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Thread: Minimum spacing between cat5 and main

  1. #1
    Automated Home Jr Member Gangsta's Avatar
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    Default Minimum spacing between cat5 and main

    Hi, can anyone tell me the recommended minimum distance between my cat 5 installation and mains wiring when they have to run parallel, to keep interference at a minimum.

    Thanks

    Graham

  2. #2
    Moderator toscal's Avatar
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    We always run them in a separate conduit. But local codes may dictate what you can and can't do.
    How long would the run be.
    Also see this post http://www.automatedhome.co.uk/vbull...ead.php?t=1287
    IF YOU CAN'T FIX IT WITH A HAMMER, YOU'VE GOT AN ELECTRICAL PROBLEM.
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  3. #3
    Automated Home Jr Member Gangsta's Avatar
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    Interesting thread that, and some interesting info on cat 6 (glad im not doing that)

    I work where we manufacture conservatory roofs, and have been given all the gutter offcuts to make a cable tray in the attic, it will run about 12" clear of mains except at 90 deg crossings. once the cable runs into the rooms, i will only have a max of 3.5in seperation (physical) between the mains and cat5. They will be parallel for approx 18 ft (behind skirting boards)

    Can you see it being a major issue?

    The 1 cat5 hybrid cable (for video) will be clear of the mains.

    Also in node 0, there is 48channel dmx dimmer about 3 ft away from the server rack - any issues here?

    Thanks

    Graham

  4. #4
    Moderator toscal's Avatar
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    I don't think so.
    But you will need to make sure the shield on the Cat5 cable is earthed properly. Also I would junk the first 1m at either end of the cable after its pulled through,this part of the cable suffers the most stresses when being laid. Also before you terminate it. Check continuity between pairs and leakage to other pairs and ground. When we test we short each pair at one end and then test at the other end, this way we will know if the pairs are all good. This is a very quick way to test the cable plus if after termination the cable has a problem you will know that it is probably something to do with the termination. Only test the cables when all the cables in the conduit are laid.
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  5. #5
    Automated Home Legend TimH's Avatar
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    "as far apart as possible" is the usual advice and 300mm/12" is often quoted as a minimum. In the UK you can't (usually) run mains and LV cables in the same conduit, you need a physical barrier or at least a 2" clear air gap between the two. Safest practice is separate trunking

    NB: The exception to this is where the LV cable's sheath is rated for the higher mains voltage, pink CBus Cat5 cable is like this so there's no issue with terminating Cbus cable in the same back boxes as mains.

    I've got lots of cables where cat5 & mains run parallel with less than 12" and I've not experienced any problems. I guess the key thing is to aim for 12" but not get too worried if you can't always achieve it.

    HTH,

    Tim.

  6. #6
    Automated Home Guru MichaelD's Avatar
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    This post just made me realise that I've carefully left at least 12" between Cat5e and mains when installing the cables, and done all junctions at 90 degrees, but then when they come out of the wall into the room, I have a complete tangled mess of network leads and mains leads before they go into devices. Never though about interference at that point!

    Don't think its caused a problem, but not sure that I can do anything about it either, I have a load of stuff hidden behind furniture that all needs both mains and network connection

  7. #7

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    Quote Originally Posted by MichaelD View Post
    This post just made me realise that I've carefully left at least 12" between Cat5e and mains when installing the cables, and done all junctions at 90 degrees, but then when they come out of the wall into the room, I have a complete tangled mess of network leads and mains leads before they go into devices. Never though about interference at that point!

    Don't think its caused a problem, but not sure that I can do anything about it either, I have a load of stuff hidden behind furniture that all needs both mains and network connection
    The whole point of CAT5 is that it uses differential signalling over a twisted pair which makes it highly immune to interference. A mains cable *usually* has two current carrying conductors carrying equal but opposite currents and whilst not twisted, the opposing magnetic fields generated by the current cancel each other out within a few millimetres (hence the reason a clamp on ammeter has to be placed around a single conductor rather than the sheathed cable)

    Whilst it is good practice to keep as much separation as possible and MANDATORY to run low and mains voltage cable in separate trunking or compartments within dado trunking I feel that some people do get just a little over paranoid about interference!

    Just think about the typical modern office where multicompartment dado trunking runs for tens of metres with CAT5 and mains parallel and only separated by a plastic divider with no interference whatsoever. I have DELIBERATLY run CAT5 cable tied to a large mains cable to see if I would get any problems and everything was just fine.
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