Hello,
Recently I was reading various threads on this forum about differential probes and isolation transformers. I’ve also read the Tektronix reference documents that tggzzz and others have pointed out, and also the EEVBlog videos #279 and #932 on the matter. I have one or two questions, I’ve not been able to find the answers in the previous threads (I apologize if they are there indeed)
I understand that powering the DUT through an isolation transformer is safer than powering it directly from the mains, provided that the DUT is really truly floating without any unwanted coupling to earth ground. One (and only one) accidental contact with any point in the circuit can happen without electric shock.
- Is the last sentence still true if one uses, in addition to the transformer, a general purpose HV differential probe ? Those which have a very high impedance between the 2 input terminals and between input terminals to earth ground, but are not galvanically isolated.
I would assume that in case of a single accidental contact, the current going through the operator, through ground, and then back to the circuit via the probe’s high resistance path would be minute and/or negligible, but am I missing something here ? Also, I’ve read that some forum members are strongly against isolation transformers, for reasons that have been discussed.
- Personal preference put aside, is it considered bad practice to use an isolation transformer and a HV differential probe (not galvanically isolated, but high impedance) at the same time ? Should one use only the HV diff probe instead, and use the transformer as a doorstop as some mentioned ?
While reading I noted that many of you have a very strong commitment to safety and I appreciate that. Rest assured I will not try anything silly, this is just a theoretical question. I’m not even at my bench. I am aware of the most essential safety principles, such as “if you don’t know how to do it safely, don’t do it”, “don’t probe live circuits unless you really need to”, “work with one hand only”, etc.
Thank you