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Cabling Nightmares - Useful Rules

 

Cabling Nightmare - Cabling Tips and Rules

Tips for installing audio and video cables - especially high definition cables. Incorrect handling, pulling and installation techniques can deform audio visual cables which can then cause reflection problems which show as ghosting or a loss of signal strength which produces "snow" like effects on the projected image. I would recommend these best practices for cable installation, some of which may be stating the obvious, but useful as a checklist. (based on BS 6701 and EN50174 installation standards which are a good basis but a little indigestible).

Cabling Basics

  • Don't stand on or crush cables during installation.

  • Don't place equipment or furniture on the cables.

  • Don't allow the cables to be kinked during the installation process.

  • Cable pulling should be done slowly, steadily and carefully with no snatching and only minimal force.

  • Be careful not to exceed the minimum bend radius of the cable: 10 times the diameter of the cable for most AV cables. This is particularly important at right angle bends in trunking which often has sharp edges.

  • Don't tighten cable ties too tightly. If you cannot move any cable inside a tied bundle, the cable tie is too tight.

  • Don't put cable ties at identical distances apart. This can lead to deformation at a certain wavelengths, which can cause "Structural Return Loss". Ideally place cable ties at random distances.

  • Cables should be supported by trunking, conduit, cable trays, or tied at less than 600 mm horizontal or 1 metre vertical spacing to take the gravitational forces off of the cable. Cable sag should be less than 200mm.

  • Best practice to ensure that all cables are concealed in trunking, conduit or inside partition walls and labelled at the ends.

  • Cable in conduit runs in excess of 30 metres with more than two 90° equivalent turns should include a pull box. Each 90° turn is equivalent to the friction of a 10metre straight conduit run.

  • If cable is pulled into long conduit lengths, an anti-friction oil free lubricant should be used that is compatible with the cable sheath (some special thin-film wipes are available for this).

  • Be sure to maintain the original physical shape of the cable.

  • AV cable routes should be separated by more than 300 mm from fluorescent lights and other sources of electrical interference wherever possible.

  • AV cables and power cables should ideally only cross at right angles to each other.

  • AV cables should be no closer than 75mm from any unprotected (power cables without screening or not inside steel conduit) 230volt 20 amp 50/60Hz power cables to avoid interference (though BS 6701:2004 and EN50174 conflict to some extent about segregation of AV cables from power – 50mm to 75mm is recommended depending on safety or electromagnetic interference).

  • Ideally AV cables should not share the same trunking as power cords or cables due to interference but if they do then spacers should be used and the cables segregated (a plastic separator between power and AV cables) to provide electrical safety.

     

    If you use a third party installer - check that they comply with these rules which should provide you with a well installed system with a long working life.

     

 

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