Mains voltage

[JohnW2]

That would put me in the church yard - dead

I've been in plenty of churchyards, but I still appear to be alive

Kind Regards, John

 

[EFLImpudence]

Both are quite common. The 'bottom-oultet ones can be a problem (as can plugs, which are always 'bottom outlet') with sockets immediately above, say, a work surface.

Is that valid reason? I.e. designing something to counteract incorrectly installed sockets.

Surely you may as well say the plug in the picture can be a problem with sockets immediately below a wall unit.

 

[JohnW2]

Is that valid reason?

A valid reason for what?

I.e. designing something to counteract incorrectly installed sockets. ... Surely you may as well say the plug in the picture can be a problem with sockets immediately below a wall unit.

I'm not making any judgements - merely indicating that bottom-outlet things (like plugs, and some walwarts) can be a problem with some locations of sockets, just as top-outlet ones (like some wallwarts) can be a problem with other socket locations.

I thought the implication of Jackrae's comment was that there might be something 'wrong' (or, at least, inconvenient) about a wallwart with a top outlet - but, I've said, with some (you would say 'incorrectly installed') sockets 'it depends'..

Kind Regards, John

 

[EFLImpudence]

A valid reason for what?

Having the lead coming out the top.

 

[JohnW2]

Having the lead coming out the top.

No, it's not a 'good reason' for that..

As I said, whilst one can 'please all of the people all of the time' (with the wallwart output in either position0 if all there sockets are (and remain - see **) 'installed correctly', if there are some sockets which were not 'installed correctly' (or ... see **) then one cannot 'please all of them for all of the time'.

[ ** one might hope that sockets would not often be installed too close to something above or below them. However, even if they have been 'installed correctly', it's not all that uncommon (I have at least one apparent example in my house - not of my doing!!) for something (work surface, wall cupboard etc.) to be subsequently installed 'too close' to the socket - in which case one cannot really say that the socket was 'incorrectly installed'.]

Kind Regards, John

 

[AdrianUK]

The mains voltage can be "all over the place". Above is the 24 hr plot from yesterday. This has been logged at 60s intervals. This is from an urban house on a typical street in a medium sized town.

 

[JohnW2]

View attachment 281554The mains voltage can be "all over the place". Above is the 24 hr plot from yesterday. This has been logged at 60s intervals. This is from an urban house on a typical street in a medium sized town.

There were certainly some brief larger 'excursions, but it looks as if it was between about 241V and 244V for most of the time.

Kind Regards, John

 

[Harry Bloomfield]

The mains voltage can be "all over the place". Above is the 24 hr plot from yesterday. This has been logged at 60s intervals. This is from an urban house on a typical street in a medium sized town.

I would guess at that being close to an industrial area, judging by the sharp excursions in some places, especial that on at the start of the graph. Certainly no industry here, and no large deviations here either.

 

[JohnW2]

I would guess at that being close to an industrial area, judging by the sharp excursions in some places, especial that on at the start of the graph. Certainly no industry here, and no large deviations here either.

I don't think one needs anything 'industrial' to get the sort of variation which Adrian has illustrated, given that the largest sudden excursion he experienced (in either direction) was only about 4V.

However, I think I may have spent my life missing something, since I've never really understood why/how changes in supply voltages are as small as they usually are. Th measured L-N loop resistance at the origin of my installation is usually slightly above 0.3Ω, which I imagine is fairly typical. On the face of it (particularly if one thinks only in single-phase terms), that would mean that if just one person downstream of me, on my phase, turned on a ~10.5kW shower (say about 44A), my supply voltage out to drop by about 13.2V - which, just with one shower, considerably exceeds any change in supply voltage I've ever seen.

In trying to find a flaw in that reasoning, I thought that it may relate to the fact that we are talking about a single-phase supply derived from a 3-phase one, such that the net neutral current at any point in time might be close to zero. However, for a start, if one started off with totally balanced loads (hence zero net neutral current) and then added 44A to just one phase, one would presumably expect there to be an increase in 44A in the neutral current. Even forgetting that, even if one ignored VD in the neutral, that one downstream shower alone would drop my supply voltage by 6.6A - which, again, doesn't really correspond with experiences.

I realise that 'diversity' (across installations) will do a lot to 'average out' these things but only up to a point. I'm sure that, at certain times of day, it's far from unknown for two, three or more people to be running showers off the same phase - which, per the above logic, ought to result in ridiculous drops in supply voltage for those upstream of them.

So, I wonder, what am I missing?

Kind Regards, John

 

[Harry Bloomfield]

I don't think one needs anything 'industrial' to get the sort of variation which Adrian has illustrated, given that the largest sudden excursion he experienced (in either direction) was only about 4V.

Well, nearer 5v, but the sudden dive with slow and steady recovery, suggests to me a largish heavy motor starting up, which suggests to me industrial loads.

 

[JohnW2]

Well, nearer 5v, but the sudden dive with slow and steady recovery, suggests to me a largish heavy motor starting up, which suggests to me industrial loads.

Many of those 'slow and steady recoveries' appear to extended over very many minutes, and I would not really have expected that of a 'largish heavy motor' - but maybe I haven't lived!

In any event, I still think that I need some education or something since, taking the simplistic (maybe naïve) view that I presented above, to drop my supply voltage by even 5V would, with an ~0.3Ω loop impedance, imply a current of only about 17A.

kind Regards, John

 

[bernardgreen]

suggests to me a largish heavy motor starting up, which suggests to me industrial loads.

Is there a railway with electric trains near you ?

 

[reds42]

So, I wonder, what am I missing?

My first thought would be that the resistance may not be uniformly spread along the supply to your house.

I'd imagine that the main supply cable feeding multiple houses has a much bigger cross section and lower resistance than the cable running from it to each individual house.

When running your 10.5KW shower it could well be that most of the voltage drop occurs on the section of cable feeding your house from the main supply, and only a small part of the voltage drop is occurring on the larger main supply cable.

EDIT: Another thought is how the main supply cables from the transformer are run. Are they simple radials from the transformer with branches out to houses along its path, or maybe some kind of ring formation from the transformer which would also reduce resistance and the voltage drop on the main supply cable. I know that there are junctions on supply cables that allow DNOs to rearrange supplies to bypass sections if needed, I believe there is one such junction in a manhole not far from my house.

 

[Harry Bloomfield]

Is there a railway with electric trains near you ?

Trains yes, electric no - not at the moment, but there is a promise on. Why?

I tell visiting kids I have my own real train set at the end of my back garden.

 

[bernardgreen]

Trains yes, electric no - not at the moment, but there is a promise on. Why?

In many place the 25kV overhead traction power for new electrification schemes is "extracted" from the existing local supply network.

A train moving from one supply area to the next supply area can have a mild but noticeable affect on the local distribution network loading and hence voltage fluctuation.
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