Mixing PoE and Non-PoE Devices (9 things to know)

What is PoE?

PoE or Power over Ethernet is a method to deliver power and data through a single ethernet cable, usually cat5 or better. Some examples of PoE devices could be IP security cameras, wireless access points, or other small sensors or RFID scanners. This allows you to run a single cable to a location without having to wire-up an additional cable for power saving significant time and complexity.

Can I mix PoE and non-PoE devices?

It is generally safe to plug any PoE or non-PoE device into a PoE providing port. Most PoE providing switches today follow the 802.3af or 802.3at IEEE standard which is widely adopted and allows for detection of PoE and non-PoE devices and negotiating power requirements and protecting against short circuits or damaging non-PoE devices.

When PoE devices enabled devices are connected to a PoE switch the devices request power by sending a detection signal to the switch and a handshake occurs to determine the appropriate amount of power to provide.

When non-PoE devices are connected to the same PoE switch that handsake will not occur and the PoE swtich will no provide power and will act as a normal data-only switch. These handshaking standards prevent damage to devices or the network.

This handshaking mechanism allows the PoE enabled devices to receive the correct amount of power and prevent non-PoE devices from being damaged by high voltages on the ethernet cable.

PoE backwards Compatibility

The two most common IEEE standards, PoE and PoE+, are backwards compatible and while PoE might not provide as much power as a PoE+ device requires but won’t damage it. A PoE+ switch can provide the correct power to a PoE only device.

Does PoE pass Through Switches?

No, each PoE powered device must be directly connected to a PoE providing port on a compatible router/switch/injector.

Can non-PoE device be plugged into a PoE port?

Yes, except when you have a passive PoE system or non-IEEE standard as outlined below which may cause issues. In most cases there shouldn’t be any problem.

A Ubiquiti switch. It can provide up to 150w of power. The two right most ports (7 and 8) are providing PoE power as indicated by the yellow light in the top left of each. The left ports (1,2,3) are not currently providing power.

When is it not safe to use PoE?

Older or propritary PoE devices may provide passive PoE systems. These systems operate on a fixed volatage, usually 24v or 48v, and do not detect PoE devices and just continuously passivly provide power. This can cause issues with devices that are not expecting the voltages and currents present as the same wires are used for both power and data transmission and unexpecting devices could be damanged or create unsafe conditions.

Some older Ubiquiti switches allowed for passive PoE as an option but it was not enabled by default in the interface and those devices are no longer available.

There is no IEEE standard for passive PoE systems so we must discuss in generalities. These systems are often proprietary and can require specific wiring schemes making them more expensive and less flexible.

Other situations where PoE maybe unsafe include running cables in ductwork which may be against code or in very wet or humid areas, where moisture can cause corrosion or electrical shorts/issues. You always want to follow your local building codes or better when making any deployment.

PoE Advantages and Disadvantages

Like anything there are tradeoffs. Here are some typical advantages and disadvantages you can expect with a PoE systems

PoE Advantages

1.) Simplified installation. PoE eliminates the need for multiple power outlets at each device location. Power is delivered over the ethernet cable making installations faster and easier. The work and cost related to installing multiple power outlets can add up very quickly.

2.) Network and Device flexibility. PoE makes it easier to install devices in locations far from available power outlets. This is especially true with IP cameras or other security devices as they are typically installed in hard to reach locations through attics, crawlspaces, or exterior walls.

3.) Cost: effective in all but the smallest deployments. The cost of installing multiple power outlets in locations adjacent to network devices can quickly get out of control. While proof of concept and test deployments can operate with a PoE injector as outlined below PoE enabled switches are the standard when you’ll have all but the smallest amounts of PoE powered devices

4.) Checking Compatibility: Issues can arise with compatibility but typically 802.3 standards are backwards compatible. Typically I only purchase PoE+ switches (802.3at) which ensures I can run most network devices available today. You do have to be aware how many powered ports on on each switch and what the total power rating for the switch is. E.g. the switch power rating maybe insufficient to power all of its PoE ports at PoE+ levels. These compatibility issues can add some complexity to planning a deployment.

PoE Disadvantages

1.) Limited Cable Length: PoE is designed to deliver power over relatively short distances. Typically up to 100m. This means that PoE may not be suitable for powering devices that are located very far away from the switch or injector or may require extra equipment to make longer runs. The longer the cable run the less power available at the end point due to electrical resistance. This can be mitigated by using pure copper cables over CCA cables.

2.) Power Limitations: PoE has a maximum power output at the swtich limited by the IEEE 802.3 standards. You can see an outline of those limitations and standards below. This limitation means that some high-powered devices may require a seperate power source or a higher cost PoE standard or be completely unavailable.

3.) Cost: PoE switches or routers with PoE can be more expensive than traditional switches. They use more power while being idle and create more waste heat.

PoE injectors and Splitters

In larger deployments it is important to plan out your network so that you have a PoE enabled switch/port available for each device that requires it. If that isn’t possible or you just need to extend a single device from a switch you can also use PoE injectors and potentially splitters.

PoE injectors are devices that can be used to supply power to non-PoE ethernet cables by injecting power into the Ethernet cable. They receive a non-PoE data-only cable on the input side, and plug into the wall for power. On the output side, they provide both data and power to any devices downstream that require PoE. This allows you to extend the reach of your non-PoE switch or port to PoE devices without having to purchase additional PoE-enabled switches.

An old Ubiquiti injector. Data comes in the ‘LAN’ port and data + power are available on the ‘POE’ port

PoE splitters are devices that can be used to split a PoE signal into two separate outputs: data and power. They receive a PoE data and power input on the input side and split it into two outputs. One output provides data-only and the other provides power-only. This allows you to separate the data and power signals for a single device such as a legacy device that requires separate connections for data and power.

PoE splitters and injectors can follow typical standards and power levels seen above but can also follow higher powered standards not seen with switches such as 802.3bt supplying 60W

Difference in PoE Standards 802.3af, 802.3at, 802.3bt (type3/4)

Most consumer devices operate on 802.3af or 802.3at, commonly referred to as PoE and PoE+. You can see a quick breakdown of some of the most common standards and capabilities. Powered Device wattage is considered to be the minimum wattage supplied to devices typically this is less than the power supplied by the PoE switch due to losses in the cabling.

TypeStandardPowered Device WattagePower Supplied Wattage
Type 1 PoEIEEE 802.3af12.95 W15.4 W
Type 2 PoE+IEEE 802.3at25 W30 W
Type 3 PoE++IEEE 802.3bt50-60 W60 W
Type 4 PoE++IEEE 802.3bt71-90 W100 W

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