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Here's a much simplified version of a mains reversal correction circuit. By using a single DPDT 230VAC relay, or two SPDT 230VAC relays, you can create a circuit which will ensure that no matter how you plug the plug into the mains outlet, the live wire will always end up on the same place at the output. This is handy when working with non-isolated mains in some European countries, where there's no standard for live/neutral position, and installations in buildings are mostly two-wired
A very very important remark here is that the circuit uses the neutral and live wires to switch between, and the protective ground wire as a reference point for the detection mechanism, so if your outlet is improperly wired and the ground output is referenced to live instead of neutral, the circuit will behave exactly the opposite and will seek to place the live wire at the wrong output, making this circuit dangerous. So you need to make sure your outlet's protective ground output is wired correctly first with a live wire detector.
I found a 220V DPDT relay (EMI-SS-2230AC), which uses 3-4mA on the windings, so the circuit can easily incorporate a residual current breaker for added protection, should the output rails switch oppositely (as mentioned in a scenario above). Such breakers usually work from 15mA fault current, up to 30mA, so a 3-4mA current through it won't be enough to trigger it.
Another important remark is that you cannot use the ground for chassis protection if the neutral after the output is also connected to the chassis. This is because the contacts may be in such an initial state that the typical neutral output is live until they switch (which takes 15-20ms), which is enough time for a short circuit between the rail and ground and may weld the relay contacts shut, or cause the RCD to trigger, or a breaker to fall.
Might be a good idea to also add a common mode filter at the input, as with traditional isolation transformer designs, the transformer helps to supress such noise (as it appears on both ends of the primary in-phase, and is not passed to the secondary inductively. Here, there's no such mechanism, and the noise must be filtered manually. Luckily, such filters come integrated in a power sockets, and can be readily attached to the chassis.
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