Well, I can think of a few reasons:
Economics
…sort of. I'm sure the clamp for a fixed cord costs less than an IEC inlet and the mating socket on the cord end. Then again, it's probably cheapest to equip the appliance with an IEC inlet (obviously one of the common types — not the oddball C10) and depend on the user to obtain/salvage the required cord. I'm rather sick and tired of the bundled cords that are all-too-often redundant, and only ever the correct length by chance…
Voltage ranges
Well, connecting a 120V appliance to 230V is generally destructive — if nothing worse, the appliance will no longer work. Power transformers will saturate hard (hopefully blowing the fuse before worse happens), switching supplies will instantaneously self-destruct, and heating elements will run at quadruple power (quite dangerously) until something breaks the circuit. So I suppose any 120V appliance with an IEC inlet should at least be designed so that it doesn't endanger the user if connected to 230V — but then again, adapters that enable connection of NEMA 1-15 or 5-15 plugs to 230V outlets are all-too-readily available (and some developing countries even have official 230V outlets that accept those plugs, which is a serious trap).
FLA (Frivolous Lawsuit Avoidance) (I made the acronym here.
)Well, counterfeit mains cords exist, as does just about anything else that can be counterfeited, and they can indeed fail catastrophically if fully loaded or subjected to a short circuit downstream. And no-one likes being sued over something that wasn't their fault in the first place. But refusing to use (for example) the IEC C14 inlet on a (230V — 120V would likely require >10A on full power) column heater is a somewhat wasteful way out of litigation, don't you think?
Reliability?
Insofar as contacts can become loose, at least. But they still usually last far longer than most appliances themselves, and don't fail outright.
Special cases
Well, we have modern electric kettles, which sit on a base for power connection (to avoid the manual connection/disconnection that was required so frequently with conventional inlets). But surely someone could make some sort of standard for them?
There's also the toasters in North America, which remain as Class 0 (the European/Australian ones are Class I) on this logic (or rather, lack thereof):
- If the user touches the casing of an earthed toaster in one hand and holds a knife (touching the live element, but avoiding the earthed casing) in the other, the current goes right through them; if the toaster wasn't earthed, this wouldn't have happened.
(Late edit: On further research since my initial post, modern toasters pretty much everywhere – including North America – have double-pole switches anyway, making the original "argument" more-or-less immaterial now.)
And, of course, there's power tools, where accidental disconnection of the power while drilling a hole (for example) would be rather inconvenient (and, depending on the type of tool, hazardous). That one I understand best; still, surely someone can come up with something for that application?
Don't ask me why some companies insist on designing their own power inlets, either. Especially Apple's goofy derivative of the IEC C8 that doesn't even enforce proper safety earthing…
Anyway, which do you think is the most important reason?
