To PoE or not to PoE

April 2018 Editor's Choice, IT infrastructure

Power over Ethernet (PoE) is a classic example of a technology that is simple but not straightforward. The ability to carry both data and power along the same cable has proven so transformative that in many industries it has become the norm rather than the exception. There are caveats, however, and a multitude of factors need to be considered when deciding whether it is the best option.

Most security products nowadays support PoE, from powered devices (PD) such as CCTV cameras, access control terminals and passive sensors, to power sourcing equipment (PSE) like DVRs/NVRs, Ethernet switches and midspans. But to say that a device supports PoE is like asking a waiter for a warm meal – there are various flavours to suit different appetites, and a selection of toppings to meet sir’s, or madam’s, particular taste.

Standards, classes and norms

The standard initially created by the Institute of Electrical and Electronic Engineers (IEEE) to standardise PoE – designated 802.3af – is broken down into four sub-classes according to the amount of power required, catering for up to 15,4 W. As the functionalities and capabilities of powered devices correspondingly expanded their hunger for power, standard 802.3at was formalised to support up to 30 W.

In the CCTV market, the majority of IP cameras, for example, are satisfied with 15,4 W, while models such as those with pan-tilt-zoom (PTZ) functionality or integrated heaters happily gobble up the extra power provided by 802.3at. A new standard called 802.3bt is currently in the draft stage, which will allow 100 W for more specialised applications.

To complicate matters further, some equipment vendors do not follow the formally recommended method of stating PoE specifications (which describes both the type and the class) and instead ignore the class modifier. For example, if only the specification ‘802.3af’ is used, this could mean the powered device can be supplied with anything across a wide range of 0,44 W to 15,4 W. Some devices even specify their power level without actually conforming to a specific standard, which can lead to PSEs and PDs not playing nicely together.

The devil’s in the details

Andries Mokoakoe, from industrial connectivity specialist RJ Connect, says that professional-class equipment tends to be more trouble-free than consumer-grade alternatives thanks to their stricter adherence to the prevailing PoE standards. But the question of whether PoE is actually the best option is a grey area. “Many factors need to be weighed up, such as how PoE compares to the cost of having a power supply for each camera, and whether there is just one or several cameras connected to the same switch,” he says.

He summarises the main points to consider as follows:

• Think about how many PoE-powered cameras might be disconnected if the switch powering them loses power.

• Ideally, make sure that PSEs and PDs adhere to the same standard to avoid power mismatches.

• The power budget must cater for all the PDs that will be connected to the PSE, so if for example four 6 W cameras are connected to the same switch, its power budget must be 24 W – which both the switch and its own power supply must support. This power budget must continually be borne in mind, because if extra cameras are added at a later stage, the switch and/or power supply might no longer be able to cope, which could result in loss of power not only to the new camera but also the ones previously connected.

• Unless all equipment is grounded correctly, a lightning surge hitting a camera can take out the connected switch too.

• Adhere to the recommended distance limit of 100 m, or preferably 90 m to be on the safe side.

“The bottom line is, when in doubt, consult a specialist with a deep understanding of PoE, its advantages and its disadvantages,” Mokoakoe says.

According to BT-SA, an ICT infrastructure solutions provider with extensive experience in the fields of access control and CCTV, the ability for different types of equipment, and from different vendors, to work together seamlessly varies from application to application. “In cases where we install our own switches, adaptability is not a problem,” says BT-SA’s Stephan van Aswegen, senior manager: data network and air conditioning, “but if we have to work with existing network switches, it is advisable to rather install an external power source to ensure stable power to equipment. This also avoids unnecessary call-outs in future.”

“Cost is a very big factor when advising a client on going the PoE route or not,” he continues. “Rather spend a little more now and save on call-out fees and upgrades in the future. If the client does not have a PoE switch, PoE injectors are required which further adds to the cost. Long-term maintenance and extra expansions costs must also not be overlooked.”

Although Cat5e has long been the go-to Ethernet cable for PoE applications, Van Aswegen advises that new installations in particular should favour Cat6 or Cat7 cable, as Cat5 and Cat5e are being phased out. When it comes to retrofit projects, therefore, the barriers to adoption of PoE technology should not be underestimated since new cabling might be necessary, or additional power sources and PoE injectors, which carry not inconsiderable cost implications.

Share this article:
Share via emailShare via LinkedInPrint this page

Further reading:

Constructive CCTV contributions to research
September 2019, Leaderware , Editor's Choice, CCTV, Surveillance & Remote Monitoring
Study leads to understanding that we need more recognition and reward for constructive participation in society.

Ensuring a seamless ultra-wideband ecosystem
September 2019 , Editor's Choice, IT infrastructure
FiRa consortium ensures an interoperable ultra-wideband technology ecosystem across chipset, device and service infrastructure through standards and certifications.

The hunt for the Carbanak group
September 2019 , Editor's Choice, Cyber Security, News
Tomorrow Unlocked has released a free four-part documentary that tells the story of the notorious Carbanak APT group and its $1 billion bank heist.

Genetec to integrate CylancePROTECT
September 2019, Genetec , Editor's Choice, CCTV, Surveillance & Remote Monitoring, News
Genetec has announced it is partnering with Cylance, a business unit of Blackberry, to bring AI-based antivirus protection to its appliance customers.

X-rays in 3D
September 2019, XPro Security Solutions , Editor's Choice, Security Services & Risk Management
Hi-Tech Security Solutions asked Greg Dixon, director of XPro, for some insights into X-ray scanning and its pros and cons in today?s volatile world.

Smart Inspection Unit developed by Roteck
September 2019 , Editor's Choice, Security Services & Risk Management
Roteck has announced a portable personnel and bag scanning unit that can easily be transported, set up and used in almost any location.

Highly adaptable wireless mesh network solution
September 2019, Duxbury Networking , Products, IT infrastructure, Residential Estate (Industry)
Rajant's Living Network infrastructure evolves and adapts to your growing and changing connectivity requirements.

Modular fibre-optic patch panel
September 2019, Jasco Trading t/a Webb Industries , Products, IT infrastructure
Telegärtner's Fibre Termination Box facilitates customised cabling in locations where large numbers of apartments or buildings have fibre-optic outlets installed.

Wi-Fi access points for SMMEs and startups
September 2019, Duxbury Networking , Products, IT infrastructure
Aruba Networks? latest offering, Instant On, delivers reliable, easy-to-manage network technology for small businesses.

Network switch for solar applications
September 2019, Duxbury Networking , Products, IT infrastructure
Duxbury Networking has released the latest addition to the Duxbury network switch range, a solar switch ideal for remote locations.