Power-over-Ethernet

Wayne Connors, of quality connectivity specialist ACCL, explains why low-grade Ethernet installations have the potential to cause equipment overheating. Even before talking legal liability issues, this situation could result in fires; which in turn could lead to insurance claims and the inevitable insurance premium increases that arise as a consequence.

Whilst Power-over-Ethernet (PoE) technology has been with the networking and cabling industry for several years, the concept of providing power across the network actually dates all the way back to the birth of the landline telephone, which to this day still receives power from the telephone passive infrastructure. Computer networking devices that are often powered with PoE technology include desktop Voice over IP (VoIP) phones, cameras, and access points. Ethernet cables, meanwhile, consist of four pairs of wires; typically two pairs are used for transmitting and receiving data with the other two pairs on a basic system being unused. By providing power to devices via the same Ethernet cable that provides the data, a single low-voltage cable is normally all that is required to install a networked PoE device.

The use of PoE equipment removes the need to run electrical cables and outlets to every location that needs to be connected to the network. Not only does this greatly reduce the cost of installing network devices, it also increases the flexibility in terms of where these pieces of equipment can be installed and mounted. Moving devices is also made a lot easier, because all that is required at the new location is an Ethernet cable.

Whilst the fundamentals of this technology are relatively simple, the actual usage of PoE depends

on the planning and quality of the installation, as well as its maintenance and enduring reliability. This is where all manner of challenges and pitfalls enter the picture.

The problem that many businesses face when upgrading an existing Ethernet network to support the very useful facilities that PoE delivers are that, whilst the Ethernet ‘standard’ is designed to support sub-standard or damaged installations, with the data speeds progressively stepping down until the connection ‘just works’, PoE technology is far less tolerant of low grade cabling and/or poor quality installations. Put simply, this means that a low-grade Ethernet cabled network, which may have been installed ‘on the cheap’ and using poor quality four-wire cabling perhaps by a budget-conscious building/facilities management company for whom the end price is everything, may only be able to support basic data networking facilities, but not a PoE installation.

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the safety challenge

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In the UK, the problem of low-grade, or sub-standard, Ethernet installations is potentially exacerbated by the fact that some network installations are several years old, and were commissioned to operate at the relatively low networking speeds seen in the last century.When PoE technology is installed, this will result in the network adminitrators trying to run the equivalent of an advanced sports car using two-star fuel. As Jeremy Clarkson on BBC TV’s Top Gear is often heard to say: “it will all end in tears.” This is so true, as we have observed that many Ethernet cabling systems are terminated in cabinets tucked in out-of-the-way places; such as under the stairs and in cupboards. They are also placed in rooms that contain filing cabinets; holding mountains of high-value company documents in very close proximity to the cabling system.

It is the time when badly planned or poorly installed PoE systems start misbehaving that potentially serious problems could start to develop. Overheating is commonplace; and in a confined space this translates into a risk of smouldering fire, which is a potential disaster-in-the-making if, as in the above scenario, filing cabinets full of paper documents are close by.

In the event of a fire or potential fire, there are also the modern health and safety issues to address. Questions can (and will) be asked by the authorities. If you, as an employer, are considered to be negligent, business insurers will rarely process a claim. Perhaps worse, even if your insurer were to consider a claim for heat damage resulting from a PoE system overloading an older Ethernet installation, there is a real risk of your insurance premiums (and excesses) rising significantly at the next renewal time.

Clearly, this situation is one that any professional business will want to avoid. Insurance is usually only there to remediate problems and accidents that could not have been foreseen. If a potential problem can be foreseen, it needs solving before it causes an actual problem in the workplace.

Understanding the technology challenge

Unlike standards such as a computer Universal Serial Bus (USB), which also power devices over the data cables, PoE is designed to support long cable lengths. Power may be carried on the same conductors as the data, or it may be carried on dedicated conductors in the same cable.

There are several common techniques for transmitting power over Ethernet cabling; two of them have been standardised as IEEE 802.3. Since only two of the four pairs are needed for 10BASE-T or 100BASE-TX, power may be transmitted on the unused conductors of a cable. In IEEE standards, this is referred to as Alternative B. Power may be transmitted on the data conductors by applying a common-mode voltage to each pair. Since Ethernet uses differential signalling, this does not interfere with the underlying data transmission. The common mode voltage is easily extracted using the centre tap of the standard Ethernet pulse transformer. This is similar to the phantom power technique commonly used for powering audio microphones. In the IEEE standards, this is referred to as Alternative A.

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In addition to standardising the existing practice for spare-pair and common-mode data pair power transmission, the IEEE PoE standards also provide for signalling between the Power Source Equipment (PSE) and Powered Device (PD).

This signalling system allows the presence of a conformant device (PD) to be detected by the power source (PSE), and also allows the device and the source to negotiate the amount of power required, from that which is available.

In theory, up to 51 Watts is available for a given device (PD), depending on the version of the standard in use and the vendor of the hardware.

Two modes, A and B, are available. Mode A delivers power on the data pairs of 100BASE-TX or 10BASE-T, whilst Mode B delivers power on the spare pairs. PoE can also be used on 1000BASE-T Ethernet, in which case there are no spare pairs and all power is delivered using the phantom technique.

As mentioned above, there are a number of technical challenges that can arise with PoE technology, either completely or, perhaps worse, partially limiting the functionality of the network to which the devices are attached.

Aside from the overheating and fire hazards identified earlier in the article, as well as the employer’s duty of care and insurance issues, if we assume a low-grade Ethernet network has been unwisely used as the basis for a PoE network

upgrade, then technical problems can manifest themselves in several ways:

a. IP telephony deployments struggle with power/heat issues.

b. Power-over-Ethernet switches and/or servers replacing key phone systems make data centres hotter; creating more technology failures.

c. The biggest heat-boosters in wiring closets are the PoE switches, which transport Ethernet traffic and act as AC power supplies for all IP phones and other PoE-capable gear plugged into the device’s powered ports.

d. Poorly maintained equipment contributes to environmental and security hazards that can disable or degrade your voice deployment. e. The power supplies in various switches and powered devices sometimes have unique reactions to AC input disturbances.

f. Lightning storms and mains power variances can cause short-term PoE problems, and result in shortened life spans and/or outright failure of the technology.

In a worst-case situation, a PoE power supply may appear to shut down (no output voltage to any port) under a heavy load condition.

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Installation quality issuesIf the installation quality is poor, there are potential operational expenditure (Opex) issues, meaning that even if the up-front installation costs, or capital expenditure (Capex) of the underlying network were a bargain several years ago, the consequent Opex issues, when a PoE or similar network upgrade is attempted, can be both time-consuming and expensive. This situation can be made worse where, for example, the installation quality of a PoE deployment has been poor; perhaps to keep your Capex costs down. In this case the Opex consequences are likely to be severe.

Other consequences include surge-in current issues, software control failures and localised overheating; all of which can waste staff time and money whilst the problems are investigated. On the indirect costs front, there is also a very real risk of brand reputation and lost sales to consider.

The problem with brand reputation and lost sales issues are that these problems are very difficult to quantify. If, for example, a long-standing company client calls with an urgent order and the network and/or Internet telephony system is/are causing problems, then sales staff may have problems fulfilling the order. This may result in the client going elsewhere; perhaps being lost forever.

The situation is made potentially worse with the rapid uptake in social media in recent years. Disgruntled customers can post their experiences to Facebook or Twitter, where other clients can,

through the joy of keyword searches, pick up on problems. This could result in further potential lost sales. Ironically, this could all be avoided by the outlay of a few additional tens of pounds (on a complete project) on the basic network cabling, which may be a Grade B or C product sourced from someone other than your usual supplier.

Solutions to the challenge of low-grade cablingA professional installation with quality components should always fit the bill for a customer; even where that client is on a tight budget. Everyone loves a supplier who comes in with a cost-effective quote, but not if the installation proves to be troublesome. The optimum cost-quality equation is something that all businesses strive for, but the calculations can all be for nothing if the underlying technology being installed is sub-standard.

Active Communication Company Limited (ACCL) is a professional data-cabling contractor that delivers exceptional results at competitive prices.

ACCL, quite simply, cannot compete with the B or C grade cabling suppliers that advertise their sub-standard products on Internet auction sites; even though the cabling may be superficially acceptable for a low-loading scenario. Like all technology, it is only when a peak-load situation arises that problems will start to appear.

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PoE technology is one such situation, as the strain that the electrical feed element places on the Ethernet cabling, driving the Powered Device from the Powered Source Equipment with a minimum voltage and current drop, can place the cable structure under strain, which rises as the cabling and elements attached to it start to heat up.

The good news is that ACCL has stood at the top of its sector for three decades; offering optimum cabling installations at competitive prices. Whatever task its engineers have been faced with, they strive to deliver on time and within the parameters of any agreement; offering a quality installation that will stand the test of time. Quality data cabling contractors will understand the intricacies and complex nature of PoE, as well as the pressure to create value engineering. However, most managers outside of the IT sector are, understandably, unaware of these issues.ACCL recognises this is exactly how it should be. A good quality cabling installation should give many years of usage, but the evolving nature of Ethernet technology, driven by the need for faster and more complex data transmissions, needs to be understood and built into a company network plan. A new Ethernet network deployment may be perfectly suitable for today, but the move towards PoE and the rising diversity of data flowing across today’s networks means that a deployment must also be capable of supporting the much higher volumes of data that will undoubtedly flow across networks in the future.

With communication companies such as BT and others now offering fibre-to-the-cabinet (FTTC) 80/20 Mbps internet connections as a baseline internet connectivity standard in most city areas of the UK, coupled with the promise of 300 Mbps in the near future, companies need to be aware that their Ethernet network resources will come under increasing strain. This is particularly pertinent as IP-based transmissions become ever more integral to the modern business. It is against this backdrop that we recommend that all companies review their existing network resources before considering upgrading to PoE technology.

Only by taking this approach can a company avoid problems further down the technology trail caused by low-grade network installations.

With those problems potentially creating an overheating and/or fire hazard scenario, as well as clear longer term insurance costs and consequences, there is clearly a lot more than meets the eye when it comes to low-grant Ethernet installations. Given that the cost of networking technology has fallen significantly in the last ten years, there may be argument to install a brand new networking system that is designed to work specifically with a PoE installation. This can often cost less that patching an existing network resource to prevent overheating and fire hazard problems in the future, as well as the very real risk of having to file an insurance claim, with all the problems this entails.

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Active Communication Company Limited (ACCL) is the UK’s leading supplier of voice and data cabling contractors.

The organisation is fully equipped to deal with technical installations within the telecommunications industry.

Previous projects include:

Roehampton HospitalGreenwich UniversityMF GlobalChelsea Physics GardensSt David’s Shopping CentreSouthampton Football Stadium

ACCL have been employed by main contractors, consultants and end users.

The company offers peace of mind in the knowledge we fully conform to all International and European standards.

All our project engineers are Prince II qualified and ensure a project runs efficiently.

Active Communication Company Limited International HouseCray AvenueOrpington, Kent BR5 3RS

T: 0333 900 0101

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