Hi everyone,

I'm after some advise from an electrician or someone familiar with power electronics on how the home electrics work in the UK.

I'm in the middle of working on a project which, if I ignore the details of the actual project for the moment, suffice to say that it uses the domestic mains supply to communicate with other devices in a similar (but in no way identical) fashion to the way that X10 works. I should add that my project is in no way compatible with X10 nor do I want it to be.

The problem I have is that communications made in this manner MUST be limited to within the one home and not effect any next door neighbours. For example, if I have device A talking to device B in number 5 Jones Street, I wouldn't want those communications to effect an identical setup in number 4 Jones Street.

This brings me to my home electrics question. As I understand it, we work on a 3 phase system here in the UK. Any home in the UK can be working off any of the three phases depending on how the homes within the street are wired up. Due to the way that my project works, I don't believe that any neighbouring homes running identical systems would be effected provided they were working off a different phase. But, is this necessarily the case? Is it possible or indeed probable that neighbouring homes would be working off the same phase electrics?

That being the case, is it also possible that if I send a command over the mains supply from device A to device B that an indentical device B working next-door could be influenced by this command? I suppose what I'm really asking is whether there's any electrical connection between the electrics of one home and it's neighbouring homes or is each home electrically isolated from the other?

Advise appreciated

Brian Hoskins

 

Alternate houses are usually connected to alternate phases, in order to spread the load across the phases.

When doing such as you are, you can cure potential problems by fitting a low pass filter on your incoming supply - but this needs a big heavy inductor!.

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Well, if adjacent houses really are connected on alternate phases then there shouldn't be a problem. My communication method transmits data on the zero crossing point of the A.C. in the same way that X10 does, so if I transmit data on the zero crossing point of number 5 Jones Street (going back to my earlier example) that data would occur at a different point on the waveform in Number 4 so it wouldn't be picked up by identical hardware working in that home. This does bring one immediate problem to mind though... what about flats? Even if adjacent houses do work off alternate phases I'd be suprised if the same were true for adjacent flats within the same block?

I understand that you could use a low-pass filter in order to avoid these problems altogether, but that would require interfering with the electrical installation within the home which does not meet the requirements of my project.

Thanks for the advice Nigel, and keep the ideas/advice/suggestions coming people!

Brian

 

If the houses are supplied by different transformers, the signal, assuming that it is of a high enough frequency, would not pass through the transformers that are designed for 60HZ.

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I'm no electronics god, i just talk too much.

 

Well I wondered if maybe each house was electrically isolated via a transformer but I didn't know if this were the case or not. Certainly, I don't know of any transformer in the electric supply of my own house and you would think it'd be noticeable - it'd have to be quite a hefty size to handle the amount of current your house could take!

Brian

 

What do you live in? apartments? a regular house? . . .

That brings a good question: In my housing tract, ive never noticed any transformers (the mains are underground) i wonder if each house has its own seperate transformer.

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I'm no electronics god, i just talk too much.

 

Here in the US you might have several houses on the same phase, on the secondary of the transformer so you could not expect the isolation of the transformer or difference in phases. Maybe the rule in UK requires a separate secondary for each house but it might help to clarify if that's important to you.

Zach - usually but not always, the transformers for underground electric service is still above ground. In most housing tracts in this area you'll see them in the front or back yard - being shared by several houses. You tend not to notice them - usually 24 or 30 inches square and maybe 36 inches high. An alternative is to put the transformer in a vault but that's pretty expensive.

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stevez

 

Well I live in a house, but that's not really the point. The point is that my project should be able to work in any home whether it be a house, apartment, flat or whatever. And, if two neighbouring houses were both to use the finished project, the communication over the mains shouldn't interfere with each other.

If I can relate it to X10, it'd be like two neighbours both installing X10 compatable lights in their home. Then, whenever their neighbour turned a light on or off a light would go on or off in their own home. That's not the exact problem I'm faced with but the principal is the same - I don't want neighbouring houses both using my project to be affected by one another.

One solution I have already thought of is to build in some kind of device key-code into my communication specification so that neighbouring homes could be set to a different code, thereby avoiding the problem. If I have to, I'll implement that solution but it's not ideal so I just wanted to get a clearer picture of how home electrics work first, to see what needs to be done.

Thanks again everyone for the input so far

Brian

 

No, in the UK we have a 'sub-station' (a large three phase transformer) that usually feeds a substantial area - so all houses in that area are fed from one of the three phases, usually alternately, off the same windings. So the X10 type scheme will 'probably' only interfere with the neighbours next door but two each way.

Back in the 70's there was a LOT of talk about through mains communication, both data and voice - it was anticpated that it would become popular and common - it was suggested that EVERY house would require their own low-pass filters. In the event this hasn't happened, and freely available cheap radio systems seem the way it's going.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

As I understand it, every residential house is on single phase power. We have two different power distribution networks, one for residential and one for industrial power. One is single phase and the other is three phase. Has any one wondered why some power pylons has a single pair of lines per arm, while others have four lines. Well this is the two different networks, residential power is not taken off the three phase network. The power to the sub-stations is also single phase. There is something called the "Ring Main" which usually resides under the roads or pathsways. Every house is connected to every other house on that particular Ring Main. There is a netted tree topology to the power distribution, if that makes any sence. There are several Ring Mains that come out of each sub-station, all stared at the sub-station.

I remember when some tw*t down our road cut through the Ring Main while extending his house. I live in a cul-de-sac and so the Ring Main is not double ended, every house further down the road lost electricity for about three days. What a wank*r!!!

As Nigel has already said the cost of power low pass filters is quite high, both in initial cost and power loss. There are plug in ethernet devices available but there is wide spread debate over the noise/interferance they cause.

 

You appear to be a little confused?. There are not seperate distribution networks for industrial and domestic supplies, ALL are three phase, and they are usually the same supply. However, for certain industrial processes, and particularly high power users, they will have their own sub-station, and may have a guaranteed extra reliable supply.

The point of feeding alternate houses from alternate phases is to balance the load and allow a thinner cable for the neutral. If the phases are perfectly balanced then you don't require a neutral wire at all - but in practice it allows the use of a much thinner neutral cable, along with three larger live cables.

The 'ring main' ISN'T external to your house, it refers to the mains socket wiring in your house, where the sockets are wired in a ring - from the fuse box, to each socket in turn, then back to the fuse box. This is done using 2.5mm twin and earth cable, so each ring has effectively 5mm cable feeding it. You usually have a seperate ring for each floor of the house, each with their own fuse.

Exactly!, a ring by definition is double ended, power distribution isn't!.

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http://www.winpicprog.co.uk

 

Nigel - I think we are talking about the same things. A single 2,400 volt line leaves a substation (a fenced in area with transformers and switchgear supplied by wires on huge towers) and runs on a pole behind a row of homes. I am sure the 2,400 volt line is one of three phases. A utility pole has a transformer that takes the 2,400 volts down to two phase power (110-EARTH-110) and feeds 4 homes so the neighbor next to me and the two behind me are on the same transformer. That seems pretty typical here in the US.

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stevez

 

It's sounds very similar, in the UK the huge substations take the three phase power from the large overhead pylons, at something like 300,000V, and transform it down to something less (I've no idea exactly what?). This is then distributed mainly using underground cables, to smaller local substations, where it comes out as 230V three phase. Supplies to individual homes use just the neutral and one of the three lives, but three phase is available if you have a need for it. In fact, in the workshop at work, where I am now, we have three phase wired into the building, but only one phase is actually used (it was installed when the building was constructed, in case three phase became required later). Being business premises which have evolved over the years, different parts of the other buildings are on different phases, and we have one actual used three phase circuit - it's for a goods lift (cased in hoist), and if a phase goes down it just sits and buzzes).

We see on the TV that a lot of wiring in the USA is on poles, including small local transformers on poles, this is fairly uncommon these days in the UK. Perhaps we only get old USA programmes? 8)

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

In Canada the newer (?) areas have underground wiring. My neighbourhood is about 23 years young and its wiring was very unreliable when new. I guess a certified electrician just twisted the wires together and insulated the connections with tape. They replaced all the underground wiring and now it is just fine. :lol:

The ghettos in the USA look like a 3rd world country, with electrical wires on poles strung all over the place, just like as shown on TV. :cry:

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Uncle $crooge

 

Yes I did get a little confussed on the ring main stuff, should probably read into itmyself rather that listening to people.

However, how can you distribute three phase on just two lines?????????

I don't doubt that the split three phase method is used, infact it's quite a good idea. But there are a lot of pylons in the UK that only carry single phase power. If the three phase method was used down our road only one third of the houses would have lost power! I seem to remember whenI looked at the line, (It was quite a while ago) that there were only three conductors, not five.

The split three phase method might be a rather recent topology for the national grid. The houses near me are only about 50 years old. When I tried to get three phase installed in my workshop, I was told that there is no chance as the nearest three phase supply is over 1200 yards away. The cost 5 years ago was quoted at £62,000, a lot for one building. The workshop is one of many only about 20 years old, built on a peice of reclaimed industrial land. There was no three phase power there 80 years ago and there is no three phase power there now. In my opinion it was a bit silly not putting in a new three phase sub-station, as it was intended to be a business park. But again I'm only going on what I've been told.