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Old 4th Jan 2023, 3:24 pm   #21
Junk Box Nick
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Default Re: Every day is a schoolday. House lighting circuits from the past.

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Originally Posted by cmjones01 View Post
LEDs, by their very nature, need some local electronics to drive them anyway, just like fluorescent tubes and other discharge lamps do. I think therefore there's relatively little to be gained by changing the supply voltage to them. It would just need slightly different electronics at each fitting. There's also the issue that different types of fitting will need different supply voltages and currents: a spotlight might have, for optical reasons, just one powerful LED driven at an amp or more with a forward voltage of about 3.5V, whereas a ceiling light panel like the ones in my office will probably give best results with several dozen small LEDs spread over its area, and the most efficient way to run them is to connect them in series and drive them at low current but high voltage.

It's no harder, really, to drive either of these from 230V than it would be from, say, 12V.

Chris
Thanks, Chris, interesting stuff – posts crossed.

I wondered if an LT supply would negate all the safety concerns regarding high voltage and earthing issues in the OP though, in reality, as many pre-1966 systems have and are disappearing through rewires this may be largely academic.
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Old 4th Jan 2023, 3:39 pm   #22
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Default Re: Every day is a schoolday. House lighting circuits from the past.

A lot of he LED units I have seen recently have the LEDs in series strings and need something over 24V to get them to light.

Then there's the whole issue of constant-current or constant-voltage drive; even if you were feeding 12V to the fitting from some sort of central transformer you would probably end up with another SMPS of some form needed to cater for the variety of different 'styles' of LED operation.
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Old 4th Jan 2023, 4:38 pm   #23
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Default Re: Every day is a schoolday. House lighting circuits from the past.

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I wondered if an LT supply would negate all the safety concerns regarding high voltage and earthing issues
It'll bring in a new set of problems though. The low voltage supply will have to deliver a lot of current. If you short that out you'll effectively be arc welding and you're likely to temporarily blind yourself and suffer serious burns.
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Old 4th Jan 2023, 6:02 pm   #24
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Default Re: Every day is a schoolday. House lighting circuits from the past.

My dad's bungalow was built in 1947 and had VIR twin wiring to lights. Someone had added earths separately, in bare wire clipped to joists in the loft. ISTR the switch back boxes were wooden. He finally had it re-wired in the early 90’s.
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Old 4th Jan 2023, 6:22 pm   #25
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Default Re: Every day is a schoolday. House lighting circuits from the past.

We had some caravans at work that had a big sargent PSU for all the lighting, the setup didn't seem to last and there are few vans, if any, with low voltage lighting circuits. Notably the company that did do low voltage lighting circuits, Swift, also make campervans and mobile caravans which generally always use low voltage lighting for ease of running off a leisure battery.

As for the lack of earth on lighting circuits, the fluorescent light fitting in my grans garage was wired off the lighting circuit as normal but the earth connection was taken from the earth feeding the mains socket.
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Old 4th Jan 2023, 6:28 pm   #26
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Default Re: Every day is a schoolday. House lighting circuits from the past.

As mentioned above, flat twin without CPC was normal for lighting circuits up to 1966. The cable in this rose is 3/.029, equal to 1.3mm² and if there is a chopped-off or hidden CPC it would be 1/.044, equal to 1mm². As also mentioned, the cable is from the last years of the imperial wiring era because the conductors are not tinned. Tinning was essential for VIR and TRS cables to prevent sulphur in the rubber reacting with the copper, but was retained for much of the currency of imperial PE and PVC-insulated cable.

Sometimes, points like this with single insulated cores appearing through a hole in the ceiling are wired in conduit, especially in concrete construction. The conduit might be usable as a CPC especially if threaded rather than slip-jointed, and a connection can be made between the box and the fitting. If fitting a class I luminaire where the conduit has not previously been used as the CPC and its continuity unproven, in addition to an R1+R2 test and Zs test, it should ideally be confirmed with a Ducter high-current continuity test.

For light switch screws where no CPC is present, surface pattresses with isolated screw inserts are obviously OK, and early metal flush boxes were often provided with nylon inserts to insulate the screws which are safe for continued use if the box is not accessible. If normal modern flush boxes with metal screw lugs are used, the screws should be covered with press-in caps as mentioned. Some switch brands include these as standard.

Regarding use of cables from this era in general, deterioration can occur although most PE and PVC cables are still serviceable. The main problems with systems of this age are through damage and unsafe modifications, rather than from degraded insulation. In an attempt to improve high-temperature performance, antioxidants have at times been trialled in the PVC composition, which caused the phthalate plasticiser to exude, react with the copper and seep from the end of the cables as the so-called 'green goo.' This is easily recognisable, and along with embrittlement of the sheath due to exposure to the elements and contact with polystyrene, is the most frequently encountered mode of insulation failure. If none of these are present, the insulation resistance tests good at 500V and there is no sign of rodent damage etc, even the oldest polymer-insulated cables are usually fit for continued use. The only other contra-indication for re-use of cables from the 1960s-70s concerns aluminium conductors, which are rare but where they are found can be a nuisance as they are difficult to terminate reliably and are known for causing overheated connections. Correct use of anti-corrosive paste and pigtailing via compatible connectors can enable existing Al wiring to be safely retained.
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Old 4th Jan 2023, 6:37 pm   #27
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Default Re: Every day is a schoolday. House lighting circuits from the past.

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Originally Posted by Nickthedentist View Post
I don't think you're missing anything, but this would be unconventional at present, and could cause a lot of confusion unless you did it exclusively for your own personal use.

Don't forget that wires have to be thicker to deliver the same power at a lower voltage, though I appreciate that the far greater efficiency of LED lamps counterbalances this to a large extent.
There is in fact a 2 1/2 page section (715 Extra-Low Voltage Lighting Installations) in Part 7 of the wiring regulations. It's one section of the "Special Installations or Locations" part.

In general, the Wiring Regulations may not be as proscriptive as some people out with the forum would suggest - provided the basic safety and reliability principles are well understood and followed. As new techniques, or expectations, arise, there is no reason why they cannot be used on this basis just because they are unusual.

I have followed the European practice of using either mains or Extra-Low Voltage impulse (or step) relays for two-way and multiple-way lighting circuits which can be more convenient and saves losses in long interconnecting wires (strappers) between switches. It's not a common technique here and so might upset some less imaginative electricians but there's nothing inherently non-compliant about it.

PMM

For situations which are entirely new there's Regulation 133.5 "Where the use of a new material or invention leads to departure from the Regulations, the resulting safety of the installation shall not be less than that obtained by compliance with the Regulations, Such use shall be recorded on the appropriate electrical certification specified in Part 6".

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Old 4th Jan 2023, 8:15 pm   #28
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Default Re: Every day is a schoolday. House lighting circuits from the past.

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Quote:
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I wondered if an LT supply would negate all the safety concerns regarding high voltage and earthing issues
It'll bring in a new set of problems though. The low voltage supply will have to deliver a lot of current. If you short that out you'll effectively be arc welding and you're likely to temporarily blind yourself and suffer serious burns.
I can understand that could be like shorting a car battery were that level of current required. However, I wonder how much current a house full of LED bulbs would be drawing in total at a lower operating voltage? My LED torch operates far longer on three AA alkaline batteries than the equivalent with an old fashioned bulb would. Lower power consumption is surely the point of LEDs.

However, having done a bit of research this afternoon, as always, it seems there is more to it than plugging in a strip of LEDs. The LED strips in bulbs are wired in series so often operating at a fairly high voltage with little step down. Depending on the arrangement and output required from the bulb there needs to be some appropriate circuitry in the bulb so ultimately it would seem simpler to work from the established standard supply voltage and step down as little or as much as needed like any other appliance.

I knew little about them until today but was curious as to what was inside beyond the light emitter so today has indeed been a schoolday.
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Old 4th Jan 2023, 9:53 pm   #29
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Default Re: Every day is a schoolday. House lighting circuits from the past.

The staircase lighting at my late brother-in-law's house in France used a bistable relay (Carpenter relay?) controlled by spring-loaded push switches (push for ON, push again for OFF) for its multi-point switching. I did find a web site for brits that explained French wiring practice that said that intermediate switches for control from 3 or more positions, were unknown in France. I have not come across that type of latching relay in the UK.

Some 30 years ago, when I wanted to be able to control the exterior light of my garden shed from both the shed and the house, I couldn't find any latching relays, so used three valve-base relays, two with 12V coils controlling the third mains relay. Momentarily pushing one push button turns on and latches the mains relay, and pushing a second button interrupts the mains coil current to turn it off. A run of 4 core telephone cable (only 3 used) connects the house and shed, which only has to carry the momentary 12V pulses required to operate the relays.

Last edited by emeritus; 4th Jan 2023 at 10:18 pm.
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Old 4th Jan 2023, 10:03 pm   #30
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Default Re: Every day is a schoolday. House lighting circuits from the past.

This is a standard device in France, called a télérupteur. It is normally a ratchet relay where a solenoid advances a cam wheel stepwise, alternately opening and closing the contacts.
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Old 4th Jan 2023, 10:30 pm   #31
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Default Re: Every day is a schoolday. House lighting circuits from the past.

Thanks for the information. I never bothered seeing how what I thought was a relay, worked. I had read about, but never encountered, Carpenter relays that use coils and permanent magnets to latch the armature stably in either position for ON/OFF switching in response to successive impulses, and thought it might be one of those.
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Old 5th Jan 2023, 6:07 pm   #32
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Default Re: Every day is a schoolday. House lighting circuits from the past.

Back in 1967, we had some kilns installed by our sister company. They had modulating control valves, with modified Satchwell controllers modified from their use in large air conditioning systems. They contained Carpenter relays, such that the valve could open, stay where it was, or close as the two term (P + I) controller required.The whole system was a combination of Elliot Satchwell. I think both companies were then part of Mr. Weinstock's very successful GEC. Before the lunatics took over his efficient asylum.
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Old 5th Jan 2023, 8:52 pm   #33
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Default Re: Every day is a schoolday. House lighting circuits from the past.

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Originally Posted by emeritus View Post
The staircase lighting at my late brother-in-law's house in France used a bistable relay (Carpenter relay?) controlled by spring-loaded push switches (push for ON, push again for OFF) for its multi-point switching. I did find a web site for brits that explained French wiring practice that said that intermediate switches for control from 3 or more positions, were unknown in France. I have not come across that type of latching relay in the UK.
It's quite common to use impulse relays for multipoint lighting switching in both France and Germany - I don't know about the rest of Europe but Finder, who are Italian, are one prominent maker of the realy type used. Intermediate switches are also used in Germany.

The relays, in their conventional form, use the coil to advance a pawl which indexes a ratchet wheel combined with a cam. The cam has alternate lobes which open or close the contacts, much in the same way as in a cord-opertaed light switch. Anything between one to four sets of contacts may be fitted in all combinations of N/O and N/C. Coil voltage may be 6, 8, 12, 24, 110 or 230 V and AC and DC types are made. Some electronic version are also made now. The range includes DIN rail and surface mounting types.

Typically, they might be fitted within the distribution board, usually a three-phase set-up, or in a separate enclosure.

This link is to one range made by Finder. It just happens to be the last type I used - many other makes are available. https://cdn.findernet.com/app/uploads/S20EN.pdf

All the large manufacturers such as ABB, Finder and Schneider make them as well as several others and some more obscure makes. A limited range is readily available in German DIY stores. They are also sold by a number of UK trade outlets but the prices seem generally to be higher than in Europe, probably because far fewer are sold.

PMM
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Old 6th Jan 2023, 12:22 am   #34
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Default Re: Every day is a schoolday. House lighting circuits from the past.

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I did find a web site for Brits that explained French wiring practice that said that intermediate switches for control from 3 or more positions, were unknown in France.
Don't trust all that you read on the web. Intermediate switches, though rare, are not unknown in France. They are called "permutateurs" in French.
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Old 10th Jan 2023, 11:29 am   #35
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Default Re: Every day is a schoolday. House lighting circuits from the past.

I once came across an interesting bit of lighting wiring in a metal flourescent fitting. Touching it had felt a bit 'tingly' and prompted investigation.

The fitting had been wired into a non-earthed circuit. The installer had found a nice three way choc-block inside, and had decided the three terminals must be for live, switched live, and neutral.

The outer two were clearly powering the light, so switched live and neutral were connected to those. (Some will be ahead of me here...)

Yes, the live was on the centre terminal, quite obviously screwed directly to the metalwork of the enclosure...

The lady of the house informed me that her late husband had fitted it more than 20 years earlier!

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Old 10th Jan 2023, 4:16 pm   #36
Lucien Nunes
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Default Re: Every day is a schoolday. House lighting circuits from the past.

For your amusement; a lighting circuit that appears to achieve the impossible. It does so by combining two long-obsolete methods that were in use a century ago but are now generally prohibited.

I'm sure we're all familiar with looping the supply cable in and out of either the light fittings or the switches, when using multicore cable e.g. twin and earth. Looping via the lights was standard for much of electrical history, but today looping via the switches is popular as it makes a neutral available to power smart and wireless switches. As it happens, the scheme in my drawing loops via the switches.

A lighting point is shown with two-way switching. The supply cable arrives at the first switch, loops through the two switches in turn and then continues on its way to the rest of the circuit. The light is fed by cables from each switch position.

But... all the cables are single-core!

What are the names of the two obsolete practices employed?
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Old 10th Jan 2023, 4:56 pm   #37
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Default Re: Every day is a schoolday. House lighting circuits from the past.

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Originally Posted by emeritus View Post
I did find a web site for Brits that explained French wiring practice that said that intermediate switches for control from 3 or more positions, were unknown in France.
Don't trust all that you read on the web. Intermediate switches, though rare, are not unknown in France. They are called "permutateurs" in French.
Still relevant to lighting wiring, the names of switches in other languages can be quite revealing as to their intent. In Polish, a two-way switch is known as "wyłącznik schodowy" which translates as "staircase switch" and an intermediate switch is "wyłącznik krzyżowy" which translates as "cross switch". I had to figure these out in a hurry when helping some relatives with the electrical installation in their house. It had been wired, but there were no fittings, just bare wires hanging out of the walls. It was all in the pre-harmonisation colours, too, blue for neutral, black for live and green/yellow for earth.

Figuring out what did what was quite a challenge. I'm quite proud of having identified wiring for an intermediate switch on the hallway light!

Chris
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Old 10th Jan 2023, 5:02 pm   #38
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Default Re: Every day is a schoolday. House lighting circuits from the past.

Re #36, I guess it could conceptually correspond with the arrangement of Fig 20 from the attached page from Odhams "Radio Television and Electrical Repairs", showing a 2-way switching arrangement recommended for new installations. The neutral (black) conductor would be routed directly from the consumer unit to the LH switch position (but not to the switch itself), rather than directly to the lighting point, with a single black wire to the ceiling rose and an additional single black wire connected between the two switch positions, possibly continuing to the next lighting point as no electrical connection is made to the RH switch itself. The Fig 20 arrangement is not given a name in the descriptive text, which is a couple of pages further on.
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Old 11th Jan 2023, 7:17 pm   #39
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Default Re: Every day is a schoolday. House lighting circuits from the past.

emeritus, and other readers, your the top illustration shows the way two lighting was often wired when using conduit, three VIR or plastic later, singles. Ted
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Old 12th Jan 2023, 3:15 pm   #40
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Default Re: Every day is a schoolday. House lighting circuits from the past.

Quote:
the arrangement of Fig 20 from the attached page from Odhams "Radio Television and Electrical Repairs"
In the electrical trade we call fig. 19 'conversion' 2-way and fig. 20 'conventional.' An advantage sometimes quoted for the 'conventional' configuration is that it does not require 3-core+earth cable.

Historically, a very common shortcut for 2-way switching of the upstairs light in a stairwell was to borrow the line from the adjacent lower hall light switch to feed the common of the downstairs switch, send a twin+earth with two strappers (L1 & L2) to the upstairs switch, and then just the switched line from the upstairs switch common to the top light fitting which took its neutral from the upstairs lighting circuit. This avoided any 3C+E but if the upstairs and downstairs circuits are separate then this results in a borrowed neutral, dangerous if one circuit only is isolated because the other can make it live again, and incompatible with RCBOs as both circuits are unbalanced. It is often necessary to correct these cheapskate bodges when installing new consumer units as the borrowed neutral can't be left in place.

There is a theoretical objection to the conventional method (fig 20) in these days of non-tungsten lighting, if the cables form a loop that acts as a radiator for interference generated by the electronics in the light (and indeed it was for the noise generated by a 50Hz fluorescent). The 'conversion' system has no unbalanced currents in any cables and is therefore preferable and used almost universally today.

However, returning to my puzzle. All the cables are single core. There is just one core run between the switches, yet the setup achieves both 2-way switching and passes the supply onwards to the next room. All the fittings are earthed, too. How is it done?
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