A Comprehensive Guide to Power over Ethernet (PoE) Switches

Network switches form the backbone of any Local Area Network, or "LAN" (pronounced "lan") for short. On this page you will learn what differentiates a PoE enabled switch from a regular LAN switch, when you should use a PoE switch versus a PoE injector and, what exactly is PoE (Power over Ethernet) technology.

What is Power over Ethernet (PoE)?What is a network switch?What is a Power over Ethernet (PoE) Switch?Benefits of PoE Switches PoE Switch or Injector - when to use which?
What is a PoE Passthrough Switch?
PoE Power Considerations
PoE Switch Limitations

What is Power over Ethernet (PoE)?

Power over Ethernet (PoE) is technology that passes electric power and data over twisted-pair Ethernet cable to wireless access points, IP cameras, and VoIP phones. It enables one RJ45 patch cable to provide both a data connection and electric power to connected edge devices instead of having a separate cable for each. Read more about Power over Ethernet (PoE) here.

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What is a network switch?

A network switch is a hardware device that connects devices ("network clients") on a local area computer network.

It makes it possible for printers, PCs, wireless access points, and other network-capable devices to connect with one another. The Layer 2 switch is the type of network or Ethernet switch that is most frequently used. Any Layer-2 Ethernet switch that adheres to the OSI model employs MAC addresses to route traffic. In order to transmit communication exactly to the recipient's connected destination port, Layer 2 switches keep a MAC address table of all connected LAN clients. Due to the fact that they "know" which ports network devices are attached to, they differ from earlier, more basic devices known as network hubs. Incoming packets were instead sent to all ports by these hubs.

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What is a Power over Ethernet (PoE) Switch?

A PoE switch is a regular Fast Ethernet or Gigabit network switch that has Power over Ethernet functionality integrated. A Power over Ethernet switch both enables communication among network clients and provides power using the same RJ45 network cable to PoE-enabled edge devices, such as VoIP phones, network surveillance cameras or wireless access points. A PoE switch allows compatible devices to work in places where power outlets or network connections don't exist. This primary function of PoE can save businesses lots of money on the costs of installing electrical and network wiring (more on that below) while still having edge devices work where they are needed. PoE switches exist in many different variations.

PoE switches can be categorized by the following attributes:

Number of PoE-enabled ports:

PoE switches can provide anywhere from four to 48 PoE output ports, also called PSE (or "Power Sourcing Equipment") ports.

Network speed

Most common Power over Ethernet switches provide Gigabit speeds (1000 Mbps) to connected devices. However, Fast-Ethernet (100 Mbps) is still around, and for many PoE edge devices, that is plenty of speed.

Managed or Unmanaged

A managed PoE switch can accomplish much more than just routing data where it needs to go and powering devices in order to satisfy more complex network requirements. A managed PoE switch can group network traffic into segments and provide much more information on the status of the network, the connected clients, and its power status among its many other features and advantages.

LCD Display Option

Some unmanaged PoE switches have an LCD display on the front panel. These LCD status screens provide network admins with real-time power information, such as how much power each connected PoE device consumes, the combined used-power total of all connected devices and the total power available. It also very useful in giving alerts about potential problems and warnings for overload, high temperature, short-circuit protection and others.

PoE Budget

The ability of the Power over Ethernet switch to power connected devices is largely determined by the size of its power supply, which can range from just above 50 watts to well over 500 watts. This power budget directly affects how much power per port the switch can deliver to connected devices.

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What are the benefits of using a PoE Switch?

Installation Cost Savings

It costs a lot of money to bring standard power to locations where there is not any. For example, say you want to add cameras to the part of a warehouse that does not have power outlets. Without PoE, you would need to consult a certified electrician since a network administrator would very likely be unable to complete the electrical installation. However, with the low-voltage application of Power over Ethernet, anyone can run network cables (or PoE network cables) from the cameras to a PoE switch. Using PoE means you also avoid the need of installing power outlets, electrical wiring and breaker boxes, which saves even more money.

Greater Flexibility

PoE edge devices can be easily deployed in locations without power outlets. Since they no longer face the limit of needing a standard outlet to work, those previously hard to reach places can now be accessed with more ease. Installing a PoE network camera high up on the wall or the roof isn’t as daunting a task anymore since you only need one network cable to get power and network connections.

(Remote) Power Management

A very helpful feature of managed PoE switches is that you can access them over the Internet or local network. This access includes being able to remotely power-cycle edge devices that may have failed. The network camera that crashed or the VoIP phone that needs a reboot no longer needs physical intervention from a person on location. All that is needed for the required restart on either device is to initiate one via the switch management interface.

PoE Watch Dog / Guard / Powered Device Monitor

Some Managed Power over Ethernet Switches can monitor all connected PoE devices and automatically initiate the restart of a device that has failed to communicate for a defined period. Such a feature can be especially useful, for example, in case a security camera stops working in the middle of the night.

Learn More

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When to use a PoE switch, and when to use a PoE injector?

A Power over Ethernet injector can be used to connect a single PoE edge device to your network.

Read more about PoE injectors here.

Deciding whether to use a PoE switch or a PoE injector comes down to how many PoE devices you need to connect. Individual PoE devices, such as the odd network IP camera at the building site or the single wireless Access Point, can be connected via PoE injectors without an issue. As soon as you need to connect more PoE devices, a PoE switch is the better choice. If a new network is installed, a sure way of future-proofing the installation is to use managed PoE switches, which can power all VoIP phones and isolate and prioritize voice traffic.

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What is a PoE PassThrough switch?

A Power over Ethernet (PoE) pass-through switch is a special type of PoE switch that gets its power from an upstream PoE switch or injector and passes power to other PoE devices, such as VoIP phones and cameras. In short, the PoE passthrough switch operates as both a PD (powered device) and PSE (power sourcing equipment) at the same time.

Here is an example of how it operates: The PoE-powered Passthrough switch receives 30 watts from a high-power PoE injector or PoE switch. The pass-through switch takes around 5 watts for itself to power its internal circuitry so it can function as a network switch. It then passes the other 25 watts on to power other connected PoE devices, which lets it function as a PoE switch.

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Maximum output wattage per port

Getting a basic idea of the amount of power per port you need so your PoE devices can work is good way to know what type of switch you should buy. You do not want to get a switch that does not have enough power per port for the mix of devices you want to connect. How much power per port is available on average for PoE devices depends on the following factors:

1. Total power budget of the switch

2. Number of PoE ports

3. System power – how much power the switch itself requires to function

To determine how much power is available per port, use this formula:

Maximum Per Port Power Average = (Maximum Power Consumption – System Power)/Number of PoE Ports

Example:Consider a managed 24-port Gigabit PoE switch that has a 430-watt PoE budget. Checking the spec sheet of the switch, you find the maximum power consumption to be 500 watts. Based on those numbers, you would get:

Max. power consumption: 500 watts

System power: 70 watts

Power budget: 430 watts

Per port power average: 17.9 watts.

While some devices you connect to a PoE+ switch may use up to 30 watts per port, some may also not use that much. However, all the PoE devices you connect will deplete the available power budget. So, if you connect 10 PoE+ devices that draw 30 watts each to the switch above, your average power port for the remaining 14 devices will only be around 9.28 watts instead of the original 17.9 watts. If the rest of the devices you want to connect will work on that amount of power, that's great. If they will not, you should consider getting another switch to accommodate the rest of the devices that need more power per port.

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What are the disadvantages of PoE Switches?

Hardware cost:
The typical Power over Ethernet switch costs a lot more than its non-PoE-enabled sibling. Take care when planning the network. How many PoE ports do you need now? How many PoE ports will you need in the future? Will a few PoE injectors in strategic locations satisfy the requirements?

Central Point of Failure:
If the PoE switch fails, the consequences are dramatic. Your entire phone system could be down, or your security cameras could be offline. Even non-PoE devices would be affected. As a precaution, backup power via a UPS is considered mandatory, and having an action plan in place for the scenario where a mission-critical component like a PoE switch fails is good practice. In fairness, this drawback is hardly exclusive to Power over Ethernet switches and applies in equal measure to regular Ethernet switches.

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