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382 posts

Ultimate Geek
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# 136770 8-Dec-2013 16:20
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Hi there,
considering even a modest PSU is rated 15-18A for the 12V DC rail (and maybe 40A for the 5V DC rail), I wonder why I do not hear more about these being used for exterior lighting? They are mass produced, which means they are cheap to get or to replace. They are fairly reliable and I would say safe (I did not hear about a house fire started by a PSU yet). They have internal cooling and if they overheat, they will shutdown.

As long as it is installed indoors (garage? workshop?) then all looks OK to me. They plug into a power point and the wiring on low voltage is not prescribed work, so you can do whatever you want without needing an electrician. Of course you need to have common sense and use properly sized cables, fuses switching gear and such, but otherwise I do not see a downside?

what do you think?

Secondly, why are not the isolating transformers more often used for garden lights? You can get then lots of power (and light) safely, while using standard fittings and bulbs (cheaper). With an isolating transformer there is no way you can get an electric shock (this is why they were created). You can easily get 1kW or 2kW isolating transformers. Not entirely sure if this requires an electrician (it is mains voltage, but at the same time safe?). This is just an idea... but the PSU thing looks doable!




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  # 947536 8-Dec-2013 16:42
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I think you should look up perscribed electrical work 1st, it covers a lot more than you may think.


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  # 947573 8-Dec-2013 17:57
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Till recently outdoor lighting has been all halogen so needed ac to not have lousy lamp life. And long cables meant it had to be low frequency so no nice electronic transformers.

An open frame 12v power supply isn't much more than a quality desktop pc power supply and doesn't have all the needless 5v stuff in it. Those get used extensively now that led is the norm for outdoor lighting.

There are still places you want a selv power supply like pool lights and water features so a common old magnetic transformer still gets used there.




Richard rich.ms

 
 
 
 




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Ultimate Geek
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  # 947587 8-Dec-2013 18:26
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Hi gregmcc,

do you suggest that 12V wiring is prescribed electrical work? I would like to look it up, could you please point me into the right direction where to look for clarifications? Many thanks.

I also know there is a document which lists what a homeowner can do even if mains voltage fixed wiring is involved. Does that help at all?




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  # 947607 8-Dec-2013 19:20
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aucklander: Hi gregmcc,

do you suggest that 12V wiring is prescribed electrical work? I would like to look it up, could you please point me into the right direction where to look for clarifications? Many thanks.

I also know there is a document which lists what a homeowner can do even if mains voltage fixed wiring is involved. Does that help at all?


here is the link for the legislation describing prescribed electrical work.

Your out clause may have been 2 (b) (i), but as the PSU is 230V that makes it low voltage which is higher than the extra-low voltage, so thus it is perscribed electrical work.

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  # 948198 9-Dec-2013 16:22
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The voltage supply itself is only 12V, the input _to_ the supply from a standard IEC lead is 230/240V. 

If that's not ok, then would that also suggest that building your own PC would be prescribed work as you're working with a 230V PSU supplying 12V hardware?






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  # 948206 9-Dec-2013 16:31
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stevenz: The voltage supply itself is only 12V, the input _to_ the supply from a standard IEC lead is 230/240V. 

If that's not ok, then would that also suggest that building your own PC would be prescribed work as you're working with a 230V PSU supplying 12V hardware?




That would be correct, building your own PC (if it includes the PSU) is perscribed electrical work.

There are quite a number of calculations that need to be done to work out the correct loading, fitting the correct protection devices to the load side and so on, unless you have the required formal training there is virtually no way it can be safely done.

A lot of computer shops know this already and some of their techs may already have the right kind of registration to legally be able to do this, some shops don't and they know it but would rather play dumb and try and get away with it.

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  # 948518 10-Dec-2013 10:07
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gregmcc:
stevenz: The voltage supply itself is only 12V, the input _to_ the supply from a standard IEC lead is 230/240V. 

If that's not ok, then would that also suggest that building your own PC would be prescribed work as you're working with a 230V PSU supplying 12V hardware?




That would be correct, building your own PC (if it includes the PSU) is perscribed electrical work.

There are quite a number of calculations that need to be done to work out the correct loading, fitting the correct protection devices to the load side and so on, unless you have the required formal training there is virtually no way it can be safely done.

A lot of computer shops know this already and some of their techs may already have the right kind of registration to legally be able to do this, some shops don't and they know it but would rather play dumb and try and get away with it.


Sorry to be pedantic, but doesn't 1 c) blow that out of the water? Assembling a PC doesn't (generally) involve more with electrical wiring then plugging connections together...

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  # 948591 10-Dec-2013 11:44
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fastmikey:
gregmcc:
stevenz: The voltage supply itself is only 12V, the input _to_ the supply from a standard IEC lead is 230/240V. 

If that's not ok, then would that also suggest that building your own PC would be prescribed work as you're working with a 230V PSU supplying 12V hardware?




That would be correct, building your own PC (if it includes the PSU) is perscribed electrical work.

There are quite a number of calculations that need to be done to work out the correct loading, fitting the correct protection devices to the load side and so on, unless you have the required formal training there is virtually no way it can be safely done.

A lot of computer shops know this already and some of their techs may already have the right kind of registration to legally be able to do this, some shops don't and they know it but would rather play dumb and try and get away with it.


Sorry to be pedantic, but doesn't 1 c) blow that out of the water? Assembling a PC doesn't (generally) involve more with electrical wiring then plugging connections together...



The computer as a whole box is an appliance and 1 (c) would apply, but the PSU as an internal component of that appliance would not, the PSU is desgined to be mounted and contained with a PC case, it is not desgined for use as a stand alone unit, as it is desgined as a component that operates at low voltage >50VAC to <1000VAC then any work done on a component that operates at low voltage is perscribed electrical work

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  # 948614 10-Dec-2013 11:53
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fastmikey:
gregmcc:
stevenz: The voltage supply itself is only 12V, the input _to_ the supply from a standard IEC lead is 230/240V. 

If that's not ok, then would that also suggest that building your own PC would be prescribed work as you're working with a 230V PSU supplying 12V hardware?




That would be correct, building your own PC (if it includes the PSU) is perscribed electrical work.

There are quite a number of calculations that need to be done to work out the correct loading, fitting the correct protection devices to the load side and so on, unless you have the required formal training there is virtually no way it can be safely done.

A lot of computer shops know this already and some of their techs may already have the right kind of registration to legally be able to do this, some shops don't and they know it but would rather play dumb and try and get away with it.


Sorry to be pedantic, but doesn't 1 c) blow that out of the water? Assembling a PC doesn't (generally) involve more with electrical wiring then plugging connections together...


That's how I'd see it too, the PSU unit in an enclosed separate case with plug-in power cord, AS/NZS approved, protection circuits already in place, the technician only ever dealing with the "extra-low voltage" out, not significantly different from plugging in a laptop charger or connecting a car battery charger to a a battery etc.  But opening up the PSU would be a different story, presumably the same requirements as for appliance service people requiring limited electrical registration.  The work installing or replacing a PSU on a PC can be done without "without exposure to live parts intended to operate at voltages exceeding extra-low voltage" so should not be prescribed electrical work.

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  # 948617 10-Dec-2013 11:59
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gregmcc:
fastmikey:
gregmcc:
stevenz: The voltage supply itself is only 12V, the input _to_ the supply from a standard IEC lead is 230/240V. 

If that's not ok, then would that also suggest that building your own PC would be prescribed work as you're working with a 230V PSU supplying 12V hardware?




That would be correct, building your own PC (if it includes the PSU) is perscribed electrical work.

There are quite a number of calculations that need to be done to work out the correct loading, fitting the correct protection devices to the load side and so on, unless you have the required formal training there is virtually no way it can be safely done.

A lot of computer shops know this already and some of their techs may already have the right kind of registration to legally be able to do this, some shops don't and they know it but would rather play dumb and try and get away with it.


Sorry to be pedantic, but doesn't 1 c) blow that out of the water? Assembling a PC doesn't (generally) involve more with electrical wiring then plugging connections together...



The computer as a whole box is an appliance and 1 (c) would apply, but the PSU as an internal component of that appliance would not, the PSU is desgined to be mounted and contained with a PC case, it is not desgined for use as a stand alone unit, as it is desgined as a component that operates at low voltage >50VAC to <1000VAC then any work done on a component that operates at low voltage is perscribed electrical work


That's fair enough, I suppose there's risk from a PSU in usually heavily perforated case if it was used for the OP's suggested purpose, and just left somewhere where it could be exposed to water, kids poking knitting needles in to it or whatever.
I'm sure Jaycar etc will sell either transformer or switchmode based PSU made for the intended purpose.

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  # 948854 10-Dec-2013 17:18
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gregmcc: The computer as a whole box is an appliance and 1 (c) would apply, but the PSU as an internal component of that appliance would not, the PSU is desgined to be mounted and contained with a PC case, it is not desgined for use as a stand alone unit, as it is desgined as a component that operates at low voltage >50VAC to <1000VAC then any work done on a component that operates at low voltage is perscribed electrical work


Oh, I'm not disagreeing there, but computer shops assembling PCs are exempted under 1 (c). Just don't want to see any SME business owners unduly freaking out 

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  # 948861 10-Dec-2013 17:49
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fastmikey:
gregmcc: The computer as a whole box is an appliance and 1 (c) would apply, but the PSU as an internal component of that appliance would not, the PSU is desgined to be mounted and contained with a PC case, it is not desgined for use as a stand alone unit, as it is desgined as a component that operates at low voltage >50VAC to <1000VAC then any work done on a component that operates at low voltage is perscribed electrical work


Oh, I'm not disagreeing there, but computer shops assembling PCs are exempted under 1 (c). Just don't want to see any SME business owners unduly freaking out 


And I would disagree there, 1 (C) is reffering to appliances, such as your jug or toaster or fully assembled PC, as soon as the cover comes off the PC then you are now preforming a servicing or assembling task, when the PSU is removed (or installed), remembering that clause 2 goes on to describe exacty what is not perscribed work and assembling a PC PSU in to a case or using it in another manor does not fall in to the defination of none perscribed work.

You just can't pick out 1 clause of the regs and say look that clause seems to fit what I think so it must be so, a full and complete understanding of all the regulations is required, and when a particular reg quite clearly defines what is not perscribed work as in clause 2


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  # 948863 10-Dec-2013 17:54
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IMO, there's a much more serious issue here - from the original post:
"With an isolating transformer there is no way you can get an electric shock (this is why they were created)"

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  # 948873 10-Dec-2013 18:08
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13.8V DC 20A switchmode benchtop PSU, for $119.00

http://www.jaycar.co.nz/productView.asp?ID=MP3078&form=CAT2&SUBCATID=999#3

D
o anything you like with the 13.8V out - it's not subject to any electrical reg.
Much less mucking around than trying to adapt a computer PSU.

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  # 948875 10-Dec-2013 18:09
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Fred99: IMO, there's a much more serious issue here - from the original post:
"With an isolating transformer there is no way you can get an electric shock (this is why they were created)"


Been quite honest here, this is the kind of thing that someone who thinks they know what they are doing, but doesn't says.

A little knowledge is a dangerious thing, this is why the electrical industry is heavily regulated.



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