Electricity: 3 phase query

Hi gang,
AIUI, out in the road there are three live wires and one neutral. The phase s of the lives are 120 degrees out of phase with one another. The potential difference between any two live wires is 440V. The potential difference be tween any live and neutral is 230V. Domestic supplies only tap one live and the neutral to give you a single phase supply, so if you want a 3 phase su pply for a workshop or whatever, you have to get the leccy blokes in to dig up the road and tap you into one of the other live wires. Do I have that r ight?
cheers.
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Oh, and before some helpful soul offers up a practical solution, such as "g et yerself a phase converter, mate, it's a lot cheaper" I should just point out that I'm NOT looking for solutions, here, I'm simply enquiring as to w hether my understanding of the basic situation is correct or not. Thanks!
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On Sun, 7 Jul 2013 06:03:20 -0700 (PDT), snipped-for-privacy@virgin.net wrote:

From a legal, technical or practical angle?
AB
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On Sunday, 7 July 2013 15:08:12 UTC+2, Archibald wrote:

"get yerself a phase converter, mate, it's a lot cheaper" I should just po int out that I'm NOT looking for solutions, here, I'm simply enquiring as t o whether my understanding of the basic situation is correct or not. Thanks !

Er, technical and theoretical. I'm already aware that the most cost-effecti ve practical solution is to hook up a phase converter to the distribution b oard via its own spur and that's what I'll probably end up doing.
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snipped-for-privacy@virgin.net wrote:

I don't really see any 'legal' angle provided the leecy board or their agents does the work. In addition to the cabling, you will need a change of meter and distribution board. I doubt that they will want to balance the loads for domestic use so your main house load can stay on one phase and the three phase go off to your workshop etc When selecting your wiring to the 3 phase load, you may want to run a neutral as well because some machines use the neutral for control circuits. Latest machines tend to use a 440-110 or a 440-24 transformer for controls. If you are buying secondhand stuff, my suggestion would be to be prepared with a neutral too.
Incidentally if you go down either the converter or inverter route, you might find this of interest. http://homepage.ntlworld.com/bob.minchin/Induction%20motors%20-%20Issue2.pdf
Some converters will use the single phase neutral as one of the output phases thus not providing a neutral in the correct relationship to the other phases. Inverters will usually only provide 3 phase output at the same voltage as the input. i.e. run from 240v single phase will only produce 240v three phase output so motors in your machines need to be dual voltage - marked as 240/440v or similar.
hth
Bob
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It's curious. I've been heavily into electronics for decades yet nothing I' ve learned it seems, is relevant to domestic/industrial electric installati ons. Though I'm intimately acquainted with the concept of phase, phase-shift and know the difference between current, voltage and power inside-out I'm stil l struggling to get to grips with this 'macro' stuff. These two fields are like chalk and cheese. I suppose an electrician would be equally perplexed if required to calculate the output impedance of a buffer/current-amplifier stage. :-/
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I mean they're clearly two different disciples entirely. In my typically mi llivolt/milliamp world, we don't have to contend with forces sufficient to rip a machine's internals to pieces as you do with power engineering, so th e need for nice, smooth 3 phase supplies simply doesn't arise in the first place!
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snipped-for-privacy@virgin.net wrote:

I've found that most sparks I talk to don't have an in depth understanding of the subject. They are taught largely by rote both in college and as apprentices. They know all the how but very little why.
There are exceptions naturally.
My background like yours is in electronics but I've learned to adapt over the years.
Bob
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On Sunday, 7 July 2013 18:58:22 UTC+2, Bob Minchin wrote:

y millivolt/milliamp world, we don't have to contend with forces sufficient to rip a machine's internals to pieces as you do with power engineering, s o the need for nice, smooth 3 phase supplies simply doesn't arise in the fi rst place!

I think you may be right. A recently qualified young electrician told me, i n regards to electrical safety, that "even just a few megaohms can kill you ." I shuddered at the time, but feel much less alarmed now in the light of your remarks.
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On Sunday, 7 July 2013 20:05:34 UTC+1, snipped-for-privacy@virgin.net wrote:

lly millivolt/milliamp world, we don't have to contend with forces sufficie nt to rip a machine's internals to pieces as you do with power engineering, so the need for nice, smooth 3 phase supplies simply doesn't arise in the first place!


in regards to electrical safety, that "even just a few megaohms can kill y ou." I shuddered at the time, but feel much less alarmed now in the light o f your remarks.
Aren't megaohms poisonous just like snakes ;-)
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...and venomous mushrooms... ;-)
Tim
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On 07/07/2013 15:32, snipped-for-privacy@virgin.net wrote:

I found doing a bit of software development work on high power HF amplifiers / transmitters was quite enlightening in that respect... It certainly changes ones TTL/5V view of the world, when dealing with 10kV step up transformers!
--
Cheers,

John.
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On Sun, 7 Jul 2013 05:59:03 -0700 (PDT), snipped-for-privacy@virgin.net wrote:

No good tapping into just one of the other live wires you need two more.
Five wires in total
L1 L2 L3 N E
Plus a new three phase meter (or another two single phase ones)
and a big hole in your bank account
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On 07/07/2013 14:43, The Other Mike wrote:

Not entirely sure, but when they replaced the main fuse and housing here some years ago, I'm sure I remember seeing four cores (three phases + neutral, with the sheath as earth). It could well be that they brought 3-phase to every house on the road when they were built in the 30s and only connected one phase at each. If I were to need 3-phase, that'd be a useful cost saving!
SteveW
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wrote:

This house (built 1911) has all 3 phases incoming - I assume so proper balance could be obtained empirically. When they built a new estate of 25 bungalows, just round the corner, some 30 years ago - they were all on the same phase. How things change.
--
From KT24

Using a RISC OS computer running v5.18
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On 08/07/2013 06:14, charles wrote:

...

It was once normal practice to connect each house in turn to a different phase. As you say, that was to achieve phase balance.

That stops people importing 400v into their house by putting an extension lead over the fence, or otherwise sharing supplies.
Colin Bignell
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On 08/07/2013 15:12, Nightjar wrote:

Which if your road is wired like that, would be a pretty cheap way of getting three phase if you get on with both neighbours ;-)
--
Cheers,

John.
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On 08/07/2013 15:24, John Rumm wrote:

When I worked for an electricity board, it was more usually done surreptitiously, in one case by cutting small holes through the wall and driving six inch nails through the neighbour's meter tails, in order to keep the electricity bill down.
Colin Bignell
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snipped-for-privacy@virgin.net wrote :

The basic numbers in the UK are 415v 3Ph. 240v single phase = 240v from any of the three phases, to neutral. 415v as measured from any phase aay of the other two.
If you have 1ph + N, you are lacking two more phases to make a 3ph supply.
--
Regards,
Harry (M1BYT) (L)
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Right, Harry. So with only two live phases you'd have your 415V potential difference alright, but it would be effectively unusable?
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