Re: [APD] Plus points

[Stuart Halliday <stuart at stuarthalliday_com>]

Andrew McLeod wrote:
> On Thu, 27 Oct 2005 14:27:20 +0100, Stuart Halliday <stuart at stuarthalliday_com> wrote:
> 
>> Another big plus point will be safely. These will be DC powered rather than AC, so no need for
>> high dangerous voltages or broken glass hazards. Therefore less of a fire risk.
> 
> I know someone who nearly set fire to their roof insulation because they used 'low voltage'
> lighting... They put too many lights on a lightweight cable (5x50w) and ran it off a transformer
> only designed to handle <150W... In the UK, we have 240V AC, and for low-voltage things we use
> 12V. As a result, the little wiring which would have easily run that lighting at 240V was
> running probably something like 20A+


, melting the wire completely. At 1/20 of the voltage, the
> current is 20x greater, which means the heating effect in the wire is 400 times greater - that's
> why car battery leads are enormously thick. AC is arguably safer as far as electrical faults are
> concerned... especially with RCDs/ELCBs etc.

Yes you're right of course. P=VI

I'm amazed at the stupid sod.
What happened to its fuse?
150W at 12V is 12.5A
200W at 12V is 20A
So the fuse should have blown.

I use low voltage (12V) lighting in my home in Scotland and I use a fuse to protect against the 
current limit being exceeded so the danger of the plastic melting can't happen.

Plus power supplies sold in the UK made to CE regulations (look for the bold CE letters on the 
power supply) limit the current. So that when the current flows too greatly the voltage level drops 
so the current stays within the safely limit.
Therefore there should be no melting plastic if the manufacturer has used the correctly rated cable.
He's used or was given the wrong power supply.
If he is to blame, shout at him, if the P/S is to blame contact the trader! Quick!


P.S.
Remember we need RCDs/ELCBs because large AC voltages kill as well.

-- 
Stuart Halliday
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