2008-03-29
The stranded wires inside patch cords are meant to be flexible. However, serious damage can result from bending or kinking them, or leading them across an office floor where chairs can be run over them. Andrew Birch, Country Manager – UK, Ireland, Scandinavia for Ortronics, spells out the dangers of patch cord abuse.
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| Andrew Birch, Ortronics |
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Patch cord abuse tends to be something of a Cinderella activity – out of sight and out of mind. The trouble is that failing to tackle the problem could also leave your business severely out of pocket as you experience lower transmission speeds across your data network or even, in the worst cases, wholesale data loss.
Patch cords are made up of thin material that will stretch, but they are simply not designed to be bent, twisted, compressed, snagged and yanked in the way that so many are.
There is a useful analogy for this: Say you are unreeling a hosepipe in a hurry; you might pull it out too quickly so that it loops back on itself and stops the water. You can usually give a hosepipe a sharp tug and the kink will come out. However, try doing that with an electrical cable – certainly one that is transmitting data at high speeds – and you will probably crush the cable inside, resulting in the consequent slowing of data transmission or loss of data.
Patch cord cables comprise a perfectly balanced set of wires; squashing them will compress their interstices into each other and that can cause electrical ‘hotspots’ and weak points which will, in turn, cause a return loss reflection down the cable. Get too many signals bouncing backward and forwards and they are liable to be deleted altogether.
Patch cords are analogous to the tyres on a car. Even the fastest racing car backed by the best team and driven by the top driver will lose races if the car is running on inferior tyres. The same principle applies to patch cords. If they are damaged then, even with the best data system, you will simply not achieve consistent transmission performance and will be risking the integrity of the entire network.
For horizontal solid-state cabling which is hidden behind walls and never moves, it is likely that the installation engineer will have adhered to the standards on bend radii and all the wiring will be neatly laid out. However, at the patch panel end in the rack or cabinet, people tend to bend patch cords down at 90 degrees to get them into the management rings and then at 90 degrees to either the left or right and again either up or down as they reach the end of the frame as they plug and unplug cabling to suit a business’s changing configurations.
The problem is that a kink in copper cabling can cause a ‘return loss reflection’. This effectively means that, as the signal is transmitted down a cable, some of it bounces back which slows down data transfer and causes error rates to increase. We also have to remember that when the cord is bent some of the copper strands, by necessity, will be stretched and, while the insulation material will have certain ‘elastic’ properties, the copper has none.
Another area in which patch cords are susceptible to abuse is at the plastic jack at the end of the cable. The tab that is designed to hold the cord in place can get broken off, especially if the cords have been place into deep connectors and are difficult to get at. Manufacturers have strived to make the patch cord plug tab more accessible and harder to break, however no solution is completely fool-proof.
If the tab has been broken off, the patch cord can still be connected, but it will not lock into its connection securely or be aligned correctly. As data transmission speeds increase and active response down becomes more of an issue, it becomes increasingly important that the cables marry up precisely so that all the gold-coated pins in the connector plugs are seated correctly.
A second issue related to the connectors concerns the use (or otherwise) of “strain relief boots” which help protect cable assemblies from extreme bending and fatigue. The polymer material from which the connector plugs are made is relatively strong and clear so that you can see the wires inside them. However, the sleeving material is not as strong and that is why it is important to include sleeves or strain relief boots running down them rather than having the cable simply plugged into the connector plugs. This prevents them from being pulled apart too easily or bent too far.
Even with the provision of strain relief boots a patch cord will start to show its age over a period of time, if it is continually flexed and bent around. The cord jackets start to get thinner making the cords more susceptible to a phenomenon known as “alien crosstalk” (AXT).
AXT is electromagnetic noise that can occur in a cable that runs alongside one or more signal-carrying cables. At the cabinet end, patch cords will be running parallel to each other and in close proximity and the disturbance caused by AXT can have a dramatic negative impact on the quality of the signals that the patch cords carry. IT will interfere with the signal, causing bit error rates to rise which will mean that the transmission will be liable to failure.
As far as we know, AXT is only an issue when we move up into the very high frequency signals – 10 gigabits and beyond (10 million-million pieces of information per second) – but these speeds are becoming increasingly common so problems related to them are bound to increase.
As are FTP (foiled twisted pair) shielded systems. Foil shielded cabling systems – whereby foil is effectively wrapped around each internal wire in the patch cord – are all but immune to AXT. However, FTP cables can also be damaged by too much bending and twisting. Also, IT departments that decide to install their own FTP cables need to ensure that the foil is connected at both ends because a foil connected only at one end creates an antenna which is also bad for signal transmission.
There are many good, technical and performance related reasons to treat patch cords with respect and this extends to good “housekeeping”. The ‘spaghetti’ of cabling that you often see in offices and data centres looks like a dreadful tangled mess but, more importantly, the disarray makes it far more difficult to trace cables and identify their purpose. If IT staff can hardly see switches and patch panels through the intertwined cable, how are they to manage the system effectively? Resulting time making moves, adds and changes can increase with less organized patching.
A completely structured and managed system, on the other hand, shows a level of professionalism among the IT staff and gives senior management confidence that their investment is being spent wisely.
Indeed, sometimes it is worth replacing patch cords. By doing so, you may find that the data system’s performance improves and this can only benefit your business by improving communication and information transfer.
However, if you are unwilling to do this, it pays to adopt a ‘good housekeeping’ approach. It is often that last few metres, as it leaves the wall and comes into your machine, that the patch cord will be most badly affected by poor handling and layout. Get that right and you will make a significant difference to the overall performance of the system.
But poor handling and layout are not the only forms of patch cord abuse. Another is using cheap patch cords which can also compromise a network.
For example, one of our systems was installed at a site, but our customers were unprepared to pay the price we were charging for patch cords. Instead, they decided to buy the raw materials and make their own. We tested the links, which were meant to be of a Category 5e standard, but they were failing even to achieve Category 5 – the old standard. By removing the customer’s cords and installing our own we were able to speed up their network significantly.
It may, on the face of it, seem an attractive option to buy the cheapest products or use “home-made” patch cords. But this is inevitably a false economy – by taking this option you are sacrificing faster transmission speeds and reliability for lower costs.
It really does (literally) pay to invest in factory produced patch cords. Let’s take a simple example. How the plug is secured to the cabling has a huge impact on the transmission performance of a patch cord. Typically, an IT engineer will mechanically crimp the plug to the cable to provide strain relief. However, this inevitably crushes the wires inside the patch cord and affects its performance, causing crosstalk and return loss signal reflections.
A factory-produced plug restraint, on the other hand, involves the use of a cable jacket which eliminates the crushing and ensures consistent pressure at the strain-relief point from plug to plug. Factory processes are often more controlled or automated, making for more consistent product performance as well.
Think of the potential costs to your business of using second rate or homemade patch cords, many of which are hidden. For example, what would be the lost “opportunity” costs – the loss of revenue and / or business resulting from slowing down or compromising the system?
It is only by producing the cords in controlled factory conditions that you can be sure you’re getting consistent quality and a reliable product.
The lessons are clear – invest in the best patch cords available and look after them if you want to guarantee the integrity of your network.
Potential dangers posed by cable sheaths
Several countries in Europe have now made it law that a low smoke zero halogen (LSZH) material is used for the outer sheath of cabling, including patch cords, rather than traditional PVC in commercial applications.
And, although it is not law in the UK that LSZH are used for the cabling hidden behind walls, most projects in this country do.
The reason is related to safety. In the event of a fire, when PVC burns, it gives off a toxic cyanide-based gas whereas cables made from LSZH material offer superior flame resistance and reduced toxicity. On top of this, the acrid smoke given off by PVC makes it difficult for people to identify exits and therefore make for exits. LSZH, on the other hand, produces little smoke.
However, although LSZH is often used behind walls in offices in this country, PVC is still used in most working areas. Around a third of the length of installed cord in a typical installation is patch cordage. That means there is a great deal of plastic in areas where people are working. On top of this, electrical cabling tends to be PVC-based as does the containment for cabling.
This begs an important question: Is it time to strengthen UK law to make it compulsory for all cable sheaths and containment to be made from LSZH material?
For further information contact Ortronics using the information below.
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Related contacts
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Ortronics UK and Ireland
Great King Street North
Birmingham
B19 2LF
Tel : 0121 515 0669
Fax : 0121 515 0667
Email : info.ortronics-uk@ortronics.co.uk
www.ortronics.co.uk |
Email Ortronics
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Source: Ortronics UK |
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