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Repairing insulation

MrJack96
What is acceptable practice to repair basic insulation when it’s been nicked. Can we use self amalgamation tape or should we cut and trough crimp? 


thanks guys
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    Interesting point Andy, but rather out of date in application as we have better methods than choc block now. If I use proper crimps, I do not need to inspect, therefore don't need an enclosure. I would be perfectly happy to join a large cable, so why not a small one using the same method? Resin filled joints basically use this method and are not inspectable, being crimped (or even screwed) joins in a cable surrounded with suitable insulation. There is no "enclosure" as such, only a mould for the resin, which is a flimsy "enclosure" I suppose, but not openable. The days of the big cast-iron box and pitch have long gone. Perhaps this is another bit that should be changed? I see no reason why suitable tape or adhesive heat-shrink should not be used, both waterproof and excellently insulated, what more could I want?
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    davezawadi (David Stone):

    Interesting point Andy, but rather out of date in application as we have better methods than choc block now. If I use proper crimps, I do not need to inspect, therefore don't need an enclosure. I would be perfectly happy to join a large cable, so why not a small one using the same method? Resin filled joints basically use this method and are not inspectable, being crimped (or even screwed) joins in a cable surrounded with suitable insulation. There is no "enclosure" as such, only a mould for the resin, which is a flimsy "enclosure" I suppose, but not openable. The days of the big cast-iron box and pitch have long gone. Perhaps this is another bit that should be changed? I see no reason why suitable tape or adhesive heat-shrink should not be used, both waterproof and excellently insulated, what more could I want?


    I guess the other characteristic is fire-proofness (is that a word?) - any kind of joint (even one that doesn't need subsequent inspection) is a weakness and is for more likely to be subject to overheating and perhaps fire than the original conductor.


       - Andy.


  • 0
    In the past I have repaired cables buried in plaster in walls with a shallow metal box and a blank plate to cover it. This can only be achieved if the owner agrees. If the owner has damaged a cable whilst drilling the wall or hanging a picture then accessible joints are good afterwards. Sometimes I have seen cables repaired by cutting them, sleeving them, rejointing them, perhaps with small choc blocks,  and then sliding the sleeving down over the joint. If the choc blocks are staggered they are more compact in size. The joint is then plastered over. If individual sleeves are used for L and N and a larger over sleeve is slid over the whole lot afterwards that seems to me to be as good as the original cable. This is easier with dot and dab walls where the joint can be easily hidden. The repair is on a cable run anyway so is in a "zone".


    Z.
  • 0
    Both of the materials I have suggested are much more fireproof than PVC Andy, please be sensible. Crimp connections made properly are not subject to overheating. This idea you have is simply daft!
  • 0
    davezawadi (David Stone):

    Both of the materials I have suggested are much more fireproof than PVC Andy, please be sensible. Crimp connections made properly are not subject to overheating. This idea you have is simply daft!


    Why the comparison with PVC? Most electrical enclosures aren't PVC and I suspect those that are are sufficiently modified to be able to pass a glow-wire test at least. In poured resin joints I'd imagine that the hardened resin forms a suitable enclosure rather than the mould. I think it's confusing to suggest that meeting the requirements for non-accessibility is the same as meeting the requirements for enclosure - 526.5 and 526.2 are quite distinct requirements.


       - Andy.


  • 0
    I think you are hopelessly confused Andy. There is no mention of the fire rating of the enclosure even if it is made of standard building materials, say wood. As wood has been used in electrical systems for many years, as back boxes, patresses, etc which contain connections, not usually joints I agree but the difference is surely minor, as the other terminals or connections could cause ignition, given a bad set of circumstances. Are you really suggesting that crimped connections are a fire risk? What or who suggests the box or whatever is for fire protection anyway, it is usually considered to protect from direct contact, and provide for mounting of accessories. I would point out that a standard junction box is far from fireproof, it is to protect against direct contact. The enclosure idea surely comes from inspection, which is a requirement of some kinds of joint, not a fire one. The fire rating of a Schnider joint box, for example, being made of plastic is similar to a plastic CU. It may have fire retardant but one cannot tell, many CUs didn't although marked as meeting the specification. By PVC I was really referring to the cables, particularly sheaths, which are inflammable if PVC.


    If you really wish to decry jointed cables you need to define why. Those regulations do not specify the "containment" which could be resin in a joint or self-amalgamating tape, they do not specify IP rating which for both these methods is at least IP67. If one took those regulations at face value as you have, resin joints would not be permitted, fire information is in section 527 which says nothing about joints. 526.3 (ii) and (iv) specifically allow encapsulated or resin joints, which does appear somewhat at odds with 526.5 I agree, this probably needs correction. Encapsulation in self-amalgamating tape is common for many services to provide waterproofing and insulation, as is adhesive heat shrink.
  • 0
    There is no mention of the fire rating of the enclosure even if it is made of standard building materials, say wood.

    I think you must have a very different version of BS 7671 to me - in mine 526.5 specifically says building material when used as an enclosure for a termination or joint must be "non-combustible when tested to BS 476-4." All the other options refer to electrical enclosure or accessory standards - which I believe usually include a glow-wire test or something similar.

    By PVC I was really referring to the cables, particularly sheaths, which are inflammable if PVC.

    But plain cables don't include joints. Yes, I beleive that any joint - even a crimped one - will be on average less reliable than the original unbroken conductor - but provided the attendent risk of overheating is dealt with (by a suitable enclosure for example) then there's no reason why joints shouldn't be acceptable.


        - Andy.

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