How do I 'scope a mains appliance?
The GND of the scope probe is connected to the case of the scope, which is connected to mains earth, so it is impossible to measure a device which is connected directly to mains, unless:


You use a special differential probe (expensive)  or
You use an isolating transformer (230V/230V or whatever your mains voltage is) to power the device. I use one when I need to probe the hot side of a power supply. The transformer makes it so that the 230VAC coming to the device is not referenced to ground, then I can connect the ground clip of my probe wherever I want to.