Polarity reversal switch

[oldharry]

So in France then you cannot have a reversed "polarity"... because the two conductors are the same namely 110 volts from earth, So a "polarity" reversing tail, or switch would be pointless as reversing the "polarity" would have no effect. Both conductors at still 110 volt from earth.

So no point either in checking the "polarity"


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Yes: Think of the ac Sine wave form as shown the AC symbol. (I dont have a graphic to hand to copy here). On the Uk system, the voltage rises to 240 (or thereabouts) then drops down to 0v at the bottom of the wave. On the 110v system 0v is at the half wave line: voltage starts at 0v, rises to +110v then drops back to zero. That conductor then becomes the return as the other conductor rises to -110v before returning to zero and becoming the return for the next +ve going pulse coming through the positive conductor. So the conductor that is carrying the positive going part of the AC cycle is still the positive line, but performing a sligthly different function.

 

[rich]

I have a cable wired arse about face,is this safe to use,

 

[Ubergeekian]

Yes: Think of the ac Sine wave form as shown the AC symbol. (I dont have a graphic to hand to copy here). On the Uk system, the voltage rises to 240 (or thereabouts) then drops down to 0v at the bottom of the wave. On the 110v system 0v is at the half wave line: voltage starts at 0v, rises to +110v then drops back to zero. That conductor then becomes the return as the other conductor rises to -110v before returning to zero and becoming the return for the next +ve going pulse coming through the positive conductor. So the conductor that is carrying the positive going part of the AC cycle is still the positive line, but performing a sligthly different function.

That's how the Americans work it, too. Except that they use 110VAC+neutral for most things and 110VAC-110VAC for big stuff like cookers and washing machines.

 

[Ubergeekian]

The French regard their supply as 'safer' because the grid supply transformers are set up so that the supply cables carry at most 110v which is less likely to be lethal if someone touches it. But it does mean their supply does not differentiate between +phase and -return as we do and may quite likely be reversed.

That's why building sites use 110V equipment: it's actually 55-55 two phase because 55VAC, though potentially unpleasant, is very unlikely to kill you or even do much damage.

 

[Ubergeekian]

I understand there is a way to wire a DPDT (double pole, double throw) switch so as to act to reverse polarity. But the largest capacity 240v switch I can find, Googling, is rated 15A. Would this be man enough to cope with boat mains intake (say maximum 2kw heaters, electric kettle, immersion)? Or could I find (say) a 20A version (at an affordable cost) somewhere?
Any other comments or suggestions welcome.

BTW I know I can use a 'reversal pigtail' and I've got one and been using it for years, but I'd like to have the potential simplicity of a switch.

With all due respect, I think you would have to be stark, staring, barking, criminally mad to install a switch which would swap neutral and live. Sooner or later it would be used, or fail, in the wrong position ... and that mistake could quite easily kill someone.

Your pigtail is the way to go.