Measuring mains voltage directly with an oscilloscope tells you far more than a multimeter ever could: the waveform's shape, its distortion, any transients riding on top of the sine wave, not just a single RMS number. In the short video below, the ALLdata team shows the practical steps for taking that measurement on a real oscilloscope.
Why this measurement needs a safety check first
Mains voltage is not the same thing as a low voltage bench signal, and a standard, single ended oscilloscope probe is not automatically safe to connect to it. Most bench oscilloscopes tie the probe's ground clip, and the instrument chassis, to earth through the power cable. If that ground clip is connected anywhere on a live mains circuit that is not already at earth potential, the result can be a short circuit, a blown fuse, or a genuine shock hazard, both for the operator and for the equipment. Before probing a mains circuit, use an isolated or differential probe, an isolation transformer, or an oscilloscope specifically floated for the measurement, and never assume a standard probe ground clip is safe to attach to a live conductor.
What the waveform actually tells you
Once the measurement is set up safely, the oscilloscope shows the true shape of the mains sine wave: its peak voltage, any flat topping caused by nonlinear loads elsewhere on the same circuit, and transients that a multimeter's RMS reading would simply average away and hide. This is exactly the kind of detail that matters when diagnosing power quality issues or validating equipment that will be connected to the mains.
ALLdata's role
ALLdata's oscilloscope range, including the Rigol DHO900 and Rigol MHO900, pairs with isolated and differential probes suited to mains and power measurements.
Not sure which probe your measurement actually needs? Talk to an ALLdata engineer.