Steve
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Post by Steve on Feb 23, 2022 16:35:52 GMT 12
Do we have any registered sparkies on the forum? I'm just going through trying to organise power to a second dwelling from a 63A feed at our gate. I've got multiple paths I can take to the granny flat - shortest is probably 45m, easiest compromise is about 55 (and includes digging up the lawn  ) and the preferred would be about 75m if I follow the intended driveway. I've calculated I won't get away with 16mm neutral screen, which is a bugger because I have a drum of it - so 25mm? I don't think the 25mm will do the longer path, but I think it should do the shorter two ok? And I'm planning to direct-bury it - I was told by someone who didn't seem all that certain that I needed a 700mm trench, with 100mm of bedding sand at the bottom. I've also been told I can then lay 150mm of fill, then danger tape and phone line at that depth, then fully backfill it - does that sound right? I know I could just hand this all off to a sparky, but the granny flat is starting to suck the available fund-pool dry so I want to do as much myself as I can, without doing something that just needs to be undone again later to be done properly. Speaking of sucking funds - has anyone ever been forced to deal with the RMA to get a driveway in? I'm facing a $26k bill to lay down a small trapezoidal shaped piece of grit seal between the road edge and my fence that I am pretty sure I could do for about $1000 if the council hadn't gotten involved. I'm very VERY  annoyed over that. And when you try to talk to them about 'common sense' they just shut you down with 'thems the rules' statements. Engineers from multiple disciplines, multiple inspections, clegg hammer tests, culvert pipes, concreting, STMS traffic management plans (we're talking a rural road with maybe 40 vehicle movements a day)... its doing my head in. Anyway, rant over  Cheers, Steve |
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Post by Radiotech on Mar 1, 2022 0:28:11 GMT 12
If you are just feeding a granny flat, you may be able to sub-main it from your existing dwelling.
What is the total loading you have worked out?
Will the granny flat have a full size oven and electric hot water heating?
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peter
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Retired, collector of vintage radios and test equipment for restoration and repair.
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Post by peter on Mar 6, 2022 22:05:04 GMT 12
'I was told by someone who didn't seem all that certain that I needed a 700mm trench, with 100mm of bedding sand at the bottom. I've also been told I can then lay 150mm of fill, then danger tape and phone line at that depth, then fully backfill it - does that sound right?'
Sounds bang on - it's what the sparkys did at my place to bury a mains cable to a garage up 124 steps from the house - ran the cable from the trench at both ends inside white conduit tubing into my garage and up to my house fusebox.
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Steve
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Post by Steve on Mar 7, 2022 8:15:11 GMT 12
If you are just feeding a granny flat, you may be able to sub-main it from your existing dwelling. What is the total loading you have worked out? Will the granny flat have a full size oven and electric hot water heating?
It could be run as a sub-main and that would have been cheaper but we want it separate and on its own meter - I'm trying to divorce the granny flat from the house as much as possible... mainly so the old folks can feel like its their own place - which it essentially will be.
Realistically it will probably survive happily on waaay less than the 63A circuit its getting but if we ever put a barn or workshop over there I want to know it can handle a decent set of machine shop equipment and power tools without causing issues.
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Steve
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Post by Steve on Mar 7, 2022 8:17:01 GMT 12
'I was told by someone who didn't seem all that certain that I needed a 700mm trench, with 100mm of bedding sand at the bottom. I've also been told I can then lay 150mm of fill, then danger tape and phone line at that depth, then fully backfill it - does that sound right?' Sounds bang on - it's what the sparkys did at my place to bury a mains cable to a garage up 124 steps from the house - ran the cable from the trench at both ends inside white conduit tubing into my garage and up to my house fusebox.
Peter, I've walked up (ALL of) your steps - I feel sorry for your sparky  I needed a rest stop on the way... |
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Post by Radiotech on Mar 14, 2022 13:36:08 GMT 12
It could be run as a sub-main and that would have been cheaper but we want it separate and on its own meter - I'm trying to divorce the granny flat from the house as much as possible... mainly so the old folks can feel like its their own place - which it essentially will be. Realistically it will probably survive happily on waaay less than the 63A circuit its getting but if we ever put a barn or workshop over there I want to know it can handle a decent set of machine shop equipment and power tools without causing issues. Ok, that's understandable. Whoever advised you on the 700 mm trench with sand and backfill etc was telling you the truth. Service main must be 600 mm down, so 700 with 100 mm of sand (to stop any rocks etc puncturing the cable) then some danger tape and backfill. If you want to add a phone line in the same trench, yes you can bury that in the same trench. Normally a trench that is 600 deep and 400 wide is dug and the phone conduit is laid on one side and power on the other so they are the same depth but separated horizontally. In any event the Telco cable must be 400 down if the surface is not protected or 300 down if it is protected by a concrete cover. |
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Steve
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Post by Steve on Mar 14, 2022 13:55:38 GMT 12
Thanks for that - yep that gels with what I was told... although I went for vertical spacing because its easier to dig a narrow trench in the rock hard clay out our way than it is to dig a wide one.
So, yesterday Dug and I dug the trench.
Then Dug got sick
I fixed him (booty-fab bush mechanic style)... he didn't like that, so while I wasn't looking he took a bite of our phone line... |
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Post by Peter Walsham on Mar 14, 2022 14:17:28 GMT 12
Hi Steve
Just make sure that your sparky (or any sparky) sights & 'signs off' your cable (making sure it's the heavier walled cable if direct burying it) & trenching - If it's not signed off you might have trouble getting it connected.
I am a retired sparky and, unfortunately, wanted to advise you, but I am unsure of the current codes of practice - but, I believe, the 'COP's' differ between a mains cable & a sub mains cable. The mains cable may be considered 'electrical works' where a sub main cable is considered 'electrical installation' (both have their own rules & regs.)
Also, another point to consider: A cable sheathed in XLPE will last a lot longer buried than a PVC sheathed cable. XLPE is also tougher.
However, don't quote me on this, as I may be wrong. I have been out of contracting for more than 10 years.
Peter
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Steve
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Post by Steve on Mar 14, 2022 15:14:08 GMT 12
Thanks for that Peter. I'm letting my electrical contractor deal with that side now... They are specifying the cable and hooking it up.
I was originally trying to do it as cheap as possible but decided it would be better to let someone who doesn't need to get their advice from the internet do it 😂
I think we'll all sleep better at night this way...
I've learned a bit though... It's interesting, the calculations for the cable even take into account things like the typical ground temperatures in different locations as part of the cable cooling under load.
Cheers, Steve
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Post by Peter Walsham on Mar 14, 2022 15:45:41 GMT 12
It can be very interesting. Doing cable sizing calculations for domestic cables buried in insulation was quite challenging.
I totally understand where you're coming from regarding wanting to save costs - but saving money often comes at a higher cost later anyway. Dr Google, unfortunately, has a lot of 'experts' (and much of it is well meaning), but a lot of the information is based on 'fantasy' rather than facts. Many years ago, I was asked to sign off a house wire that the home owner had wired himself. Totally against my better judgement, I gave in & went to look at the job, but I quickly decided that I didn't want to become involved, as the job was generally untidy. It was a hell of a battle to get away from the address afterwards, as a family member had blocked me in! As luck (for me) happens, the house burnt down not long after, and the cause of the fire was deemed to have been caused by a join in the mains cable, which had overheated, buried inside a wall, where I wouldn't have ever been able to see it. The join was done with strip connectors & taped up. No amount of 'normal' electrical testing would ever have shown up that. Thank god I hadn't put my name on the piece of paper, as the onus would have come back to me.
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) and the preferred would be about 75m if I follow the intended driveway.
annoyed over that. And when you try to talk to them about 'common sense' they just shut you down with 'thems the rules' statements. Engineers from multiple disciplines, multiple inspections, clegg hammer tests, culvert pipes, concreting, STMS traffic management plans (we're talking a rural road with maybe 40 vehicle movements a day)... its doing my head in. Anyway, rant over 
I needed a rest stop on the way...
