extra low voltage 'ring'?

[MortarThePoint]

37 minutes ago, SteamyTea said:

Making sure it cannot get too hot.

Keeping the temperature safely below the combustion temperature of all the nearby materials.

Oh, I'd incorporate a thermal shutoff and PTC fuse. But as I say I haven't done enough thinking yet

[SteamyTea]

7 minutes ago, MortarThePoint said:

But as I say I haven't done enough thinking yet

Thinking is overrated.

If I said/typed what I was thinking, I would be in prison, frequently.

Edited January 16, 2023 by SteamyTea

[MortarThePoint]

Interestingly, if you adopted a completely centralised approach where all lights are directly powered by a centralised controller, you could probably wire it in 0.5mm2 T&E (which is apparently going to be available) if using 48VDC. Extending Table F6 to 0.5mm2, that should be 88mV/A/m. A 10W 48VDC light at 33m (66m round trip) would then suffer a voltage drop of 88mV/A/m * (10W / 48V) * 66m = 1.2V or 2.5%. I would expect that with a good choice of central control location, pretty much all lights could be <10m so suffer less than 0.367V --> 0.8% voltage drop. Another plus for 48VDC over 24VDC which would suffer 4x the percentage voltage drop.

 

You'd have lots of long cables to run, but have only one central brain to which all switches communicated. A 10m 0.5mm2 cable would probably cost about £2.

Edited January 16, 2023 by MortarThePoint

[joth]

5 hours ago, MortarThePoint said:

On 12/10/2022 at 14:24, joth said:

24V is for home automation and LV lighting, all speced and installed by myself.

I have a couple of questions (I'm learning):

1. Why 24VDC rather than 48VDC?
2. Where do you get your bulbs? I have seen lots of 24VDC strips, but not bulbs
3. Bulb fittings, I would like to use standard bayonet or threaded bulb fittings

 

1. LED strips only (?) come in 12V or 24V versions, with 24V the far superior. This is most of the low-voltage lighting, using constant-voltage dimmers. The other items are some accent / marker lights; these are constant current and only have about 3V forward voltage on the diodes so 24V vs 48V is moot (unless putting a LOT of them on one dimmer channel).

2. Yes. 24V CV LED strips, and various 300mA and similar constant current LEDs is small low-level wall marker lights and such like.

3. Good luck!

 

[MortarThePoint]

Of course that centralised approach to automation isn't limited to low voltage DC lighting. I have just done a radial lighting layout for the house GF and it uses 79m of 1.5mm2 t&e and 84m of 1.5mm2 3core&e (both could be thinner). I think with a centralised approach at the CMU that could all be replaced by 173m of 0.5mm2 t&e. If the centralisation was better (e.g. at hall), then I think that could be reduced further. The 84m of 3core&e is for switches and assumes 4m for each switch. If I didn't want to use wireless switches, I could use low voltage/current bell wire costing about 5p per metre or 50p per switch.

• 79m of 1.5mm2 t&e and 84m of 1.5mm2 3core&e 79m*£0.43/m + 84m*£0.61/m = £34 + £51 = £85
• 173m of 0.5mm2 t&e and 126m of bell wire 173m*£0.20/m + 126m*£0.05/m = £35 + £6 = £41  [£81 is using 1.5mm2 t&e for light]

_________________

Cables:

• https://www.tlc-direct.co.uk/Main_Index/Cable_Index/Twin_and_Earth/index.html
• https://www.tlc-direct.co.uk/Main_Index/Cable_Index/Three_Core_Grey/index.html
• https://cpc.farnell.com/pro-power/bellwirecca/bell-wire-cca-conductor-100m/dp/CB14615 [though would prefer multi strand]

Potentially dubious PCBS:

• 16way WIFI relay board £12 https://www.aliexpress.com/item/1005003297328162.html
• 16way USB relay board £14 https://www.aliexpress.com/item/1005001666658945.html
• 32way ESP32 relay board £110 https://www.aliexpress.com/item/1005004281943758.html  [NOTE: choose correct version if doing own firmware]

 

Edited January 16, 2023 by MortarThePoint

[MortarThePoint]

If adopting any weird and wonderful wiring solutions, I think it would be wise to make provision for it to be changed to a more normal setup if required (e.g. selling the house). In the centralised approach, that would be a matter of running t&e or 3core&e from light positions to switch positions. In the future a Sparkie could come along and connect that cable to the light and the switch and then you'd have a more normal setup. Still not a conventional radial, but I think it would still be classed as a radial, just with one light on each spur and a mega junction box. The extra cost of running t&e or 3core&e from light positions to switch positions would suck but think of it as insurance. It could be done with cheap 1.0mm2 t&e so in my GF case cost 84m*£0.33/m = £28 of cable. If you allowed a Sparkie 30minutes for each one (generous) then it would cost about £20 each to rewire.

 

Would be much harder is you omitted switches entirely. Then I guess you could still route the 'not connected' t&e cable to the appropriate location (in oval conduit with slack) for a backbox etc to be cut in later and hope that nobody damages it before it's needed as there wouldn't be a safe zone to remind you the wire is there.

 

In the BEFORE case you could connect the Earth to the light and switch and so avoid the cable wandering off.

 

For reference, I saw MK Logic Plus switch (K4871WHI) has the following Terminal Capacity: 4 x 1mm², 4 x 1.5mm², 3 x 2.5mm², 2 x 4mm², 1 x 6mm²

[MortarThePoint]

In fact you could use Single&Earth (example, though more expensive than t&e so defeats the point slightly) for the automation wiring just to the SWL & Earth terminals of the lights and the rest of the light wiring is as per a normal radial. CTRL and 'Normal Radial' would have to share their Neutral so as to work with an RCD or MCBO which you would definitely want.

 

 

Could even completely wire the light ready for the change and only need the switch rewiring. CAREFUL: couldn't be done in the no switch scenario as then there would be a hidden dangerous wire (though should only be Neutral as you wouldn't power the radial's Line).

All of this will kill your cat!

Edited January 16, 2023 by MortarThePoint

[joth]

That seems crazy amount of cable to pull. In the before case I see 4x T&E per light fitting. That's on top of a data bus If you have smart switches (knx or Loxone tree).

 

In my build we did one switch line T&E per light fitting, direct from the lighting cabinet to the light, plus the control bus linking up switches. I can still convert this to more or less conventional if ever needed by replacing the lighting cabinet with a bank of 24V to mains relays. Your other 3 T&E seem overkill 

[MortarThePoint]

1 hour ago, joth said:

That seems crazy amount of cable to pull. In the before case I see 4x T&E per light fitting. That's on top of a data bus If you have smart switches (knx or Loxone tree).

 

In my build we did one switch line T&E per light fitting, direct from the lighting cabinet to the light, plus the control bus linking up switches. I can still convert this to more or less conventional if ever needed by replacing the lighting cabinet with a bank of 24V to mains relays. Your other 3 T&E seem overkill 

It is a lot of wires to pull, but in my case that doesn't take long as I have an open ceiling void atm.

 

I count the following to the light in the before case:

1. T&E from radial IN
2. T&E from radial OUT (not for all)
3. T&E to switch
4. single&E to CTRL

And at the switch:

1. T&E to light (only E connected)
2. bell to CTRL

The bold is what a normal wiring would have.

 

Your setup is need having only one cable to the light and only one cable to the switch. I get that you could revert your setup to something a bit more normal, but that would still be quite an unusual setup. As I understand it, my original BEFORE/AFTER drawing (3 posts back) is your layout with the addition of the light to switch cable.  That drawing could be improved by pre-connecting the light to switch cable at the light end (but note, the blue wire would need a brown sleeve in the switch). This newer layout would allow it to revert to a totally standard radial setup with some wires left behind.

 

The main issue I see (other than the amount of wires) is the bell wire shares the same containment as the T&E between light and switch. Sparkies would normally twitch at that (low voltage and mains sharing the same containment) but there are two things in its favour:

• All the bell wire (and the single& earth) would use permitted (aka 'safe') zones as if it was mains
• The CTRL would be in an earthed metal cabinet with appropriate labelling. If signals need to exit this metal cabinet for attachment to something (e.g. Raspberry Pi / PC) then an optically isolated USB connection could be used.

If you have used T&E between your switch and the cabinet, then you could revert to a system without relays:

1. At cabinet, connect one switch wire to Line
2. At cabinet, connect other switch wire to SWL of light

This would create an usual star circuit, but be easy for a Sparkie to understand. Here is a rewired example with just two lights, but more would just be similar:

AFTER:

red and different blue for clarity, earth omitted but would be wired.

 

Edited January 17, 2023 by MortarThePoint

[MortarThePoint]

This is perhaps a clearer drawing of that rewire star circuit (before and after):

red and different blue for clarity, earth omitted but would be wired.

 

The main downside of this type of star network is that there are two round trips for the current path to the CU and so the voltage drop is larger than if just one current path to CU and one to switch. Probably weighing up 2x10m vs 10m + 4m and probably comparable to a radial circuit that has longer current paths to the light as have gone via other lights rather than direct.

Edited January 17, 2023 by MortarThePoint

[MortarThePoint]

For clarity and to stay on thread topic, all of the before diagram could be 48VDC (or 24VDC), as indeed could the after diagram. [Note: with 1.0mm2 T&E BEFORE: (2*10m)*44mV/m/A*(10W/48V) = 183mV --> 0.4%, AFTER: double that so 367mV --> 0.8% if still at 48VDC or 77mV --> 0.03% if mains].

Edited January 17, 2023 by MortarThePoint

[Alan Ambrose]

I don''t know if this helps any or just makes life more complicated - our 4-year old conversion was wired with 4-wire to the light switches, which seems pretty sensible.

 

The extra wire was the N bus - this allows the standard mains set-up to be converted to mains powered wifi smart-switches. I have used this on a few occasions e.g. for outside lights.

 

I was very grateful to find the N already there, rather than having to try to borrow it from somewhere else (which is, of course, dead dodgy). I appreciate that this is already 'old-tech'.

[MortarThePoint]

16 minutes ago, Alan Ambrose said:

I don''t know if this helps any or just makes life more complicated - our 4-year old conversion was wired with 4-wire to the light switches, which seems pretty sensible.

 

The extra wire was the N bus - this allows the standard mains set-up to be converted to mains powered wifi smart-switches. I have used this on a few occasions e.g. for outside lights.

 

I was very grateful to find the N already there, rather than having to try to borrow it from somewhere else (which is, of course, dead dodgy). I appreciate that this is already 'old-tech'.

 

If going the more standard route, I had planned to do 3core&e between light and switch. You can now get smart switches that don't require Neutral (e.g. Sonoff). I guess they periodically charge a capacitor via the light at too low a current to light the bulb. May not work with all bulb types, I don't know.

[MortarThePoint]

Well here is a wiring strategy that falls back to a very standard approach by only rewiring back near the Consumer Unit. Nothing needs doing at the lights or the switches.

The only thing that is weird about the "Mains Normal" end result is that it is a star circuit rather than a radial. That's because each light (or group) and switch is on a spur off a central set of bus bars.

 

The Sense Input in the mains "Mains Smart" case is a bit tricky but could be done in a couple of easy ways:

• Relay switching e.g. 5V logic using a mains coil
• Mains optoisolator (e.g. Aliexpress, though that uses about 0.4W for the opto which is disappointing)

[MortarThePoint]

11 hours ago, MortarThePoint said:

Well here is a wiring strategy that falls back to a very standard approach by only rewiring back near the Consumer Unit. Nothing needs doing at the lights or the switches.

The only thing that is weird about the "Mains Normal" end result is that it is a star circuit rather than a radial. That's because each light (or group) and switch is on a spur off a central set of bus bars.

 

The Sense Input in the mains "Mains Smart" case is a bit tricky but could be done in a couple of easy ways:

• Relay switching e.g. 5V logic using a mains coil
• Mains optoisolator (e.g. Aliexpress, though that uses about 0.4W for the opto which is disappointing)

 

I'm concerned that the Mains Smart has Neutral side switching. Subject to confirmation, it looks to be allowed by BS7671 but still feels funny. It feels less safe than Line side switching as the light fitting will still have Line voltage present when changing a bulb with the light off, rather than in the normal situation when there would be Neutral present which is close to Earth potential.

Edited January 18, 2023 by MortarThePoint

[joth]

38 minutes ago, MortarThePoint said:

 

I'm concerned that the Mains Smart has Neutral side switching. Subject to confirmation, it looks to be allowed by BS7671 but still feels funny. It feels less safe than Line side switching as the light fitting will still have Line voltage present when changing a bulb with the light off, rather than in the normal situation when there would be Neutral present which is close to Earth potential.

 

Yeah totally agree neutral switching feels weird. I considered this just for some of the equipment inside my control cabinet: for efficiency it's nice to power down the DMX dimmer modules when not in use. They have a combined L terminal to power the dimmer and passthru to the lights being dimmed, but the N terminal is only required to power the module's internal logic (the light fitting's N line returns straight back to the RCBO, not via the dimmer module). So for simplicity it felt nice to just switch the N line on the dimmer module to power it down, as this way the switched load is only about 2W per dimmer, not the sum of all light fittings.

I didn't do this in the end, even though the switched N line is purely internal to the cabinet and not out to the fitting. (In fact ultimately I replaced the cheap AlieExpress dimmers with Whitewing ones with much lower standby current per channel, and so now I just leave them permanently powered)

 

 

(Full disclaimer: I haven't really followed the rest of your recent posts - it all seems technically possible but adds so practical overhead for something hopefully never needed, it is very far from the philosophy I followed I don't have much to add.)

 

[Carrerahill]

On 16/01/2023 at 13:53, MortarThePoint said:

Not so sure what you mean about thermal safety, but some thoughts (48VDC):

1. Wiring: Similar current limits will apply, though perhaps a factor of Sqrt(2) will come into play (DC vs AC), so de-rate On Site Guide figure by say 33%. I expect if limited to 5A / 7A, you'd be OK in all installation methods with 1.0mm2 / 1.5mm2 and have up to 240W / 336W of light at your disposal with out any diversity, probably double with diversity. 240W is something like 30no. 8W bulbs or 75m of LED strip.
2. DC:DC converters: A DC:DC converter could run with an efficiency >95%. If 90% efficient and a 9W light, you need to dissipate 1W of heat. Radiative heat loss alone would get rid of 1W from around 5cm x 5cm at 75C (22C ambient), but that wouldn't be the only heat loss method. [Note: 75C is hotter than the PVC allows] Convection if open will probably dominate and conductive if a spot will help. I haven't really run any proper calculations on this, but it feels manageable.
3. Intelligence: Average power would be in the uW range when light not on. When light on, it would be dominated by the relay (if not MOSFET controlled) and likely 0.1W.
4. Local Switch: like a Bluetooth remote so power in uW range.

 

The low voltage itself goes a long way. What are you thinking of for the intrinsically safe? To have it as a product you'd have to do EMC testing etc.

 

Based on 6A on a 48V system, the volt drop would be about 2.2V at 10m of 1mm² (0.0185 Ohms)- at 25m it would be 5.55V. 

 

You would want to use about 3.0mm² (0.00615 Ohms) wire for anything up to 26m run, 4.0mm² (0.00471 Ohms) for up to 34m and so on.

 

If it was 24V it would be even worse - around a 8.5mm² cable for 6A at 34m.

 

I think (know) the whole thing could be done by an individual with a lot of time on their hands and a real passion for DIY systems but it's not going mainstream.

 

240V supplies are becoming safer and safer and I just don't see an issue with using 240V throughout and using SELV power supplies at source. 

 

We are now doing warehouses with HV (11kV) distribution within them to cut down on cable sizes and site transformers around the warehouse as needed - so things are sort of going to opposite way. 

 

You talk about making your own lights, assume you will make an LED luminaire? Then its SELV anyway and you are running it from a driver/transformer anyway.

 

 

 

 

 

 

 

[MortarThePoint]

29 minutes ago, joth said:

 

Yeah totally agree neutral switching feels weird. I considered this just for some of the equipment inside my control cabinet: for efficiency it's nice to power down the DMX dimmer modules when not in use. They have a combined L terminal to power the dimmer and passthru to the lights being dimmed, but the N terminal is only required to power the module's internal logic (the light fitting's N line returns straight back to the RCBO, not via the dimmer module). So for simplicity it felt nice to just switch the N line on the dimmer module to power it down, as this way the switched load is only about 2W per dimmer, not the sum of all light fittings.

I didn't do this in the end, even though the switched N line is purely internal to the cabinet and not out to the fitting. (In fact ultimately I replaced the cheap AlieExpress dimmers with Whitewing ones with much lower standby current per channel, and so now I just leave them permanently powered)

 

 

(Full disclaimer: I haven't really followed the rest of your recent posts - it all seems technically possible but adds so practical overhead for something hopefully never needed, it is very far from the philosophy I followed I don't have much to add.)

 

 

It would be foolish anyway to work on an automated light setup only taking note of the wall switch and ignoring the fact that the automation could have turned the light on.

 

The number bayonet is a much better solution that a threaded bulb for this sort of reason. The threaded section of such a bulb is Neutral.

[MortarThePoint]

6 minutes ago, Carrerahill said:

Based on 6A on a 48V system, the volt drop would be about 2.2V at 10m of 1mm² (0.0185 Ohms)- at 25m it would be 5.55V. 

You're a a bigger scale than my humble domestic needs. 6A at 48V is nearly 300W and that may be more than the entire house's lights. At 10m would be 20m of current path s twice as bad as you suggest. I'd hope that I would only have maximum 10no. 10W lights on at any one time so that's 100W total. If they were all at 10m on the same 1.0mm2 spur that would be (100W / 48V) * (2*10m) * 44mV/A/m = 1.8V --> 4% which is too high.

 

I'm preferring the star network approach in which you have only single light or light groups on each spur. If a group they all get controlled together. I don't think any group would be more than 4 lights and so unlikely to exceed 40W. 1.0mm2 cable at 10m would suffer 0.7V --> 1.5% under that scenario which is OK, not great. I'd prefer to use 1.5mm2 cable as it isn't much more expensive (+37% at TLC).

 

17 minutes ago, Carrerahill said:

We are now doing warehouses with HV (11kV) distribution

Interesting, I guess there is no equivalent to an RCD or RCBO as your toast too quickly for it to trip.

[MortarThePoint]

Some prices for reference, all per 100m drum from TLC (though Prysmian is around for similar):

• T&E : 1.0mm2 £33.50, 1.5mm2 £43, 2.5mm2 £64, 4.0mm2 £108, 6.0mm2 £162, 10.0mm2 £275, 16.0mm2 £428
• 3&E : 1.0mm2 £44.50, 1.5mm2 £61

[Alan Ambrose]

>>> You can now get smart switches that don't require Neutral

 

That's true. I think they're a bit of a bodge though and if you look at the reviews they don't work well for some people - so I wouldn't want to rely on them as a long term solution.

 

If you have an existing house wired without neutrals to the switches, I can understand that it's an easier option than stealing neutrals from someplace.

 

 

>>> We are now doing warehouses with HV (11kV) distribution within them to cut down on cable sizes and site transformers around the warehouse as needed

 

Makes sense when you need 'proper power' everywhere. You probably run these in man-sized metal conduit or a cable tray well out of everyone's reach though - presumably you wouldn't put them in plasterboard stud walls.

 

In a lowish energy house, I agree with MortarThePoint, I expect to be using only 100-200W of LED light total - say 30 off 12V 5W MR16s and 25 off 12V 2W G4s. In practice, you'll probably want to switch these in say 12-16 groups.

 

[MortarThePoint]

Some useful dimensions for 3&e cable:

https://www.expertelectrical.co.uk/6243y-cable#product-specs-dimensions