Craftsman Posted October 23, 2012 Share Posted October 23, 2012 Hi New to this as you can see, just ordered a new van at the NEC and am planning our first trip to France next summer. I understand that when abroad this reversed polarity thing is an issue. I've got an idea what it actually means but how exactly will I know that the supply is reversed before I plug in and what do I need to do to be able to use it safely? What will happen if I mess up? (Is it dangerous? Should I get wifey to plug it in and stand well back to be on the safe side)? In layman's terms if possible please. I'm obliged. Link to comment Share on other sites More sharing options...
malc d Posted October 23, 2012 Share Posted October 23, 2012 You need to buy a polarity tester from a camping / caravanning shop. You just plug it into a socket in your van and it will tell you if there are any problems. You can make up a SPARE connector with the blue and brown wires reversed that will solve the problem. ( Some people say there is no problem with polarity being reversed ). I suggest you enter " reversed polarity " into the forum search facility and you will find this has been discussed many times before. Link to comment Share on other sites More sharing options...
drako Posted October 23, 2012 Share Posted October 23, 2012 I have found that reversed polarity generally only arises when campsites have the standard European household 3 pin outlet, instead of standard camping outlet. It is still relatively frequent in some french campsites, as well as in spain and portugal. I have a reversed polarity tester permanently plugged into a short lead with UK female plug on one side and standard campsite plug on the other, I can then quickly connect this to my European 3 pin adaptor and plug the lot into the campsite socket (this has the other advantage of quickly being able to figure out which of the outlets actually has power to it - a frequent problem in spanish and portuguese campsites, where the previous occupant has blown the fuse). If all ok I replace that lead with the lead to the van, if not I plug in a home made polarity inverter in between - as described in the previous post. With this system, the van is never plugged in without having first tested polarity, better safe than sorry when you've spent all that money on a van and are several thousand miles away from home ... Cheers Link to comment Share on other sites More sharing options...
Tony Jones Posted October 23, 2012 Share Posted October 23, 2012 A thread has just begun on this on the PMH forum. I've made a detailed and wise (!!!) contribution to it, if you want to look. Link to comment Share on other sites More sharing options...
Dr Dave Posted October 23, 2012 Share Posted October 23, 2012 The subject of reversed polarity is confused by mixing up Direct current with Alternating current, DC has fixed polarities one always positive one always negative this is polarity in the DC sense. Reversed AC polarity does not mean positive or negative with respect to the other wire but with respect to earth. The following is a very simplistic explanation in which transmission faults are ignored. Neutral the blue wire is at or near to earth potential due to it being connected to the star point of a three phase supply which is also connected to earth at the supply end so normally (but don’t do it) you would not get an electric shock by touching the neutral wire. Live however is always at 240 volts above earth (neutral) consider that your body can be at earth potential by standing on or touching some earthed surface you will be in effect the neutral conductor. For example you could have one hand on a earthed pipe and the other touching a live wire you can see from this that 240 volts will pass from one arm to the other through your chest potentially killing you. Or at least cause none fatal shock. This does matter? Yes if you have single pole switched sockets which are designed to just disconnect the live wire when turned off. In a reversed polarity situation it would disconnect the neutral wire leaving your appliance always live when plugged in. Picture the scenario you have bread stuck in your toaster and switch the socket off before you prod the knife in but unknown to you the polarity of the supply is reversed IE: you have not disconnected the live wire but the neutral. Your left hand is steadying the toaster so is at earth (or neutral) potential and your right hand that is doing the prodding with the knife comes into contact with the element which is still live and you are in for a shocking experience. This is probably why continental vans have un-switched sockets so you are encouraged to unplug the appliance if you have a problem. So forget the positive and negative polarity debate it is the transposition of live and neutral that will cause the danger and could kill you. As stated this is a simple quick explanation why you should be cautious. Hope this helps Dave Link to comment Share on other sites More sharing options...
sshortcircuit Posted October 23, 2012 Share Posted October 23, 2012 Reversed polarity in a "healthy" circuit presents no problems unless you want to take appliances apart and stick your fingers into live circuits when the hook up is still on. Your van is new so should be a "healthy" circuit. Waste money on reverse leads, circuit tester,etc if you want, but simply don't dabble and just forget Link to comment Share on other sites More sharing options...
vindiboy Posted October 23, 2012 Share Posted October 23, 2012 Excellent simplistic reply and explanation from Dr. Dave, a simple Polarity Tester from a Camping outlet about a fiver, easy to use and understand, get one. Link to comment Share on other sites More sharing options...
trigrem Posted October 23, 2012 Share Posted October 23, 2012 Do not assume that sites with European Camping sockets never be reversed polarity, I have experienced reversed polarity on Frenck and Spanish sites with European outlets. Don;t worry too much reversed polarity is only a problem if you stick your fingers on to a electrical contact when you think you have switched it off, ie if you are changing a mains light bulb and you have switched the light of, and then you stick your fingers in the fitting you will get a shock if there is reversed polarity.. Link to comment Share on other sites More sharing options...
david lloyd Posted October 24, 2012 Share Posted October 24, 2012 Dr Dave - 2012-10-23 7:23 PM The subject of reversed polarity is confused by mixing up Direct current with Alternating current, DC has fixed polarities one always positive one always negative this is polarity in the DC sense. Reversed AC polarity does not mean positive or negative with respect to the other wire but with respect to earth. The following is a very simplistic explanation in which transmission faults are ignored. Neutral the blue wire is at or near to earth potential due to it being connected to the star point of a three phase supply which is also connected to earth at the supply end so normally (but don’t do it) you would not get an electric shock by touching the neutral wire. Live however is always at 240 volts above earth (neutral) consider that your body can be at earth potential by standing on or touching some earthed surface you will be in effect the neutral conductor. For example you could have one hand on a earthed pipe and the other touching a live wire you can see from this that 240 volts will pass from one arm to the other through your chest potentially killing you. Or at least cause none fatal shock. This does matter? Yes if you have single pole switched sockets which are designed to just disconnect the live wire when turned off. In a reversed polarity situation it would disconnect the neutral wire leaving your appliance always live when plugged in. Picture the scenario you have bread stuck in your toaster and switch the socket off before you prod the knife in but unknown to you the polarity of the supply is reversed IE: you have not disconnected the live wire but the neutral. Your left hand is steadying the toaster so is at earth (or neutral) potential and your right hand that is doing the prodding with the knife comes into contact with the element which is still live and you are in for a shocking experience. This is probably why continental vans have un-switched sockets so you are encouraged to unplug the appliance if you have a problem. So forget the positive and negative polarity debate it is the transposition of live and neutral that will cause the danger and could kill you. As stated this is a simple quick explanation why you should be cautious. Hope this helps Dave Electrickery Eh? Link to comment Share on other sites More sharing options...
Brian Kirby Posted October 24, 2012 Share Posted October 24, 2012 Craftsman - 2012-10-23 5:36 PM Hi New to this as you can see, just ordered a new van at the NEC and am planning our first trip to France next summer. I understand that when abroad this reversed polarity thing is an issue. I've got an idea what it actually means but how exactly will I know that the supply is reversed before I plug in and what do I need to do to be able to use it safely? What will happen if I mess up? (Is it dangerous? Should I get wifey to plug it in and stand well back to be on the safe side)? In layman's terms if possible please. I'm obliged. I assume your new van will be brand new, so 2012/13 build. It will have a main 230V on/off switch, and probably one, or more, miniature circuit breakers (MCB). The main switch will incorporate a residual current device (RCD). This device continually monitors the current flowing on the live and neutral circuits as they pass through it. If there is any imbalance between the two, it "assumes" current is flowing to earth (the residual current), and immediately disconnects the supply by switching the main switch off. This happens in milliseconds, and the trigger is an imbalance of around 30/1000 of one amp, or 30 milliamps, which is deemed "safe" in terms of amperage and duration. RCDs have a "test" button alongside the switch which should be periodically pressed after connecting the van to mains. In an ideal world you would do this each time you connected to a strange supply to check the functioning of the RCD, but RCDs are very reliable, and this is probably overkill. A test before each trip would be wise, and if the mains switch fails to disconnect when the button is pressed, the unit should be checked by an electrician and, if faulty, swapped. This device is your life saver, and is the most important safety feature of your mains installation. The MCB/s are the modern version of fuses, but are re-settable electro-mechanical switches, that respond more quickly to overload. If the current flowing on any circuit exceeds the design load for the circuit, the breaker will pop open to isolate the circuit. These are to protect the wiring, not you. This is because overloaded wiring gets hot, and is a source of fire, so breaking the supply is the logical response. It is possible your van may be supplied with a device that combines both functions. It is called a residual current device with overload protection (RCBO). It will look like a mains switch, and will have the test button, but will will monitor current flow as well as imbalance. It will probably be of 16A or 10A capacity, and will monitor the total current flowing in your van. This may be combined with additional, lower rated, MCBs protecting low current circuits. Reversed polarity has been explained by others above. Your mains switch (RCD / RCBO) will function normally irrespective of polarity. Reversed polarity therefore presents no additional risk at this point. Your MCBs may switch both live and neutral, called double pole (DP) MCBs, or just the live, called single pole (SP) MCBs. The theoretical danger is if your installation has SP MCBs, when reversed polarity feeds the circuit via what is designed to be the neutral cable, so by-passing the SPRCD. However, the current flowing in must flow out and will then pass through the MCB, or flow to earth. If to earth, the RCD/RCBO will in any case isolate the supply, and if an overload arises the MCB will be "popped" by the excess current, so although not functioning strictly as designed, it will still function to protect the wiring. Therefore, as near as dammit, reversed polarity makes no difference to the safety of a modern, properly installed, 230V electrical installation, and can be discounted as a safety issue. It is wise, however, to carry a mains tester plug in your van (most caravan/motorhome accessory outlets stock these - W4 or similar), and use it every time you connect to a new supply point, not so much for reversed polarity, but for an absent earth connection. If you see no earth indicated, just try another supply socket. Some supply boards in some countries have very odd characteristics and missing earths, while not common, are one of them. Link to comment Share on other sites More sharing options...
HWO Posted October 24, 2012 Share Posted October 24, 2012 Some new vans have a reverse polarity indicator built into the power supply already. Autotrail is one. HWO Link to comment Share on other sites More sharing options...
Brian Kirby Posted October 24, 2012 Share Posted October 24, 2012 Brian Kirby - 2012-10-24 1:46 PM.................... The theoretical danger is if your installation has SP MCBs, when reversed polarity feeds the circuit via what is designed to be the neutral cable, so by-passing the SPRCD. ................ Apologies, just re-read the above, and noticed a typo too late to edit! :-) The reference to an "SPRCD" (Bottom line)) should read "SP MCB". Hope that wasn't too confusing. Link to comment Share on other sites More sharing options...
Zydeco Joe Posted October 24, 2012 Share Posted October 24, 2012 Got back 2 weeks ago from our first trip in our 7 year old van to France for 6 weeks. On this trip we did come across the reversed polarity problem a few times on different campsite. On the Autotrails the electric unit has a warning light that tells you that you have plugged into a "reverse polarity" site. To get over this I have short lead (same as normal orange lead only smaller)with one of the plug wires wired up wrong ........ i.e earth wire ok but other two wired up backwards. This puts the polarity right with no problems. The lead only cost me about £3 and I changed the wires myself in 5 mins,got it at the show at Malvern. Also I took again a short lead with a French two pin one end as some sites still have this and not the three pin.If any site still using the two pin and is reverse polarity just turn the plug upside down when you connect and all is ok. This worked for us. Link to comment Share on other sites More sharing options...
Craftsman Posted October 25, 2012 Author Share Posted October 25, 2012 Thanks to all who responded. Much appreciated. Link to comment Share on other sites More sharing options...
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