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Thread: Flexible ducting laying on wires

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    Flexible ducting laying on wires

    Hello. My house is old and have the live and neutral wires running from bobbin to bobbin in the attic space. I'm now installing a evaporative cooler and there will be flexible ducting all over the wires. So I was wondering if there are any regulation that state that nothing is allowed to touch the wires or sit on top of it. I'm still in the early install stages so if it is required that ducting be suspended away from the wires I can address it.

    Thanks

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    Diamond Member AndyD's Avatar
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    Eeek I'd strongly recommend you steer well clear of the wiring if it's the old knob, cleat and tube type install. Usually the wiring was only single insulated and unsheathed and there's a high likelihood the vulcanized rubber or cotton insulation will have deteriorated to a point where anything contacting it could become live. To be honest I'd strongly recommend it was rewired, it will be well past its serviceable lifespan. There's also the issue that you'll probably not find anyone who knows how to work on that stuff, nowadays you'll even struggle to find sparkies who can install mineral insulated (MI or Pyro) or make a wiped lead joint anymore, it's a shame but those old skills are dying out.

    On a personal note I'd be very interested if you could attach some photos so I can see a few areas of the wiring.
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    Thanks for that info Andy, I attach a picture so you can see what it looks like. I probably should have qualified "old house" it is circa 1962, fortunately the wiring is the more modern red and black wires, somewhere around a 3 or 4mm2 Click image for larger version. 

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    Diamond Member AndyD's Avatar
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    I can't tell from the photos if they cotton covered or PVC but either way it's unsheathed so it should be free from contact with other services and items such as ducting. Have you ever seen inside one of your sockets? I'd be interested to know if the earth and the neutral connections are linked at each one.
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    Quote Originally Posted by AndyD View Post
    I can't tell from the photos if they cotton covered or PVC
    definitely PVC

    but either way it's unsheathed so it should be free from contact with other services
    So just for clarity, if it is open wires like that then no contact with other services (eg ducting). If the wiring was flatwire would it then be OK, or when would it be OK?

    Have you ever seen inside one of your sockets? I'd be interested to know if the earth and the neutral connections are linked at each one.
    Earth is separate, steel conduit running down the wall, then earthed at the top in the attic where it exits the brickwork.

    Thank you for the answers
    G

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    Follow up question:

    If for some reason the ducting has nowhere else to lay than over the wires (eg ducting being huge and no other place to put it), can I create some sort of insulation between the wiring and the ducting? If so, what will be acceptable?

    thank you

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    Diamond Member AndyD's Avatar
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    Quote Originally Posted by Goobie View Post
    So just for clarity, if it is open wires like that then no contact with other services (eg ducting). If the wiring was flatwire would it then be OK, or when would it be OK?
    The difference between wires and cable is that wires are just insulated and cable has insulated internal conductors an outer sheath for added mechanical protection as well. Wires without containment is not an acceptable installation because they would be unsheathed.

    Quote Originally Posted by Goobie View Post
    Follow up question:

    If for some reason the ducting has nowhere else to lay than over the wires (eg ducting being huge and no other place to put it), can I create some sort of insulation between the wiring and the ducting? If so, what will be acceptable?

    thank you
    My first thought on the fly was to suggest wrapping the wires in self amalgamating tape in order to sheath them ie basically create your own cable but this would effectively be creating a cable that doesn't contain a CPC (earth wire) which in itself is not acceptable.

    I guess you could use a piece of drain pipe with a lengthways slit in it and carefully put it over the wires and secure it somehow as a capping wherever the flexiduct will be crossing the wires. Bottom line is whatever you do is going to be less than ideal at best and illegal/unsafe at worst. If it was my house and, as you say, there's conduit drops down to all the accessory points such as sockets and switches etc then for me a rewire in flat twin and earth would be a no brainer. If it's a modest house it should take you maybe a day with a helper and cost you a couple of rolls of cable and an RCD (earth leakage breaker) and maybe a couple of lengths of earth wire to upgrade the bonding whilst you're at it. Even if you just rewire the circuits in the roof space that are the problem at the moment you can always complete the rest over time.

    Obviously, what ever you do, assume that old wiring is out to kill you so isolate and do the usual dead tests before restoring supply to any final circuits you disturb whilst working. No offense, I know I'm stating the obvious.
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    Bronze Member ACEsterhuizen's Avatar
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    Sorry to butt in but a few pointers which you could maybe check whether this type of wiring in fact still complies with all regulations. (besides all the other test eg insulation resistance etc etc) (or maybe get an installation electrician to do it for you)

    I have to second Andy and recommend a complete rewire it's much cheaper than the loss of life and/or property.


    6.4.5 Open wiring

    NOTE Open wiring consists of single-core insulated conductors that operate at not
    more than 250 V to earth; however, this is not a recommended installation method
    for new installations. Amdt 5


    6.4.5.1 Open wiring shall not be installed:

    a) under thatched or wood-shingle roofs,
    b) in parts of a roof space where the working height is less than 750 mm,
    c) in roof spaces that are intended to be used (or are used) for storage,
    unless the wiring is suitably protected against mechanically damage,
    Amdt 5
    d) within 1 m of a trap door unless the wiring is suitably protected
    against mechanical damage, or Amdt 5
    e) where it will be in contact with flammable material.


    6.4.5.2 Each conductor of an open wiring system shall be visible where it
    is installed on, over, or next to beams that can be used for walking on, or
    it shall be suitably protected against mechanical damage. Amdt 5

    6.4.5.3 Conductors shall
    a) be fixed at intervals not exceeding 1,5 m to building elements such as
    walls, rafters or purlins, Amdt 5

    b) if there is no ceiling, be at least 3 m above floor level,
    c) Deleted by amendment No. 5.
    d) Deleted by amendment No. 5.
    e) Deleted by amendment No. 5.
    f) be supported within 600 mm of the point where they enter conduit or
    other building elements, and Amdt 5
    g) be fixed in such a way that the fixing method does not impair the
    conductor insulation. Amdt 5
    6.4.5.4 Where conductors enter a conduit, the conductors shall not be
    strained. Metal conduit shall project enough to allow a bush and an earth
    clip to be fitted. Amdt 1; amdt 5
    6.4.5.5 Where the current-carrying capacity of conductors is impaired by
    thermal insulating material, the appropriate correction factors shall be
    applied.


    the bold is where i will look first judging by your pic.
    Last edited by ACEsterhuizen; 27-Jan-16 at 02:15 PM. Reason: clarify

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    Thanks for the useful info

    How would thermal insulating material impair the current carrying capacity of the conductors?

    thank you

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    Diamond Member AndyD's Avatar
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    A cable carrying a current produces heat internally along its length. The thing that limits a cables current carrying capacity, apart from volt drop, is how hot it gets because if it gets too hot the insulation material becomes compromised. Obviously a cable that's running in or on insulation material can't lose heat as fast as one that's running in free air so to compensate we have to either ensure the load current is reduced by installing a smaller value circuit breaker or increase the cable size which in turn reduces the heat produced in the cable.

    There's tables in the regs that dictate how much current a cable can carry depending on how it's installed and cable manufacturers also produce their own figures.
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