Originally Posted by Walker
No differences. Internally, the PID runs everything off 12VDC anyway. When you connect higher voltage than this, it drops it down. When you connect AC, it recitifies it and makes it DC.
I don't think there are any con's other the possible the availability of components like fuses, switches, contactors, etc.
But I don't think there are any pro's to doing this, more imporantly. If you are concerned about the risk of electric shock, then you just need to make sure you limit the current going to the controls on the front of the panel. The PIDs need less than 300 mA of current, so if you put a tiny fuse on the line that feeds power up to the face of your panel, you can control everything with low current devices.
DC is not any safer than AC when you get down to the basics of it. And it's not voltage that is important, but AMPS. You can kill yourself with a 12VDC car battery, because that thing has the capacity to send a LOT of amps through you.
While it's true that it's current that kills you, it's only part of the story.
300mA is more than enough to stop the heart (which is incidently why a 12v could actually kill) BUT here's the difference and why low voltage is safer to work around:
Skin resistance. Skin typically toss out about 1-4kohms of resistance.
V=IR, and higher voltages result in higher currents. 12v to skin results in a miniscule amount of current. 220V results in a not minscule amount. That's why GFCI's are designed to trip off around 5mA of stray current.
A 300mA fuse probably won't pop if it's going through you, but depending on where it goes (worst is a way that sends it through your heart) it could be dangerous.
as for how 12v could kill? if the voltage was put in subcutaneous...it'll conduct through the blood, which is much more conductive.