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Discuss Casting Resin vs Encapsulating Resin for filling outdoor junction boxes in the Electrical Tools and Products area at ElectrciansForums.co.uk.

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  1. barnaby91
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    barnaby91 New EF Member

    Location:
    United Kingdom
    I have a repair job coming up - a garden has had 240V lights fitted, with which the junction boxes have been filled with magic gel - they haven't been filled correctly and there are problems with the outdoor lights (the 240V doesn't help with the sensitivity to moisture). I have an idea that the problem is moisture in the junction boxes tripping the circuit breakers. I have poured water out of some of the boxes, some of which have had forks and other garden tools put through....

    Anyhow, due to the price of magicgel, I am going to remove all remnants in the boxes, dry out the junction boxes with a heat gun and get the complete system working and then fill the junction boxes with resin to form permanent joints that can't be pierced with forks etc as they are in the garden environment.

    My question for the thread is, 'what is the difference between encapsulating potting compound and standard casting resin?' Both seem to be polyurethane resin, but the potting compound is around £17 for 1kg whereas the casting resin which is around £7 a kg. I can't see why the casting resin wouldn't serve the purpose of sealing the junction boxes and forming a hard block around the joints.

    Some knowledge on resins or jointing would be appreciated and look forwards to your help.

    Thanks,
    Barns
     
  2. Strima
    Online

    Strima Electrician's Arms

    Location:
    St Neots
    Sounds like unsuitable junction boxes have been used. Are they plastic by any chance?
     
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  3. barnaby91
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    barnaby91 New EF Member

    Location:
    United Kingdom
    Yes, the job does look like it has been done to a high standard, although some methods are to be questioned.

    They are indeed plastic junction boxes, probably fit for the job if they were screwed to posts above ground, but instead they are buried in the flowerbeds and asking to be forked and filling with water..

    Also the magic gel intention was great, but the boxes weren’t full so the chocolate blocks and joints were actually sticking out above the gel..

    I also came across a light that didn’t exist, turns out they must have run out of fittings and stuck what looks to be a conduit corner piece on the end of the swa. Needless to say it was full of water and I imagine a major cause of the system tripping whenever the lights were turned on.

    The family member who’s garden it is said that the original electirician who fitted the lights etc couldn’t find the fault, an old school electrician came and said it would need completely renewing and rewireing (I suspect he thought it was easier than finding and fixing the fault).

    I’m relatively new to the electrician trade, having completed the courses to install solar pv mainly, but she asked me to have a look and the first junction box I opened had water inside. I suspect it won’t be that hard to fix once all the boxes aren’t opened, dried and encapsualted. The garden certainly wasn’t a cheap job, when it was installed, it was knocking on 20k and the electrics worked flawlessly for about 6 months until the water ingressed I imagine.

    Will the resin behave with the plastic, or am I asking for melting?
     
  4. Des 56
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    Des 56 Trusted Advisor

    Location:
    Gliese 581C
    Here is a look at a traditional skill that shows jointing at its best
    Your problem is on a much more basic effort,however, the end result needs to be the same,a safe joint


    Basic armoured cable joints these days reflect advances in the chemistry of a convenient insulating compound,at the same time relying on that compound to also be its mechanical protection,this is where the modern joint loses points
    You could always make your own enclosures,maybe use adaptable boxes and fill them with a packet of compound or bitumen,they will give the forks a hard time in future
     
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  5. Taylortwocities
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    Taylortwocities Electrician's Arms

    Location:
    Oxfordshire
    Fantastic, the skill of the old-time jointers. And he did all that work with the hot solder and pitch without wearing any PPE on his hands!
     
  6. Vortigern
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    Vortigern Electrician's Arms

    Location:
    England
    Business Name:
    F.H. Electrical
    How strange, why cut a cable to joint it, could have just left it whole in the first place.
     
  7. Taylortwocities
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    Taylortwocities Electrician's Arms

    Location:
    Oxfordshire
     
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  8. Spoon
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    Spoon Trusted Advisor

    Location:
    Lancashire
    If they are sticking a fork through the boxes doesn't it mean that the installation is not at the correct depth?
    Maybe if you put some flagstone, or similar, above the boxes then its harder for them to put a fork through it.
     
    • Agree Agree x 3
  9. ruston
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    ruston Trusted Advisor

    Location:
    Northumberland
    I agree . The customer should have heeded the old school electrician.
    It does not sound as the installation is fit for purpose.
     
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    • Agree Agree x 1
  10. Strima
    Online

    Strima Electrician's Arms

    Location:
    St Neots
    Pratley boxes and magic gel with maintenance free connections. Should have been done right the first time.
     
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  11. Des 56
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    Des 56 Trusted Advisor

    Location:
    Gliese 581C
    My money is on that garden fork in the opening post:)
     
    • Funny Funny x 2
    • Agree Agree x 1
  12. davesparks
    Online

    davesparks Trusted Advisor

    Location:
    guildford
    The old school electrician was probably advising the best course of action rather than the easiest. The joint boxes have been installed in a location where they are being damaged by foreseeable use of the ground, this is bad design and not fixable by just replacing the joints.

    Drying the boxes out and filling with compound is a bodge and doesn’t fix the problems.
     
    • Agree Agree x 2
  13. Spoon
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    Spoon Trusted Advisor

    Location:
    Lancashire
    That's why I suggested putting a flagstone or similar above the box. At least it will give it some protection.
    Yes still not great but better than just sticking soil above the box.
     
    • Agree Agree x 1
  14. HandySparks
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    HandySparks Trusted Advisor

    Location:
    Hampshire
    Business Name:
    Neish Electrical Services
    So, if the joint boxes are getting damaged, what about the cable?
     
    • Agree Agree x 2
  15. Marvo
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    Marvo Gender Confused Staff Member

    Location:
    South Africa
    I've used standard hobby type polyeurethane resin for joints on LV cables before when I've been working in far flung places where other options weren't available. I made a test block of cured resin first and IR tested it at 10KV before I committed to using it in the cable joints. As an extra precaution I also used a few wraps of self amalgamating tape over the crimped ferrules as well so they weren't in direct contact with it.

    I suspect with the hygroscopic nature of polyeurethane resins the official potting resins may go through processes to ensure they're dry and packaged accordingly and hence give predictable dielectric properties whereas with DIY casting type resin this probably isn't a concern. In your situation I would recommend you buy the official potting resins and pay the extra to be honest.
     
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  16. 7029 dave
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    7029 dave Trusted Advisor

    Location:
    bedfordshire
    Can you not get the joints above ground.?
     

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