Measure mains voltage with oscilloscope

Sometimes there are needs to measure mains voltages with oscilloscope. You must be very careful when measuring voltages on the mains with any measurement instrument. The mains voltages are absolutely deadly. Measuring mains voltages with multimeter can be dangerous. Trying to do the measurement of mains voltage with oscilloscope is potentially more dangerous, because typically oscilloscopes are are grounded devices that have the ground side of the probe connected to the equipment case. Doing connection to mains voltage slightly wrongly can end up causing short circuit, damage the probe, your oscilloscope or electrocute you.

If you are using a traditional oscilloscope that is mains powered, ALWAYS MAKE SURE YOUR SCOPE IS GROUNDED BECAUSE THE GROUND IS THERE FOR YOUR SAFETY!

Usually my first choice when needing to measure mains voltage with oscilloscope is to use a completely isolated scope-meter. I have UT-81B scope-meter for this purpose. I can use it with multimeter probes just like a normal multimeter, but get oscilloscope view on the it’s screen.

If I need to use my mains powered desktop oscilloscope, then my first choice is to use a CAT rated differential probe which has been designed to measure the voltage levels I want to measure. That’s the best choice.

I do not want to connect my normal oscilloscope probes anywhere near the device that is powered directly from mains outlet. In some cases I might consider doing measurement to mains voltage devices if I can power the device under test through mains isolation transformer.

Here are some videos on measuring mains voltage with oscilloscope:

Measuring Mains Voltage with Oscilloscopes

Correct use of the oscilloscope when probing circuits connected to mains

EEVblog #279? – How NOT To Blow Up Your Oscilloscope!

Check also Using oscilloscope safely with AC mains and measuring mains with oscilloscope and Using oscilloscope safely with AC mains discussions.

2 Comments

  1. Tomi Engdahl says:

    EEVblog 1415 – Reverse Engineering the DP10007 Differential Probe
    https://www.youtube.com/watch?v=GOk1BYKSsOI

    Reverse engineering the Micsig DP10007 high voltage differential probe.
    Turning the PCB into a schematic.

    EEVblog 1413 – Oscilloscope Current Probe TEARDOWN + DEMO
    https://www.youtube.com/watch?v=suf3VWqs5zw

    Teardown and measurements with the Micsig CP2100B 2.5MHz oscilloscope current probe.
    Also a demonstration of mains switch mode power supply current and noise measurement, and also some performance tests.

    Reply
  2. Tomi Engdahl says:

    Everything you need to know when buying/using an Oscilloscope! EB#49
    https://www.youtube.com/watch?v=d58GzhXKKG8

    In this electronics basics episode we will be having a look at the biggest mistake you can do when working with an oscilloscope. But I will not only show you how to do safe mains voltage measurements but also show you all the basics when it comes to oscilloscopes. That means I will show you how to choose one, how to do simple voltage and current measurements and finally how FFT works. I will explain passive probes, triggering, voltage & time division, measuring functions, the cursor function, AC & DC coupling and single mode capturing. Let’s get started!

    Reply

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