I'm a bit lost about the CAT ratings (protection ratings) for oscilloscopes (and multi-meters).
There are many tables for which category is needed for which application (for example here or here,) but those tables are all for household/industrial applications with AC current.
My situation is somewhat different, however, so I don't know which category I need. We are developing a robot, powered by a 320V DC 17A supply (itself powered from 380V AC 3 phases.)
The goal is NOT to measure the 380V AC, but to be able to measure anything downstream from the supply (stability of the 320V DC supply, voltage inside the 320V DC motors, voltages on various PCBs, etc.)
More precisely, I'm currently trying to specify what battery powered scope we will need to work on this project. Normal scopes powered through mains can't be used because they tie earth and ground together, causing the supply to detect earth leakage and shut down.
EDIT : Concerning Andy Aka's question:
- Without the earth leak detector, the GND and +320V DC should be floating relative to earth (not tested.)
- We use a Bender Iso-685-D (English datasheet) to measure earth leak resistance (resistance between earth and GND and between earth and +320V.) If measurement is below about 1Mohm, it triggers the shutdown of the 320V supply.
- From what I observed experimentally (and understood from datasheet,) the Bender is destroying the pure floating behaviour of the supply by generating +-50V (high resistance) between earth and the DC wires and checking the current in the resistor.
- When connecting a scope (with GND of probe on GND wire,) we short GND wire and earth, making the Bender detect an earth leak (which is true, as we are shorted to earth.)
- Experimentally, we realized that when we connect the scope (when supply is powered off) and try to turn on the supply, the Bender prevents it due to earth leak.
