Electronics > Beginners
OScope Safety Question
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KungFuJosh:
Hi, I'm not quite a newb, but I am when it comes to oscilloscopes. I've read a lot of mixed opinions regarding safety, and I would like to see if my setup makes sense, and whether or not I should bother with a differential probe.

I have a DS1054Z connected on a surge protector to a GFCI outlet. I have an isolated transformer (Toroid ISB-060W) with a verified floating neutral, also connected on the same surge protector to the same GFCI outlet.

Any DUT goes to the IT, and I don't use any adapters to defeat the earth. I'm generally only testing audio equipment like tube guitar amplifiers, and microphones. I may test guitar pedals too, but those are low voltage and I can battery supply them. I also have a Tekpower TP3005P bench supply for DC but I haven't tested that yet to see if it's isolated or not.

Generally speaking, I probably designed and built 99% of the amps or mics or pedals I'm testing with my scope. I'm obviously very family with the circuits and I'm not going to connect the ground clip to B+ and blow anything up.

All that said, what do you think? Is my setup sufficient / does it make sense? Should I bother getting a differential probe, and if so, what models should I look at?

Thanks,
Josh

PS. Yes, I've seen the "How NOT To Blow Up Your Oscilloscope!" video. ;)
David Hess:
That is how I do it. The idea is that with the isolation transformer, the power line ground can be moved to where the oscilloscope's probe ground is attached.
KungFuJosh:
Thanks!
bhishmar:

--- Quote from: David Hess on August 18, 2018, 12:35:34 am ---That is how I do it. The idea is that with the isolation transformer, the power line ground can be moved to where the oscilloscope's probe ground is attached.

--- End quote ---

Would you please care to elaborate on the above  point?

I have read carefully both KungFuJosh query & ur reply.
But I am missing the point on "power ground being moved to DSO-ground"
rstofer:

--- Quote from: bhishmar on September 03, 2018, 05:09:59 pm ---
--- Quote from: David Hess on August 18, 2018, 12:35:34 am ---That is how I do it. The idea is that with the isolation transformer, the power line ground can be moved to where the oscilloscope's probe ground is attached.

--- End quote ---

Would you please care to elaborate on the above  point?

I have read carefully both KungFuJosh query & ur reply.
But I am missing the point on "power ground being moved to DSO-ground"

--- End quote ---

As soon as you clip the scope probe ground to some point in the circuit, that point is now earth ground by way of the BNC connector and the fact that the scope is grounded.  That is the way it's going to turn out whether intended or not.



Note that GFCI protection does not extend beyond the isolation transformer because it is looking for the current balance between the hot and neutral wires that only reach the primary of the transformer.
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