Electrical cable to the new shed. Sparkies?

I want to install a sub board in a shed 120m away from domestic premises in a rural residential area.
The cable run would be 120m from board to board.
The supply to the house is 2phase rural. (phases are 180° apart)

On the sub board I want to have one lighting circuit & 3 power circuits.
The maximum on the lighting circuit, including fans would not exceed 2400watts (10amps) with everything on at once.
The maximum on the power circuits would not exceed 6Hp in motors at once, allow 4800watts (20amps).

The cable will be in a conduit underground for 110m.

It would be best if we could run both phases to the shed & split/balance the load across them.

My question is ‘what cable do I order?’

I want to dig the trench & lay the cable & conduit & then have a registered sparky finish the job.

If I do the dirty work, I can afford to spend more money on the cable.

Any help would be appreciated.

PS. I don't need a lecture about the dangers of electricity.:rolleyes:
I've been working with it for 28 years. ;)

Cliff be very careful with high voltage power, it can be very dangerous.
Best left to a sparkie.

Al :D

I would recommend organising a sparkie first, make sure that he is willing to let you lay the cable and get his recommendation on size. For a run of 120m I would reckon that the cable would have to be fairly substantial.

thats a lot of diging. good luck, sparky will be happy with you doing the durty work.

G'Day Cliff,
The SAA Wiring Rules is at work :(
can find out to-morrow:)
Might I suggest you run it past the Sparkie who you are going to get to finish it.
See what he wants$$$$$$$$$$$$$$$$$$$$$:D
Over that distance some might go up the next size if things are close to the current limit.
You can run it in Circular, in Conduit, Building wire in Conduit; what else:confused:
Won't be Cheap.
It will come down to whoever signs the dotted line:eek:

Well as I see it, Cliff just wants to dig the trench and lay the cables He didn't say any thing about connecting it up.

Cliff

AS3000 says that on Final Subcircuits the whole load has to be taken into consideration for the maximum concerned. The fact you are placing it over two phases means that is only half each for each phase. So you need to calculate the total wattage and allow half for each phase.

So cable has the following maximum loadings
2.5mm2 = 4800watts protected by a 20amp circuit breaker
4.0mm2 = 6000watts " " " 25amp circuit breaker
6.0mm2 = 7680watts " " " 32amp circuit breaker
10.0mm2 = 9600watts " " " 40amp circuit breaker

The other thing you have to allow for is voltage drop because of the distance over 25metres.

The trouble is there is so many variables it would be better to ask the lecky what size cable and and conduit or go and buy AS3000 you cand download it from Standards Australia for about $90. Go here

http://www.standards.com.au/catalogu...AS778112015227

G'day Cliff,

As Barry said, there are a heap of variables here so I'd be hesitant to recommend a cable size in case you bury it and then the sparky refuses to connect it because he reckons it's wrong. I'd get quotes from a couple saying you'll be laying the cable yourself (believe me, most'll be more than happy not to have to do the dirty work) and get them to give you the cable size.

When you're digging the trech, the SAA wiring rules state that you have to have at least 500mm cover to the top of the conduit, you have to use heavy duty 'orange' conduit and each supply must have 100m spacing from other services. That's a heap of digging :eek:

Have fun :)

I've got the rules....
I know the colours...
I know the dept....
I know the wire sizes for currents...
I just can't figure out what I need to use over that distance.

I got a quote, the bloke mumbled something about 35Amp cable & the prieck didn't show up when I had a ditch digger on site for plumbing work so F$%K him, he misses out.

I'll get the ditch digger out again & I'll do it myself.

Looks like you will have to read the rules and work it out. Two runs of conduit and use building wire you may have to get some special rolls as standard is only 100 metre rolls as you can't make buried joints, although a mate of mine used to put a junction box in the middle of a run, join the cable with connectors and fill it up with silicone to keep the moisture out.

You can get the formula to calculate the voltage loss from the rule book. Conduit comes in 4 metre lengths. You will need about 62 to 63 lengths. Going to be xxxxxxeeee.

Cliff,
will ask sparky next door as soon as I see him. He works for Ergon now, travels around testing equipment, often gone for a few days at a time.

Mick

The conduit is the cheap bit....
You can get 3 bits of the new building wire down a single 25mm conduit & 5 down a 40mm no sweat so that won't be a problem. (shame about the heat:rolleyes: )
I was hoping for something BIGGER! :D

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Originally Posted by journeyman Mick

Cliff,
will ask sparky next door as soon as I see him.....

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Ta.

I'm coming to see you as soon as I find some good legs. :confused:

Well, when it comes to bathroom cabinets, I'm a leg man, have you ever seen good boo..... Oooooo yeah, I remember now....:rolleyes: ... but they weren't permanent. ;) (& the mirror did funny things to them :o )

We want a bathroom cabinet that is up off the floor & all the legs that we have seen so far a CWrap with a capital CW.
I'm going to try Lincoln Sentry tomorrow

Cliff,
didn't you like any of the legs at Wood's? (Cnr of Scott & Doyle Sts) They might also have other models they can order in. So might Lincol Sentry for that matter but I've been pretty unimpressed with their service to date. Spend a bit of money with them but they haven't got any catalogues (out of print for over a year) and don't keep much stock. I've had problems getting a partiular product as they don't always keep it in stock. Faxed an order in to them a week prior last time to find that it was still in the fax tray!:mad: They obviously don't want my business. End rant:o

Mick

Quote:

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Originally Posted by journeyman Mick

Cliff,
didn't you like any of the legs at Wood's?

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Nah.

Quote:

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Originally Posted by journeyman Mick

...Lincol Sentry...I've been pretty unimpressed with their service to date...

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You couldn't complain about their service, they wouldn't know what you were talking about. :p

They are THE rudest people in Cairns. Full Stop. :mad:

I looked at Bretts in Brissy when I was there & I've looked in Woods & Bunnies here in Cairns.
Bretts & Woods have the same stuff.
I don't know what Bunnies have 'cos whatever it was, it's out of stock. :rolleyes:

The reason that Lincol Sentry are on the end of the list is 'cos I've got no where else to go now. :(

Hi Cliff, Not a real easy question you have there. The first step is to determine the maximum demand.

Lights = 3A for 1 to 20 light points
socket outlets = 10A for 1 to 20 outlets
motors = 100% of highest load and 50% of remainder

Lets assume you arrive at 30A. It probably is easiest to put this on one phase only because of the small load and simple twin and earth run.

The 3 factors determining circuit length and size are:
1. maximum demand (ie current carrying capacity) (not likely to be limiting factor in such a long run)
2. Voltage drop (pretty important here)
3. Short circuit temperature

Most of this is in AS 3008 1.1 (electrical installations - selection of cables - Australian conditions for up to 0.6kV)

Basically 2.5mm2 buried in conduit has 31A current carrying capacity
and 4mm2 has 40A current carrying capacity.

The voltage drop for 120m of 2.5mm is about 29V and for 4mm is 18V (both way over the 5% limit allowed)

I would try to accurately work out the maximum demand and then run through the calculations to see if you can get away with a single run of 4.0mm twin and earth in conduit.

Cheers
Pulse

Happy to help more if needed...

I had a quick look through the book at 10mm2 (plenty of current capability) cable using one of the tables that says it has a volt drop of 3.59 mv/am (Vc) the formula is Vdrop = Length X current X Vc / 1000.....so assumming 30 amps max demand (as pulse has worked out) 120X30X3.59/1000 = 12.924 which is just over the 5% (12V) allowed. If the Max Demand was 27 amps or less then it would come in under 12 volts. I think 4mm might be a bit light on and as you say you can spend more on the cable if you do the dirty work your self...size does matter here :cool:.

My suggestion to you is to get your local sparky who will eventually finish & sign off on the job to work it out properly for you. Also ask about your load sharing, I'm not sure you can do it over 2 phase rural (basically 2 X 240 1 phase not 415 between them) because it can't be balanced so the neutral will take all the load anyway. I've been in industrial work too long to really know what I'm talking about with this though :o

Reg

I'm pretty sure you can't balance 240v rural. MAybe Cliff isn't talking Country power which by its definition is not as flashy as city power, but ultimately more diverse and practical.

In light of this I have an extension lead, 1.5mm, plug is a bit ratty and a few bare wires if it helps Cliff. :D

G'day.

Cairns sparky who does big jobs has said to go for 10mm² 3phase neutral & earth circular through a 40mm HD conduit.

It won't be cheap but I won't have problems running what I want & I'll have a spare core if I need more power.;)
It's going to be about $950 for cable & conduit & $140 for a ditch digger for the weekend. That's heaps cheaper than the original quote I got.
Mind you, I've seen the cable & it going to be like wrestling with a python to get it in the conduit & in the ground. :rolleyes:

The Rural 2 phase is done with a centre tap pole trany on a SWER line.
It gives you 2 phases 180° out of phase so if you load up both phases, hardly any current needs to flow in the neutral at all. If one phase only is being used, the whole load goes via the neutral.
If I put the lights on one phase & the most commonly used tools IE Lathe & dust extracter, on the other, that will share the load that is on most of the time. That's what I'm on about with trying to balance the load across the phases.

Thanks all for your comments.

Cliff,
This may be of help. There is a calculator at the bottom of the page.

http://www.powerstream.com/Wire_Size.htm

Oh, in the calculator, our 240 volt single phase is what I believe someone here referenced as two phase.

Cliff,
I dont know how you figure it over there, but in the states, its boils down to this, 30amp underground cable is one thing, and yes you would need to consider voltage drop @ 120 meters , then next up amperage cable readilly availably is 60 amp underground cable or ( #6/3 uf ) as we call it and voltage drop wouldnt be an issue as money for any thing inbetween those two sizes would be nonstandard in the states and cost a fortune. We go from 30 amp cable to 50 amp indoors and from 30 to 60 underground, is it not the same over there?


8

Cliff,
I was by no meaning trying to tell you not to figure for the drop in voltage , just giving you a rule of thumb, If you wish to calculate it , I found many online sites that will do it for you if you know the specifics of the wire you plan to use, a guide to figuring it can be found at http://www.tycothermal.com/assets/No...-DROP-0901.pdf

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Originally Posted by Cliff Rogers

G'day.


It's going to be about $950 for cable & conduit & $140 for a ditch digger for the weekend. That's heaps cheaper than the original quote I got.
Mind you, I've seen the cable & it going to be like wrestling with a python to get it in the conduit & in the ground. :rolleyes:



Thanks all for your comments.

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Cliff as far as putting the the cable in the conduit, just lay the cable out full length of your ditch but not in the ditch then start at each end and run each length of conduit on the cable to the centre and glue it as you go. Pulling a single length of conduit at a time over the cable is easy. When finished just tip the conduit into the ditch and cover it.

Why not use single insulated building wire instead of round cable. Building wire should be heaps cheaper than round cable and you can run your extra conductor at the same time to use later if need be.

Quote:

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Originally Posted by Barry_White

Cliff as far as putting the the cable in the conduit, just lay the cable out full length of your ditch but not in the ditch then start at each end and run each length of conduit on the cable to the centre and glue it as you go. Pulling a single length of conduit at a time over the cable is easy. When finished just tip the conduit into the ditch and cover it.

Why not use single insulated building wire instead of round cable. Building wire should be heaps cheaper than round cable and you can run your extra conductor at the same time to use later if need be.

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I had the conduit trick covered, ta.:)

Does single insulated building wire come in 10mm²?

You can get building wire in 10mm, but the sparkies I spoke to when I was running the cabling for my shed all advised against it. Apparently not so good around here as there's been cases of ants eating the insulation and wires shorting. Maybe just a very localized thing though.

Mick

There were a stack of houses build out at Clifton Beach in the '90s when underground power became trendo up here that went the same way.
The bloody ants ate all the insulation on the stuff in the ground.

I know that the orange stuff on the circular is much stronger than the white poop on building wire.

Mine might cost more but it'll be there when 3 phase comes up our road. :D

And dont forget...

Dial 1100 before you dig! :p :p :p :D

I did the 'dial before you dig' bit a while back. :D
Telstra send you a map of approx where they think it is, (very rough) & a list of registered cable finders in the area & tell you to hire the cable finder.

The only thing out the back near where I'm going to dig is my water line from the dam & I know where it is. (famous last words... I've mowed it before today. :rolleyes: )

We went through this a couple of years ago. The dial before you dig sent a map. It was the wrong one, scaled to such proportions it would easily show the line from Melbourne to Brisbane. Really helpful.

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Originally Posted by outback

We went through this a couple of years ago. The dial before you dig sent a map. It was the wrong one, scaled to such proportions it would easily show the line from Melbourne to Brisbane. Really helpful.

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That's a bit crapola!
And at what cost did they flog this less than useful service off at?

On the subject of burried lines, in the states we had so much trouble with that, that they took the maps away from the utility companies and hired it out to a company call OUPS in my state, Ohio Utility Protection Services, they come out paint lines on the ground for you where not to dig with a bit OUPS on top , then send the bill to the correct utility company they just saved from you cutting the cables or lines. That anonym to me is a bit comical. OUPS ......


8

Just think of the benefits of the ones you cut into this time... You can mark them for next time.

We had the RADAR cable in Butterworth (Malaysia) not only dug up but lifted up so high that it snapped. An 8 inch lead sheilded cable. Had to get the Poms out from England to fix it then we had to pump it full of Nitrogen every week thereafter. In order to do that you had to first remove the Vipers and Cobras from the cable pit.

I had power run to my shed 110m from the mains junction box.

Just two cables were laid around 10mm2 each, at a guess, in orange conduit.

This was to power my shed but also my house if I ever build one.

No earth cable is run along the ditch, just connected at the shed.

Not sure how many cables you are running to your shed?

As for the ditch digger pray for no rocks, big or small.

I hired the dingo digger with ditcher attachment; the rocks would derail the chain, a pain in the ass to put back on.

You must decide on the depth as you go, for going back to correct is not easy.

I think this is something I should have looked more carefully at, as I would hate running more cable just for the house.

Once again it comes back to very little information available, books on electrical wiring:rolleyes: .

It sounds like you have a hell of lot more of an idea than I do.

Good luck

Pulpo

Cliff,
Is the EARTH Wire required?
Can you get away without it,
and put down an EARTH Steak.....................OK!!!!! I know Stake:p :p
Something to chew over:confused: :o

Quote:

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Originally Posted by Pulpo

I hired the dingo digger with ditcher attachment; the rocks would derail the chain, a pain in the ass to put back on.

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Did you have to pedal backwards to get the chain back on?? :p

Al :D

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Originally Posted by Pulpo

...No earth cable is run along the ditch, just connected at the shed....

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Quote:

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Originally Posted by Ivan in Oz

..Is the EARTH Wire required?....

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That was the old way of doing it but it seems that they don't like multiple earth systems any longer... they want a single earth connected at the first switchboard. :(

In your case Pulpo, your shed may have been the first switchboard.

How did you go Cliff?

Now I've had to go through the exact same exercise and I thought I would share the info I have obtained.

For building wire General Cable's website have published the ratings for their cables which are taken from AS3008. Here's the link to the PDF for single core cables you are looking at.

http://www.generalcable.co.nz/Austra.../4.1.2.1.6.pdf

They also have the multicore cable specs as well but they all start at 25mm2 for this supplier at least.

The thing that seems to have been overlooked is the fact that you already have a run from the supply to your house. Have you calculated the length of that run and the voltage drop for that distance? I have a 100m run to the meter box so Im using 25mm2 mains which will give me 74.53A per phase over that distance.

The formula is just a variation of that posted earlier. That is

A= 12 (being the 5% of 240V allowed) / (mV/Am / 1000) / length of run in metres

As an example the loss due to the resistance of 16mm2 wire is 2.95 mV/Am

For your run of 120m, 16mm2 wire will give you 33.89A

This is before you add in the length of run to your house. Depending on what is supplying the house, you may need to up the size of the wire or worse still the mains supplying the house.

Remember that this info has all been relayed to me Cliff. I trust that the sparkies on the forum can clarify whether this is accurate.

Quote:

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Originally Posted by boban

How did you go Cliff?....

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10mm² 3phase neutral & earth circular through a 40mm HD conduit.
It is in the ground but not connected at each end yet.

I take it your house is not too far from the supply

Yeap, the cable I put in is from my house to my new shed, 120M run.