| Electronics > Beginners |
| Classic don't-blow-up-my-scope question |
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| DDunfield:
--- Quote from: Ian.M on February 20, 2019, 06:30:52 pm ---Floating a scope, even a modern one with minimal visible exposed metalwork is still a *LETHALLY* *DUMB* idea when working with any voltage above 50V, as you don't know the insulation rating of the front panel controls. All it takes is a scope floating at HV with one metal grubscrew in a small plastic knob to electrocute you. This is not hypothetical - people have died floating scopes. Also modern scopes with SMPSUs are likely to have excessive noise levels if not grounded as per manufacturer's recommendations. --- End quote --- Very good point - and I actually agree with you. If you read my posts, I'm not advocating floating a scope. But I remain unconvinced that floating the DUT is actually any safer than floating a modern scope. In the past it was obviously so because one of them was a huge metal box attached to whatever it thinks ground is ... but IMO they've come to similar levels (neither of which I would consider particularly safe). To put forth your arguments: You don't know the insulation rating between the internal parts the DUT manufacturer thought were at ground potential and equally easily touchable parts on the outside. And the DUT may also have characteristics which make it more noisy or otherwise operate out of spec. when not properly grounded. To reiterate my first comment, telling people to float the DUT because doing it that way is "safe", allows people a false sense of security that what they are doing is safe - it is not. What most people seem to miss is that as soon as you connect a grounded test lead to a part of the DUT that is not normally at ground potential, it is no longer "floating safely" and is in fact "ground reversed" - at least one part normally hot is at ground, and all the parts normally at ground are hot. Not something I like having on my workbench. There ARE better ways! Dave |
| metrologist:
My grandfather would grab house mains all the time. He thought it was silly how afraid people are of mains. I saw on the front panel says 300V RMS CAT I. Measurement Category I: This category is for measurements of voltages from specially protected secondary circuits. Such voltage measurements include signal levels, special equipment, limited-energy parts of equipment, circuits powered by regulated low-voltage sources, and electronics. |
| David Hess:
If it is a two power pin transformer, then it is completely safe to hook to the oscilloscope and this is an excellent way to monitor the AC power line. If you are worried, then double check with an ohmmeter from primary to secondary to verify isolation. |
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