Polarity - does it matter?

Discussion in 'Motorhome Chat' started by Barclaybasher, Jul 12, 2012.

  1. Barclaybasher

    Barclaybasher Funster

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    I've just bought a polarity meter and am going to make up a reversed hook up lead.
    What is puzzllng me though is - on the continent 2 pin plugs are used and these can obviously be put in either way round - what is different over there?
    :Confused:
     
  2. acting_strange

    acting_strange

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    At the risk of Pappajohn etc jumping on me....Polarity doesn't matter with an AC current as by it's very nature AC "flip-flops" between Pos and Neg anyway...

    BUT WITH DC current it matters a great deal.....POS to POS and NEG to NEG...never cross them over....
     
  3. John & Joan

    John & Joan Funster

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    As long as there are no problems it makes no difference as the polarity swaps 50 time a second.

    If you do interfere with any of your electrics take the lead out of the mains supply socket and you will have no problems.

    John
     
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  4. Linda and Steph

    Linda and Steph Funster

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    What about the 2 pin 12 volt plug, does it matter which is +ve ?
     

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  5. hilldweller

    hilldweller Funster Life Member

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    Double pole switching. We have single pole switches and circuit breakers. When they switch off it's safe no matter which wire is live.
     
  6. Gromett

    Gromett Funster

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    Polarity does matter. I have to get to work now but if no one else points the reason by the time I get back I will post why... Sorry.
     
  7. hilldweller

    hilldweller Funster Life Member

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    Mostly yes, it should be marked on the plug.
     
  8. Reallyretired

    Reallyretired Funster

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    Polarity does matter with AC as it isn't just like DC switching poles 50 times a second. With AC mains only one 'pin' is live and this is the one the switches need to be in.


    I'm sure one of our electrical experts can explain much better than this.
     
  9. Dodgey

    Dodgey Funster

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    Yes!

    If you just plugged in a say a light it would probably work, most 12 volt DC, or any DC devises are polarity consious. A major issue here is also many DC devises will likely be 'negative earth', ie the case if metal, or any screws, will be connected to the negative side so if reversed the case would be possitive and as the MH is negative earth you risk a short, which whilst it wont kill you per say could blow a fuse right up to catch fire.
     
  10. RickJ

    RickJ Read Only Funster

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    As has been said, things will work either way round because it's AC. However, it is a safety issue.

    The two wires in AC supplies are "live" and "neutral". The neutral is notionally at earth potential, while the live carries the "power". The result is you won't get a shock if you touch the neutral, but you will if you touch the live (and another part of you has a connection to earth).

    In our fully 3-pin UK system the two are never confused, which means that the supply can safely be switched off just with a switch on the live side. This is how a switched 13A socket is made, and most appliances have the on-off switch only on the live wire.

    In Europe a lot of appliances are 2-pin, so the switches are double-pole - they switch both wires because you don't know which way round it's going to be plugged in.

    The problem comes when you hook-up a motorhome wired with UK 13A sockets, using UK appliances. If your live & neutral is reversed, then the "neutral" pins in the 13A sockets will actually be "live", even when the socket is switched off, etc. Everything will work, and you probably won't get any shocks, but should you get a fault in the wiring or an appliance, then there is a greater risk of shock or fire.

    Unfortunately, the Europeans, esp. the French, are totally cavalier about wiring up outlets, so you can never rely on the blue hookup points being the right way round, even though there is a clear spec. about which pin should be live and which neutral!

    Always best to have a polarity-reversing adapter available for the hookup cable.

    Rick
    (ex-camper and caravanner, looking for a camper van)
     
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