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Widget for joining 3-core mains flex

Discussion in 'Electronic Components' started by Coleman, Jun 1, 2007.

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  1. Coleman

    Coleman Guest

    I am in the UK. I want to ask for info about joining 3-core mains
    flex on an appliance that may have to carry up to 3,000 Watts.

    I usually extend the mains flex by soldering but the finished join is
    too bulky when winding the flex or pulling it around a corner.

    When I make my 3 joints I slightly offset each one so that it is not
    beside another one. This helps make a slimmer overall joint but it
    makes for a longer joint (about 2.5 to 3 inches) and with insulating
    tape it is still too bulky.

    (A) Is it safe to use heat shrink insulating tubing for each join
    and have each join beside the other? Then I might use a single layer
    of insulating tape to bind over and protect the 3 joins.

    (B) Or is there some widget which can help with this? Perhaps a
    small moulding which is made up of three very small metal tubes held
    by moulded plastic to be close together but not touching. I could
    put a wire into each end of a metal tube and then solder the wires
    into it. (It's just an idea.)

    Any info?
  2. TMC

    TMC Guest

    Nor would I pull leads around corners.

    I would either replace the lead on the appliance with one long enough for my
    purpose or use an extension lead fully unwound the get near to the point of
    use and plug the appliance into the lead.

    Where the lead on the appliance is very short say a couple of metres I use
    an extension lead with a rubber socket on one end and an RCD plug on the

    For the load you describe I would use a 2.5 t&e cable fully unwound

  3. Palindrome

    Palindrome Guest

    I don't know of any safe way of making an inline cable joint that will
    allow the joined cable to be wound neatly on a small diameter drum. As
    well as providing electrical insulation, the material has to provide
    strain relief, abrasion resistance, water tighness and a load more.

    The nearest thing is probably crimped sleeves used to make offset joints
    to the wires, with heatshrink tubing insulating individual cores from
    each other and an adhesive-lined heat-shrink extra-thick outer tube
    overall. The outer tubing extending far enough along the cables for the
    adhesive to give strain relief. But that will be much less flexible
    that the typical continuous cable and the strain relief will be much
    inferior to that provided by continous cable - particularly if the cable
    is subject to self, or extrnal, heating. It may be ok for some fixed
    wiring but certainly is not for cable being wound on a small diameter drum.

    If the cables to be joined have clean and uncontaminated rubber outers,
    self-vulcanising tape can be used in place of, or under, the
    adhesive-lined outer tube. That will be able to take higher temperatures
    and still maintain some form of strain relief. But is still far inferior
    to that required for safety.

    The only safe solution is to replace the whole of the two cables with a
    single one.
  4. Why not just replace the flex with one of the length you want?
  5. Guest

  6. Bob Mannix

    Bob Mannix Guest

    But that is about twisted flex joints (the key is in the name :eek:) ) rather
    than soldered joints, which is what the OP was talking about. Hardly ideal
    but still not twisted flex joints and therefore not subject to the dangers
    described in the article.
  7. Lurch

    Lurch Guest

    New flex with no joins.

    I'd only entertain the idea of joining a mains flex if it were with a
    plug and socket arrangement or soldered\crimped if it were on a piece
    of equipment that wasn't dragged round corners on regular intervals.
  8. Palindrome

    Palindrome Guest

    I would suggest that soldered joints covered with normal heat shrink and
    insulating tape, "lack tensile strength, abrasion resistance, general
    robustness, spillproofness (they can make a small spill live), good
    insulation, petproofness & small childproofness."

    The marginal advantage of soldering the joints has to be balanced
    against the greater risk of failing during flexing, as the soldered
    joint will form a flexure discontinuity and stress points.

    Of course, soldering with acid flux would be an even greater problem.
  9. Then you are dangerous beyond belief. You cannot do this - it violates UK

    You must add a socket and a plug to connect the two cables.

    Any other joining method will result in potential loss of fire insurance and
    possible prosecution.

    Why do you need such a long cable?
  10. Guest

    I also thought it was pretty obvious what also applied to soldered
    joints. Solder is weak stuff too, though I've not seen any significant
    failures from soldering pretwisted flex (at LV). But not everyone
    twists enough before soldering.

  11. Palindrome

    Palindrome Guest

    You can buy Permanent Mains Flex Connectors that don't involve plugs and
    sockets, eg

    "Waterproof" versions are also available, for outdoor use.
  12. These are frowned on in many jurisdictions, however if they are approved in
    the UK then they can be used there.



  13. Guest

    Whats the problem with them? Ours all have cord grips.

  14. Palindrome

    Palindrome Guest

    In the UK portable equipment has to be provided with a fitted plug - in
    recognition of the fact that many people were incapable of correctly
    fitting (and fusing) one themselves.

    So, what are the chances that one of those will correctly choose and
    wire one of the above? Or use a non-rugged one outdoors, drag it around
    corners, let it fall into a bucket of water, etc?

    Many (most?) do not have anything to limit the bending radius of the
    cables at the point of entry close to the fixed cord grip. So strands of
    the cores break, leading to the risk of fire, failure, etc.

    Few are vapour-tight or even water-tight. As the are often dragged
    around through damp grass, left in the shed, etc - there is a real risk
    of corrosion..

    Bear in mind that a typical application is to "repair" an electric
    garden tool - where the user has cut the cable...

    Replacing the two cables with a single, contiguous, one is by far the
    best solution.
  15. Or in recognition of the fact that everywhere else in the world gets a
    fitted plug.
    The ones I've seen have cable grip and strain relief at each end similar
    to that found on plugs
    I'd suggest that most things likely to be used in the garden will use the
    garden tool type of plugs since a ready made extension can be bought for
    less than the cost of extending the lead.
    Maybe. But most garden tools have a plug/socket arrangement at the
    appliance to make lead changing easy.
  16. That's a safety break, for many reasons.
    If you drop something like a hedge trimmer, it won't be left
    dangling around your nuts on the cord looped over your
  17. Indeed. Also makes storing the tool easier - or adding an extension. And
    those extensions with the appliance plug/socket on them often can be
    bought for less than the cost of the cable from the same store.
  18. Huge

    Huge Guest

    Methinks you worry overmuch. I've been doing this for years, although
    it's solder, adhesive heatshrink (don't forget to put it on *before*
    soldering the joint), more adhesive heatshrink over the whole thing
    then insulating tape. OK, it isn't that bendy or pretty, but it'll
    go on a drum and I've never, ever, had a joint fail, and there's one in
    the lead for my big mains drill.
  19. Huge

    Huge Guest

    Jesus Christ, do you drive? You're about 300 times more likely to
    die in a car crash. Get a grip.
  20. Huge

    Huge Guest

    My recently purchased Bosch trimmer, although it had the inconvenient
    "needs 2 hands" feature (the reason God created gaffer tape) did not
    have a plug/socket, making it inconvenient to store. I fitted one.
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