Diode Isolated Ground
Diode Isolated Ground
(OP)
I've been refurbishing some older equipment lately and have really noticed how safety practices have improved. I've seen switches and fuses placed in the neutral line. Many grounds were placed to points that wouldn't always make a good connection. Even HP made a line ground connection to a long circuit board trace.
That got me thinking about an old HP application note I saw in the 70's. To reduce ground loop currents they placed a 35A bridge rectifier in series with the AC ground lead. + & - were shorted together. One AC went to ground and the other to the line ground. This would give over a volt of isolation from the line ground. While I basically like the concept, I wouldn't like to be in a witness stand and being asked questions about it! Anyone else remember this?
I hope we all think more about safety now. Ground connections are the first things I look at when I get a piece of equipment in. Often I add a redundant connection or move the ground. Every piece I connect to my HYPATIA 309 High Current Source for a timed stress test. This has become one of my favorite pieces of equipment with lots of uses besides stress testing.
That got me thinking about an old HP application note I saw in the 70's. To reduce ground loop currents they placed a 35A bridge rectifier in series with the AC ground lead. + & - were shorted together. One AC went to ground and the other to the line ground. This would give over a volt of isolation from the line ground. While I basically like the concept, I wouldn't like to be in a witness stand and being asked questions about it! Anyone else remember this?
I hope we all think more about safety now. Ground connections are the first things I look at when I get a piece of equipment in. Often I add a redundant connection or move the ground. Every piece I connect to my HYPATIA 309 High Current Source for a timed stress test. This has become one of my favorite pieces of equipment with lots of uses besides stress testing.





RE: Diode Isolated Ground
Magnetically-assisted breakers (eg SquareD QO series) and normal fuses would probably pop first (but maybe not).
Slow blow fuses and thermal breakers would probably be sufficiently slow to react that the diode would pop open leaving the chassis hot and ungrounded. Ouch.
RE: Diode Isolated Ground
Gunnar Englund
www.gke.org
RE: Diode Isolated Ground
RE: Diode Isolated Ground
My understanding is that overvoltage (more common) would typically puncture the junction and short the diode, but that overcurrent (less common) would melt something (perhaps a bond or an internal wire) and would open the diode.
In this case we ARE talking about overcurrent as the diode tries desperately to blow the fuse or breaker.
So I wouldn't rely on overall statistics of diode failures.
Perhaps the diode bridge selected was specifically chosen for its robust overcurrent characteristics and its ability to reliably kill off even the slowest fuses and breakers.