3 phase power to my Shed!

[simonl]

Hi all,

With a few financial goals ticked off in the last few months, I'm looking at options wrt supplying power to my shed. SWWMBO has even offered to make it my birthday present, including 3 phase if it's indeed doable. Until a couple of weeks ago, I had envisaged running single phase to the shed from the house. ATM we only have single phase at our house. Recent purchases and potential future purchases have made me look at the possibility of supplying 3 phase to the shed. I did have the option of connecting 3 phase to the house but the builders wanted an extra $2500 for that luxury and at the time I figured I would never need it! :doh:

So far everything is looking promising. There is definitely 3 phase in the power pit. I have a couple of mates who are sparkys, and while they have not looked at the setup, they seem to think it is doable. There is one stumbling block that I can see however, from the power meter, the power needs to somehow get from one side of our (concrete) driveway to the other. There is a piece of 100mm sewer pipe that goes from one side of the driveway to the other side to facilitate running services without digging up the driveway. I have excavated and exposed it to find that the plumbers have used it to route the polypipe for water supply to the house through it. Where do I stand wrt now routing some orange conduit through there? Its about 3M in length and so the power will be running next to the water for about that length.

I'm just trying to establish as many facts as possible before spending any money :U Also what sort of circuit should I consider to be sufficient for my needs? The shed is about 100M from the power meter. While I'm not qualified to make these decisions/calculations I have used an online calculator to work out some basics. 16 sqmm 3 phase cable should be able to provide about 40A (allowing a maximum of 5% voltage drop) maybe even 48A or so. I can't see that I will EVER draw that amount of current, since I never operate more than 1 or maybe 2 tools at any one time. Even if I was to purchase a machine tool that required say 5 HP, it would not go near that. Bearing in mind that I am not setting this up as a commercial venture, it's purely a hobby and will remain that.

Will 40A do?

Cheers,

Simon

[Uncle Al]

Being far from an expert in these things, I believe that your 48 Amps from 16mm cable is 'per phase'. Dunno how many horsepower that equates to on a lathe or mill, but would be absolutely heaps for a home workshop.
I have 10mm 3 phase cable to my shed which is about 30 metres from the meter box, and have no problems with hobbiest sized lathe and tablesaw, dusty etc.
As for running a conduit next to a water pipe, again speaking from a non expert point of view, there shouldn't be a problem.
I'm sure someone with an electrical trade background will soon join in and enlighten us all.

Good luck with your project,
Alan...

[bob ward]

Where we are, the house is 70m back from the road and my shed is another 80m back from the house. When I went to extend the 240V from the house to my shed I was advised by the electrician that because of voltage drops over those distances I first had to upgrade the cables to the house.

Given that I was going to have to trench from the road to the house to the shed and lay new cable from the road to the house to the shed, installing 3 phase while I was at it was a no brainer. The extra cost for 3 phase was 2k, which covered the 4 core cable, a 3 phase meter board at the house and a 3 phase sub-board in the shed.

Well worth it I reckon.

[Young Flyer]

I agree with above comments. If you intend to run 3 phase to the shed your should also upgrade the house and meters at the house, then extend 3 phase from your main switchboard to the shed sub-board.

Admittedly this is no cheap job, but well worthwhile. I have achieved the above over several stages including installation of a 12KW Grid Connect Solar System on my shed roof. The whole process included upgrading the street supply lines to 25mm2 so there should be no limitations on future additions. The Shed is supplied with 3 phase on 16mm2 underground cables.

BTW in Queensland (probably Victoria too) all underground power must be a minimum 600mm below ground & marked above ground if longer than acertain dimension (sorry can't remember that bit from 3 years ago).

OTO if you find the cost too great to do all the above. You can still send single phase to the shed subject to the limitations of the house load calcs and your street connection. Don't forget VFDs are now reasonably priced so as long as you have the single phase capacity 3 phase machines can be driven off single phase via VFD. I have just had a VFD installed to drive a 5HP DE. Due to the soft start capability of VFDs the max current draw is much lower. For my situation although I have 3 phase to the shed, single phase + VFD was a better solution.

[simonl]

Thanks Alan, Bob.

The house is on a battle-axe block with the house about 60M from the street. Power cable to the house from the street is 35sqmm cable and so should not need upgrading. At the time of building I thought that 35 sq mm cable was a bit over the top but a sparky mate said that cable size was based on providing power to other parts of the block and not just to the house.

The power meter is not at the house but at the entrance to our driveway in a pillar. The pillar is about 2M from the power pit. There is a sub panel or a distribution board on the house.

What I propose is to run new 3 ph cable from the street to the pillar (about 2M in distance) and upgrade to 3 phase meters. The power for the shed will run direct from the pillar to the shed, bypassing the house. So, the shed will have 3 phase but not the house which may be an odd situation but not a big deal as far as I can see.

Well, this is my cunning plan at this stage. If I run into a hurdle or it costs way more than I can justify then I will revert back to the original plan and run single phase from the house to the shed.

Cheers,

Simon

[simonl]

I agree with above comments. If you intend to run 3 phase to the shed your should also upgrade the house and meters at the house, then extend 3 phase from your main switchboard to the shed sub-board.

Admittedly this is no cheap job, but well worthwhile. I have achieved the above over deveral stages including installation of a 12KW Grid Connect Solar System on my shed roof. The whole process included upgrading the street supply lines to 25mm2 so there should be no limitations on future additions. The Shed is supplied with 3 phase on 10mm2 underground cables.

BTW in Queensland (probably Victoria too) all underground power must be a minimum 600mm below ground & marked above ground if longer than acertain dimension (sorry can't remember that bit from 3 years ago).

OTO if you find the cost too great to do all the above. You can still send single phase to the shed subject to the limitations of the house load calcs and your street connection. Don't forget VFDs are now reasonably priced so as long as you have teh single phase capacity 3 phase machines can be driven off single phase via VFD. I have just had a VFD installed to drive a 5HP DE. Due to the soft start capability of VFDs the max current draw is much lower. For my situation although I have 3 phase to the shed, single phase + VFD was a better solution.

Thanks, you posted this while I was typing. I have been informed that power must 500mm in ground (top of the conduit) and in fact if it is buried deeper then it's current carrying capability must be downgraded. Running new cable to the house is certainly not an option. There is an established garden, retaining wall and 400 sq M of concrete driveway over the top of it! In any case, given the above circumstances I think I have it covered without disturbing power to the house…….. I hope!

VFD's certainly provide (some) options for people with single phase but it is certainly not a be all end all replacement to 3 phase. I am currently running 3 VFD's (soon to be 4) but 3 of the 4 are used for their variable speed properties. However, buying a 3 phase machine to run on single phase can get a lot more complex than simply using a VFD. Changing from star to delta is probably as simple as a conversion can get. The last few weeks I have been looking at SG. Some have been quite simple, manual machines but some I have looked at are hydraulic with auto feed. Try running that on single phase with VFD! I'm sure all the hydraulic valves and switchgear will all require 380/415 which is not going to happen without some major modification, least of all a VFD that will need to be rated to 4HP! It's not just a matter of setting the ramp up times to 5 seconds or so to reduce currents.

Simon

[Ropetangler]

Simon, IIRC in Tasmania the rules were and maybe still are that if you are adding a heat pump for home temperature control, the 3 phase connection was much cheaper. It was explained to me that all I had to do was say that I was going for a 3phase heat pump, and the connection would be made for say $1500, (I'm not sure of the correct amount now, but we'll say 1500). If however I had no plans for a heat pump, but just wanted to run a 3 phase sawbench or any other machine tool, compressor, welder etc. it would cost what ever it cost them to install it, which could be anything if they had to run the extra line a few kms for example, and I would have to pay for the transformer, with any subsequent customers connected to that transformer getting a free ride.
From what I understand to be your situation, the 3 phases are available, but just ask your Sparky mates if you need to have some domestic 3 phase item in order to qualify for a cheaper connection cost, - it may still be cheaper to connect 3 phase to the house, even though you have no need for it, except to qualify for cheaper connections.
Another route may be to build a rotary phase converter, and run all your 3 phase stuff off the one device with just a decent single phase incoming supply. Good luck whichever way you choose to go,
Rob

[simonl]

Simon, IIRC in Tasmania the rules were and maybe still are that if you are adding a heat pump for home temperature control, the 3 phase connection was much cheaper. It was explained to me that all I had to do was say that I was going for a 3phase heat pump, and the connection would be made for say $1500, (I'm not sure of the correct amount now, but we'll say 1500). If however I had no plans for a heat pump, but just wanted to run a 3 phase sawbench or any other machine tool, compressor, welder etc. it would cost what ever it cost them to install it, which could be anything if they had to run the extra line a few kms for example, and I would have to pay for the transformer, with any subsequent customers connected to that transformer getting a free ride.
From what I understand to be your situation, the 3 phases are available, but just ask your Sparky mates if you need to have some domestic 3 phase item in order to qualify for a cheaper connection cost, - it may still be cheaper to connect 3 phase to the house, even though you have no need for it, except to qualify for cheaper connections.
Another route may be to build a rotary phase converter, and run all your 3 phase stuff off the one device with just a decent single phase incoming supply. Good luck whichever way you choose to go,
Rob

Hi Rob,

Thanks for the insight. Yes, a RPC is another option for me. One of the members here (Harty) showed me one that he has, made from a 3 ph motor and an old 3 ph arc welder. Connected to a 15A power supply, it could produce enough power for probably most, if not all my needs. That will definitely be my backup plan if I need to run a machine with switching/sequencing gear like a surface grinder with auto feed.

Look, in all honesty I'm just happy to be getting power to my shed, instead of running 2 extension leads from the house. It's been quite restrictive TBH but I have until now worked around it. BUT, if I can have 3 phase for a bit of extra cost and maybe some hard work then I have a crack!

Cheers,

Simon

[Ropetangler]

I know what you mean with using an extension cord /s Simon and real 3 phase is the best if it is realistically possible, lets hope that it is no big drama in your case.:2tsup:
Rob.

[bob ward]

Look, in all honesty I'm just happy to be getting power to my shed, instead of running 2 extension leads from the house.......

That sounds familiar. At the end of 80m of extension lead the air compressor could only start up when the tank was empty, and the welder was a bit feeble.

[Young Flyer]

Simon,
Undertand your more detailed description of your power connections.

Yes you have an unusual situation, it all depends on the 3 phase equipent you want to connect and your projected maximum load in the shed.

Like others have said,it was definitely cheaper for me to combine Solar Power install & the three phase upgrade; but still an expensive exercize. BTW the Solar system now contributes a total $9,000p.a. to our budget.

As stated I have 3 phase to the shed, but for a 5HP DE (Delta) a 5KW Powtran VFD was definitely the easier and more efficient option. I'm currently converting my simple 100mm flex hose connected 3HP DE to fully ducted 150mm PVC, including a vent system. This will soon be ready for a custom BP Cyclone which will be vented outside.

I was fortunate to have expert advice from both the Guru BobL and local cabinet maker WWF member John Samuel. Both have enthusiasticly contributed to this major project in my timber boat building workshop.

[simonl]

Simon,
Undertand your more detailed description of your power connections.

Yes you have an unusual situation, it all depends on the 3 phase equipent you want to connect and your projected maximum load in the shed.

Like others have said,it was definitely cheaper for me to combine Solar Power install & the three phase upgrade; but still an expensive exercize. BTW the Solar system now contributes a total $9,000p.a. to our budget.

As stated I have 3 phase to the shed, but for a 5HP DE (Delta) a 5KW Powtran VFD was definitely the easier and more efficient option. I'm currently converting my simple 100mm flex hose connected 3HP DE to fully ducted 150mm PVC, including a vent system. This will soon be ready for a custom BP Cyclone which will be vented outside.

I was fortunate to have expert advice from both the Guru BobL and local cabinet maker WWF member John Samuel. Both have enthusiasticly contributed to this major project in my timber boat building workshop.

Thanks. Sounds like you have a great setup. Boat building always brings up bitter/sweet memories for me. My Dad spent 17 years building a yacht. Being the only son in the family, who do you think was expected to help him on my weekends? :~

It was a Bruce Robberts Spray, 40 ft steel hull. Over-engineered and well built for ocean going. Biggest trip he did was from Mordialloc to refuge Cove and back. He was in his late 60's when he did that. I think he spent so much time building it that when it was launched and finished, he didn't know what to do with himself. Go figure!

Simon

[BobL]

When I extended my shed in 2011 I decided to upgrade the shed power supply.

Our house has only single phase and as at the time we were supposed to be getting underground power and meter upgrades in our street within 12 months I was going to wait for that to connect the house to 3P but decided, while the sparky was upgrading the shed power to run 3P wiring from the house to the shed (50m run).

I already had a 20A SP line to he old part of the shed but the conduit was too small for the 3P wiring so I just left the 20A line in place and dug a new trench for the bigger 3P wiring/duct and ended up with a 40A SP connection in the new part of the shed.

Now in 2014 the underground power upgrade in our area has been suspended. Meanwhile I've installed 5 single to 2 phase 240V VFDs on machines in my shed, 3 x 1.5kW, 1 x 2.2kW and 4kW. Only the latter, which drives a compressor, is not used for speed control.

As my shed is small and full, the likelihood of shoehorning a big 3phase machine into it is looking vanishingly small and am now wondering whether I really need 3Phase. About the only reason I would like to have it now is to be able to test 3Phase motors on full 415V 3phase.

In terms of power draw, my highest power draw at any one time is
- while woodworking: using my 3HP table saw and 3HP DC and the 5HP compressor kicks in. I have the table saw running on the 20A circuit and the other 2 on the 40A line so its no problem.
- while metal working: when using 15A welder / plasma cutter I use a 1/3rd HP squirrel cage ventilation fan and the compressor kicks in. this is all on the same (40A) line - also no problem

[Burnsy]

I ran 3 phase to my shed then wired my house circuit off my shed when I built my house. I am not sure what the difference in cable cost was but I remember it was $500 more for the meter. I now find this state of the art meter (7 years ago) is one way and if I want to put solar on my house with return to grid counter I am up for a complete new meter which from emory was a few grand - so it didn't happen!!

Back to 3 phase, I have not found the need for it but may one day so am not sorry I did it. I think if it is not a huge additional expense, it is a "nice to have option" so do it when you first wire up. After all, who wants to dig their trench as many times as Bob:o

[BobL]

. . . . . . who wants to dig their trench as many times as Bob:o

In my next life I'll be considering a tunnel so then I can just run all the services through that. :D

[simonl]

A tunnel? Now that's what you call commitment! Well, had a visit to my sparky mates place today. I said to him, how much will the cable cost to run 3 phase to my shed, 110M away from the power meter? $5 per meter per conductor. So that's 1 for each phase plus neutral and earth, 5 wires. So about $25 per meter :o Since I need 110 metres, it's more economical to run individual conductors since it's easier to buy per metre. The cost of this little exercise seems like it may be quite high! Still, I can't help think that if I don't do it when I can that I will be kicking myself long after the pain of the initial cost has subsided... Simon

[Stustoys]

Hi Simon,

Look at it this way, for single phase you'd only save $10 a meter

Stuart

[simonl]

Hi Simon,

Look at it this way, for single phase you'd only save $10 a meter

Stuart Well, sort of. I wouldn't have to go to the meter box at the front pillar, only to the house in that case which would be about 45M not 110M. Was thinking yesterday, that will teach me for building the shed shed far away from the house! Simon

[Young Flyer]

Thanks. Sounds like you have a great setup. Boat building always brings up bitter/sweet memories for me. My Dad spent 17 years building a yacht. Being the only son in the family, who do you think was expected to help him on my weekends? :~

It was a Bruce Robberts Spray, 40 ft steel hull. Over-engineered and well built for ocean going. Biggest trip he did was from Mordialloc to refuge Cove and back. He was in his late 60's when he did that. I think he spent so much time building it that when it was launched and finished, he didn't know what to do with himself. Go figure!

Simon

Ah! sounds like you suffer from an unfortunate DIY boat building experience. Very unfortunate that your father's dream project took so long, that he could not fully enjoy the fruits of his (& your) labour in his senior years. A 40ft "Spray" is a large very capable yacht, your father may have just lacked enough interested /compatible bodies to help him sail it on longer ocean voyages.

That said I was involved in a Classic Yacht regatta in Scotland last year, where a 70 y.o. Itallian sailed his 70 footer from Italy to Scotland single handed (but he had also sailed the same yacht across the Atlantic numerous times & around the world twice - all single handed!) Such a man just requires the skills, fitness and absolute committment.

I have been a competitve (small boat) sailor & spare-time boat builder /restorer for 40 years. Sadly I have heard many stories similar to yours. The fundamentals of boat building are similar, but more complex than house building. Both require good project management, facilities, skills & the right tooling.


Back to your main subject - 110M 3 ph connection to shed - suggests your Sparky has done/should do a load calculation and spec your "Building Wire" to keep voltage drop to a minimum. Also cost your 3ph switchgear etc. as that can easily exceed the wire cost.

Agree, do well it now, or regret later.

[simonl]

Thanks young flyer,

I think the majority of my fathers enjoyment was in the building of it. Most of it was built while he was fully employed at a fitter/turner so a lot of it was done on his weekends/public holidays (that's where I came in :(() Much of the engineering side of things was done from scratch at his work in his lunchtime & before/after work. It's only now that I realise how much I learnt from my dad during those years. I helped dad sandblast the hull and zinc spray it top to bottom, it took weeks/months and it was mostly over summer in 40 degrees. Not much fun when wearing one of those suites. I remember having to vacuum up the sand before zinc spraying, being so hot (let alone in a steel hull) sometimes your sweat would roll off onto the new steel. Dad would have a go at me saying not to contaminate the new steel! Halfway through, the diesel driven 3 cylinder compressor itself. Dad bought the white metal and hand scraped new bearing journals for it. As a young teenager that job seemed to take a "lifetime" yet in reality it probably took a week and we were back at it. Anyway, in the early 90's Dad's engineering firm closed down and he never found another job. A combination of his age and a lack of a will to find a new job meant he went from being unemployed to being retired. He worked on the boat full time until it was launched at Mordialloc Creek. He was a lost soul after that, since it consumed so much of his life and now it was done.

He managed a few sailing trips here and there, but being a grumpy old man, he found it difficult to attract any willing participants to come along to help. The yacht sat idle for a couple of years before Dad found the courage to eventually sell it. It was hard for him but once he detached himself from it, he realised it was a phase in his life that had run it's course. With the money from the sale, Mum and Dad bought a near new 4x4 and some camping gear, and did some pretty impressive major trips to Qld, WA, Tassie etc. etc.

I portray my memories of it in a negative way but nothing in life is all negative. Some positives for me are that I got my sea legs! It came at a very heavy cost though, never had I been more sick than sailing from Westernport through bass strait and into Port Phillip heads, 4M swell and I was on a ride from hell with no way off, I fed the fish the whole way. If anyone has seen the movie Team America, it was like the vomitting scene in that movie……..

But, no matter what the weather, when or where I never get sea sick anymore! :U Thanks Dad!

Anyway, enough of memory lane.

Just for the record I have an update on costs for upgrading my meter box to 3 phase power. For a standard call out fee for the truck/crew the power company will charge $124.62 and it will cover the first 30 mins. After that it will be $50.21 per 15 mins. On top of that is the cost of my electrician to do the wiring of the meter box.

So, if the job to connect 3 phase to my meter box takes 1 hour, then I will be up for $124.62 + $100.42 + Electrician for an hour. The callout fee includes the cost of the new meters.

For that price, I'm going to have 3 phase connected to the meter regardless whether or not I decide to connect 3 phase to the shed.

Simon

[rusel]

HI
I have not read all post here but I thought I would add my experience of getting 3ph to the shed.
When the electrician came and quoted me he told me the best was to run the same size cable that came in from the street which meant to be able carrier 62 amps per ph. can not remember the cross section. I ask why and he told me it the cheapest cable around as the make so much of it the for to run anything else would cost more....so I have 186 amps available in the shed...

My shed is about 6mt from the house so run my cable above ground much easier to do

R

[Young Flyer]

Simon,
Thanks for the expanded tale of boat building & sailing. I'm glad you realise what a unique experience it was to go through the sweat & tears of steel boat building in summer!

When I was 32 I had plans drawn for a 42ft centre cockpit steel ketch and dreams of doing the Pacific Island cruise to Tahiti etc. That was whilst living in Fiji for 5 years. Years later after several other postings we were back in Brisbane 3 kids in tow & a mortgage etc. etc. The quote to have the hull built escalated from AUD32k to AUD60k end of that dream.

We have chartered yachts for short cruises on holidays, since that early dream I have had several racing yachts all timber and under 6 Metres - most were self built or restored. Also for 5 years crewed off shore & coastal races as navigator on OPBs.

Now I'm about to build a 7.7M cruising Cutter to my own design. Yes it will also be trailable, that way it lives at home in my workshop and we can tow it almost anywhere without being delayed in some harbour due to bad weather i.e. 3 days to tow (north or south) from Brisbane to the Whitsundays, instead of 1 - 3 weeks on water subject to weather. Mooring, maintenace & insurance is a fraction of that required for a "hole in the water to pour money into".

Back on main topic, yes three phase connection has several advantages, particulatly if you install solar grid connect. Its much easier to spread your house load across phases, install a Tarrif 33 (reduced hours) meter & put your bedroom aircons, pool pump, irrigation pumps etc. on that; basically any load that you don't need during peak grid load hours - even Solar HWS booster can go on tariff 33 meter. Not sure about your shed power going on Tariff 33?? So I appreciate $$$s can be budget limiting but look at the global picture of your energy needs - improve the efficiency of all your electrical devices, install solar HWS or gas if you have not already - maximise the use of off peak electricity prices.

The challenge is not just yes or no to get 3 phase power to your "Man cave"! having three phase at your meter box can still provide lots of new options.

Cheers,
David

[Marc]

When we installed the solar system, our house s/board had to be upgraded and at the time I ask the electrician to replace the whole switch board and upgrade to 3 phase. The difference wasn't that much. To run the 3phase to the shed wasn't that much of an issue either since I can go under the house and then underground for a few meters to the shed, sub board, etc.

The cable sizes usually go as follows. From the pole on the street to your mains bracket and into your switchboard box to the meters it is 4 core 16mm2 aluminium. This can carry 100 amp max per phase. From there it is up to you but to give you an idea, for a 10, 15, 20 amp 3phase powerpoint (5pin ) you only need 2.5mm2 copper that is. A 20 amp powerpoint in 3 phase will run any domestic and semi industrial size motor you can think off including a largish L'invincibile combination machine. The 20 amp 3 phase 5 pin powerpoint are the one with the skinny pins. Don't install 4 pin powerpoints since 4 pin goes into 5 but not the other way.

Up from that is the 32 amp per phase that requires 6mm2 per phase so a 4 core + earth cable. A 32 amp 3phase powerpoint will carry any size welder you want including a old fashion pig also known as a bullet welder of 400 amp. A real power hog. The 32 amp 5 pin power point is the one with the thick pins and you can only plug in 32 amp plugs and not 20 amp ones. Since you will not be welding at 400 amp all the time, a compressor with a 7hp motor can also go happily on the same 6mm cable.
If you decide to install a factory in your backyard with a team of 3 Tig welding machines, two 10hp compressors and a couple of large plasma cutters working at the same time, I suggest 50 amp power points and a 4 core plus earth 10mm cable. (only joking, but just to show that usually we overdo it with cable sizes.

[simonl]

When we installed the solar system, our house s/board had to be upgraded and at the time I ask the electrician to replace the whole switch board and upgrade to 3 phase. The difference wasn't that much. To run the 3phase to the shed wasn't that much of an issue either since I can go under the house and then underground for a few meters to the shed, sub board, etc.

The cable sizes usually go as follows. From the pole on the street to your mains bracket and into your switchboard box to the meters it is 4 core 16mm2 aluminium. This can carry 100 amp max per phase. From there it is up to you but to give you an idea, for a 10, 15, 20 amp 3phase powerpoint (5pin ) you only need 2.5mm2 copper that is. A 20 amp powerpoint in 3 phase will run any domestic and semi industrial size motor you can think off including a largish L'invincibile combination machine. The 20 amp 3 phase 5 pin powerpoint are the one with the skinny pins. Don't install 4 pin powerpoints since 4 pin goes into 5 but not the other way.

Up from that is the 32 amp per phase that requires 6mm2 per phase so a 4 core + earth cable. A 32 amp 3phase powerpoint will carry any size welder you want including a old fashion pig also known as a bullet welder of 400 amp. A real power hog. The 32 amp 5 pin power point is the one with the thick pins and you can only plug in 32 amp plugs and not 20 amp ones. Since you will not be welding at 400 amp all the time, a compressor with a 7hp motor can also go happily on the same 6mm cable.
If you decide to install a factory in your backyard with a team of 3 Tig welding machines, two 10hp compressors and a couple of large plasma cutters working at the same time, I suggest 50 amp power points and a 4 core plus earth 10mm cable. (only joking, but just to show that usually we overdo it with cable sizes.

Crickey!

My head hurts. :doh:


My power needs are not goint to be massive. A 40A circuit spread over three phases will be plenty for me. My sparky mate just emailed me a quote for the wire. 120M of 16mm 4 core plus earth will be $1500. 50mm conduit to suite will be $14 per length. Not sure of his hourly rate but I will pay him cash. We used to work together on shift, he very pedantic and does a good job. Whatever he asks for in labour I'll be happy to pay.

Firstly though I need to organise the 3 phase connection. I'll need to use a local sparky for that since my mate lives about a hour away and it's a waste of his time to do that part.

Cheers.

[matthew_g]

I finally bit the bullet 16 months ago and had 3ph put to the shed,
$5400
For a 200amp service. Beats the hell out of the phase converter because now i can run my big welder and AC

[simonl]

For a 200amp service.

:oo:

I'm thinking 20A per phase and/or a total of 60A for 3 phase will be plenty. I don't even think I could draw 200A from the house without upgrading the service and the entire street!

How many machines would you run at once to draw a total of 200A from your supply?

Simon

[Marc]

The power rating for the standard 16mm 4 core wires for a 3 phase service mains is nominal 100 amp per phase. Any ordinary 3 phase system will be able to deliver 300 amp at the switchboard. Just like any ordinary single phase mains will deliver 100 amp at the switchboard. The limitations are usually in the wiring inside the house or the shed.

[simonl]

The power rating for the standard 16mm 4 core wires for a 3 phase service mains is nominal 100 amp per phase. Any ordinary 3 phase system will be able to deliver 300 amp at the switchboard. Just like any ordinary single phase mains will deliver 100 amp at the switchboard. The limitations are usually in the wiring inside the house or the shed.

I see. Thanks for the info.

Simon

[BobL]

You may need to check your local supply. In WA its 63A per phase as a standard connection.

[shedhappens]

You may need to check your local supply. In WA its 63A per phase as a standard connection.

Agreed, supply amperage seems to vary from place to place, my brother fitted a phase converter in his shed and had to allow for 80 amps at his switch board.
I also have 3 phase, 80 amps/ph at the house and 60A at the board in the shed, 3 x 20 amp outlets on one side of the shed, the other side of the shed sooner or later will get a 50 and 2 x 20's maybe, that all depends on IF I get a spark eroder some day?

shed

[Theberylbloke]

Hi simonl,

Starting with an upgrade to your meter box is a good idea. From reading your thread it seems like the reticulation in the street is underground and your meter box is not far from the pit. On this basis your mains to the meter box don't have to be huge. 4 x 16mm Copper may do the job. It will depend on the electrical load in house. One phase will end up with shed load plus the house and it has to be big enough for the total. The other two phases will be the same size. Given the short length of your mains 4 x 25mm copper would probably not cost much more in the big scheme of things. The thing to watch will be how much space you have in the water pipe under the driveway as 25mm mains may require a bigger conduit than will fit with the water mains in place. BTW underground electrical conduit comes in 32, 40 and 50mm dia, so you may get an idea of how much space you have from that. 16mm copper is usually, but not always, rated at around 80 amps per phase. Aluminium conductors somewhat less.

With regards to the sub mains from the meter box to the shed, ask your sparky if he is going to run an earth wire to the shed or will he drive an earth stake at the shed and create a MEN point there. The later is probably the cheaper option. Disclaimer. I don't know if you can do that in your state or not.

The size cable you run will be determined by voltage drop and that depends on your proposed load. How the cables are run will affect the amount of load they can carry without overheating. The more accurately you calculate the load you are going to connect, the easier it will be for the sparky to calculate the cable size you will need. Given your shed is 110m from the meter box (plus 5 or 6 meters to get down to the underground conduit and back up again) voltage drop will be your enemy. Make sure your sparky knows the ins and outs of AS3008 which is the gospel on cable ratings. In my experience, a lot of sparkys are lacking in this area.

Cheers

The Beryl Bloke

[simonl]

Hi Beryl,

Yes the sparky told me that he intends to run 4 core + earth. I asked if that was necessary and he said yes. So that's that sorted. He also said 16mm cable will be ample for my intended use, allowing 120M in total length. Going to use 50mm conduit, although when I did the slab in my shed I cast 32mm conduit up through the slab. I have test fitted 16mm 4 core + earth and it just fits, hoping that I will be able to use the existing 32mm conduit and somehow find a 32mm to 50mm adapter. The pipe under the driveway is 100mm sewer and it has 32mm blue line class 12 poly pipe running through so there should be ample room.

When I started this thread, I was only looking into the possibility of 3 phase, now after doing the research it's looking more and more likely that I will pursue it.

One thing I forgot to ask him, how does earth leakage protection work with 3 phase machinery? Or do you only get that luxury with single phase stuff that uses the neutral return? Given that the concept works by comparing the current flow in the active to the current flow back through the neutral, and any discrepancy is attributed to an earth leakage somewhere. How would a system determine an earth leakage in a 3 phase system (for example an induction motor), where if all phases are equal, no current flows through the neutral?

Simon

[Theberylbloke]

Hi simonl,

Three phase earth leakage works the same as single phase. It just looks for current balance in the circuit, if it is not balanced the circuit breaker assumes the imbalance is current flow to earth and will trip. It doesn't matter if the neutral is in use or not. Quite a few three phase machine tools have some single phase load for the lights, DRO, coolant pumps or control circuitry although the later two could also be 415 volt items. Providing the current going into the machine on the active conductors equals the current coming back out on the active conductors plus any neutral current, all will be well with your RCD.

When earth leakage started to get popular (legislated for power circuits perhaps?) the circuit breakers were not cheap and one often used trick was to use a single three phase breaker with 2 single phase power circuits through it. I don't remember how that was wired up.

There are adapters available to go up or down one conduit size and you can use a couple of these together to go as many sizes as you like.

Cheers

The Beryl Bloke

[simonl]

Hi simonl,

Three phase earth leakage works the same as single phase. It just looks for current balance in the circuit, if it is not balanced the circuit breaker assumes the imbalance is current flow to earth and will trip. It doesn't matter if the neutral is in use or not. Quite a few three phase machine tools have some single phase load for the lights, DRO, coolant pumps or control circuitry although the later two could also be 415 volt items. Providing the current going into the machine on the active conductors equals the current coming back out on the active conductors plus any neutral current, all will be well with your RCD.

When earth leakage started to get popular (legislated for power circuits perhaps?) the circuit breakers were not cheap and one often used trick was to use a single three phase breaker with 2 single phase power circuits through it. I don't remember how that was wired up.

There are adapters available to go up or down one conduit size and you can use a couple of these together to go as many sizes as you like.

Cheers

The Beryl Bloke

Once again Beryl, Thanks!

Simon

[Jon_77]

Simon,

Just a heads up - 16mm 4 core + Earth requires a minimum of 50mm conduit. 25mm 4 core + Earth requires 63mm.

Whilst you can fit either sized cables in smaller conduit, it wouldn't pass code.

Hope this helps.

Cheers
Jon

[simonl]

Simon,

Just a heads up - 16mm 4 core + Earth requires a minimum of 50mm conduit. 25mm 4 core + Earth requires 63mm.

Whilst you can fit either sized cables in smaller conduit, it wouldn't pass code.

Hope this helps.

Cheers
Jon

Thanks Jon, my sparky did not mention this. Looks like I may have 32mm conduit coming up through my slab for zero use! I haven't had time to scratch myself last couple of weeks. Now I'm away for 4 days on a course. Hopefully September will quieten down a bit work and home wise and I can follow this up with some actual work.

Simon