Structured Cabling : do's and don'ts. Although the maximum cable length for a Cat 5e/6/7 structured cabling system
is often reported to be 100m, this length is inclusive of patch and drop leads. Cable testers however, when set to perform a 'Basic Link' test, take this into account and you will find that the maximum
length is set to either 90m or 94m depending on the standard you are testing to. Also, because the length is measured with a Cable Analyser it is not the physical length of the run but the copper length that
is measured. The copper length is longer due to the twists in the cable pairs, so if a run looks like it might be over 85m it would be wise to check it before it is tied up and terminated.
Care should be taken when pulling cables in to ensure that they are not kinked or nicked. Structured cabling routes should be planned to avoid fluorescent light fittings and power cables (exceptions can be made in the case of optical fibre). They should
not be run in the same conduit as power, or the same channel of a trunking system, and where they are run parallel to power they must be at least 60mm apart (BS7671-92) . Crossing power cables is allowed but
it must be at right angles, and some form of bridge should be used. A means of supporting structured cabling systems should be installed, such as cable tray or cable tie fixtures. Tying cables to ceiling hangers is not permitted.
Cables should be tied at a minimum of 500mm intervals on horizontal runs and more frequently on vertical runs, with no more than 48 cables in a loom. Cable ties should only be finger tight to avoid crushing
the cables as this could affect the cables performance characteristics. Do not use cable tie guns or staple guns. In all structured cabling, care should be taken when pulling cables to avoid damage due to snagging. Partitions should be used to separate the data cables
from power, and bridges should be used where data cables have to cross the power cables. When terminating patch panels, cable bunches should not exceed 48 cablesAll structured cabling terminating should be carried out according to the manufacturer's
instructions and guidelines, and the standards for generic cabling systems. The cable sheath should be stripped back no more than 13mm from the point of termination and the twist rates should be maintained.
Cable ties MUST be fitted to the individual RJ45
modules in the patch panels and outlets to support each cable. Excessive amounts of cable should not be left in the outlet back box. Care should be taken when attaching the outlet faceplate not to kink, trap or strain the cable.
All cabinets must be grounded. Where shielded
cable is used the earth should be clean and where two cabinets are linked with a copper backbone (shielded or unshielded) a minimum of 10mm˛ ground wire should also be installed to cross bond the cabinets.
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