To the customer, at the incomer, it doesn't really matter. The customer might find it handy to know the 'firing order' of the phases, which can be determined by a phase rotation meter - a tiny three phase motor, or a neon light/ LED gadget. That way he can ensure his three phase motors run in the correct direction first go. Otherwise he take a 50/50 chance, connect a motor, then hope it runs the right way. If not, two of the phases need to be swapped over to correct it - absolutely not fun, on some of the massive beasts I used to work on, so I made sure they were right.
A bit of a generalisation. Mine (18th century) had, like all the neighbours, a single phase coming in overhead, replaced in the last 30 years with a single phase (one fuse) underground supply to the original meter.
May not be at zero, but just a few volts of difference. Actual voltage depends on how well your flat is balanced against other properties or the other two phases. Plus the supply type. It is rarely a perfect balance and the voltage will wonder about constantly, as you and neighbours switch items on and off. Try it and see for yourself.
Yes. SWMBO used to work in a 'posh' grammar school. They had a Linux room for the A level computing students. It was fed off one phase.
They needed an extra mains outlet in one corner, so the electricians drilled a hole in the wall from a socket in the next room, and added a spur. On a different phase.
I forget how she found out, but there were no markings and two of the sockets, on different phases, were about a metre apart.
She complained and was labelled a troublemaker. She was 'advised to leave' shortly afterwards.
There are a couple ways to do three-phase. Delta and Wye.
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Wye is wired with respect to Neutral. In the top diagram there, you can see the three phase "loads" are all with respect to the neutral. Now, on the face of it, the Wye has some possibilities for single phase operation. At the potential expense of the balance.
The Delta on the other hand, doesn't use the Neutral, but, it also doesn't lend itself particularly well to "doing tricks". Maybe the Delta would be suitable for running three phase induction motors, where the load on each phase would be relatively balanced.
Now, as the article above describes, higher levels of your electrical distribution system, could use Delta during transmission, then use Delta to Wye transformers at the lower level.
I would say the neutral, is local to the Wye side of the transformer. You can reference the neutral to earth, for some sort of grounding strategy I suppose. Maybe one of the grounding experts knows the practices answer.
Also, the second diagram in that article, shows (neatly), how a three-tin-can configuration could be built for Delta-wye.
And there are lots of things transformers don't tolerate all that well. I'm really surprised flames don't shoot out of them more often, considering the nature of loads put on them. A three-phase induction motor, by comparison, the transformer *loves* that. No harmonics. No digital crap. Hardly anything to hum about.
3-phase is more efficient and since it is rare for a feed to be above
100A per phase, you will need 3-phase if you want to charge your EV and heat your house with electric.
Soon if they ban gas the only alternative is electrical heating.
Neutral will be "created" at the substation. The substation will have a three phase transformer in a Y configuration - with the centre of the Y connected to earth. This centre point becomes the local neutral[1]. The connection to earth on is used as the return to the grid - i.e. the HV side is only 3ph, and only the LV side its 3ph + N.
You may then have separate conductors that carry the neutral and earth to the property. This is a TN-S earthing arrangement. Or more commonly these days, they use a combined Protective Earth and Neutral (aka PEN) conductor to the property, and then separate them out into E and N there art the main cutout. This is a TN-C-S supply.
Neutral will be close to earth potential (it is joined to it
*somewhere*), but may not be exactly. In any given property its carrying the same load as the live so since it does not have zero resistance it will have some voltage drop on it. So at point of use it may be rise a bit away from true earth. (and the live will fall a bit toward it)
PME (TN-C-S) supplies will suffer less from this since the neutral is separated from the earth at the property, and there are multiple connections to earth along the way.
(its the main reason that neutral is considered to be a live wire)
On Fri, 28 Aug 2020 10:26:17 +0100, John Rumm snipped-for-privacy@nowhere.null wrote: [snip]
My flat was built in 1909 and I believe the main wiring was done in
1947 (I think it was lighting only in the front rooms until thenwith gas for the rest and in the close). In 2019 the cables and cable heads were upgraded by Optimum (for Scottish Power). At that time the workers told me that quite a few flats (not mine) had no working earth.
I told the guys that SP said it would be okay to make mine three phase free of charge but they were unconvinced :-)
From that timeline, is it possible to infer what the earthing system would be (a) in 1947 and (b) in 2019? Is there a way of finding out - by looking - what it is now?
Chances are its TN-C-S. You may have a yellow "PME" sticker on the cutout somewhere.
If you follow through the pictures here:
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You should be able to work out what you have. Note that depending on area, the local installers may use different brands/styles of head end cutouts.
Normally on TN-C-S the main earth connection will emerge from the side of the main cutout. On older TN-S installs its usually easy to see it connected to the sheath of the incoming supply cable. The tricky one is new TN-S supplies which use the same equipment and look exactly the same as a TN-C-S supply - the only difference it the position of links inside the cutout (which you can't see with the lid on)
Out in the country, including round here, I occasionally see overhead LV on poles ranging from L+N, 2L+?N to 3L+N and also 3L+N+E
My brother and his 2nd wife lived next door in the EOT and 1st house in of a terrace. They knocked through into one house and even after having work done by an electrician there are no warnings about phases even though they still have two meters and two 'fuseboxes'.
I simply feel that unless there is an awful coincidence, the fact that every three premises will be on a different phase would be OK unless the area is right at the end of a long cable run. Have you ever looked at the mains waveform, let alone the differences between phases? Its not a new problem we have factories in my road and after putting in a beefed up sub station no more problems. Brian
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