Using existing lighting wiring for 12V

[Justin Passing]

Mate wants to do this, with rechargeable battery solar charged.

Is it permitted to use ELV on standard cabling at the same time as normal mains on the sockets?

 

[Tigercubrider]

so do you mean he intends to have a ring main with 240v AC still connected and add 12v DC?
so all his 12V equipment will be live with 240?

If I was using a mix of voltages and AC/DC I would keep everything separate and use non compatible outlets.

 

[Justin Passing]

No he'd disconn the lighting ccts from mains, and go instead to his 12V system by the consumer unit.

Is there a reg about using the same cable type with different voltages? His existing light switches would be DC as well... What's the DC rating for those??

 

[ericmark]

Two problems, cable size for increased amps, and volt drop. With LED lighting designed for 12 volt DC the voltage range typically 10 - 30 volt, so should be OK volts wise if correct bulbs used.

Assuming some where there is a item rated 6 amp this means total 72 watt, my living room light is 48 watt.

I have done it with a farm in the Falklands, but used 24 volt centre tapped, so could use mixture of 12 and 24 volt.

However this was in the 80's so fluorescent fittings, not LED, and also inverters back then used a far bit of power on stand-by. Today they are far better, so personally I would use a 5 amp socket connected to original 230 volt lighting supply, and a connect the lights to a 5 amp plug, and have a second 5 amp socket connected to an inverter, then really easy to unplug from one socket and swap to other, so you can both use 12 volt at 230 volt although not at same time.

 

[Justin Passing]

Thanks
So the cabling is ok to use from an identification point of view.
OK.
Switches? Switches are often rated far lower for DC current than AC. I believe they prefer different contact materials to not degrade.
(Keep a "points file" handy )

As far as I know, a LED lamp fitting is going to be a string of a few LEDS, and a resistor to limit the current, so a small voltage drop wouldn't be significant.
I see 1sq mm is 18.1 mohms per metre. Can look at that.
Yes, 60 or 72 watts per floor could be a limitation, though your 48W sounds like a lot, though our kitchen is up there.

 

[bernardgreen]

a LED lamp fitting is going to be a string of a few LEDS, and a resistor to limit the current,

That is true for LED strips and tapes

but for other 12 Volt lamps there is invariably a driver to produce a controlled current through the LED element(s).

Some of these drivers will maintain the correct current irrespective of the supply voltage ( within limits )

 

[ericmark]

If using 12 volt do not want to waste power, so use bulbs I linked to which will not need a driver resistor. Look at lumen per watt.

Living room 22 foot by 18 foot so large, and one single light fitting, so use an 8 bulb chandelier with 8 x 6 watt SES candle bulbs. Which is really not enough, so also have display cabinet lights which add to it. Last house slightly smaller living room, with two chandeliers with 5 bulbs each, tried 3 watt and not bright enough so went to 5 watt, so 50 watt.

I did on old house use a 4 foot and 5 foot fluorescent in kitchen, the 5 foot was 65 watt, they stopped making the 65 watt fat tubes so went to 58 watt, then to 22 watt LED replacement, but son when he started living there swapped it for 16 x 3 watt down lights so 48 watt just for half of kitchen.

Small 16 foot caravan and with all the lights on it used around 14 amp. OK rarely used them all, but that was just the 12 volt also some 230 volt as well.

The Lidi smart LED light strip I use in the display cabinet 12 volt 15 watt powered by a 12 volt 24 watt power adaptor it is bright but nothing on the packaging to say what the lumen output is, and as a basic rule of thumb if not lumen stated they are for decoration only, unless lumen stated they can be very inefficient.

 

[333rocky333]

There is a table in the Regs for identification of cables, Ac and Dc was both Red and Black, till the Ac colours changed, not sure what Dc is now.
You can always over sleave the cores if need be or i guess its still ok to mark them + and -

 

[Justin Passing]

No expert but from what I've seen it's the mains LEDs which have the regulation, presumably because the rectification is rough. If you can flatten the peaks of the half sine waves you reduce flicker.

Even car "bulbs" I've cut up have a resistor in. (Some need a protection diode too - maybe not the latest.) The forward voltage goes -ve wrt temperature, so they'd be keen to "run away" and at around 3.2 volts don't fit 12 V very well - which I imagine are the reasons for the R. The R was on the chip on the ones I looked at.
Best practice in the application notes is one R per LED, but that's wasteful.
Sure you want efficiency, which means under-driving them, but that reduces output and they get a lower price. So reducing the voltage a bit is probably a good thing, especially considering the substrate tº/W is high.

If there's nothing to say you can't mix LV & ELV with same cabling I guess it's ok, but yes, markers would be appropriate.

Still don't know about light switches. Does anyone have a copy of BS EN 60669-1 2018?

 

[mattylad]

The cabling is fine, for anything marked with a 230v rating it is generally "upto" 230v etc.

 

[bernardgreen]

Still don't know about light switches

A light switch designed to switch 230 Volts AC may not be suitable for switching 12 Volts DC

AC voltage changes polarity 100 times a seconds and at each change there is a point in time where the voltage is zero.

When a switch is switched OFF an arc is formed as the contacts are separating.

A 3 mm gap between the open contacts will not ( normally ) allow an arc to persist. The arc will ( normally ) extinguish when the voltage wave form goes through zero volts.

With a DC supply the voltage does not go through zero volts and hence if an arc is formed then it may persist until the switch is damaged.


( normally ) = when the load being switched is not inductive. Motors and magnetic transformers are inductive loads

 

[Justin Passing]

A light switch designed to switch 230 Volts AC may not be suitable for switching 12 Volts DC

AC voltage changes polarity 100 times a seconds and at each change there is a point in time where the voltage is zero.

When a switch is switched OFF an arc is formed as the contacts are separating.

A 3 mm gap between the open contacts will not ( normally ) allow an arc to persist. The arc will ( normally ) extinguish when the voltage wave form goes through zero volts.

With a DC supply the voltage does not go through zero volts and hence if an arc is formed then it may persist until the switch is damaged.


( normally ) = when the load being switched is not inductive. Motors and magnetic transformers are inductive loads

By "don't know about", I meant I don't know what their DC specification is, if any. Discussions about modes of failure, contact materials, speed of switching, spark temperature or duration, protection diodes or suppressor capacitors etc might be technically interesting but this comment from a random forum (2018):
"I spoke at length with MK and they were adamant that their range of AC switches were not suitable for use on DC and could not give a derating factor."
tells me no, you can't use ordinary mains light switches. Any consequential problem would see you as incompetent. An insurer would call it part of an electrical installation, which would evidence of conformity which you can't provide.

Caravan or boat switches may well be appropriately rated electrically, but may still not be approved for use in a house, I don't know.
It may be that by now one of the domestic accessory mfrs has got their switches approved for DC - please let me now if you find one.

One could use relays to switch the DC, with a tiny current to the light switch, but then the worms in the can surround the relay suitability, enclosure and whatnot.

The cabling is fine, for anything marked with a 230v rating it is generally "upto" 230v etc.

Ta.



I found some stuff - dumping the refs here...
https://electrical.theiet.org/wirin...echnical-considerations-for-dc-installations/

The wiring colour codes make mains cable OK for DC, part 10 of:
https://www.electricaltechnology.org/2020/07/electrical-wiring-color-codes-nec-iec.html
1sq mm is 18.1 mohms per metre, by the way. Could also be a problem.

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I have just found reference to SELV and FELV circuits. (Sub 60V)
SELV would not be suitable I think, because you need to connect 0V to Earth to reduce EMI.
FELV may be a suitable standard, but
"The SELV cables must be double insulated or pass through plastic conduits especially when they are likely to come into contact with other circuits."
probably applies to FELV as well, and wouldn't apply to existing mains wiring.

 

[flameport]

The wiring colour codes make mains cable OK for DC, part 10 of:
https://www.electricaltechnology.org/2020/07/electrical-wiring-color-codes-nec-iec.html

That information is outdated, colours for DC circuits are red/white or red/blue/white depending on how many conductors are used.

It would be far easier to buy a 12VDC to 230VAC inverter and install it adjacent to the consumer unit, using all of the existing lighting circuits and accessories.
Any minor losses in the conversion from DC to AC would likely be no worse than the losses of using 12V DC over long cables.