In article ,
Doug Miller wrote:
*Anything* that
causes those currents to differ by more than 20mA will

I've seen that figure quoted twice; it depends on the rating of the device.

The one on the incomer to our house, previously mentioned, is rated at
30mA. The one I use on my electronics workbench for equipment I am working
on is rated at 10mA

--
Stuart Winsor