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[LongRunner]

For the first time since I joined, I got a real idea for one Since the USA still allows small Class 0 appliances (toasters, rice cookers, even kettles if they have a plastic case) I figured double-insulating myself from them is an appropriate analogy; sure they have constitutionally protected free speech (which we don't in Australia) but so much else about 'Murican culture is so deeply screwed-up that for my sanity, I have to reject American media by default (exceptions evaluated case‑by‑case, not that I have many).

As usual I designed it in Inkscape, but exporting at the final resolution gave a rather uneven appearance on the stars; so I had to export at 8× scale and then downscale in GIMP, but then replace the double-square symbol and smiley (which got blurry from downscaling) with those from the initial 1× export.

UPDATE: Added a lightning bolt to make the meaning clearer.

[Behemot]

whaddaya mean class 0 with plastic case, that's class 2 then?

[LongRunner]

whaddaya mean class 0 with plastic case, that's class 2 then?

The heating element's outer covering has to be earthed, to prevent it from making the water live.

[Behemot]

the wire which is actually heating is usually insulated by some ceramic or cement layer, if they are sufficiently sure it could never crack for example by using two different layers) or something similar, so that the wire would make contact with the element metal casing, I don't see why not - and in such form, its double insulated hence class II

[LongRunner]

They're insulated with granular magnesium oxide (MgO), which breaks down if moisture gets into it (a regular occurrence).
The ends aren't always well-sealed and it's also quite common for the metal covering to split open after enough thermal cycling.
Besides kettles, various other appliances (clothing irons, electric ovens and old-style cooktops, washing machines etc.) use the same type of element.

(Technically we in Australia once used a different type of kettle which didn't require earthing – using a bare element in a heavy ceramic jug.
They did at least interlock the lid with the power connector, so weren't really that unsafe as long as you didn't pour the kettle while it's on. Probably safer than the South American “suicide showers”, which come in a plastic casing with no thermal protection and rely on an earth wire in the water input/output to drain away leakage currents. But the bare elements had a relatively short life in water, so required frequent replacement.)

I'm sure it's possible to use more-stable materials (many old irons and waffle-makers insulated their heating elements with ceramic beads for example), but MgO‑insulated tubular elements are relatively cheap and support high heat density, so manufacturers would need a compelling reason to choose anything else… (Nowadays the ceramic beads are largely relegated to industrial annealing mats.)

[Behemot]

that's crazy using such thing, it's also quite reactive being alkaline oxide, it not just breaks up, but reacts with water creating hydroxide which than eats through the metals

[LongRunner]

Yeah, and that's one of the reasons (besides slow warm-up) I seldom use the oil-filled heaters; tending to prefer the basic convector with bare zig-zag elements (they're bulletproof as long as they're competently made – and provided they use only resettable thermal cut-outs, not a one-time thermal fuse which may age out). While well‑built models thereof are relatively few nowadays, the DēLonghi HSX33**(F)(T)(S) are among them (here in Australia I have the HSX3324FTS).
All current non-oil-filled DēLonghi convectors are Class II as well (including their entry-level HCM2030).

For those worried about small pieces of flammable material falling into the heater (and willing to pay a premium), DēLonghi also have PTC convectors in their range.
(If I did go for an oil-filled heater, that would also be from DēLonghi given that they cover them with a 7-year warranty.)

On the off-chance I find another appliance with a better element construction, you can be sure I'll post about it…