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it's a bad practice to design appliance in such a way to assume that neutral will have low voltage, because in case of neutral failure in three-phase circuit you can get full voltage there, and there can be a couple of volts difference (sometimes more) between neutral and ground even in normal circumstances
it's better to cut off both live and neutral at the same time anyway, especially if there's no standard which is which. also, as device designer you don't know if it'll be used on a circuit that has neutral and phase where you think it'll go or not. (ie british appliance used on unpolarized circuit, like type F. adapters exist)
Who's using three phase in a setting where these types of plugs are used? In the US, at least, three phase circuits use very different receptacles and plugs.
The fact of the matter is that the switch has to be placed somewhere. And it's safer to place the switch between the load and the live wire, rather than between the load and the neutral wire. Designing a system where the live and neutral can easily be known makes it easier to do the safer thing.
you don't have to have three phase circuit to be affected by floating neutral in three-phase substation upstream. in some places in us there are 208v interphase three-phase circuits, which give 120v phase to neutral, which is distributed as a pair of wires as single-phase circuit. this is also normal way to deliver single-phase power in europe, as it's most efficient use of conductor. (from 400v three-phase circuits) in case more power is needed than single-phase circuit can deliver, three-phase circuit is installed
if there's switch on device, it's 2p1t meaning both phase and neutral are switched. if it's permanent, non-pluggable circuit, like lightning, it's okay if only phase is switched (neutral is connected permanently)
Yeah, you're probably right. I'm in over my head on this discussion.
I am reminded of my first day in an electrical engineering circuit theory class, when the professor made very, very clear that he was teaching us theory and fundamentals, and that the real world of electricity required a lot more safety built into the procedures and designs, because not everything behaves the way the undergrad textbook describes.
So I've learned something new. Thanks.