Fun with electrics

I’ve seen people wiring up stuff that I wouldn’t trust to put batteries in a torch, never mind light switches.

I’ve seen qualified¹ electricians that fall in that category.
I recall the second time I met one such who used to work for the contract holders @ Kensington Olympia Exhibition Halls.

The second time was shortly after he started working for Vinci – the current FM contract holders at the hospital.

¹ If I did anything like the stuff I’ve seen, I would die of shame.

Nor do I but it was for cheapness at a time when people had not much to plug in […] Not sure why the requirements have not changed now that people have so much stuff

They sort of have. 32A ring circuits are largely out of fashion in favour of 20A radials; both are still allowed, but – at least speaking to practising electricians – radials are encouraged on new work.

Since then we have stupidly changed the colours of three phase live conductors from red, blue and yellow to colours including black.

In part because unlike the old colours, the new ones don’t have one phase and neutral looking the same to someone with a common form of colour blindness.

A change introduced by the EU with the UK as the driving force behind it (other countries being largely meh about the subject), it’s worth noting.

More modern switched mode power supplies are probably better, and get the power factor close to 100%, and very likely somewhat lower. I understand how you’d design to do that, but I’ve not actually tested any.

Since around 2000 switched mode PSUs in consumer equipment have had to comply with EN61000, which mandates minimum power factors for anything that can’t meet a get-out clause. If your PSU has a universal voltage input, the chances are it’s got a unity power factor, too. The parts to do it are commodity and cheap; designing unity power factor SMPS with them has been part of my day job for a lot of the past couple of decades.

Indeed it is not the same, and it’s a very subtle way of cheating the consumer.

Not really. There are two points to note:

1. Smart meters still read Watts, at least in the UK. They can also read VA and VAr, but at present they read Watts – just like the spinning disc does.

2. Even if you don’t derive useful work from them, getting the VAs to your property still costs the Grid and DNO money: transmission equipment has to be sized for VA and not Watts, if nothing else. Given that unity power factor has been a requirement for a lot of consumer equipment for two decades, it’s not too unreasonable to consider the possibility of using metering of VA to focus minds in the future.

I read a very interesting article a couple of years back⁰ on the noise in the power distribution net produced by switching power supplies. It was quite impressive! As I recall, the article claimed this was a potentially huge problem for the net, but as far as I can tell it hasn’t lead to a collapse yet.

⁰ Our 1st year students had a home assignment, where they were supposed to measure the power consumption and active/reactive components on a number of things of their choice and do some calculations. Of course many of them used their laptops for this and many got really weird results, which we could later attribute to the SMPS messing up the sine waves so that the meters couldn’t make heads or tails of them…

I read a very interesting article a couple of years back on the noise in the power distribution net produced by switching power supplies. It was quite impressive! As I recall, the article claimed this was a potentially huge problem for the net, but as far as I can tell it hasn’t lead to a collapse yet.

When the new PFI built hospital buildings were commissioned the massive increase in computer based systems, with SMPS, quickly showed limitations in the power feeds.

Basically the site has multiple factors pushing those feeds to the limit:

1. For decades the site has been known to have a rather high peak voltage, this stresses PSUs on the installed kit and to ease the problem many systems have a dedicated UPS which frequently “could do better” on the harmonic feedback into the supply
2. Imaging systems totally replaced “wet film”, all these systems had SMPS
3. The new build combined the user base from three other sites in the city, space was at a premium, so the step-down transformers were placed in uncooled plant rooms on the top of the building.

End result, major overheating of the transformers and also the distribution boards at various places in the building – those high frequency harmonics and resistive elements like switch gear, fuses, joints and transformers just don’t mix.
Checks were being done, looking for overheating in the boards, and a bank of lights tripped out while they had one of the panels open. In the resultant semi-dark it was obvious that the board was visibly overheating…

They have now installed filters to reduce the harmonics and cooling has been improved for the transformers

Would you care to explain how a spinning disc meter is capable of recording watts?

Well, watt-hours really, of course, since it’s an integrator; but:

https://en.wikipedia.org/wiki/Electricity_meter#Electromechanical

Oh joy. Spam on the RISC OS forums!

Still, it bumped this thread. Reminds me of the horror story that was the electrical setup when I first took possession of this house (August 2006). I should point out that I hold NVQs in domestic electrics, including the Level 3 qualification that covers up to BS7671:2011, ie 17th Edition wiring regs with 2011 amendment. I suppose I should do the refresher course for 18th edition now.

So when I first got the keys to this place the electrics were an absolute mess. The heating system had originally been hot air, so there was an empty cupboard with a 10mm2 TE cable going to it (and to a disconnected secondary fuse board). The main fuse board was an old Wylex 6+1 with rewireable fuses.

Of course all that got ripped out and replaced with a brand new Wylex split load 6+6 board (6x RCD, 6x non-RCD). Initially I’d put the two existing ring circuits on the RCD side but the system just tripped as soon as it went “on load”. (I later traced the fault to the combi boiler that had been installed in 2000, some muppet had crossed the neutral and earth in the spur leading to the boiler.)

Ended up partially re-wiring the house. I’ve since reconfigured the board with a replacement bus-bar and RCBOs instead of a bank of MCBs on an overall RCD. Removing the 2-DIN width RCD gave me a 14-way consumer unit. So I now have the following:

20A RCBO radial power circuit for home cinema / hi-fi (with surge / RFI filtered sockets)
6A RCBO outside lighting
32A RCBO ring main for laundry room
40A RCBO for shower
40A RCBO for cooker
16A RCBO for air-con
32A RCBO downstairs ring main
32A RCBO upstairs ring main
6A MCB downstairs lighting
6A MCB upstairs lighting
32A MCB ring main for IT equipment / servers (not RCD protected, all sockets marked as such)
16A MCB radial spur to fridge / freezer (non-RCD)
20A MCB feed to garden, provision for summerhouse (non-RCD as installation will be have own RCD)
20A RCBO feed from solar inverter

I should get a photo…

Rather than dropping a lot of irrelevant stuff into the forum, I’ll just point you to https://heyrick.eu/blog/index.php?diary=20210502

(precis: this place is three phase with country farmer wiring and a water heater installed by a bloke who somehow managed to live in rural France and never come across three phase)

Scary, Rick.

One quibble:

Technically there’s no such thing as a single phase motor because there’s nothing to set up a rotating magnetic field when there’s only one phase. Instead, and in order to even get the motor started, a second phase is usually faked using a capacitor.

That’s only true of brushless motors. With brushes and a commutator, the only reason to have a capacitor is suppression of electrical noise – the motor doesn’t work by a rotating magnetic field at all, and works perfectly well on DC or single phase AC (although the required supply voltage might be different for DC or AC, due to the variation of the impedance with frequency).

A second phase can also be faked using an offset shorted turn, in what is called a shaded pole motor – usually only for fairly small motors, typically turntable motors for gramophones.

Rather than dropping a lot of irrelevant stuff into the forum

Seems I already did, way back when… 🤷

That’s only true of brushless motors.

Fair point. I was probably talking at that point about the washing machine, yes? You won’t have brushes on one of those.
Three capacitor is to engage a second winding to kick the motor into turning (it’s on the schematic ;) ).

“Washing machines live longer with Calgon^H^H^H^H^H^H Immortalis GPU” music emoji

Stuarts lost the plo-ot, Stuarts lost the plo-ot… naff music emoji
Told you not to suck on those wires…

I haven’t assiduously gone through the lot for existing corrections, but early on Rick asserts that UK round pin sockets were 5 and 13A.

It was 5 and 15A, bringing it much closer to the French 16A standard. Both existed in 2 and 3 pin designs.

And although I don’t actually remember DC distribution, I believe the round pin sockets (and there were 2 pin 2A ones as well) harked from those days, though I could be mistaken there!

And although I don’t actually remember DC distribution, I believe the round pin sockets (and there were 2 pin 2A ones as well) harked from those days, though I could be mistaken there!

There were also 3-pin 2 amp sockets. And I remember shopping for Christmas lights, and being asked whether we were DC or AC. That would be early 1950’s.

but early on Rick asserts that UK round pin sockets were 5 and 13A.

The big difference between 2,5,15 amp and 13 amp is that the 13 amp plugs are fused. This makes ring mains possible, and gets away from the situation is our first (1949) house which had 7 sockets for the whole house. This of course resulted in “Christmas trees” of splitters stacked in each socket.

I eventually rewired the whole house.

It was 5 and 15A

Thanks. The only time I ever actually came across these things was the crew section of the SS Canberra. The houses I’ve been in all had modern sockets.

which had 7 sockets for the whole house.

Sounds like this place. Unless you mean three phase, in which case there are numerous sockets (with and without neutral).

I eventually rewired the whole house.

I should, but the price would be horrible (I can’t do it, it must be a registered professional). Given some of the older stuff is crumbling rubber, I leave it the hell alone unless it’s a risk in which case I trace back to the connection and either disconnect it (as in the electrics to the entire outbuilding where kitty lives) or rewire a small section.

I keep meaning to bring some electricity into the kitchen (instead of a long extension lead with a three way splitter (up to 3500W)), but time and a general lack of competence with drills gets in the way. :/

India still has 2A, 3A, 5A & 15A round pin sockets. Not infrequently the plug bodies are a grade of plastic that softens with moderate heat, with predictable consequences…

softens with moderate heat

Probably fine in parts of India, but then other areas might regularly be described as “moderate heat” ?

Oh, I think they’ll stand ambient temperatures okay. It’s only when there’s a bit of electrical heating going on that problems arise. It only takes a bit, whereas Bakelite or similar plastics will stand a fair amount of heat. I suspect Bakelite also conducts heat away better than cheap thermoplastics, and also that dodgy connections and inadequate conductor cross-sections may be more common in India.

dodgy connections and inadequate conductor cross-sections may be more common in India.

A work colleague suggests that “elves and save tea” isn’t a regularly used phrase. His descriptions of his father’s factory and, worse, the factory of a family friend, show that they leave a little to be desired on that front.

“elves and save tea” isn’t a regularly used phrase.

That one had me scratching my head for a while!

That one had me scratching my head for a while!

Well, he said it’s not a regularly used phrase! (And he’s right.)

I’m guessing the work colleague is Indian, although I’m fairly sure there are plenty of other places whereof the same might be said.

Incidentally, Rick – if your phase-to-phase voltage is 390, then phase-to-neutral should be 225, if the supply is balanced. (And if it’s not, then you’ll have two or three different phase-to-neutral values…less likely, but also possible, two or three different phase-to-phase values…well, certainly different, but hopefully by a much smaller amount…)

if your phase-to-phase voltage is 390, then phase-to-neutral should be 225, if the supply is balanced

Reminds me of an incident at work. The incoming supply was via overhead cable, 3-phase. Various parts of the site were supplied with different phases. During one thunderstorm, the overhead cable was struck, and one phase disconnected. The first obvious symptom was that some desk lights went to a dull orange, while others were extremely bright. When we checked we had around 150 volts on one phase, and 300+ on another one.

Shortly afterwards one of the maintenance crew was despatched to RS for a lot of new contactors for the air conditioning, as the originals had either burned out or welded shut.

Fortunately the computer room 3-phase UPS was detecting on the missing phase, so switched over to battery power.

A more sustained issue was that the test area was run from one phase, and all the switched-mode PSUs there drew all their current from the peak of the sine wave, resulting in flat tops. The other two phases showed peaks at those points, like classic 3rd harmonic distortion.

Rather than dropping a lot of irrelevant stuff into the forum, I’ll just point you to https://heyrick.eu/blog/index.php?diary=20210502

As a qualified electrician (Part P / 17th Edition BS7671:2011 – need to do the refresher course for 18th Edition at some point) that is bloody terrifying. Rick – how have you not been killed to death?

Rick – how have you not been killed to death?

Killed to death? There’s an alternative, like slightly killed? ;)

How is simple. Don’t poke a sleeping bear with a stick.

PS: Have you seen rural Spanish wiring?