12v lighting on a domestic environment

I have done several such installations, in off grid homes without any mains supply.

The regulations seem to be mainly written for mains voltage installations, and one might have to accept some departures from these regulations.

For example it can be a challenge to achieve fast enough disconnection times, but does this matter at 12 volts ? Is a CPC even required at 12 volts ?

The last one that I did was originally 3 wire DC at 12/0/12 volts, with 12 volts for lighting and 24 volts for appliances. Recently changed to 3 wire DC at 26/0/26 volts with 26 volts for lighting and most appliances, including some very substantial loads. 

I'm not so sure of the advantages of 12V - at one twentieth of the voltage you need twenty times the current to provide the same power - e.g. 12W at 12V is 1A - compared with just 50mA at 240V. So if anything the risk of fire probably increases rather than decreases. In the original part P of the building regs, ELV lighting (with a few exceptions) was notifiable because of these risks. The increased current also means increased voltage drop - so likely to need larger conductors rather than smaller ones. Also you'll likely close the door to some of the safety devices that can reduce those risks - RCDs or even AFDDs. If you're thinking of 12V d.c. then be aware that d.c. arcs are much harder to break than a.c. ones - so in some cases you may need specifically d.c. rated accessories (esp. switches and protective devices).

If it were me I'd probably just protect the wiring system - e.g. with earthed steel conduit (even flexible steel conduit would do - and not that difficult to install really), with suitable steel boxes behind ceiling accessories. In the old days MICC/pyro wiring might have been another option, but that's pretty rare these days.  Just keep it all on the warm side of any thermal insulation to avoid problems with condensation.

   - Andy.

Please can someone advise how using 12v systems in the domestic environment would viewed in terms of compliance with the Wiring Regulations?

Compliance isn't an issue - the Wiring Regs have different provisions SELV/PELV and FELV systems - just a matter of picking the system you want to use and refer to the corresponding section.

   - Andy.

Andrew Turner said:

Reduced fire risk

Really? Especially if DC?

Andrew Turner said:

Reduced of risk at touch point's (switches)

Specialist switches are necessary ... our usual UK-style light switches are AC only and unsuitable for DC operation.

Andrew Turner said:

Possible reduction in cabling costs.

As others have said, lower voltage = higher current = more copper = more cabling cost (or higher losses = more energy cost).

The IET have a couple of publications on this:

• https://shop.theiet.org/code-of-practice-for-low-and-extra-low-voltage-direct-current-power-distribution-in-buildings
• https://electrical.theiet.org/guidance-codes-of-practice/publications-by-category/building-management-and-maintenance/practical-considerations-for-dc-installations/