Cable Installation Practices

The design and installation of structured cabling systems in the UK should be compliant with the published editions of BS EN 50173, BS EN 50174, BS 6701 and BS 7671 which are current at the date of installation. The Quality Assurance provisions applied to the installation should be compliant with the published edition of BS EN 50174 which is current at the date of installation. It is the responsibility of the contractor to ensure that they are fully aware of the content of these standards and how they apply to any particular installation carried out by them. It is important to be aware that certain aspects of the specifications are legally binding. In particular, BS6701:2010 states:
                All telecommunications cabling and telecommunications equipment shall meet all the
                requirements of the BS EN 50174 series of standards
                                - this relates to both owners of premises (Clause 4) and
                                  installers of telecommunications cabling and telecommunications equipment
                                  (Clause 5)

 

The following are some basic rules/guidelines that should be observed as part of any structured cabling installation.

 

Pathways

Consider future access requirements and try to avoid installing cable where it will not be possible to access it for future Moves, Adds and Changes (MACs).
Wherever possible use walkways and corridors for main cable routes as these provide relatively easy access to the cables with the minimum of disruption to the user’s staff.
Way up benefits of using ceiling voids, sub-floor voids or surface mount trunking as each will have its relative merits when it comes to costs, ease of pulling in cables, presentation of work area outlets and ease of future access. Much will depend on the fabric, age and design of the building in to which the cabling is to be installed.
Avoid areas with high levels of potential electromagnetic interference (EMI) such as lift plant rooms or rooms housing X-ray or MRI scanners. Separation distances between data cables and specific EMI sources are as follows:

Source of EMI

Minimum Separation

Fluorescent Lamps

130mm

Neon Lamps

130mm

Mercury Vapour Lamps

130mm

High-intensity Discharge Lamps

130mm

Arc Welders

800mm

Frequency Induction Heating

1000mm

Additionally:

  • Swept corners in cable containment should be used wherever possible as this helps to avoid long term damage to installed cables.
  • Avoid sharp edges and protect horizontal to vertical transitions.
  • No cabling should be laid directly on to ceiling tiles.

 

Containment

Ensure that mats, baskets, trays, conduits and trunking are large enough for the number of cables to be accommodated
                       - a calculated 60% fill ratio will actually completely fill the containment due to air gaps
                       - allow an extra 50% space for future expansion, moves, adds and changes,
                          i.e. containment should only have a 40% fill ratio at the time of initial installation

                           Trunking Fill Ratio Pictures

Bends & junctions reduce the amount of available space.
All containment should be either vertical or horizontal, never diagonal.
Power and data should never share the same compartment in any containment system. Power and data separation distances depend on the type of cable and the nature of the containment:

 

                                     Cable Management System

Cable Type

Non-Metallic

Open Metallic

Perforated Metallic

Solid Metallic

Coaxial

300mm

225mm

150mm

0mm

Class D, E or EA U/UTP

100mm

75mm

50mm

0mm

Class D, E or EA F/UTP

50mm

38mm

25mm

0mm

Class FA S/FTP

10mm

8mm

5mm

0mm

 

Cable Installation

Ensure that, for copper twisted pair cables, a maximum pulling force of 110N (11kg) per cable is not exceeded. Cables should run freely out of boxes or off reels and should be fed around tight corners. Installed cabling should be generally free of tension, with only the self-weight of individual cables being carried. Avoid pulling in cables in cold conditions (<0oC) as the copper wires become brittle below this temperature and may snap if bent or stressed. 
Allow cables that have been stored in low temperature conditions to warm up before attempting to pull them in. Avoid installing cables in areas of high temperature as there is a direct correlation between temperature and attenuation.
Ensure that minimum cable bend radii are maintained. These should be greater than 8 times the cable outside diameter (OD) during installation and greater than 4 times the cable OD after installation. As a general rule of thumb cables should not be bent any tighter than they would be if wrapped around the outside of a coffee mug.

Correct and Incorrect Cable Bend Radii

It is strongly recommended that cables are loose laid in containment in order to minimise the risk of Alien Crosstalk (cable to cable interference). Where cables are loose laid in horizontal cable tray/basket they should be secured with a cable tie around the outside of the tray/basket at a maximum of 1m intervals to prevent cables from falling out of the containment. If, despite acknowledging the above, the client insists on bundling of the cables, then they should be formed into bundles of no more than 24 cables using loose fitting cable ties or hook & loop (e.g. Velcro®) straps spaced at 500mm intervals. Cables should be secured at any change in direction, either horizontally or at a horizontal to vertical transition.

Cables in open basket

Within cabinets the cable bundle size should not exceed 24 cables.
Vertical cabling should be formed into bundles of no more than 24 cables and should be supported at 500mm centres or less where accessible. Wherever possible measures should be taken to avoid securing cable bundles to each other.

Cables in vertical basket

Where cabling is suspended horizontally, supports should be provided at no more than 1200mm centres.

 

Earthing, Grounding & Bonding

Wherever possible this should be left to a qualified and competent electrical contractor. All earthing, grounding and bonding should be carried out in accordance with the EN50174-2 and EN50310 standards.
The use of full height earthing bus bars in cabinets and racks is recommended and earth wires linking patch panels to these should be as short as possible. Braided earth straps are better than solid conductor earth wires as they have a larger overall surface area and provide a lower impedance path to earth for unwanted signals.
Shielded cabling solutions should always be adequately earthed at the patch panel end only. Earthing at both the patch panel and work area outlet can cause ground earth loops to be created.
Earths on shielded patch panels should never be ‘daisy chained’ together but each patch panel should have its own, discreet connection to the earthing bus bar.