Yes, it was 0.5mA or less per device, but no one working on an EGC expects it to have current, and the shock from even 0.5mA could cause a reaction that in turn causes an injury, for example falling off a ladder.
UL should have never permitted the EGC to be used as a grounded conductor.
In an AC system, the EGC will _always_ carry some current.
From looking around the web, I believe that the capacitance of romex is something like 10-20pF per foot wire-wire. Roll out 100 feet of romex, connect the black wire to a 120V hot, the white wire to the neutral, and connect a meter between the bare wire and the neutral, and you will measure 'phantom' voltage. Connect a sensitive current meter and you should see something on the order of 50 micro-amps.
I would be interested in seeing the true history of the UL requirements, but my _guess_ is that the UL standard included a maximum allowed _leakage_ (via capacitance, insulation conductivity, etc). At the time the standard was created a rather large (by today's expectations) current would flow _through_ the insulation, so to permit devices to actually be manufacturable there had to be a significant amount of leakage permitted. Guessing further, as insulation systems evolved and power requirements for things such as timers dropped, eventually we reached the point where some bright engineer said 'I could run this sensor on the 'allowed leakage' for a switch, and thus meet the applicable standards.'
Of course, this is a change between _unintentional_ current allowed to pass to the EGC, and _intentional_ use of the EGC to carry small currents. But at some point this becomes a 'religious' argument, not a true safety argument.
There _will_ always be some current on the EGC. Does it really make a safety difference if you have 50uA of current on an EGC because of insulation leakage, or the same 50 uA because of intentional use of the EGC to power a device, or the same 50uA because of capacitive coupling from hot to bare?
IMHO a more realistic approach would have been for the limits of permitted intentional current on the EGC should have been reduced as technology improved and the expected unintentional current went down.
-Jon
