What is a PoE switch and how to pick one for your IP camera system?

Concept

A switch (Switch) is a network device used for electrical signal forwarding. It is a device that performs information exchange in a communication system. The most common switches are Ethernet switches, telephone voice switches, fiber switches, and so on.

The POE switch, in layman’s terms, is a switch that supports power supply through network cable . Different from ordinary switches, it can realize data transmission and power the network terminal (such as an IP camera) at the same time, eliminating the needs to install a separate power cord.

Standard vs Non-Standard

You will find both standard and non-standard POE switches in the market. Another term for them is active and passive PoE.

The standard/active POE switch has a built-in POE control chip. After the powered device (PD) is connected, the PoE switch will send a network signal before, trying to detect any PoE power receiving device.

The POE switch will then start to supply power to the PD device until it reaches stable transmission. If the device is disconnected from the network, the POE switch will quickly stop powering the device and repeat the detection process to detect whether any PoE terminals are connected to the switch.

The standard is set by IEEE and if you want to purchase a standard/active POE switch, make sure the device is compliant with IEEE standards such as 802.3at or 802.3af.

Non-standard POE switches have potential safety hazards. They don’t come with the POE control chip and thus are unable to recognize PoE powered devices and will directly send voltage and current to any connected terminals (regardless of whether it is a PoE camera or not), resulting in excessive transient voltages, and could burn out any devices connected to it easily.

However, since non-standard POE switch is relatively simple to assemble and manufacture without not much technical components, the cost of a non-standard POE switch is cheaper, and thus also has a certain share in the market. BUT please be aware for passive non-standard POE switch, power is delivered immediately without negotiation.

We would recommend consider getting a standard (aka. active) PoE switch especially if this is your first installation to prevent from unwanted hazards. And all the selection below would be based on a standard PoE switch.

Power Gauge Per Port

Never confuse the power gauge per port with the total budget. This is extremely important to see whether the PoE switch you select can support your camera properly.

The power output of the POE switch per port can reach 15.4W or 30W, which is in compliance with the IEEE802.3af/802.3at standard.

The output is different depending on the standard. For example, IEEE802.3af does not exceed 15.4W, and it can supply power to devices with a maximum power consumption of less than 12.95W due to the loss of power transmission.

Similarly, a POE switch that complies with the IEEE802.3at standard (30W per port) can supply power to devices with a maximum power consumption of less than 25W.

Here you will see the slight difference of power standard between PSE (power supply equipment) and PD (powered device) due to power loss over transmission. Just keep in mind that as long as both PD and PSE follow the same standard 802.3af or 802.3at, they would be compatible with each other.

For most PoE switch that supports 802.3at protocol, it is almost always backwardly compatible with 802.3af.

There is also a new PoE standard officially approved by IEEE in September 2018 called 802.3bt. This standard was born to meet the requirements for more power-demanding PoE terminal devices. It can be used for power supply and data transmission up to 90W on the basis of 802.3af and 802.3at, a breakthrough for the limitations of supplying just 30W per port.

Note, PTZ cameras almost always need 802.3at despite if it is just a 4X mini PTZ dome as it requires more power to drive the motors of the camera. Meanwhile, 802.3af is for fixed cameras. If you plug a PTZ camera into a 802.3af standard POE switch, the PTZ camera will have various types of underpower issue such as losing connection intermittently, spinning around without control or turning on/off during night vision etc.

It is to be noted that we’ve seen customers getting confused by the “per port power supply” due to poor product description of some PoE switchs. For example, a 4-port 802.3af PoE switch with a total budget of 60W actually can only provide 15W per port. Some PoE switches would tend NOT to include the per port feature in the product description, which is important to determine whether the switch can support PTZ cameras.

Total Power Budget

A POE switch can accept different numbers of terminal devices (PDs).

Therefore, the total power of the POE power supply must be considered.

Under the IEEE802.3af standard, if the total power of a PoE power supply of a 24-port PoE switch reaches 370W, then it can supply 24 ports (370/15.4=24), but if it also supports IEEE802.3at standard (the maximum per port power supply is at 30W) and are powering exclusively PTZ cameras that need 803.2at standard, then only 12 ports can be powered (370/30=12).

Thus, it is important to calculate if the total budget is sufficient to power ALL the cameras.

Let’s do a quick math quiz:

Jack needs to install 4 bullet fixed IP cameras, 3 of Sunba 305-D4X and 1 of Sunba 601-D20X. He had a 8-Port 120W PoE switch supporting both 802.3af/at protocol. Can he make it with the current equipment?

Of course NOT. To power all the cameras, he will need:

4 of bullet fixed IP camera = 4*15 = 60 W

3 of 305-D4X = 3 *30 = 90 W

1 of 601-D20X = 1*30W = 30 W

Total = 60 + 90 + 30 = 180W

Whoops. Jack obviously needs to add another switch or upgrade the current switch to accommodate more power.

100 Mbps vs 1000 Mpbs

The required bandwidth output for PoE switch needs to be considered as well. The actual bandwidth that you can use is typically only 60-70% of the theoretical value, so the available bandwidth of for PoE switch is roughly 60Mbps (for 100Mbps switch) or 600Mbps (for Gigabit switch).

IPVM also found some switches can only reach less than 50% of the theoretical value.

So bandwidth-wise, how many cameras can be connected to a single switch assuming the switch utilizing 60% of the bandwidth?

For example, a 1.3 megapixel 960p camera usually takes 4M, with a 100M switch, you can connect 15 (60M/4M = 15).

Meanwhile, a 2 megapixel 1080p camera can take 6M. So with 100M switch, you can connect 10 (60/6=10).

Gigabit PoE switches (1000M, so with 600M bandwidth) can definitely take more IP cameras with sufficient bandwidth.

These are all based on the assumption if you are using H.264 as the encode format. If your camera is H.265, then the bandwidth taken for each camera can be reduced for at least 50%.

Of course, for each camera, the higher the resolution/FPS, the higher the required bandwidth. To lower the bandwidth, many surveillance projects choose to stream at low FPS (12-15).

If the cameras connected to the switch are causing issues such as “frame-drop/freezing/stuttering” , it is a signal that you might need to upgrade the switch to Gigabit, lower the FPS for each camera to save more bandwidth budget, or put another switch into the system to reduce the bandwidth pressure on the existing switch.

Ok, then how to pick the right PoE switch?

  1. Determine the number of network terminal device (IPC) for your application.
  2. Determine the total power budget required for all those IP cameras.
  3. Make sure the PoE switch is standard.
  4. Check the PoE protocol required (e.g. 802.3af/at) for your IP cameras and make sure the PoE switch is compliant with any standard required by the IP camera.
  5. Calculate the required bandwidth.
  6. Sometimes Important: Check the size of the PoE switch. Some installation requires the PoE switch to be put into an electrical box with restricted size.

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