Ah you have been handed the poison chalice of 'just measuring'.

First, if you are looking to see if you need to be adding filtering, it will not be just mains frequencies you are interested in, so the normal meter on the AC setting will probably not do - a scope or even a measuring receiver or a spectrum analyser may be more use as the switching spikes will extend to some MHz spectrally speaking (due to microsecond risetimes.)
Measuring common mode current for EMC purposes is commonly done with a clamp meter with a ferrite core and a dummy load and the instruments on the secondary. Measuring common mode voltages does require some thought as to 'relative to what exactly '  and in a professionally setting normally involves a LISN. (more info)

The limits you will be looking at will not be expressed in volts and milliamps, but as power in  a given spectral bandwidth and this can be hard to deduce

This sort of thing ( many thanks to Tim for putting his course notes on-line)

Mike

Ah you have been handed the poison chalice of 'just measuring'.

First, if you are looking to see if you need to be adding filtering, it will not be just mains frequencies you are interested in, so the normal meter on the AC setting will probably not do - a scope or even a measuring receiver or a spectrum analyser may be more use as the switching spikes will extend to some MHz spectrally speaking (due to microsecond risetimes.)
Measuring common mode current for EMC purposes is commonly done with a clamp meter with a ferrite core and a dummy load and the instruments on the secondary. Measuring common mode voltages does require some thought as to 'relative to what exactly '  and in a professionally setting normally involves a LISN. (more info)

The limits you will be looking at will not be expressed in volts and milliamps, but as power in  a given spectral bandwidth and this can be hard to deduce

This sort of thing ( many thanks to Tim for putting his course notes on-line)

Mike