Thank you Shane, I hadn't considered the issue of RCDs, it's all second hand machinery that was permanently wired with solid earth and armored cable, and I tend to think of RCDs as protection for hand tool "saw thru the cable" kind of stuff.
Also the current main switchboard is old and has no RCDs at all, but does have a spare 3 pole breaker.
Cable run is about 15 m, 3 m from switchboard to wall of house + 7 m to the workshop then a 5 m run in the workshop.
That is based on an aerial conduit, extra if it has to run down the wall and be buried then up the wall of the workshop.
Maximum demand is rather low, the machines are maximum of 3 horsepower and I could live with only one operational at a time, if it would reduce costs to have just one outlet and swap plugs.
I would definitely offer you the job if I was in Adelaide but I live in Canberra.
If you ever visit the East Coast send me an email and I'll shout a round.
Best wishes
David
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Cheers David.
Thats a reasonably short run. Typically you'd run a single 3P supply from the main board to the shed, sub-board within the shed with 3P and 1P circuits from there. No RCD on the 3P supply to the shed, no MEN at the sub-board. RCD on the 1P circuits, not necessarily on the 3P, depending if they are hard wired or plug-in types. The existing 1P supply from the house could simply be made redundant. Dont forget to earth the actual shed itself, and use UV stabilised conduit for the overhead supply. It's a very straight forward situation and any licensed contractor will have no problem with the installation.
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> Maximum demand is rather low, the machines are maximum of 3 horsepower and I could live with only one operational at a time, if it would reduce costs to have just one outlet and swap plugs.
That demand is *INCREDIBLY* low. (Does not make engineering sense; except I suppose you got the machines very affordably from failed factories).
I can't keep phases and ponies straight; this table says FIVE amps.
https://www.rm-electrical.com/wp-content/uploads/2014/11/MOTOR-CURRENT-RM-Technical.pdf
Speaker wire (good 16 gauge, 10 Amps) would be plenty for that run; except you need the several wires together, good melt-down performance, and for-certain >>415V insulation.
However the gauge should align with the available fuse/breaker. In my land 15A is the low limit on 1P/2P trips, and I'm not sure about 3-pole trips. Granting 15/16A, the wire looks like "house wire". My-land's "NM-B" is rated 600V, though not sold as H-H-H-N-G.
If there is only one worker (you), and nothing that runs by itself (air compressor), then just wire them all up; safer (imho) than plugging.
That demand is *INCREDIBLY* low. (Does not make engineering sense; except I suppose you got the machines very affordably from failed factories).
I can't keep phases and ponies straight; this table says FIVE amps.
https://www.rm-electrical.com/wp-content/uploads/2014/11/MOTOR-CURRENT-RM-Technical.pdf
Speaker wire (good 16 gauge, 10 Amps) would be plenty for that run; except you need the several wires together, good melt-down performance, and for-certain >>415V insulation.
However the gauge should align with the available fuse/breaker. In my land 15A is the low limit on 1P/2P trips, and I'm not sure about 3-pole trips. Granting 15/16A, the wire looks like "house wire". My-land's "NM-B" is rated 600V, though not sold as H-H-H-N-G.
If there is only one worker (you), and nothing that runs by itself (air compressor), then just wire them all up; safer (imho) than plugging.
Well, Australian horses are more powerful than USA ones
I mean, most advertised "5 HP" motors in the USA could not be called that in Aus, you'd be prosecuted.
I was amazed at the claims I saw while in the USA, kind of like the old Total Peak Music Power in amplifiers, except without even the small-print weasel words .
So those numbers are sustained real power.
But yes, within what could have been done with 1 phase.
However if you already have 3 phase, they do make sense - because a 3 phase motor will be smoother, better torque at start, probably more reliable because no start/run capacitors to fail (I have had this happen).
They were affordable, not from failed factories but surplus from local university and scientific institute where 3 phase is standard.
Anyway the breaker is 20 Amp so the wire should be at least that, and the cable I have is so.
Yes, probably no need to switch sockets.
Australian standard sockets are very safe but for sure a nuisance to have to swap, it was just a fallback option.
Best wishes
David
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I was not referring to the size of your animals. Only that I can't figure 3-phase loads on two thumbs.
The main economic point of 3-phase is reduced cost of copper when wire diameter becomes non-trivial. You are apparently loading only to 1/3rd the smallest wire you are allowed to use (for mechanical robustness). A single-phase 240V 16A line saves 2 strands of wire and conceptually a shave of insulation (though probably limited again by mechanical robustness). "Common sense" says that what would be good for a large factory might be mis-aimed for one guy with four machines. Of course fine machines at tag-sale prices may invert the bargain.
The main economic point of 3-phase is reduced cost of copper when wire diameter becomes non-trivial. You are apparently loading only to 1/3rd the smallest wire you are allowed to use (for mechanical robustness). A single-phase 240V 16A line saves 2 strands of wire and conceptually a shave of insulation (though probably limited again by mechanical robustness). "Common sense" says that what would be good for a large factory might be mis-aimed for one guy with four machines. Of course fine machines at tag-sale prices may invert the bargain.
I see the main benefit of 3 phase as the much better motors that are possible.
A 1 phase installation only saves one strand of wire over 3-phase, 3 core + earth, less than $20 for my job.
I think 3 core + earth is what I will have done, looks like most 3 phase welders are delta connected so there is little need to add a neutral for some possible future compatibility.
Now I just have to replace the coil in the grinder contactor relay with a 415 V unit, or possibly add a small incandescent lamp in series with the 240 V coil.
Worse case, I can just install a switch and lose the no-volt release feature.
I understand why the university ordered it with every OHS safety option but for my one man workshop that particular option is practically redundant.
Best wishes
David
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Thanks for more heads-up that I should consider.
The shed is steel sheets on a timber frame but the sheets don't actually touch, a quirk of the replacement of old 4 ft panels with new metric 1200 mm sheets.
It never has been earthed, but that doesn't say much because the construction was unapproved and very shonky.
I am inclined to leave it as is, if that's allowed.
The 240 V cable is in UV stabilized conduit but it has still faded and presumably is embrittled to some extent.
I planned to have the new cable run in a steel pipe for durability, also if it's allowed.
Best wishes
David
Metal conduit heats up, even if you paint it white. It weighs a lot more, needs to be earthed, is (generally) not flexible, and how to form a 'drip loop' at the entry at either end?. Metal conduit is simply not used for your purpose.
It is sounding as though you are starting to have your own ideas, and perhaps looking around for information so that you can DIY.
I don't have a problem with that, its your house, your family, and you assume the risk, all of it. My advice is generic and academic in nature.
There is no such thing as a xxA cable. Current rating depends on length of run, load and deratings based on the environment. You need to get the fault loop impedance right, that is the #1 thing. This means that if there is a fault, the circuit breaker will trip. There can be instances where this will not be the case, easily demonstrable with active to earth through the ~1000 ohm impedance presented by hand to foot.. and the MCB holds in, circuit is closed, and you die. Yeah, I know, sounds extreme.. but it does happen, but always to 'other people' - for now.
There is quite a bit more to it than 'oh your load draws 6A, find a 6A cable'. These guys should not be commenting on such things. Speaking frankly they should be moderated out. With frankness in mind, IMO this whole thread should be moderated out.
I'd say its time to jump off the audio forum for electrical advice and get three quotes for the work from local electrical contractors. You know what to look for, 3P MCB at the MSB, MD conduit overhead on a catenary, sub board in the shed, RCD protected 1P and 3P outlets plus light.
I can 100% tell you that the contractor will give you a better price is he supplies everything, including the cable, and the cost of the cable is negligible WRT the total cost, which will be based mostly upon labour.
There are so many 'know it all' customers out there, with parts they have scrounged from here and there, and the job always costs them more. My advice to you is that you let them tell you what you need, and based on 'what you now know', select the best candidate to perform the work.
Best Regards.
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Well, yes, I have the idea to put up a frame for kiwi fruit to provide shade between the house and workshop.
They require a substantial structure so it could be pipe, if I can do this in a way that an electrician can later use then so much the better.
Ok, thank you for your response and frankness.
I will take your advice and not continue with this thread.
Best wishes
David
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