Hi All,

I need to take some measurements of a 480VAC line using my Siglent SDS1204X-E. I was planning on using 3 channels measuring with respect to GND. My scope inputs say they tolerate 400Vpk. Our line runs hot at 495 VAC (rms), so If I measure relative to GND, I have 286 VAC (rms), which is 404 Vpk.

Now my probe is 10:1 so I get 40.4 Vpk at the scope input which is OK right?

Measuring this will not damage my scope?

 

My probes (Siglent PP510) state the Max input voltage for 10x attenuation is 300V RMS CAT II. So the 286V RMS should be OK I think.

 

IMO you're near the safe limit of the probes rating and you should always consult the probe pamphlet for frequency derating.
Personally for low impedance elevated voltages I would use 100:1 probes for additional voltage rating safety. Their designs typically permit 1.5-2.5kV usage and better creepage management and materials.

What are you hoping to see with a scope ? Will a DMM not do what you need ?

 

@tautech is correct, especially if the line is tied to a very low impedance source. Disastrous consequences would happen in case of a failure of the probe or any mistake.

Using a 100:1 probe or a fully differential would be the recommended path - when choosing the 100:1 probe, make sure it is from a reputable source, as there are many probes in the retail market that may be incredibly optimistic in their specifications.

One interesting aspect is that several probes from Probemaster are rated for 500 or 600V:
https://probemaster.com/3900-series-scope-probes-100-mhz/
https://probemaster.com/pm6139-special-purpose-probe-853-068-00/

 

Thanks guys, I currently only have the factory supplied probes that come with the scope.

We were trying to assess a phase lag imbalance transient when a VFD was switched on at work. Someone blew up our fluke Scopemeter with the 1000V differential inputs, so I was going to use my personal scope to try to catch it. Ended up finding another Fluke to use which is not easy with Covid right now.

Thanks for the info guys. I see some money for HV probes in my future...

 

Yes this a tricky one when you need to scope several phases and need to outlay on HV probes vs differential probes which are more versatile. While you might not need differential probes for this job the outlay for 3x HV probes gets you well on the way to buying at least one and obtaining more versatile probing solutions for the future.
At least they are not scope specific unless you buy $ probes powered by the scope so the cheaper diff probes can be used on any scope you might get at some later date.