There has, for some time now, been a debate as to whether cables in a horizontal cable run should be bundled or loose laid. The argument always went that cables that had been neatly dressed in to bundles were more professionally installed that those that had been loose laid, something that may well have been the case. However, times and technologies change and there are now good technical reasons why the loose laying of copper data cables in horizontal cable runs should now be carried out.
As the frequency of the signal travelling down a copper wire increases the signal migrates further and further away from the centre of the conductor until, at a certain frequency, it no longer actually travels down the conductor at all but actually travels as an electromagnetic field around the outside of the conductor. When two or more wires carrying high frequency signals are laid next to each other the electromagnetic field travelling around one of the wires can cause a current to flow in the other wire, thus generating what is known as Near End Crosstalk (NEXT).
Further increases in frequency cause the field to expand further away from the surface of the conductor, to the point where the signal is travelling outside the overall sheath of the cable. At these frequencies current will be caused to flow in the conductors of another cable placed in close proximity. This is known as Alien Crosstalk.
The worst case scenario for Alien Crosstalk is where multiple cables are laid parallel to each other over extended distances, something that is seen when cables are formed in to bundles. One way of mitigating the risk of Alien Crosstalk is to create physical separation between adjacent cables. Another is to ensure that cables do not run parallel to each other over extended distances. The easiest way to achieve both of these objectives is to loose lay the cables so that they lay randomly within the containment. Another, more expensive, way of mitigating Alien Crosstalk, particularly at frequencies used to transmit data rates of 10Gb/s and above is to use shielded cables that prevent signals from migrating outside the overall cable sheath.
The growth in deployment of POE enabled devices and the increasing amounts of power that these devices demand has led to concerns over the build up of heat within the cables that are carrying the power. As the level of current is increased the amount of heat generated also increases, which causes the attenuation of the conductors to increase, thus limiting the length over which signals can be driven. It is, therefore, vital that measures are taken to minimise the risk of heat build up within cables used for POE applications.
It is inevitable that cables in the centre of a bundle will heat up more that those that are on the outside of a bundle or those that have air around them. This is because cables in the centre of a bundle are less able to cool down through radiation of the heat. The situation is exacerbated when there are multiple cables in a bundle that are all being used for higher powered POE applications. Cables that are loose laid have greater air gaps between them, allowing air to pass more freely around them and, thus, allowing heat to be radiated more freely.
The loose laying of copper data cables in horizontal cable runs should no longer be seen as messy or a sign of shoddy workmanship as this method of installation has good technical benefits when it comes to high frequency data transmission and high power POE (POE+/POE++). Cables that are loose laid should be prevented from escaping from the containment through the use of cable ties that are secured around the outside of the containment every 500-1000mm along the length of the containment. Also, cables should be secured at any change in horizontal direction or at the transition from a horizontal to a vertical cable run.
Cables in a vertical cable run should be bundled in groups of no more than 24 cables and should be secured to the vertical containment every 500mm. Bundles of cables should be individually secured to the vertical containment and not secured to other bundles.
Maxxam Cabling Solutions recommends that copper data cables installed in horizontal runs are loose laid in order to maximise performance and get the best value out of the investment in the cabling infrastructure.