How Much Power Does a Cisco Catalyst Switch Use?
If you are a network engineer, there comes a point in your life when you are asked or you need to know the power requirements of your network switches. This type of topic is rarely covered during training, which makes it difficult for people working in networking environments to know things like this. So, here, we have covered this topic in detail. So, make sure to read till the end.
Understanding the Power Basics
Before jumping to the power requirements of a network switch, first, you need to understand how power is calculated.
Power = Voltage x Current (or P = VI)
Here, Power is measured in Watts (W), Voltage is measured in volts (V), and current is measured in Amperes (A)
To better understand things right from the start, let’s take an example of a garden hose, where voltage is equivalent to the pressure in the system and the current is equivalent to the rate of flow and wattage is the total amount of water that comes out of a hose. Now, assume you need to fill a tank using the hose. You can either turn on the normal faucet or use an external pump. While the tank will fill in the case of the normal faucet, the same tank will fill quickly in the case of the external pump.
In the same way, if the network switch you have needs more power, you can increase the voltage to generate more watts.
How to Calculate Power Requirements of a Cisco Catalyst Switch
When you buy a new switch, you may need to provide power requirements to someone such as an electrician so that you have enough power to operate a network switch.
Now, remember that every component such as a linecard, supervisor, and PoE device that you have plugged into your switch will draw some power. So, it is critical to ensure that not only the switch but also other plugged devices of the switch will have enough power to draw.
If you are working with a switch in the Cisco Catalyst or Nexus 7K line, the good news is that you have a very useful tool called the Cisco Power Calculator (Free, CCO Login Required). This calculator will help you build your switch with certain linecards and output the power requirements.
Steps to Calculate Power Requirements of Cisco Switches
Go online and launch the Cisco Power Calculator tool. Once it is opened, select the product family from the dropdown. Choose or enter the required details such as the specific chassis model, supervisor, redundant supervisor if applicable, and input voltage.
For input voltage, there are four choices. The first two choices i.e. -48 Volts DC and -60 Volts DC are used if you are connecting the switch directly to a battery as the source and you are using it for phone systems or telecom equipment to avoid any noise and provide assurance against power outages. Here, the DC voltages are negative to reduce corrosion. The second two options are 100-120 volts and 200-240 volts.
In the majority of the Cisco switches, AC power is used for deployment to supply the power to the switch either from a wall outlet or from a UPS.
Now, how do you know which AC power you should use?
It depends on the country you are deploying the switch in. While some countries have a standard voltage of 100 – 120 volts, other countries have a standard voltage of 200-240 volts.
So, find out the standard followed in the country where the switch is being deployed. You can get information about standard voltages in the country from an electrician.
Read About: How Does a Cisco Switch Work?
Another thing you need to know about is the existing or new electrical wiring. If you are installing a network switch and need to use the existing outlets or UPS, get in touch with an electrician or building management to determine what voltage you have available for use.
However, if it is a brand new installation and you can tell the electrician about what to install, you can run through the Cisco Power Calculator using both voltages and see which option works better for you.
In this post, we are selecting 200-240 volts and Sup720s. On the next page, you will need to select which linecard will go in each slot. In case you select a PoE linecard, then you will need to mention the number and type of PoE devices attached to that linecard.
You also need to consider your future requirements while deploying network switches. For instance, suppose now you have only two PoE linecards and each of them is partially filled with some PoE devices. You need only a small power supply and a lower voltage circuit from your electrician at this point. However, you may need more PoE devices in the future and will need more power at that time. So, if you know that you will soon be expanding, you can get a bigger power supply and ask your electrician to wire the electrical circuit accordingly.
Let’s say you select this chassis with 4 PoE linecards and tell the calculator that you will be connecting 96 Cisco 7941-G-GE phones. This calculator knows the power drawn by every PoE device in the list. So, all you need is to know the number of devices you need to connect.
Finally, the calculator will tell you the power requirements of Cisco switches.
This way, you can calculate the power requirements of not only Cisco Catalyst switches but also Cisco 9300 switches and various other series switches.
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