Discuss Casting Resin vs Encapsulating Resin for filling outdoor junction boxes in the Electrical Tools and Products area at ElectriciansForums.net

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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 ÂŁ17 for 1kg whereas the casting resin which is around ÂŁ7 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
 
Sounds like unsuitable junction boxes have been used. Are they plastic by any chance?
 
Sounds like unsuitable junction boxes have been used. Are they plastic by any chance?
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?
 
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
 
How strange, why cut a cable to joint it, could have just left it whole in the first place.
 
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.
 
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.

I agree . The customer should have heeded the old school electrician.
It does not sound as the installation is fit for purpose.
 
Pratley boxes and magic gel with maintenance free connections. Should have been done right the first time.
 
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.

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.
 
Drying the boxes out and filling with compound is a bodge and doesn’t fix the problems.

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.
 
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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