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230VAC input protection against to reverse connection

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Member level 5
May 27, 2010
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Duisburg, Germany
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Hi all,

i have a circuit for AC load. Does anyone know, how can i protect circuit and let it work normally.
if user put power socket in reverse direction. if phase and neutral change places.

i did not know how to search about it in google.
Thank you.

Best regards

i made this circuit to control amplitude of selonoid with microcontroller.
i meant, in case someone give power in other direction(Neutral instead of Phase und Phase instead of Neutral).
what should i add in the begining of circuit to let circuit work normally, if power socket connection 180degree turned, if phase nd neutral change places.
i hope i could explain.

thank you.

The polarity in the AC supply reverses 50 or 60 times a second so the circuit would be unaware which wire went to phase and which went to neutral. The only time it would make a difference is when a third (maybe Earth) connection is also present. On most single phase power distribution systems the neutral and Earth are bonded at the power source (sub-station transformer) so it would be normal to see different L-E and N-E voltages but L-N should be the same either way around.


If you are using a non isolated power supply then providing your insulation is correct, as said it, will not matter which wire is L or N. If you insulation is inadequate, which it sounds that it is, then connecting the incoming neutral to the chassis would under most circumstances be safe, but under a fault condition (break in neutral feed anywhere) would cause the earthy connections to be live. In any case the neutral could be at a couple of volts AC and with only the supply fuse in series with it, so a neutral connected chassis touching a proper earthed point would cause very high currents to flow and burn out your mains lead.

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