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Running cables through same hole

Discussion in 'Audio Visual' started by chriselevate, 18 May 2018.

  1. chriselevate

    chriselevate

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    I have a feeling there'll be some warnings/advice on this but I'm hoping not o_O

    When running cables through joists... is it ok to use a 25mm hole to run lighting, mains, speakers and coax cable through (the same hole) or is it advised to split them up?

    Thanks
     
  2. Lucid

    Lucid

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    Lighting and mains together should be fine from a signal interference point of view. Check with the sparks though about electrical safety depending on the number of cables you plan to run through a single hole.

    Coax and speakers cable - keep that well away from mains cables - particularly speaker cable. Mains oscillates at 50 times a second, and that's 50Hz, which is well within the audio band (20Hz-20,000Hz), so you'll hear the 50Hz hum because speaker cable isn't shielded against hum. Keep 30cm/1ft separation between mains and speaker/coax cables running parallel to any mains cables for more than a metre or two. If the cables have to cross mains circuit or low voltage lighting wiring then do so at 90 degrees.

    How are you wiring your speakers?
     
    Last edited: 20 May 2018
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  3. ericmark

    ericmark

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    You have the 1/3 rule, you should not drill a beam for first 1/3 of it's span, so only the centre 1/3 can be used, also when running low voltage cables (230 volt) all other cables must be also rated at the maximum voltage which is supplied, so although the speakers and TV coax is classed as extra low voltage, to be run with low voltage they would need to be rated at 230 volt which is simply not going to happen, with metal tray it is permitted to fit a divider and extra low voltage one side and low voltage the other, however since the tray is earthed and surrounds the cables, the two separate voltages are in a Faraday cage so there will be no capacitive or inductive link between them.

    You do need to use some common sense, two cables running together for 2 inches is not going to allow much of a capacitive or inductive link so both low and extra low voltage cables running through the hole in a TV stand is not really a problem, but if there is a series of holes then there will likely be a problem.

    With AC supplies the feed should be what is called balanced or matched, at 50 Hz this is unlikely to cause a problem in most cases, however with LED lighting the traditional method of wiring a two way switch has been found to allow enough energy transfer with inductive and capacitive linking to cause the LED to glow dim, as a result it is common to include a bleed resistor in the bulb to remove this small current and stop them glowing.

    With the very small currents involved with speakers and coax you can expect to have problems, using Ali-tube power cable will likely reduce the problem, I have never tried using it, the idea of the cable is it can be used in walls without RCD protection as drilling or nailing through it will cause a short circuit and trip a standard MCB, it has not really caught on, but if it is impossible to separate mains and data, then the ali-tube cable will likely stop any 50 Hz RF from being transmitted from the cable. Personally feel that's using a sledge hammer to crack a nut, but it is an option.
     
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  4. chriselevate

    chriselevate

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    Guys that’s really helpful!

    So you’d suggest sticking to running all cables through the middle 1/3 of the joist and group speaker/coax cable together and group lights and mains sockets together and get 30cm between them?

    I think in a nutshell that’s the easiest without going down the route of shielding them to run them in the same holes? Is that right?

    Thanks again for the excellent and detailed advice. Really appreciate it.
     
  5. JohnD

    JohnD

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    Cables for co-ax, internet, phones and speakers can be run behind skirtings if you wish.

    But not power cables in case you are electrocuted when you drill or nail into them (it is not a safe zone)

    This is most easily arranged if you are renewing the skirtings anyway, or remembered to allow for it when they were fitted.
     
  6. DIYnot Local

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