roubaixtuesday wrote:The appliance sees the *difference* between the two. 'Cos it's AC, that difference is the same regardless as to which way around the two are wired.
Doesn't affect the way the appliance will run, but not to be recommended on any appliance with a 3-pin plug. Some double-insulated appliances with only a symmetric 2-pin connector (e.g. lawn mowers), it's not possible to control which lead is 'live' - and I don't suppose it matters, they always have a 2-pole on-off switch.
Incidentally, the 'neutral' wire derives from, and is connected to the fourth, neutral wire in 3-phase power distribution, which, if the phases are perfectly balanced, is superfluous since it conducts no current. However, in domestic power supply where each household gets a single phase, it's not possible to get complete phase balance, so the neutral wire is needed. It's usually earthed at the substation. Once the 3-phase is split into single phase, the neutral carries the same current as the live.
This reminds me of the experience of a former colleague which he once related to me. He'd bought an old second-hand record player, and, being a qualified electrical engineer, he thought he'd just take it apart and check it over before using it. He discovered that the appliance, despite having a metal case, had no earth lead: instead, someone had soldered a wire between the neutral supply lead and the casing. Perhaps someone can explain why this made the player a death-trap?