Sorry to chime in late.
Just to add my 2 cents in.
I haven't read the ISO spec. just what has been said here.
First is the test spec 24V @ 100mA a max, min or nominal test spec?
You should really download this spec - Do they have to?
Here the characteristics described on page 4: "... the camera is operated with a 24Vdc power supply and 240 Ohm resistor
connected across the camera synchronizer terminal in series
(see figure 6)..."
-> with a not so accurate 5% tolerance resistor it works out to be: 95.2mA ~ 105.2mA
Second if the spec doesn't specify where the test is to be taken (across the Hot Shoe or the sync terminal)
The ISO-10330:2002 treats both terminal equally and does not make a distinction between the hot shoe or the sync terminal with their diagrams like some posters here would like to suggest otherwise...
That would lead me to think the test spec is worded 24V @100mA max.
Correct - This is the margin that the spec allows for the photographer to setup his studio! Again from a quote on page 14 of the ISO-10330: "The requirements given in 4.2
(ie. any 1 of the photoflash units shall be 30mA at maximum
) permit up to three photoflash units to be connected in parallel with a single camera. When more than three photoflash units are connected in parallel with a single camera, care should be taken not to cause the sum of the currents flowing through the camera to exceed 100mA.