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Thread: Cable joints in trunking

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    Cable joints in trunking

    Hello all, I was taught to never join cables in trunking. Is this compliant?

    Regulation 6.3.7.1: Joints and terminations of cables, cores and conductors shall be made in accordance with manufactures instructions or the appropriate part of SANS 10198. FLEXIBLE CABLES SHALL ONLY BE JOINED USING TERMINATION BOXES, CABLE COUPLERS OR MANUFACTURES JOINTING KITS.

    My question is for the joining of a twin and earth cable using ferrules

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    Gold Member Sparks's Avatar
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    You already have the answer.

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    Clive287 (30-Jul-17)

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    Sparks , I have to disagree with you -
    The definition for flexible cables will be the common cabtyre and SANS 10198 refers to cables up to 33kv and nowhere in the SANS 10198 can I find a reference to Twin and Earth.

    I find no reason that states you may not join T&E in trunking.If the T&E is ferruled and heatshrink over it should pass all test's

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    Gold Member Sparks's Avatar
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    Like you, I was taught not to. By crimping ferrules you are reducing the diameter therefore carrying capacity of the cable. By pulling the cable through the pipe, bends, elbows and all, you are placing the joint under strain, creating a weak spot. By having a joint you are compromising the integrity of the wire and the insulation. Have you ever worked on an old installation and see the green muck that sometimes forms on the cable? Do you think heat-shrink will prevent this? If you are happy after considering all this, then by all means make the joint in the conduit but, as you can tell, I would neither do nor recommend it.

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    Diamond Member Justloadit's Avatar
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    Quote Originally Posted by Sparks View Post
    Do you think heat-shrink will prevent this?
    Heatshrink works well if used correctly. This method has been succesfully used in underwater/submersible motor installations.
    The trick is to ensure you have the correct size heatshrink for the application, and that sufficient length of heatshrink is used before and after the joint to improve integrity of the sealing, and lastly a good quality temperature regulated if possible heat gun with the correct nozzle for use with the heatshrink.

    You can also get heatshrink tubing from Hellerman Tyton, which has glue on the inside of the tube, which when heated to shrink melts the glue to improve the sealing.

    The great part of heatshrink is the speed at one can complete a good quality joint.
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    Clive287 (30-Jul-17)

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    Gold Member Sparks's Avatar
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    Agreed but, how many contractors, handymen and DIYers do you think will go to the expense and trouble to do it right with the right equipment? I prefer to not start a precedent which will end in disaster.

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    Diamond Member Justloadit's Avatar
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    Quote Originally Posted by Sparks View Post
    Agreed but, how many contractors, handymen and DIYers do you think will go to the expense and trouble to do it right with the right equipment? I prefer to not start a precedent which will end in disaster.
    Whats stopping them right now fiddling with electrical installations. They already are and making areas dangerous, with a simple screw driver and pliers and a roll of insulation tape.

    The OP was asking if joints were allowed in trunking. My understanding is that qualified staff would be working in these areas, and to make life a little easier, I would take it for granted that qualified personnel would pitch up at a site with the correct equipment. The information I posted was to help professionals with another way to make the joint safer which they may not been aware off.
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
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    Thanks everyone, as I already mentioned I don't make joints in trunking. What I'm gathering from everyones input is that it seems as though it is compliant, which I find a little disappointing. ..

    We all know that a joint may not be made in conduit (even elbows & tee-pieces) but thought there would maybe be a regulation that included trunking. Seems as though I'll have to pass them as compliant from here on

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    Diamond Member AndyD's Avatar
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    There's lots of issues under discussion here. I haven't combed through the regs so please feel free to point out anything I say here that's not correct. A few thoughts that spring to mind;

    I'm pretty sure there's a requirement somewhere in the regs that requires cable joints be contained in an enclosure to at least IP44 specifications. I'd guess that if the joint itself already exceeds IP4x ie an SWA resin joint for example then the joint itself would fulfil this requirement.

    If the joint is something like a choc block where there's visible bare parts then I think there's a requirement that it be accessible for maintenance but inacessible without the use of a tool.

    I don't think there's any requirement to derate a cable with a crimp ferrule joint due to reduced current carrying capacity as a result of wire compression within the crimp. I think however you've got to be careful what crimps are used with solid copper conductors, not all crimped terminals are suitable so it would be down to manufacturers recommendations. I have to say that a crimped uninsulated type ferrule joint with 2 layers of adhesive lined heat shrink has always served me well and proved to be very reliable. I recommend using the same make of crimping tool and ferrules if possible, it generally gives better results. Also obviously calibrate the crimping tool regularly to avoid the problem Sparks mentioned where the wires are significantly reduced in CSA inside the joint.

    I don't think we can allow what DIY'ers and unauthorised actors are capable of doing to dictate the methods used by professional electricians, I think the deterrant for them must come from a different angle.

    In the old days we used to make solder joints to extend cables. It's not a very fashionable solution nowadays but it's certainly reliable if done correctly and very neat if done with heat shrink to insulate and sheath afterwards. I've started using solder sleeves in the last couple of years, they're kinda the best of both worlds because you don't need a soldering iron or flux or solder, just a heat gun and they come pre-insulated so you just need heat shrink for the outer sheath. Also available in odd configurations for multiple wires and dissimilar wire sizes etc, they're transparent also which means you can visually check the flow of the solder and also visually check joint integrity for future inspections. Only problem is that they're not cheap (about R5 each).

    I think bottom line with regard to the original question is that cable joints in trunking may be compliant depending on how they're done.
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    Good day everyone
    Just some additional info regarding cable joints
    It is not your regular heat shrink that is used on submersible pump joints,their is a specialized resin that the submersible heat shrink produces when heated up for waterproofing.
    Also once the individual cores are heat shrinked an overall heat shrink would further waterproof the entire joint.
    These heat shrink kits are used where the joint cannot fit between the pump casing and the borehole shaft.
    I usually prefer using an epoxy resin kit for submersible pumps.
    Secondly most of my joints i overlap the conductors as i find it dodgy having the core going in halfway in such a short distance of the ferrule. Once crimped i solder the ferrule taking care not to damaged the PVC insulation.
    Working out in the farms i have found countless joints that explode due to electricians believing that their joints are 100%,although resin kits stipulate a certain size for cable with or without armour i always upsize and use additional insulation between conductors.

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