I need to measure harmonic distortions on a 230V 50Hz AC mains circuit. The Tektronix P2220 probes I have for my scope are rated for 300V CAT II when set to 10X impedance. Are these probes safe to use with 230V mains, or should I look into a 100X probe?
300 Cat II is okay for connection to low power fused mains circuits up to 300VDC or 300V RMS (fault current under 100A, I think).
If you've got an industrial mains circuit or one otherwise capable of high fault currents, Cat III or higher would be necessary.
That also assumes your scope can directly handle an input of +/-31V (eg. 10V/div).
Note also the limitation on voltage on the reference relative to earth!
I use a Tek TPS2024 for mains measurement- the isolated channels are a big advantage (though you have to sign a contract every time you power it up not to exceed the 30V limit).
It's probably okay, but I wouldn't do that directly. Because that is going to be 340V Peak. I have used this probe directly for 300VDC measurements before and that's never been an issue.
But you could always go cheap and make yourself a voltage divider. If you want to plot that offset you can do it from the math menu on your scope.
We use the P5122, P5100A for that sort of stuff at my work.