No Isolation Trasformer = BOOM! or Yeeoooooow! Isolation transformer = OK Hook the isolation transformer to your device under test, not your scope. If you hook the isolation transformer to your scope, the scope ground will become live when you hook it to your circuit. I shocked the livin' %$&#%&$% out of my boss this way once, he leaned on the scope chassis and touched the meter frame of my bench. Not good for one's long-term employment prospects. Another time I hooked a scope to a TV with one of the mains wires connected directly to the chassis. Two wire cords should be outlawed, but the US lags behind everywhere else in this regard. BOOM! so much for my scope ground lead. Also not good for one's long term employment prospects. Expensive differetnial probes are unneccesary IMHO. I have one I've never used. --Lawrence Jinx Sent by: pic microcontroller discussion list 02/16/2003 08:45 PM Please respond to pic microcontroller discussion list To: PICLIST@MITVMA.MIT.EDU cc: Subject: Re: [EE]: Measuring AC mains with a O-scope. > > Does this change the way one could connect O-scope probes ? > If your scope has internal grounding... it would be blown to hell I wouldn't even think of measuring mains without an isolating transformer. I have a small 150VA one that goes on either the scope or the circuit -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics