On 17 Mar 2003, at 8:07, Ray Gallant wrote:

> I would like to add to the question on this topic which was not answered
> before.  While measuring AC mains with a two channel scope in differential
> mode (just probes tips, no probe grounds), what is the maximum voltage that
> can be measure if the spec for a single channel is 400Vpeak?

Assuming UK mains, one side is at or near earth potential.
With your scope earthed, one probe will still see full mains voltage across it
and the other will see just the difference between your local earth and the
earth at the substation.
If the supply you were measuring were truly isolated then each probe could
retain it's 400v rating (to scope body=earth) giving a total of 800v.


George Smith

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