configuration needs more power than a single power supply can provide, then you will need to use the combined mode. The only problem with the combined mode is that there is no power redundancy, which means if one power supply fails, another supply cannot fully support the power requirements, and one or more modules of your network might get disrupted.

How much power is available with different Cisco switch power supplies?

Here is an overview of the available power for different power supplies:

1. 1000 W AC Power Supply

Redundant Mode:

• Chassis = 1000
• PoE = 0

Here, chassis power includes power for the supervisor engine, inline cards, and the fan tray.

Combined Mode:

• Chassis = 1667
• PoE = 0

2. 1300 W AC Power Supply

In this supply, the backplane consumes 10 W in both types of modes.

Redundant Mode:

• Chassis (max) = 1000
• PoE (max) = 800
• Chassis + PoE + backplane < 1300

Combined Mode:

• Chassis (min) = 767
• Chassis (max) = 1667
• PoE (min) = 433
• PoE (max) = 1333
• Chassis + PoE + backplane < 2166

3. 1400 W DC Power Supply

In this, the backplane takes 10 W in the redundant mode.

Redundant Mode:

• Chassis (min) = 200
• Chassis (max) = 1360
• PoE (max) = (DC input – [Chassis (min) +backplane]/0.75)* 0.96

In the case of PoE (max), this power supply has 0.75 efficiency, and PoE has 0.96 efficiency.  The DC input can vary for this power supply and is configurable.

Combined Mode:

N/A

4. 2800 W AC Power Supply

Redundant Mode:

• Chassis = 1360
• PoE =1400

Combined Mode:

• Chassis = 2478
• PoE =2545

To calculate the power requirements and check that your system has enough power supply, you must add the power consumed by the supervisor engine(s), the installed modules, and the fan trays.

Are you looking for a Cisco switch power supply? Or, do you need help with deciding the right power supplies for your Cisco switches?