Sensing mains input current in offline SMPS

[Flyback]

Hello,

We sometimes monitor the input current to our offline SMPS’s by using a diff probe and scope to observe the voltage across a sense resistor at the input to the SMPS (as in the attached diagram).

Why is it that the reading is always more noisy (and this is seen as ‘more ‘fuzz’ on the scoped waveform) when the sense resistor is placed in the Live line as opposed to the Neutral line?

 

[Pommie]

Is the neutral earthed in your country?

Mike.

 

[Flyback]

Thanks Yes it is