Time for dedicated outlets!

bumperdo, you need to read cleeds post above. A separate ground on the sub-panel is contrary to the NEC.

Yes, National Electric Code

Yes, National Electric Code

Got it - I'm in Canada eh!

Yes, it is either
12-2 Romex or 10-2 Romex...."cleeds" is on it!
You can debate which one to run for a 20 amp duplex outlet but what you have is a Black Positive conductor, a White Neutral conductor, and a Green Ground conductor. 
In the Service Panel: the 20 amp breaker will have only the Black wire,
   The White will be attached to the Neutral Bar and the Ground to the 
   Ground Bar.

Sir cleeds,
If I may, the power company does not supply a ground wire.
You only have three supply wires coming in from your utility/power company.
2 are the supply wires...Positives...one for each half of a 200 amp service or whatever your home has. The third wire is the Neutral wire.
No ground comes to your home.  Your ground is made-up via a 6' copper grounding rod driven in the ground.