Power without the struggle: how to get the best from PoE

01 Sep 09

Power over Ethernet (PoE) compatibility is now a standard feature on most network cameras, and is gaining popularity across the spectrum of IP-Surveillance and access control applications.

Indeed, a growing proportion of IP devices now do not offer a conventional power connection at all.

However, PoE technology has much more to offer than the obvious cost and time savings of being able to wire equipment for power and data using a single connection. This article shines a spotlight on these little known features of PoE and how you can use them to get the most out of your networked security installation.

Wired for power

Before elaborating on the more subtle aspects of PoE, it is worth giving a summary of the different PoE-enabled devices that are available, as this is the best way to understand the basics of the technology and how it is used.

Any equipment that is designed to receive its electrical power requirement from its network connection is known as a powered device, or PD. PDs are typically application-specific devices found at the edge of the network.

They include network cameras, access control panels and card readers, wireless access points and VoIP phones. They must be installed at specific locations, often far from the nearest power outlet, so there is a clear benefit to reducing their installation requirements to a single network cable.

At the other end of each PD’s network cable, there must be another device which can deliver the electrical power onto it.

Such devices are collectively referred to as power sourcing equipment (PSEs) and are divided into two types, known as midspans and endspans, according to their location on the cable.

A midspan injector is used to add PoE capability to an otherwise data-only connection. So typically a network switch channel is patched through a nearby midspan, to add PoE capability before the cable run continues out to the PD.

An endspan combines both PoE injection and network data connection and is typically a PoE network switch. In this case all that is required is a direct network cable connector between the PoE switch and PD.

Optimised power delivery

With midspan injectors and PoE switches widely available to support the growing array of PoE-powered devices on the market, security installers have a straightforward option for power delivery to devices where no local outlet is available.

But PoE is more than an option or afterthought: if it is regarded as the default means to wire power to IP devices, and if systems are designed with PoE in mind, then installers can fully exploit all the other advantages that PoE offers over conventional power wiring. These advantages include:

• Universal application: the majority of PoE equipment on the market today is compatible with the IEEE 802.3af standard, which means that PDs and PSEs around the world can be relied upon to connect instantly, without the inconvenience of dealing with a range of bulky or incompatible external power supplies. Standard cat 5e or similar cable is used.

• Flexibility of location: cameras or wireless points can easily be relocated post-installation to meet the changing needs of the site, without the time and expense of installing new electrical outlets.

• Safety: PoE employs an isolated, safe voltage level, so cable does not have to be buried or installed by a qualified electrician. The PSE will only enable power delivery to recognised devices and will cut power in the case of an overload or short circuit, or if the device is disconnected. Non-PoE devices can be connected to PoE switches and no power will be enabled; the link will just be a regular data connection.

• Efficiency: The safe PoE voltage is also high enough to carry power efficiently to cameras over a regular gauge network cable. Each PD can also have a power class - an indication of how much power it may require - which enables PSEs with a limited budget to allocate it effectively between its ports.

• Reliability: PoE power is standardised and managed and is less susceptible to accidental unplugging or loose connectors. Importantly, deploying PoE across a network means that all remote devices draw their power from a single, central source. This means that an uninterruptible power supply (UPS) can be used for back-up, and that devices can be disabled and reset remotely.

Enhance the network

All of these aspects can be taken into consideration and capitalised on when a networked security system is designed. For example, the universal connection to devices and ease of relocation without new electrical cable means the installation should be more predictable and repeatable, so the time and expense built in as a planned contingency can be reduced.

Also, device power requirements can be planned and budgeted for, with UPS back-up if desired, and the enhanced power management and control available should reduce the frequency and expense of engineer call-outs post-installation.

In addition to this, however, is a feature inherent to PoE that transforms the way networks can be designed, in terms of both the network's structure and its physical layout. Because power and data are carried on the same cable, this same power can be used for the nodes of the network itself, as well as the powered devices found at its edge.

This is of particular relevance to IP surveillance and security networks, where equipment must often be distributed across large sites, so Ethernet's 100 metre cable length limit becomes an issue.

For such installations, PoE-powered and forwarding Ethernet switches and repeaters, such as Veracity's OUTREACH range, can be used to extend and distribute the PoE-enabled network across the whole site, with all network power still reliably delivered from a backed-up central source.

This self-powering ability of PoE-enabled networks is further enhanced by the advent of the recently-finalised PoE Plus standard (802.3af). PoE Plus is backwards-compatible with the current standard, but increases device power from 13 watts to over 25 watts.

This means that a single cable run can be distributed to several cameras or access panels, or to other powered accessories such as lamps and door interlocks. It also makes PoE possible for external cameras which require additional power for fans or heaters.

Edge switches can be installed in optimal locations, or can be used to add new devices to the network, without the need for electrical cable.

Scalable and flexible

Power over Ethernet technology is universal, flexible, safe, efficient and reliable by design, and these features yield returns on investment even when PoE is simply used as a replacement for traditional DC or AC wiring.

But in addition to being a highly efficient means of delivering power to devices, they also provide scalability and flexibility even for installations where PoE is not required.

As long as they incorporate careful power management technology, PoE-powered edge switches and repeaters can be deployed to enable an optimised PoE-enabled network to extend across the entire site.

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