Bill Posted November 1, 2006 Share Posted November 1, 2006 A letter on page 21 of MMM for November, from Michael Durrant, reads “Had a discussion..over the pros and cons of safety regarding polarity status and why it is less important to Continentals than to us Brits”. He has a point. After all, the van doesn't know the nationality of its owner. I tried looking in John Wickersham's book on building your own – he just says reverse polarity is a bad thing, without explaining why. So, to rephrase Michael's question slightly, if I did hook up on a site with reversed polarity what, exactly, would the consequences be? Link to comment Share on other sites More sharing options...
Roy Posted November 1, 2006 Share Posted November 1, 2006 Hi Bill, This is a subject which has been well aired in the past. If you click the search box and enter the subject you will see what has been said about it. Roy. Link to comment Share on other sites More sharing options...
tonyishuk Posted November 1, 2006 Share Posted November 1, 2006 Most single pole switches switch on the live feed. If the switch is fed neutral, it means that the rest of the cuircuit is live. I.e if there is a malfunction and the appliance would be left live after being switched off. Double pole switching would avoid this, but who would know if your leccy kettle, toaster is double or single pole switched ? (All that shiny metal could be live :D Link to comment Share on other sites More sharing options...
enodreven Posted November 1, 2006 Share Posted November 1, 2006 Hi, I agree with "tonyishuk" from my little knowledge most appliances in the UK only utilise single pole switching which means when you turn the switch off it only turns off the live wire, which for the most part is perfectly satisfactory as long as the wiring has been installed correctly. However, if by some accident the wires had being crossed/REVERSED eg. the live wire was put into the neutral side and the neutral was put in the live side, when you turned your single pole switch off it would only turn off what was now the neutral thereby leaving the appliance still fed from the reverse side eg. along the what was supposed to be the neutral side. This would have the effect of making the appliance live even though you had turned it off also in the UK we only fuse the live feed so if you had a fault on an appliance that had its own fuse even when/if the fuse blew, albeit the appliance would stop working, it would still be live as the fuse would have effectively only cut off the route of the neutral ?? Oh and by the way from what I've been given to understand most of the switching on the continent is done with double pole switches which effectively cut of both the live and neutral so it doesnt matter so much if the live and neutral are reversed ? Hope that helps Link to comment Share on other sites More sharing options...
mom Posted November 1, 2006 Share Posted November 1, 2006 I guess this is where I start to get confused. Everyone seems to talk theory, but I would like to know what the "real", "practical" issues are. I used to check polarity, but after realizing that many sites are reversed in France, and realizing that most of us Brits aren't actually aware of reverse polarity and camp on regardless, then I stopped bothering. We have an electric jug, phone chargers, interior lights and the fridge on 240V. That's about all. Many times, when I have asked of a neighbour "Did you notice that polarity is reversed?", the answer has been, "Not for me! Mine's OK." When I have questioned further, it transpires that he or she actually didn't know what polarity was, they had no tester and assumed it meant "the power worked or it didn't". We're all still alive. But having said that, it may be due to someone else's graces! So is anyone actually able to say that reverse polarity in the context of this posting is truly dangerous to health? Link to comment Share on other sites More sharing options...
Clive Posted November 1, 2006 Share Posted November 1, 2006 If you have a modern motorhome it will be equipped with an earth leakage current detecting main circuit breaker. These breakers do this by accurately comparing the current flowing in the NEUTRAL wire with that flowing in the LIVE wire. If these currents are not almost identical (because some has flowed elswehere - like via earth back to the transformer) then the trip will operate disconnecting both LIVE and NEUTRAL connections. If you have an appliance with an earth leakage fault and the Mains hookup is connected correctly then the earth leakage trip will operate when you switch on that appliances ON/OFF switch. If the mains hookup is connected with reverse polarity and you have an appliance with an earth leakage fault then the trip will operate as soon as you connect your hookup irrespective of the appliances ON/OFF switch. If you have an OVERLOAD situation then the circuit breaker supplying the circuit which has the overload will open irrespective of supply polarity. If this overload is because of an earth fault then the earth leakage trip will operate anyway. So, I would not worry about reverse polarity unduly as faults will get picked up one way or another. But, The latest Autotrails, Autocruise, Kontiki, Bessacar and Timberland motorhomes include an indicator lamp to warn of reversed mains polarity. C. Link to comment Share on other sites More sharing options...
Basil Posted November 1, 2006 Share Posted November 1, 2006 Hi Mom, In answer to your question, in the wrong circumstances yes. If you have reversed polarity on an appliance that has single pole switching and a fault, say a damaged and bare wire touching the case, and you then touch that case as you made a contact with something that was earthed then the current would go to earth through you. It would then be up to divine intervention whether you were still here or somewhere else!! If others wish to ignore the fact that they may have RP thats their decision, I will always check and correct if I need to. Mind you knowing my luck I will lean on the only van on site that has reverse polarity with a fault to earth and earth it out through me!!! ATEOTD we all make our own decisions. Bas Link to comment Share on other sites More sharing options...
enodreven Posted November 1, 2006 Share Posted November 1, 2006 Hi, In reply to MOM direct question "So is anyone actually able to say that reverse polarity in the context of this posting is truly dangerous to health?, THE ANSWER IS YES ? Its up to the individual to decide whether they want to do anything about it but i would strongly suggest that they check every time they connect to a new supply and if its reversed they should DO SOMETHING ABOUT IT ? I hope that is clear enough ? Brian Link to comment Share on other sites More sharing options...
colin Posted November 1, 2006 Share Posted November 1, 2006 Is reversed polarity dangerous? Yes and No, if an appliaince is working correctly, proboly not, but say you have a mains bulb blow, you switch it off and change bulb, when bulb is out of fitting you have a bare live contact, ok you proboly won't stick your finger in the fitting, but then again you might acidently. Link to comment Share on other sites More sharing options...
Clive Posted November 1, 2006 Share Posted November 1, 2006 Then again as the bulb has blown you probably won,t know if the switch is ON or OFF when you test it with your finger???? Link to comment Share on other sites More sharing options...
Brian Kirby Posted November 1, 2006 Share Posted November 1, 2006 On the whole, I'm with Clive. The provisos are:1 Your 'van does have an RCD main switch, you have tested it, and it works. Older 'vans may not be so equipped.2 Your appliances all have double pole (DP) switches. Older appliances mostly do not, and not all new ones necessarily seem to have.3 Your site hook up has a good earth connection: in the absence of this your RCD is unlikely to function if there is a earth fault. Most have, but there are a few of the others around.Of the three, 3 is the most important to safety - irrespective of polarity or RCD switches - 1 is the next most important, again, irrespective of polarity, and 2 is the gilt on the gingerbread. If you score 3 out of 3, broadly, polarity won't affect your safety.If 2 is missing, you could possibly be at risk of shock/fire if the site earth is poor. Provided the RCD is present and working - and the earth is good - however, I think the risk is rather theoretical.If you just happen to have a older 'van without an RCD, do get one fitted. It'll be the best electrical safety move you could make - remember the risk isn't just shock, electricity going wrong also causes fires.The most important safety feature by far, however, is the site earth connection. As Clive says, most 'vans have RCDs and most modern appliances are tending to be DP switched. Combined, these virtually eliminate any risk associated with reversed polarity. Additionally, I understand some 'van manufacturers are now fitting double pole switches and circuit breakers on the internal electrical circuits as well, so their 'vans are just about bomb proof.However, in the absence of a proper earth, all that is as nought!I think we may have focused too much on polarity, when we should have been giving more attention to testing the earth. Just having one is a good start: fortunately the great majority of sites do achieve this - but I have encountered a couple recently that didn't! The simplest answer is to disconnect and try another pillar, it is highly improbable there will be no earth anywhere. If you can't, stay disconnected. After all, your 'van should have the autonomy to survive a night or so without a supply. However, more of safety a problem, potentially, is the quality of the earth, and how you can tell.Clive might like to respond further on this, but I've no idea how you can test whether the site connection does, actually, provide an adequate earth connection. I'm sure the great majority do, but a simple tester that doesn't trip the RCD on the site supply pillar would have been a comfort on one or two sites I've visited! Or should we just bash in an earth spike when unsure? Link to comment Share on other sites More sharing options...
gerannpasa Posted November 2, 2006 Share Posted November 2, 2006 Most of the foregoing is true, and good advice. How long does it take to test for and rectify wrong polarity? I have a £5 tester from Maplin, a crossover cable I made myself for a tenner (you can buy them). I plug in, jump in the van, turn on the mains switch, turn off the mains switch, jump out of the van, unplug. plug in X-over cable, replug, back in van, retest ... job done. It takes about 30 seconds. Is it worth the risk for £20 and less than a minute? Gerald Link to comment Share on other sites More sharing options...
enodreven Posted November 2, 2006 Share Posted November 2, 2006 I totally agree, we can pontificate over the problem forever and as you say for around £20 its just not worth taking a chance. and Don thanks again for the tip about the spell checker in the Google task bar Welcome to the site "gerannpasa" [QUOTE]gerannpasa - 2006-11-02 12:17 AM Most of the foregoing is true, and good advice. How long does it take to test for and rectify wrong polarity? I have a £5 tester from Maplin, a crossover cable I made myself for a tenner (you can buy them). I plug in, jump in the van, turn on the mains switch, turn off the mains switch, jump out of the van, unplug. plug in X-over cable, replug, back in van, retest ... job done. It takes about 30 seconds. Is it worth the risk for £20 and less than a minute? Gerald[/QUOTE] Link to comment Share on other sites More sharing options...
mom Posted November 2, 2006 Share Posted November 2, 2006 [QUOTE]gerannpasa - 2006-11-02 12:17 AM Most of the foregoing is true, and good advice. How long does it take to test for and rectify wrong polarity? I have a £5 tester from Maplin, a crossover cable I made myself for a tenner (you can buy them). I plug in, jump in the van, turn on the mains switch, turn off the mains switch, jump out of the van, unplug. plug in X-over cable, replug, back in van, retest ... job done. It takes about 30 seconds. Is it worth the risk for £20 and less than a minute? Gerald[/QUOTE] Thankyou everyone for your replies. Gerald, I agree, but I wanted to know "why" this is important, and whether the polarity/earth issues were discussion amongst theoretists and editorial arse-protecting, or whether, and why, it was a real life issue. Brian clearly felt that reversed polarity was life threatening, but in a world where so many of us do things simply because we are told to, or because it's always been done that way, I have developed a habbit of asking for clarification! The jist of most, but not all, of the postings above suggest that the problem poses a real danger, and most have gone a fair way to explaining why. Thanks for that. I have a modern RCD fitted, I'm not sure which of my appliances are double pole, and I have an earth checker, but obviously quality of earth is harder to check. So I'll go back to my pluging-in ritual of using the tester and searching for the correct crossover cable.Thanks again, everyone. I'm really tempted to start a new thread about why we have to unroll our electricity cable completely, when under full load in my van it remains stone cold throughout! But that would be unfair! Link to comment Share on other sites More sharing options...
Don Madge Posted November 2, 2006 Share Posted November 2, 2006 [QUOTE]Brian Kirby - 2006-11-01 11:17 I think we may have focused too much on polarity, when we should have been giving more attention to testing the earth. Just having one is a good start: fortunately the great majority of sites do achieve this - but I have encountered a couple recently that didn't! The simplest answer is to disconnect and try another pillar, it is highly improbable there will be no earth anywhere. If you can't, stay disconnected. After all, your 'van should have the autonomy to survive a night or so without a supply. However, more of safety a problem, potentially, is the quality of the earth, and how you can tell.Clive might like to respond further on this, but I've no idea how you can test whether the site connection does, actually, provide an adequate earth connection. I'm sure the great majority do, but a simple tester that doesn't trip the RCD on the site supply pillar would have been a comfort on one or two sites I've visited! Or should we just bash in an earth spike when unsure?[/QUOTE] Brian, We often find sites with no earth connection in places like Turkey and Morocco and sometimes Portugal. I just bang one of my large tent pegs into the ground and use one of my jump leads to earth the van. It took a bit of searching for the spot to connect to on the van. I have in the past poured a bucket of water over the spike to help (not sure that it does any good). I was once informed on another list by a so called expert that the van would not earth that way. We have been using the system for years. We also used it many years ago on the radio when camping in Turkey, it improved reception considerabley. Any comments Clive? Don Link to comment Share on other sites More sharing options...
Basil Posted November 2, 2006 Share Posted November 2, 2006 Hi Don, Yours is a valid method of putting the potential of the vehicle chassis as earth, providing there was less than 1 ohm resistance (the specific requirement for maximum resistance in an earth circuit) between the chassis and the ground. With regard to earlier comments on RCCD's, they are not neccessarily triggered if there is leakage to earth. I have had a case myself where whilst crawling about under the van I had a spark, with a flash and sufficient power to make me jump, from the exhaust and handbrake cable. That was on our current vehicle with a RCCD perfect earth and a RCCD on the house, none of which tripped. so I would not neccessarily rely on being ok soley on having RCCD's fitted. The cause of problem turned out to be a 28v AC voltage (measured from the chassis to earth, stake in the ground), which I accept in this case is not life threatning, caused by damaged wiring from a tyre blow out having got moisture into the sheathing. The RCCD's were subsequently tested and found to be ok and I have never found a satisfactory explanation of how this could happen from my understanding of how RCCD's work as I thought an imbalance should have been immediately been picked up and the RCCD operated. Bas Link to comment Share on other sites More sharing options...
colin Posted November 2, 2006 Share Posted November 2, 2006 [QUOTE]Basil - 2006-11-02 11:49 AM Hi Don, Yours is a valid method of putting the potential of the vehicle chassis as earth, providing there was less than 1 ohm resistance (the specific requirement for maximum resistance in an earth circuit) between the chassis and the ground. With regard to earlier comments on RCCD's, they are not neccessarily triggered if there is leakage to earth. I have had a case myself where whilst crawling about under the van I had a spark, with a flash and sufficient power to make me jump, from the exhaust and handbrake cable. That was on our current vehicle with a RCCD perfect earth and a RCCD on the house, none of which tripped. so I would not neccessarily rely on being ok soley on having RCCD's fitted. The cause of problem turned out to be a 28v AC voltage (measured from the chassis to earth, stake in the ground), which I accept in this case is not life threatning, caused by damaged wiring from a tyre blow out having got moisture into the sheathing. The RCCD's were subsequently tested and found to be ok and I have never found a satisfactory explanation of how this could happen from my understanding of how RCCD's work as I thought an imbalance should have been immediately been picked up and the RCCD operated. Bas[/QUOTE] This I believe will have been from the nuetral side and not live side, its a problem I have encountered many times. First time it happened to me was at my parents house, I used to get shocks from the taps, just enough to sting me, it turns out when house was replumbed and plastic main in pipe fitted earth was lost, they had a damaged ring on cooker and this was 'leaking' to earth throu the nuetral, but as there was no earth it went throu me. I complained to father who said there was no problem untill one day he didn't have his slippers on then he got shock. I have since become a bit of an 'expert' at finding these problems as I often pad around bare footed Link to comment Share on other sites More sharing options...
sshortcircuit Posted November 2, 2006 Share Posted November 2, 2006 [/QUOTE] This I believe will have been from the nuetral side and not live side, its a problem I have encountered many times. First time it happened to me was at my parents house, I used to get shocks from the taps, just enough to sting me, it turns out when house was replumbed and plastic main in pipe fitted earth was lost, they had a damaged ring on cooker and this was 'leaking' to earth throu the nuetral, but as there was no earth it went throu me. I complained to father who said there was no problem untill one day he didn't have his slippers on then he got shock. I have since become a bit of an 'expert' at finding these problems as I often pad around bare footed[/QUOTE] Please note that water and gas pipes are not means of providing an earth within a domestic premise. In your parents house there would appear to have been a fault to the existing pipework to the taps and you were then completing the earth path. Many older house used the water main as an earth which as you have found out could create potentially lethal conditions. With respect to a motorhome a neutral to earth fault (bared neutral to chassis) could go unnoticed as neutral and earth at same potential. However with a reverse polarity situation the chassis would then become live and like your tap situation if you provide the path between the chassis and earth, the ground, then a potentially lethal situation exists. Have an RCD fitted, test is regulary, use a simple Maplin polarity tester and give electicity a lot of respect. It kills. Link to comment Share on other sites More sharing options...
colin Posted November 2, 2006 Share Posted November 2, 2006 Yes they now have a proper earth conector. I believe the nuetral in basil's case was from the a/c curcuit not 12v dc Link to comment Share on other sites More sharing options...
Basil Posted November 3, 2006 Share Posted November 3, 2006 As sshortcircuit says, Earth Continuity Cross Bonding as it is known should be cross bonded to the main earth at the consumer unit and not via the service pipework for other utilities, so whether metal or plastic it should have no effect on the bonded earths. Regarding a neutral short, I am still not convinced that was the problem as these devices work on the balance between what enters them and what leaves them so they should drop out if that balance is out regardles of whether it is on the line or the neutral. If the circuit is leaking electricity at some point covered by the RCCD then there is a difference from what is 'entering' the circuit at the live to what is 'leaving' the circuit at the neutral as the amount leaving would be what was entering les the loss. So I am still not convinced that you should rely on and hope that RCCD's are the be all and end all of safety devices in the wrong circumstances, but are just another part of overall safety that should start with having all things correct in the first place i.e. for me a good earth is the number one priority followed by correct polarity. Just my opinion FWIW. Bas Link to comment Share on other sites More sharing options...
Philman Posted November 3, 2006 Share Posted November 3, 2006 Most, if not all, Polarity Testers also indicate if the earth is missing. This is not that unusual and can create a potentially ( forgive the pun ) lethal situation. Earth and Neutral are not necessarily at the same potential at the outlet. They are connected at the sub-station or distribution board but not at the van or campsite bollard. Phil. Link to comment Share on other sites More sharing options...
Clive Posted November 3, 2006 Share Posted November 3, 2006 Its would be difficult to cover all the points raised in sufficient detail without boring everyone. If this debate is over your head then take professional advice. Don,t DIY if you are not qualified when it comes to mains voltages. 1) All the mains hookups come from transformers which provide three single phase outputs each phase being displaced by 120 electrical degrees from the others. The common point of these three phases is NEUTRAL and this will be bonded to ground at the transformer. Ideally the loading on each of the phases will be similar which results in very little current flowing back up the NEUTRAL wiring to the transformer. If however it is not well BALANCED then there will be a significant voltage drop in the NEUTRAL. Back some distance away at the van you can measure this voltage between the NEUTRAL connection at the van and earth. This voltage can quite easilly be 28 volts. Perhaps this is the 28 volts that was measured in a previous posting? 2) If a van has a genuine UNBALANCE CURRENT EARTH LEAKAGE CIRCUIT BREAKER fitted then you should be protected against earth faults irrespective of polarity. As has been said if you haven,t got one then get one. 3) If there is no earth connection at the hookup then there is no path to earth between you should you touch a live connection inside the van. (Don,t test this with your body!!) However if there is a fault within the van between the electrical system and the chassis this WILL be detected when someone connects the van to ground, like getting in or our. The RCD should trip on this occasion. Ideally earth resistance should be quite low, but an RCD should trip with an earth resistance of 100 ohms or so. A single tent pole hammered into the ground is unlikely to provide a sufficiently low resistance in a dry condition. Long copper plated earth spikes in wet soil are more efficient. From my viewpoint a bad earth is far more dangerous than a reverse polarity of the mains supply. Having said that one should always disconnect the supply before changing a light bulb. 4) The typical antenna impedance for a radio set can be anything like 50 ohms, or 75 ohms or 300 ohms. All higher resistances than that associated with mains earth bonding. Link to comment Share on other sites More sharing options...
Brambles Posted November 4, 2006 Share Posted November 4, 2006 Oh for goodness sake, lets answer Moms original question. NO, it is not a major problem to be concerned about. You would have to have multiple faults for it to be a serious issue, and even with multiple faults, which is unlikely if you get your electrical installation and RCB checked occassionally, you still have to have other cionditions met to be life threatening. The chances of an electric shock with iether correct or reverse polarity is much the same. Most appliances now are double insulated and have double pole switching so polarity does not matter. The professionals have been arguing and changing their minds about earthing and polarity for years and still debating it, and so much so we have different earthing arrangements across the country in different areas, and indeed iacross Europe. But these clever bods came up with a good safety protection solution that woud work in all cases. The RCCB, measuring imbalances in current through the live and neutral. Works european wide and is so effective at protecting us the Motorhome builders were made to fit one in every mains hook up installation. It solved the problem of reverse polarity, if it ever was a problem in the 1st place. As I have said, if you have a series of faults the chances of a shock are the same if you have reverse polarity or not. Jon. (can I get of my soap box now before the flack comes flying in my direction from all of you) Link to comment Share on other sites More sharing options...
Brambles Posted November 4, 2006 Share Posted November 4, 2006 Oh sorry Clive - think you have said much the same as me!! sort of. You must have posted in the long time in takes me to write and post a message. Link to comment Share on other sites More sharing options...
Basil Posted November 4, 2006 Share Posted November 4, 2006 brambles, You are of course entitled to your opinion, as is everyone else, but your statement that it is no more dangerous to have reverse polarity is wrong. Bas Link to comment Share on other sites More sharing options...
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