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I'm building an interactive portrait gallery with seventy portraits, each back-illuminated by an LED lamp. The lamps draw less than 30 mA at 230 Vac, and each is switched using a small optocoupler/phototriac, under microcontroller, er, control.

Given the very low current draw of the lamps, standard 3-core mains cable seems to be considerable overkill. (All of the wiring will be hidden within the gallery structure, out of the way of prying fingers; we have a mains bus, from which I can tap the connections for each lamp.)

Would a three-strand section of ribbon cable be up to the job? Some specs I've unearthed are rated to 300 Vrms (and up to 1 A), which would seem to be suitable. But what consideration would I have to give to voltage spikes?

I want to build something safe, but a lighter cable would make construction much simpler.

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    \$\begingroup\$ I'd be concerned about the thickness of the insulator more than the copper. slight kink or rip and you've got exposed live wire and the interactive gallery could end up more interactive than you planned. \$\endgroup\$ – MandoMando Jan 31 '13 at 15:07
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    \$\begingroup\$ I doubt that anything based on "data" cable would meet code and/or pass inspection. There are "flat wire" systems available from various manufacturers, but they are all rated for low voltage only. I would seriously consider switching to low-voltage lamps for your pictures; then you'll have a much wider choice of wiring options. \$\endgroup\$ – Dave Tweed Jan 31 '13 at 15:20
  • \$\begingroup\$ Could this be made acceptable with an isolation transformer plus suitable low-current fuses / ECBs? \$\endgroup\$ – pjc50 Jan 31 '13 at 16:18
  • \$\begingroup\$ It depends on how deep your pocket is, but why not wire it all up to code for general lighting use? That way, if you want it, each led station could take a much more interesting load some time in the future. \$\endgroup\$ – Bobbi Bennett Jan 31 '13 at 16:24
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    \$\begingroup\$ ~230vrms = ~320v peak = no safety factor... what if it's 240v or 250v rms?. Don't do it. You can get quite skinny mains cable (NOT data cable) readily enough, or wire the LED's low-voltage as neither the micro nor the LED will really be 230v... they will be maybe 5v at most. \$\endgroup\$ – John U Jan 31 '13 at 17:02
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Mains cabling doesn't just have to supply power to your lamps; it also has to be safe in the event of a fault. If your lamp short circuits, you don't want the cable to burn out or start a fire before the fuse blows (if you're in a fused plug country like the UK) or the breaker trips! So standard 3-core mains cable probably is appropriate. See also MandoMando's comment on the correct insulation. Or as Dave Tweed says, use low voltage lighting and a mains transformer (perhaps look for garden or outdoor lighting systems)

EDIT: if the rest of the installation is up to "double insulation" standards with no exposed metalwork, then 2-core mains cable would be acceptable, saving some space.

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If your wires are contained within the gallery structure, it may be acceptable to use hookup wire. This could be as small as 1mmOD. You don't say where you're based, so I can't tell you exactly what would be required to be up to code in your jusrisdiction but generally speaking you would need to:

  • Have a structure which completely encloses the wires, with no openings over 4mm
  • The structure must be strong enough to not break (allowing access to the wires) either as a result of being banged or knocked, or if someone fell against it.
  • The structure would have to be either a suitable insulator, or made from metal with good ground bonding.
  • The ends of the wire must be anchored so they can't break loose and go wandering about making contact with e.g. the metal housing.
  • The current in the wire must be limited by an impedance, fuse, breaker etc... . The aim is to prevent the wire overheating and either melting the insulation off or starting a fire if the LED fails short.

An alternative approach would be to use different LEDs. If you could power them from 12V dc, for example, you wouldn't have to worry so much about electrocution (and if you are in the EU you'd avoid the LVD), and you'd just need to take precautions to prevent fire.

Edit to add: This answer is based on the electrical equipment rules. Depending on the size of your gallery, building codes may be more appropriate.

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