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Wire for 12v in-ceiling services

Discussion in 'General Electronics Discussion' started by Deggy, Aug 19, 2016.

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  1. Deggy

    Deggy

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    Aug 19, 2016
    Hi all,

    I'm planning on building some home automation projects over the next few months. Initially multi-room audio and lighting control.

    I live in Australia where we have some very strict laws surrounding electrical work. Because of this, I'm planning to keep 240v out of my projects and do all of the in-ceiling work at 12v (low voltage work below 50v is exempt from the requirement for a certified electrician to do all work, which is ironic because from an overall risk perspective, I think that high current 12v DC is probably more challenging than 240v ac).

    My plan is to construct a distribution board which will carry a 240v ac to 12v dc transformer, appropriate fuses and microcontroller activated relays for energizing individual circuits.

    I've built many 5v microcontroller projects, but never something this big. My main concern is the wiring requirements for high-ampage 12v applications - I don't want to have a roof fire!

    Because of this, I'm planning on installing a busbar on the distribution board with relays controlling individual circuits going into the roof, rather than installing a 12v ring-main in the roof. Individual systems should be low power (less than 5 Amps) with no total circuit length of more than 40ft, so I figure that if I use 10awg wire with a 5a fuse on each circuit I should be safe from an electrical standpoint.

    I'd appreciate any advice based on the above, and particularly any practical suggestions for the cable to use?

    D
     
  2. Bluejets

    Bluejets

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    Oct 5, 2014
    Cable sizing seems ok.

    Although awg is not a common reference to wiring here in Aus (except for automotive) there is a quick reference here ..........

    http://www.calculator.net/voltage-d...ance=40&distanceunit=feet&amperes=5&x=48&y=14

    It may be that there is no licence requirement for 12v dc work, segregration from any 240v systems is still a legal requirement. One of the many reasons that bulk cabling licence is required for phone/network/data etc.systems.

    I would be getting a check on any power supply unit to ensure it complies as well in-so-far as isolation is concerned.

    Only other thing I am curious about is why an "x" number of 5Amp circuits for microcontrollers?
    mmm..ok...maybe led lights.

    Just let it be known, there are also requirements under SAA wiring rules for installation of these even though they are low voltage.
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Heh, technically you require a license to run cabling for your network.
     
  4. Deggy

    Deggy

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    Aug 19, 2016
    The 5a is a ROM for planning. No LED lighting, but I'll be putting some small TPA3116D2 amplifiers up there, so 5a seems represents a safe maximum too.

    Unfortunately, the laws run up against reality here because I've talked to electricians ( I'm doing a Reno, and all 240v is being done properly, not DIY) and when I get on to the 12v side they really don't have any interest or knowledge.

    So I'm going with behaving in a reasonable manner and taking the correct precautions, that's why the main transformer is going outside the roof space. There will be small 12 to 5v regulators up there in individual systems, but I'm less worried about them.

    Are there any resources available, rather then paying for a copy of a standard, that can explain what compliance looks like in terms of separating the DC and AC sides? Does that mean physical, electrical or both? I'm planning on using clipping to get the 12v cables above the in place insulation into free air to also reduce the fire risk and achieve physical separation from the 240v which runs along the floor.
     
  5. Deggy

    Deggy

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    Aug 19, 2016
    I'm pretty sure that in Australia I'll pretty soon need a license to breathe.

    The problem with regulation is the unintended consequence when you have a novel application and/or can't actually find anybody competent or interested in what you're doing.
     
  6. Sunnysky

    Sunnysky

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    Jul 15, 2016
    I use a 85W 19V laptop charger for distributed on AWG16 to power all the LEDS outside.
    It works but wire losses are great.
    I would suggest you use a centralized 48V PSU.
     
  7. Deggy

    Deggy

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    Aug 19, 2016
    Really, you need a license to run a bit of cat5? Whatever next.
     
  8. Deggy

    Deggy

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    Aug 19, 2016
    I had been trying to keep everything at 12v and hadn't considered 48v. My concern with that is that the in-roof systems are made more complicated because at the moment everything I'm using runs on either 12v or 5v. I guess that I might need to consider the voltage drop in a circuit, but the 12v side is pretty tolerant (typically 9-12v).
     
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    The rules are pretty simple. :-D
     
  10. Deggy

    Deggy

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    Aug 19, 2016
    This isn't telecommunication cabling, it's providing power only.

    That said, from what I can see this is an open (I.e. not restricted). It does not connect to the public telecommunication system at any point. If I do run Ethernet then it will also terminate at a jumper box and so is also open.
     
  11. Bluejets

    Bluejets

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    Oct 5, 2014
    If you use the link I provided, it shows only 0.4V drop over 40 feet so ****- all really.

    Does not matter......rules is rules, Sol, just as oils ain't oils.

    The big thing is it is in an environment where mains supply lives and breathes. :)


    For the former, it's probably because there is nothing in it for them.
    For the latter, you will find in many trades, there are those that know because they bother to do the long haul study and those that simply" don't give a damn". Mine sites are full of them.:eek:

    For shortcut to SAA requirements knowledge, none I know of.
     
  12. donkey

    donkey

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    Feb 26, 2011
    let me tell you a story bout a man I will call ML
    ML had bought a house and tried some home automation, mixed with networking and POE stuff. a friend of his saw this and asked ML if he would ever consider selling the house, ML and his friend came up with a figure that was so high that ML thought he would be rich. however when the building inspection came as ML had no one "qualified" that signed of on the cabling it all had to be removed before the house could be sold. the only reason his friend wanted the house was for that reason.

    having said that there are alternatives in this day and age.
    mysensors.org has a community willing to get you started. wires aren't needed for transmission as there are wireless moduels (WIFI, NRF24L01, 433mhz, EOP) now inside the walls I would personally NEVER install anything, because I stand on the side of caution I would always want to see a home made item.

    so depending on the system you want to install a simple compliant solution is to use multiple compliant transformers (If you want to go hardcore chuck an RCD on it but not needed) use wireless where possible including things like wifi extenders, NRF24L01 repeaters etc. this will save a lot of issues with the legal side. if you want to negate ALL legal issues you can use battery powered item on the home made side and then buy a few hundred SLA batteries and power converters. this has the added benefit of working during a blackout
     
  13. Bluejets

    Bluejets

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    Oct 5, 2014
    One thing for sure, if you must jump up and crawl around in the ceiling , follow the new laws and isolate the power at the main switch.
    In many instances the mains ( if aerials) will still pass through the same space and remain live but at least you will have a better chance of surviving if something is not quite right up there.
     
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