As old as this thread is, I have to correct Trumpy on Australia/NZ extension cords:
Under official definitions, there are no (legal) "light duty" extension cords here; by "light duty" flex we mean H03VV-F (circular) or H03VVH2-F (flat), and their dimensional equivalents in AS/NZS 3191. Those only go up to 0.75mm^2, so they can't be used under the regulations for Aust/NZ extension cords (no doubt abrasion resistance is also a factor); therefore, no company here manufactures trailing sockets to fit H03VV-F (much less H03VVH2-F).
For ordinary-duty extension cords (as used in homes or offices), we of course use H05VV-F or the equivalent thereof. Heavy-duty extension cords here mainly use a flex (also specified in AS/NZS 3191) with the same dimensions as H07RN-F, but usually in PVC. "Extra heavy duty" isn't actually a type of flex with still thicker insulation, but just means a heavy-duty flex with 1.5mm^2 (or larger) conductors.
Otherwise, Trumpy is correct that 1.0mm^2 is the basic conductor size (for 10A); with 1.5mm^2 for 15/16A (and it can also be used to reduce voltage drop in longer 10A leads, of course). All legal versions are earthed, too.
The basic type of extension cord here has just a single socket; compared to many other arrangements, this is very sensible, and would be close (as far as reality allows) to fool-proof if it wasn't for the existence of the unprotected double-adaptors ("piggyback" plugs - common on some extension cords - also create the exact same hazard, just in a cosmetically different form).
