3 wire rural Scottish supplies

It must be some sort of bonding wire.

Ok im joking really,

2011 wrote: »

I would much prefer a three phase supply myself for obvious reasons. I don't work on small installations so I haven't dealt with this.

Apparently the waveforms of both phases have a half-cycle offset, or 180 degrees apart (rather than 120 degrees). This means that the phase to phase voltage is 460V rather than 400V as we have over here between phases.

I have just retuned from Cuba, I believe that this might be the distribution that they commonly use there. Smaller loads can use 110V where as larger can use 220V and socket outlets are provided for both.

Cuba likely inherited a version of the US system. They seem to primarily use 110V 60Hz with some hotels providing 220V, due to predominantly European guests.

Using NEMA 5-15 110V sockets for 220V is asking for trouble as someone's going to plug in a 110V device.

US 220/240V sockets have the pins oriented horizontally.

In a Cuban hotel they'd be safer providing Schuko sockets for 220V if they've a lot of European tourists.

To be quite honest I don't really see the advantages of the US system. In my experience of it there isn't enough power available for a lot of heavy rated kitchen appliances. Typically they keep everything below 1500W even though in theory you can go up to 1800W at 120V it's kinda pushing the pins to the limits.

Then you've a version that supports 20Amps where one pin is horizontal and the socket has a T shaped slot on one side that accepts both 15 and 20 amp plugs. However it's not that common. The result is you've people using "cheater plugs" to connect 20 amp plugs to 15 amp sockets.

Then if you want to connect a dryer or even some washing machines with internal heaters you need special sockets for 220/240V. It's also an issue for decent portable air conditioners and you can't really use plug in heaters that output much heat.

In general it's a messy system that leads to overloading in my experience anyway.

It reminds me a bit of the old British installations with the round pin BS546 plugs where you'd umpteen incompatible sockets used in the same house resulting in loads of adaptors in permanent use.

There were 3 wire 127V 50Hz systems in Europe eg in Italy and Spain. They were 220V between two lives and 127V live to neutral. You'll still find remains of them in very old installations in Italy where there can be two lives and no neutral.

That's also partly why most continental plug systems weren't ever polarised as they're designed to assume either leg of the circuit can be 127V or 220V, so appliances are designed to be safe in either polarity.

In the EU our present-day system BS1363 plugs, are the only commonly used mains connector that's always polarised - systems like the French, Swiss and Danish plugs are only polarised if used with an earthed plug that only fits one way.

Incidentally, all appliances sold here also meet those standards both because of the single market and also Schuko is still referenced in the standards here albeit no longer installed. It was defined in IS 180. Also appliance connectors like the 'figure of 8' commonly used on small appliances is never polarised. So even used with our plugs and sockets it random at the appliance end.

European lamp sockets for example are designed with a big cuff to shroud the screw threads on Edison bulbs because you can't be sure that the screw isn't the live as a plug can go in either way into a wall socket. That obviously didn't ever mater with bayonet bulb sockets as they use pins and aren't polarised.

The only appliances that didn't were probably things like ancient televisions that used hot chassis - not something you'd have been likely to encounter after the 1950s.

The contemporary European and UK 230V systems are very straightforward and generally very safe.

Concentric service cable is definitely fairly common in urban England. It's usually associated with direct buried cables

Was it used here that much?

ESB seems to have mostly used ducts rather than direct burial.

I've definitely seen strange looking service cables in some older 1920s houses here that had underground services. I'm assuming it was some kind of of concentric cable. Looked like it was wrapped heavily in a protective tape a bit like what you'd see in some gas piping.

You sure it's not like the old Italian system?

They used to have 127V for 'lighting" which supplied lights and also a smaller 3 pin 10amp socket.

Then you had power which was 220V and supplied larger 16amp sockets.

They then dropped the 127V but retained two different 220V circuits.

There were two meters. One charging a lighting rate and the other a "power" rate. So using the washing machine or the water heating cost 2X using the lights.

The sockets still exist, but they're all 230V and supplied from a single meter.

The downside of it was that people would just connect everything they could to the cheaper system which resulted in fuse blowing and overloading risks.

Apparently the origin was that the power companies were competing with gas lighting in the early 20th C, so they sold lighting and power as different products.

Lackadaisical wrote: »

Isn't 690V is just the star version of 400V delta 3 phase though? - Used to be 380/660V now 400/690V still fully DIN/CEN/CENELEC/IEC stuff.

Slightly backwards there or something.

400v 3 phase gives 400v phase to phase, and 230v phase to N or star point.
A motor connected in delta has 400v across windings, in star 230v.

If a 690v 3 phase system is in use, it gives 400v phase to neutral.
So a motor connected in delta would have 690v across its windings, and 400v in star.