How many have 3 phase in a DOMESTIC house

[not done it yetParticipant @notdoneityet]

I wonder why the UK is so backward?

Not backward at all. When did Thailand actually get a grid? Power is transmitted over the grid as 3 phase. Wiring for small items such as most domestics is so much simpler with three wires, or even only two. There are very few domestic air conditioning systems, and commercial ones do use 3 ph. A belt from the 230V mains can be fatal from a single phase, let alone getting one from 415V.

What voltage is your domesticc wiring? The Americans clearly put safety before I^2R losses and/or heavier guage conductors. The Uk is much the same as all of Europe, so not alone being 'backward' as you suggest.

[MuzzerParticipant @muzzer]

Posted by John Olsen on 20/10/2016 01:47:38:

Incidently three phase welders of the older style, eg with just a transformer, actually only used two phases, with a transformer primary connected to them. The rod can only have single phase power going through it.

John

If you search for manuals etc on the Miller website you can see typical circuit diagrams for the old 3-phase transformer-based welding sources, such as the CP-300. Some models clearly show a 3-phase transformer and 6 diode rectifier bridge (page 10 in this example). The voltage variation is done by means of a variable tap on the secondaries. One advantage of a 3-phase transformer / rectifier arrangement is that the output voltage is smoother without the need for an output choke.

True, it's not always the case that they are 3-phase. If you want a controllable AC and DC source, it may be simpler and cheaper to have a single phase transformer and some form of regulator. The downside is somewhat sizeable load currents and an imbalanced load on the 3-phase network.

By way of example, I have a Miller 320A/BP welder (AC-DC TIG / MAW) from the 1970s that uses single phase (luckily for me). At 300A output it takes the best part of 70A from the mains. The control is done by means of a pair of enormous magnetic amplifiers (one for each half of the waveform) operating at the 50Hz mains frequency, feeding into a large DC choke forming an interleaved buck converter. This makes it the lowest frequency switched mode power supply (SMPS) I have worked on by quite a way. Excellent control down to 5A or so but the controls are complex and expensive. At the time it was pretty much state of the art. This control method would not work so well on a composite 3-phase waveform so is a good example of a high power single phase source. Nowadays, high frequency inverter sources make this kind of arrangement redundant. The decision to run from single or 3-phase is more down to convenience and acceptable mains loading.

Murray

Edited By Muzzer on 20/10/2016 11:19:09

[EmgeeParticipant @emgee]

Colin

Seems you misunderstood the comments made re splitting 3 phase supplies to 3 different consumers.

All UK consumers will have their own meter whether it be single or 3 phase depends on the type of supply required but in every case will be a single dedicated meter.

Emgee

[AjohnwParticipant @ajohnw51620]

Posted by Colin Whittaker on 20/10/2016 04:34:34:

Three meters for three phases!

Here in Thailand most big houses have a three phase power supply because of all the air conditioners. The three phase power is measured with a single three phase meter. I wonder why the UK is so backward?

Colin

Mainly because the primary source of heating in houses was once coal and then coal gas and the natural gas and now increasingly imported gas. The grid has probably been around a lot longer here too. We don't really need air con here but it is increasingly used in factories and offices that have 3 phase anyway. Mainly down to people and gear heating the place up. I should mention vast areas of glass windows to at times.

No idea when our local area in Birmingham was "wired up" but the vast majority of the distribution is underground. Something they don't seem to be able to afford now so must have been done long ago.

John

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Edited By Ajohnw on 20/10/2016 11:01:23

[SillyOldDufferModerator @sillyoldduffer]

Posted by Colin Whittaker on 20/10/2016 04:34:34:

Three meters for three phases!

Here in Thailand most big houses have a three phase power supply because of all the air conditioners. The three phase power is measured with a single three phase meter. I wonder why the UK is so backward?

Colin

Jumping to a general conclusion from insufficient evidence I'm afraid. Single 3-phase meters aren't unusual in the UK.

Here's the opposite case: I have a friend who has built a couple of houses in rural Thailand. He's had all sorts of fun and games with the electrics: aluminium cables, disconnected earth wires, live ends dangling in the crawl space, connections made by twisting bare wires together, and – best of all – L and N reversed by the electricity provider outside the property.

Does this mean that all electrical installations in Thailand are equally bad? No.

Dave

[Colin WhittakerParticipant @colinwhittaker20544]

Dave,

It was supposed to be a tongue in cheek comment but I guess I omitted the necessary smilicon.

But your friend's comment about Thai house electrics doesn't sound too wrong. I've given up trying to keep the house wiring correct and I'm concentrating on keeping it non-fatal.

The worst electrics I ever encountered was in Egypt. An electrician out there only needs one tool, square jaw pliers with plenty of scotch tape on the handles. Grub screws from switches and sockets are simply discarded and a bare wire inserted through the cable hole and back out of the grub screw hole and twisted back around itself. Earths? What's an earth? Fuses? No they keep on blowing? And don't get me started on the jointing of the paper insulated telephone trunk cables.

Edited By Colin Whittaker on 20/10/2016 12:42:41

[Martin 100Participant @martin100]

Posted by Ajohnw on 20/10/2016 10:58:07:ld mention vast areas of glass windows to at times.

No idea when our local area in Birmingham was "wired up" but the vast majority of the distribution is underground. Something they don't seem to be able to afford now so must have been done long ago.

Not seen any 'new' developments in urban areas where the distribution is overhead, underground is by and large faster to install, safer and more reliable.

Distribution, at least at 33kV and below is also moving underground in many regions of the UK to both reduce supply interruptions and the level of work undertaken at height. Above that voltage level the line loading and associated cable cooling requirements are a major consideration and the economics of huge excavations and providing a zero development area around the cable route work against 100% undergrounding.

[AjohnwParticipant @ajohnw51620]

Posted by Martin 100 on 20/10/2016 14:07:58:

Posted by Ajohnw on 20/10/2016 10:58:07:ld mention vast areas of glass windows to at times.

No idea when our local area in Birmingham was "wired up" but the vast majority of the distribution is underground. Something they don't seem to be able to afford now so must have been done long ago.

Not seen any 'new' developments in urban areas where the distribution is overhead, underground is by and large faster to install, safer and more reliable.

Distribution, at least at 33kV and below is also moving underground in many regions of the UK to both reduce supply interruptions and the level of work undertaken at height. Above that voltage level the line loading and associated cable cooling requirements are a major consideration and the economics of huge excavations and providing a zero development area around the cable route work against 100% undergrounding.

I meant that the lot tends to be underground in B'ham Martin. There isn't much overhead around at all. In the various over spill estates etc there may be as when installed it will have been more or less open country. I remember one in particular that used to sort of tug at my hair.

Some people also feel that it's not a good idea to live in house that is directly over one of the high voltage feeds. Pass I've never seen a map.

John

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