huh. Interesting. How would the safety implications of running 240v DC differ from running 240v AC? (my understanding is that the amount of copper required would be the same.)
From what I've seen, 48vdc is usually just two leads sticking out from the equipment in question.. you just strip the ends of the wires and screw 'em in. I don't think I'd be comfortable doing that with 240v. I guess that's just a simple matter of standardization.
If you get bit (shocked) by DC, you let go, drop it instantly - AC will not allow you to drop it, you have to be pulled off. If anything its safer. Also, DC has lower loss over a given conductor. The problem historically with DC was changing from a high voltage for transmission and low voltages for loads, something changed by solid state devices.
>If you get bit (shocked) by DC, you let go, drop it instantly - AC will not allow you to drop it, you have to be pulled off. If anything its safer.
I know I was once shocked by 120v AC while working; I was reaching around a metal PDU with 15-15R plugs to plug something in. As I couldn't see, I was guiding the prongs in with my fingers, and I didn't get my fingers out of the way before it made contact. ouch. (let us just say that I was younger and... a lot less careful than a sysadmin ought to be.) Fortunately, the case of the PDU was grounded (I think it was a baytech RPC) and the case of the server above it was grounded, and everything was screwed in well, so the circut went through my fingers and arm and into a chassis. my impression was that my arm bounced between the PDU and the next server up for a while before I managed to jerk my shoulder back and pull my whole arm out of the rack.
Apparently I'm not a very good conductor, or there was something up with the breaker, 'cause it didn't blow the circuit. I wasn't hurt, save for maybe some light bruising, and no downtime resulted, so it turned out okay, but I'm much more careful now (and my PDUs use C14 receptacles, making this problem impossible, at least without a knife.)
That's actually pretty normal - your body doesnt conduct well, people die because of current in the sub 500ma range, a bigger issue is once hold of AC, sometimes you cant drop it.
Yeah, I considered setting up a GFCI after that, but decided that was probably a bad idea in production. I've become religious, though, about GFCI on the test-bench, as that's where most of the stupid happens anyhow.
From what I've seen, 48vdc is usually just two leads sticking out from the equipment in question.. you just strip the ends of the wires and screw 'em in. I don't think I'd be comfortable doing that with 240v. I guess that's just a simple matter of standardization.