Quote:
Originally Posted by astral highway
Chris: thank you -
I’m not sure though how I can check the grounding of my bench power supply without opening it up.
Is the output socket marked ‘ground’ next to ’-ve’ likely to be connected to mains safety earth? Otherwise what is the possible configuration here
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A quick ohmmeter test between the negative output terminal and the mains plug's earth pin will tell you. There is frequently a 'ground' or 'earth' terminal on the front panel which is connected to the case metalwork and thus mains earth, but is unconnected to the output.
It's conventional for the output of bench power supplies to be floating with respect to earth. For a start, it means it's safe to connect power supplies in series, which is often handy (even if you just want +/-15V for an op-amp). For example, I have an ancient (germanium power transistors! yay!) Solartron power supply in front of me which has two outputs, both floating, and features an extra earth terminal on the front panel if you want it. The ubiquitous Farnell LT30 family work the same way - the L30-5 behind me has red and black output terminals and a separate green earth terminal. In the office there's a modern Chinese switch-mode bench supply whose output is definitely floating and I don't think it has an earth terminal anywhere, though the metal case is connected to mains earth.
Chris