Electrical cable to the new shed. Sparkies?

[Cliff Rogers]

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.
I've been working with it for 28 years.

[ozwinner]

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

Al

[Wood Butcher]

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.

[Gaza]

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

[Ivan in Oz]

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$$$$$$$$$$$$$$$$$$$$$
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:

[Barry_White]

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

[Gibbo]

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

[Cliff Rogers]

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.

[Barry_White]

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.

[journeyman Mick]

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

[Cliff Rogers]

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 )
I was hoping for something BIGGER!

[Cliff Rogers]

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

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.... ... but they weren't permanent. (& the mirror did funny things to them )

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

[journeyman Mick]

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

Mick

[Cliff Rogers]

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

Nah.

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

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

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.

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

[Pulse]

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...