Does the oscilloscope probe ground have to be connected to the circuit board ground? For the experiment today, let's look at the oscillogram of the 50V AC signal. Use channel 1. Is the GND of channel 1 connected to the GND of the circuit board? Then touch the AC signal live wire with the probe of CH1. Do you have to use CH2? You can't use the CH1 probe and ground directly to connect the live and neutral wires. Although the AC power is 50V, because I connected it in this way, I tripped and it exploded.
The ground wire of a general desktop oscilloscope is connected to the ground wire of the commercial power through the oscilloscope plug. Therefore, connecting the ground wire of the oscilloscope to the zero wire or the live wire is equivalent to short-circuiting the zero wire or the live wire to the ground. Of course, it is necessary to trip.
For a non-isolated desktop oscilloscope, measure the voltage between zero and live wire, it is best to use CH1 and CH2 to measure the two separately, and then calculate the pressure difference between the two by "subtraction" in the "MATH" function of the oscilloscope .
Or the landlord directly buys an isolated oscilloscope. The probe ground of the isolated oscilloscope is floating relative to the oscilloscope ground and the ground. Generally, the isolation voltage can reach kV level, and it can be safely connected directly to the neutral line or the live line.