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Underground Junction Box Problem

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  1. #1
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    Default Underground Junction Box Problem

    I ask myself why do I want to get mixed up in this? So, please bear with it even though the story is a bit long winded.

    The story is… I had a call over the weekend from a friend on a nearby rural property worried that a circuit breaker (actually a RCBO/RCD) on their switchboard kept tripping and turning off power in the house, could I help.

    It turned out that there are three circuits connected to the RCBO and it was easy to isolate the guilty one. So far so good.
    The house power circuits were O.K. but the guilty circuit ran underground to the water tank pump about 50 metres away. Hmm, you might have a faulty pump motor says I, oh it also goes to the shed says he. The shed was a later addition to the property and I was told that the “electrician” tapped into the pump circuit to get power for the shed. The “electrician” has since returned to Sydney and isn’t likely to be seen again.

    It turns out that the “tap in” was done by cutting the conduit and cable going to the pump, fitting a “home made” J Box, and running a conduit and cable from there a few metres underground to the nearby shed. Arrrgh, running a new conduit and circuit to the shed from the switchboard would only have involved about 10 metres of trenching and avoided this problem.

    The J Box is 600 underground, below a garden which is watered frequently. Once the pump was disconnected the problem remained, so I said dig it up and let us see what we have, since there was a high “index of suspicion” that the “tap in” might have something to do with the problem. I didn't megger the circuit as the RCD was still tripping when the pump circuit was connected.

    The attached photo is the result. Clearly water ingress has been an issue. Also, as a result of trying to find the “tap in”, the garden is now a bit trashed so he is not particularly popular! It is highly likely that the garden will now be “relocated”.

    The conduits running vertically in the photo are the original conduit that was cut to fit the J Box, and the conduit running out the RHS is the “new” conduit and cable going a few metres to the shed.

    The question now is how to organise a fix that is compliant. I seemed to recall that past editions of AS3000 sort of covered such situations by requiring that all connections should be “reasonably accessible”. But, I can’t find any “reasonably accessible” clause in the current AS3000, and certainly not in Sect 3.11 which covers underground wiring systems. Section 1.7 has lots of stuff about things being done in a safe and reliable manner etc, which might sort of cover the situation.

    Where AS3000 was once quite prescriptive it is now seems mostly about good practice and lets you make up your own mind about how things are done. It is certainly a lot fatter than it was in the “olden days”.

    I must admit that I can’t see anywhere in AS3000 that either allows or disallows J Boxes to be installed in the ground, but the way it has been done doesn’t seem to be a particularly sound practice to me given the current problem.

    My initial thoughts are to have a proper 3 way 32mm J Box installed and also have a pit installed to provide reasonable access. Perhaps a DIY pit constructed from four 600x600 concrete pavers with another paver on top as a lid. The alternative to the pavers idea is a proper plastic pit if one can be fitted. Other services are within 100mm of the electrical service so that is another issue to be addressed for fitting a pit and being compliant with separation from the other services (but not impossible to deal with).

    I am looking for any creative and compliant suggestions as this really isn’t my field of expertise which is industrial maintenance rather than domestic installations. Any thoughts on components, brands etc are more than welcome.

    Before anyone presses the “call an electrician” button, many of you will be aware from my past posts that I am a “mostly retired” electrician and still hold a NSW Contractors License, so there is a fair chance that the new electrician is going to be me, or at least I will be asked to organise the job.

    Thanks in advance for any help and suggestions.
    Last edited by phild01; 1st Nov 2021 at 03:24 PM. Reason: corrupt image data removed

  2. #2
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    Quote Originally Posted by chalkyt View Post
    ??? no pic
    Suspect a problem with loading!
    Last edited by Uncle Bob; 2nd Nov 2021 at 07:49 PM. Reason: Removed wall of text

  3. #3
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    Shed loading is practically nil... it is used as a garage and only has a fridge in it. The pump is disconnected and the problem remains. I am going out there today to megger the circuit as I didn't have it with me yesterday.

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    epoxy cable joint.

    Or rerun the entire thing and do it properly.

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    Any conduit run underground is potentially going to be filled with water, TPS will be fine in the water but a junction box is submerged exposed electrical connection and will present a high resistance connection.
    Best option is to bring any junctions to the surface either by rerouting the conduit so the existing cable reaches above ground or replace the run of cable.

    The only other option is to waterproof the existing junctions probably by encapsulation with either epoxy or liquid insulation:
    https://www.jaycar.com.au/liquid-ele...black/p/NM2832
    Not sure on the compliance side of things for this option.

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    I like your thinking but to install a J Box in a pit 600mm down in the ground is ambitious as no way you could work on it easily. I have joined cables for underground with Scotchcast joints but they are only for joining cable and it is done on the surface before burial.

    My only suggestion is start again eliminating the use of a J Box underground.

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    Thanks for the replies so far. This is the missing photo... don't know where the original went.


    img_8496_1.jpg

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    Quote Originally Posted by chalkyt View Post
    Thanks for the replies so far. This is the missing photo... don't know where the original went.


    Well that was always going to be problem free !

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    Quote Originally Posted by chalkyt View Post
    Thanks for the replies so far. This is the missing photo... don't know where the original went.
    Certainly not watertight looking at the lockrings. It would have been a difficult job cutting back the conduit and not cutting the insulation and then getting enough slack in the conduit and cable to make the termination.

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    Thanks for all the responses. A bit of scratching around today seems to suggest that the general opinion is that if AS3000 doesn't say you can't do something, then you can... provided that you are prepared to declare that it is workmanlike, safe, good practice etc in the event that the s*@#t! hits the fan.

    It seems like fitting a proper J Box and filling it with a resin kit would be an appropriate way to go. Some kit manufacturers even have "Y" jointing kits that go up to 32mm and something like that might be adaptable to 35mm conduit, although the J Box and resin kit idea should work the same.

    Being somewhat retired I am not in the business of taking work from those who are trying to earn a quid. I just do the small jobs or solve problems that no one else wants to know about, so with some idea of what the job might entail, I will flick it to one of the local contractors. At least is seems that resin filled joints underground would be "compliant" and avoid any hassles with pits etc.

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    Yes Bros, I agree. I would have just run a separate feed to the shed which probably would have been just as quick as digging down to find the conduit, fiddling to cut it, making up and fitting the J Box and trenching across to the shed anyway. But I am sure he saved 5 metres or so of cable and conduit which must have been worth at least 10 bucks retail!

  12. #12
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    Quote Originally Posted by chalkyt View Post
    At least is seems that resin filled joints underground would be "compliant" and avoid any hassles with pits etc.
    ..based on what my sparky said at this place, for domestic cable routes pits aren't an option or approved for use like on say a distributors network. ie: I had to run separate circuits to their own sub board for the house and shed from the main board in the driveway.

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    Yes Bart 1080, that was my gut feeling and what I would have done, however a local wholesaler sell lots of epoxy kits and reckons "everyone is using them". I must say that particular technology appeared long after I stopped digging trenches and running cables so I had concerns about mucking around with epoxy that I have never used and finding a half hardened mess halfway through the job. I have suggested that the owner pass the job over to one of the "better" and more up to date local contractors and let them make the decision about what to do.

    Meanwhile, emptying the J Box of water, letting it air a bit, and a dry with a hot air gun has returned the earth leakage resistance to near infinity on my insulation tester and got them out of trouble for now. So it is business as usual until the issue is repaired properly.

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    Quick and dirty instinctive answer is neutral silicon filling the box after doing new connections. but that is a Non-Tradie guess
    "A big boy did it and ran away"

    Legal disclaimer denying responsibility to be inserted here.

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    Quote Originally Posted by Moondog55 View Post
    Quick and dirty instinctive answer is neutral silicon filling the box after doing new connections. but that is a Non-Tradie guess
    I think you mean silicone, not silicon.
    https://en.wikipedia.org/wiki/Silicone
    https://en.wikipedia.org/wiki/Silicon
    “What a fool believes, he sees. No wise man has the power to reason away”- The Doobie Brothers

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    Quote Originally Posted by UseByDate View Post
    Yes I did, will that work??
    "A big boy did it and ran away"

    Legal disclaimer denying responsibility to be inserted here.

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    Quote Originally Posted by Moondog55 View Post
    Yes I did, will that work??
    Probably.
    “What a fool believes, he sees. No wise man has the power to reason away”- The Doobie Brothers

  18. #18
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    Quote Originally Posted by chalkyt View Post
    Also, as a result of trying to find the “tap in”, the garden is now a bit trashed so he is not particularly popular! It is highly likely that the garden will now be “relocated”.
    If the end result is a non compliant hack (silicon or epoxy filled Jbox), suggest to take a few photo's, offsets (yes more than 1) from a permanent point/s and depth to accurately locate it for the next time...if there is one.

    The last couple of years I've also added a physical marker using a simple length of 20mm orange conduit from the item of interest underground to the ground surface. Been a couple of times I was looking for something and was out by just a shovel width. and simply a wider scrape of the area and found the orange marker pipe saving a bit of digging...particularly when some areas have had 300mm or more of additional fill applied post install of the underground asset but no update of the detail captured on the depth - eg: 100mm inspection cap, water tee joint to extend one day etc etc

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