Bob Minchin wrote,

>The real way to do this is with a current transformer which provides
>safety isolation and is easily made from a miniature audio
>transformer salvaged from and old fashioned transistor

Amen, Bob,  this is the way to go.  I would go further to say that I
hope the line current is that of a somewhat pure reactance,
that is, sinusoidal in nature.  If you are monitoring the
current into an off-line rectified switching supply, say,
you will have huge current spikes only at the peaks of the
AC voltage. Standard formulas for RMS values which would
apply to a sinusoidal current, don't work for this case. Perhaps
some code which detects the frequency, thus the period, and
roughly integrates the current waveform would help.

                                 Mike