Since posting this thread, I've found that at least one manufacturer (Dikkan Cable) actually does list a 13A rating for 0.75mm2 (along with 8A for 0.5mm2) on their pages for H03VV-F
(Although their pages for the 90C flat flexes, H03V2V2H2-F
, still list the very conservative "British" ratings for whatever reason; for the record, their page for H03VVH2-F
is obviously unfinished, with no ampacity numbers to see, while their H05VVH2-F
page lists the optimal-condition ratings similar to their circular flexes.)
It also occurred to me that many kettles (and toasters, among other items) have cord storage in the base, actively encouraging
operation while coiled. Fortunately, the geometry is such that only 1 or 2 layers can
be wound into most kettle bases, with their supplied (short) cords. (Even a compact 1L kettle, which I bought just this last Saturday, doesn't quite make it to a 3 layer coil. It's a Breville BKE320
in case anyone's interested; and it is
rated for the 2.4kW maximum in Australia/NZ, with an H05VV-F3G0.75 flex.) Of course, if you did replace the cord with a longer one then you might be able to get another layer or two in - not that modern appliances make it easy to
(apart from the IEC 60320 types, obviously).
I conclude, then, that having a 0.75mm2 flex for 10A, or 1.0mm2 for 13A, is quite safe for 2 layers (as in typical kettle bases). And, indeed, boiling the BKE320 at full capacity (which took just under 3 minutes) only made the cord lukewarm (if that), as felt by hand (quickly unwound from the base after the boil finished). I did a second, longer test with a bigger kettle (Russell Hobbs Montana 3090
, same 2.4kW rating and 0.75mm2 flex but 1.7L capacity), but the effect still wasn't much greater after 4 and a half minutes to boil. (Mind you, I had to wind its cord in reverse to make 2 layers, and then
use a short extension cord to be able to connect power to the bit still accessible.
I've also tested before what the effect of coiling up a cord under its rated load is; with 10A (using a 2.4kW room heater) through 1.0mm2 (standard fare for Australian extension cords), 5 layers gets warm but not excessively, and 10 layers gets hot to the touch but still far from melting down. (I'd estimate that above 10 to 15 layers is where the real danger begins, but you'd need a pretty long cord to do that easily; extension reels
are a different matter, but as has been mentioned in previous threads, many modern ones include a thermal cut-out to guard against exactly this condition.)
Not that this stops Breville from saying in their manuals (albeit under the "safeguards for all electrical appliances", instead of for kettles specifically) to unwind the cords before use...