Reverse Polarity - what is the problem?

[Brambles]

Hi Basil. Say we have reverse polarity and fault in the wiring that touches the case of an appliance. It could equally be the live or the neutral, so odds are even the fault is dangerous. Ahhhh! but the switch is in the Live wire and that would protect you if it was a live wire shorting to the case. Again the odds are the same because at some point you are going to switch the appliance on and touch the case so the switch in the live does not really protect you. Then comes the fuses, now if the live was fused in say the plug, and the live touched the case, AND it was earthed then the fuse would blow. If the neutral was actually the live because of reverse polarity and touched the case then the earth would still protect you because of the fuse in the distribution box, but as already been stated we have an RCCD and that would also give us protection. As far as I am concerned if you have faulty equipment it is dangerouse whether you have reerse polarity or not and as I think yourself have stated we should make sure we have a working RCCD. I still say it is NOT dangerous to have reverse polarity in itself and am still waiting to be proved wrong. Jon.

[Basil]

Hi Brambles, If you read what you have written unless you have double pole switching then reverse polarity is inherantly more dangerous as the faulty appliance would be live at all times even when the switch is turned off, therefore making the reversed polarity situation more dangerous as the appliance could be touched inadvertantly. In the event of a fault with immersion heater it could make the water heater and the water to the taps live in the event of a fault in the wrong circumstances. All the switches (5) in our van are single pole and whilst I respect all you have said that there would need to be a set of circumstances to cause the problem, it does not alter the fact that reverse polarity is inherantly more dangerous than if it was correct. Bas

[sshortcircuit]

Brambles "I still say it is NOT dangerous to have reverse polarity in itself and am still waiting to be proved wrong." An Edison Screw lampholder has the outer screw connected to neutral with the live connected to the centre pin. Reverse polarity will result in the thread now being live. How often do individuals change lamps without switching off at the mains. Even swithing off at the light switch is not conclusive as it could be a two way switching. A fundimental test before energising an electrical installation is to confirm polarity. As we live in a real world we must take precautions to ensure safety at all times and a simple polarity checker and reversed extension is a simple preventative measure

[Clive]

Its a legal requirement for both LIVE and NEUTRAL poles to be insulated from users. This applies equally to Edison screw light bulbs. The screw outer should be insulated. However if there exists a short between the screw thread and the outer metal fitting which the lampholder is fitted into and the mains polarity is reversed the RCD will trip and disconnect both poles BEFORE the light switch is turned on. Normally the moment you plug into the hookup. Who has Edison thread lamps in a motorhome anyway? You could of course fit an isolating transformer so that no pole was connected to earth????

[Brambles]

Clive has answered what I was going to say on edison screw lamp holders, And has made the point there are none at mains voltage in your motorhome unless you have your own table lamp you take with you. So how many people stick there fingers in the lamp holder changing a bulb? But you miss my whole point. You have single double or whatever switching and that protects you I agree while the appliance is switched off, but at some point you will switch it on be it today, tomorrow or when ever, and then it will be live. So you get electrocuted tomorrow instead of the 1st time you touch it (because it was not switched on the 1st time). Is it more dangerous because you can get a shock sooner, NO, it is just as dangerous. So , still it is no more dangerous to have reverse polarity on the cable to your Motorhome. Jon. (Edit) P.S. You could argue that having an extra extension to reverse the polarity is more dangerous. It is one more earth connection that could become faulty or increase the resistance of the earth path.

[Basil]

OK have it your way, I will continue to test and correct and know in my own mind that I am taking a safer and more responsible option than you. Still each to their own. Bas

[sshortcircuit]

Its amazing how some people fail to be prepared to accept common sense advice. It is a fundimental requirement to check, before an electrical installation is energised, that the polarity be confirmed. (BS7671:2001 - 131-13-01, 713-09) By testing and reversing, by use of a reverse lead, then your are at least attempting to meeting this fundimental requirement. Unfortunately RCD devices can go faulty and to put ones reliance on this to prevent electrocution is foolhardy. Electricity kills very quickly and you do not get a second chance. Simple testing and precautions are all that is needed.

[Brambles]

Good point. So how does that reguation make it more dangerous in practice, because I cannot see it from a practical piont of view. It may make it more dangerous when you have someone doing alterations to your wiring while it is hot and expects the blue wire to be Neutral but to the end user does it make a difference? In France it does not make a difference or in many other Euroean countries so why does it make a difference in the UK? Jon.

[mom]

Wow!  Now I see why starting a conversation on reverse polarity is unpopular... two opposing camps.  My original question (and apologies to Bill as it was his thread), was on the "practical" consequences.  And it has come down to statistics and wiring regs.  There is clearly no easy answer to my question.
Firstly I want to thank everyone who replied... this is what I have distilled from your answers...

1. Electricity is dangerous.
2. Although we have good protection with RCDs, things can still go wrong.
3. When everything is going well, , when no faults exist, there is no practical difference.
4. When a fault is in progress, having correct polarity "may" give you the edge in safety.
5. When becoming "polarity conscious", we should also consider and check earth.

From now on I will check polarity and correct where I can.  However, it seems to me that this in itself will never protect me from all the dangers.

Thanks again!

[Clive]

You could always never connect the mains electrics to your motorhome and depend totally on 12 volts or gas + solar panels. Many of us enjoy "wild camping" where this is exactly the case. Who is going to start the thread on the safety of gas systems then? As I said previously don,t meddle with things you are not qualified to, High voltages can be lethal. But then again so is gas heating (I never sleep with the gas heating turned on) and also driving. Perhaps the yanks have things right sticking to 110 fairground volts for houses?? Must go and remove the dead rockets from the top of our motorhome. C.

[colin]

[QUOTE]Brambles - 2006-11-05 12:45 AM Good point. So how does that reguation make it more dangerous in practice, because I cannot see it from a practical piont of view. It may make it more dangerous when you have someone doing alterations to your wiring while it is hot and expects the blue wire to be Neutral but to the end user does it make a difference? In France it does not make a difference or in many other Euroean countries so why does it make a difference in the UK? Jon.[/QUOTE] The following is in capitals because its not getting throu IN UK WE HAVE SINGLE POLE SWITCHING, WHEN YOU SWITCH OFF A SOCKET ONLY THE LIVE IS SWITCHED OFF. IN EUROPE (not sure which countries) THEY HAVE DUAL POLE SWITCHING, BOTH LIVE AND NEUTRAL ARE SWITCHED OFF. IF YOU HAVE SINGLE POLE SWITCHING AND LIVE/NEUTRAL IS REVERSED THEN YOU STILL HAVE A LIVE CONECTION, EVEN IF SWITCHED OFF

[sshortcircuit]

[QUOTE]Brambles - 2006-11-05 12:45 AM Good point. So how does that reguation make it more dangerous in practice, because I cannot see it from a practical piont of view. It may make it more dangerous when you have someone doing alterations to your wiring while it is hot and expects the blue wire to be Neutral but to the end user does it make a difference? In France it does not make a difference or in many other Euroean countries so why does it make a difference in the UK? Jon.[/QUOTE] Sorry for the delay in replying. To many "Low Flyers" last night. The reason I draw attention to the standards are that there is no point in your motorhome being wired and tested to comply with these standards, which include a polarity check, and then connecting it up incorrectly. Whilst it would be nice to think that we are safely protected by an RCD we are in a real world. Polarity is reversed and RCDs do go faulty. How often are motorhomes parked up in the continent with the awning out and all the electrical acutriments out to make another living area. As prevoiusly suggested changing a lamp in a table lamp, which can come with small ES type lamps, can be fraught with hazards. Switch off at the socket and change the lamp. During the process you touch the screw, or break the lamp touching the fillament. Now you had thought you had switched it off but because of reversed polarity and a faulty RCD its "good night from him". "Altering your wiring whilst its hot" Cowboy talk. Any competent electrician would confirm isolation. "Differences in European countries. As indicated in another post they use double pole switching which is the safer option. I hope the message has got through. Check polarity and compensate if required. Better safe than sorry!

[spartan3956]

I would like to say as a safety issue, On my first trip abroad many years ago i took the electricity set up as being the same as ours , No added advantage of forums such as this. It was only when i stepped out of the Motor Home i had a Belt which is a technical term in the trade for a shock. I had held onto the body work of the camper and when i touched the ground and became the earth, not a pleasant experience. The whole camper had become live. insulated from the ground by the tyres. I always check the polarity and earth situation before i couple up to the MH I must say is getting better in Europe but Never take electricity for granted. Pete

[Brambles]

Hi again. You are giving me a lot to reply to here. Can we just clarify we are talking about reverse polarity in the rest of Europe here and not the Uk. I assume most of those who have a revresed wired adapter lead is with european plugs and not uk. "IN UK WE HAVE SINGLE POLE SWITCHING, WHEN YOU SWITCH OFF A SOCKET ONLY THE LIVE IS SWITCHED OFF." Not true! You can buy single pole sockets but majority are double pole. We are talking about Reverse polarity in Europe not UK. "IN EUROPE (not sure which countries) THEY HAVE DUAL POLE SWITCHING, BOTH LIVE AND NEUTRAL ARE SWITCHED OFF" This is because reverse polarity as we are calling it exits everywhere, but in actual fact both wires are "hot" and balanced around the earth potential. Which may or may not be a floating earth. Can be iether centre tapped or floating. This is the reason for them using double pole switching. "IF YOU HAVE SINGLE POLE SWITCHING AND LIVE/NEUTRAL IS REVERSED THEN YOU STILL HAVE A LIVE CONECTION, EVEN IF SWITCHED OFF", but in europe they use double pole switching, but we will assume on the van you have single pole. As the voltage on both conductors can be live you have a problem either way. The diffrence will just be a few volts, I'll come back to this later. I am not saying it is safe, just it is equally dangerous iether polarity. Sparten, was a fault found on your van after you got a shock. Or was it a fault on the earth supplied on the campsite which you have connected to your chassis. That would still have existed with your 'polarity' reversed or not. Conversly if it was a live wire in your vehicle shorting the chassis then had the 'polarity been reversed you would still have got a shock, but not in the UK as neutral is bonded to earth. The reality is reverse polarity is still no more dangerous. Now back to testers and balanced earth sytems. In europe the supply is often balanced around the earth potential. Varying loads by users connected to the supply will cause the balance point around the earth to change. This means some people will find when they do the test it shows polarity one way, and yet later in the day or next day it shows a fault and plarity is the wrong way. Surely some of you must have seen strange effects when testing, but most of course just to the test and not repeat it, other have a permanent test unit in the vehicle and so will have noticed it. But the whole point is if you have faults it is just as dangerous with either polarity, all I am saying is it does not matter which polarity you have a fault is just as dangeroius and the odds on you getting a shock are the same, and if you have an RCD and get your van safety checked regualrly you minimise these situations to a minimum. While on the subject of earthing, there are some very good arguments for earthing your chassis, but I choose not to because I do not trust the earth on some poorly maintained euopean sites and if the earth becomes live then so does my Motorhome but not the ground around it. Granted I could get a fault in my vehicle wiring which makes it live and I get a shock as I step out from the cab, but as I regularly check my vehicle wiring for safety, then the risks are lower than those on a campsite. Also my RCD 'should' protect me. But again a 30mA current before it trips can still give a nasty short fast belt. I think in one of the previous posts someone stuck a tent peg in the ground to connvet the chassis to. Not a bad idea as at least then when you have a fault to chassis hopefully a fuse or trip will fire. On some other points - Electricians often hot wire things - ask them! Granted if you have a single pole switch and change a light bulb and touch the connection inadvertantly ( it happens by i experienced people as well as skilled, "oh look, just poke that bit of dirt out...oops!!) you will get a shock ( assumming you are touching another path to earth). But that is in the UK, not in the rest of Europe where we are concerned about reverse polarity! All sites installations are tested in the UK for correct polarity by law as has been mentioned. So it is NOT a problem in the UK having recerse polarity on the supplies. Hence why the Regulation are a major contibution to safety, In europe as I have mentioned things are different and unless they change their earthing system reverse polarity is not a factor to safety and you are just as at risk with either polarity. Jon.

[sshortcircuit]

Brambles "So it is NOT a problem in the UK having recerse polarity on the supplies" Utter garbage. You put to much trust in all thing being correct and we live in a real world. Wherever you are test and be safe

[Brambles]

To clarify "its not a problem having reverse supplies in the UK" I am refferring to the supplies being reversed at the outlet not actually having your hook up connected in reverse. NO! it is not a problem in the UK. Have you ever tested a hook up outlet in the UK and found it was revesed. No you have not, and if anyone did they would probably report it to the site manager, and once a year they are tested and it would be fixed also. SO! IT IS NOT A PROBLEM IN THE UK. Why don't you stop arguing and try asking me to explain where you mi-understand what I am tryig to say. I am right, and I have obviously sewn seeds of doubt in your minds and you are defending your own arguments against what I am saying. This topic is getting out of control. As far as I am concerned I have put forward my side of the debate and there is nothing more I can add, only reinforce what I am saying unless someone comes up with a sound reason why I am wrong. I am more than happy to accept I am wrong but am yet to see the sound reason why. In the meantime DO carry on testing, do not let me put you off, not that I will because you all think I am totally wrong. Fine, everyone is entitled to their own point of view and opinion. Mine is based on practical reality, and not the theory of what might go wrong. regards Jon.

[sshortcircuit]

Brambles Unfortunatey the praticle realities are 1 Does the electrician test every outlet or just a sample? (The fact that an annual test is required should suggest there is a possibility of problems) 2 Has any work been carried on the site since the inspection. Believe it or not errors can happen 3 Have the utilities carried out any works that has changed to polarity. Not unknown. Its a real world we live in and all the above and others can happen, so testing is just a logical safe proceedure. How do you find it so difficult to accept common sense advice?

[Philman]

One of the side effects of reversed polarity is that a few built-in battery chargers will not work.

[Keith T]

what an intersting - and exciting - thread.....! When abroad we always test using standard tester, and 50% of time it's ok, but there is absolutely no consistency, even on the same site. Equally, it does not seem to matter which type of socket is being used. WE carry 2 sets of connection leads for use over these, one with 'twisted' positive and negatives. However, when in Uk (which admittedly is mostly on CC sites), we never check - is there any risk in UK systems on reverse polarity then - I have always (perhasp wrongly?) assumed there isn't?

[Brambles]

An explanation and does the following make sense?. (P.S. don't make the assumption I am disagreeing with you - you will see as you read on) For example, you have 'correct' hookup. A fault developes on the live to earth on an appliance - you could get a shock. However hopefully not because a fuse or trip will have blown. But if an earth fault exists you get a shock. OK, It requires 3 faults, the fault in the appliance, the RCD not working, and an earth fault. Now if you had reverse polarity and earth bonded neutral supply, that fault would not have given you a shock. so in effect reverse polarity would have been safer. However! Most equipment/appliances which are not double insulated carry a risk of a metal part becoming live (like your fridge) and have extra precautions and insulation on the dedicated live wires which are switched. This is to reduce the risk of them ever shorting to the case etc. In effect the live terminals and cables are 'double' insulated. However the neutral dedicated wires are not afforded the same degree of insulation and protection and are more likely to have a fault shorting to the metal case or whatever. So with normal polarity you have higher risk of the supplied neutral shorting to something you could touch. No problem because neutral is not hot so to speak. However when you reverse the polarity of the supply that same fault with the neutral wire will cause the case to become live(hot). If the earh is at fault and does not cause a trip to operate (fuse or RCCB) then you will get a shock. So the argument is you are more likely to get a neutral short to earth if using non double insulated appliances. A metal cased heater in winter would be a good example, or your electric fridge. Maybe some other item you use like a seperate metal cased older battery charger. Anyway the risk of shock is higher with reverse polarity along with three other faults, 1. in the appliance, 2. your RCD does not work, 3, there is an earth fault so fuse does not blow. So the risks in both cases require 3 faults and neutralis more likely to short to something you could touch. That the 'real world' And yes that argument holds true for neutral bonded earth supplies. In Europe many countries had a floating supply (france for example) and consumers supplied their own earth, and others center tapped earth (both supply lines are 'hot' and balance around the earth). In these cases polarity does not matter one bit. It is virtually the same either way. Hoever there is a move in Europe now to more and more bonded neutral supplies and polarise sockets and habits die hard with electricians and some have wired up sockets with no regard to polarity. So we now have many sites where as in the UK polarity does matter. As earthing on some sites in Europe (uk included if site owners try to avoid testing costs - it happens) is a bit of a mess, and supplies are not maintained as well as they should be it is important to test for polarity and correct accordingly. In many cases this is not going to make any difference but in many it will as neutral earth bonding is used. What is very important is NOT to have neutral earth bonding in your Motorhome, 1. it is not permitted, 2. because it gives rise to dangerous situations if other faults occur e.g reverse polarity, or floating supply or centre tapped earth supplies. Now I have argued against everything I was saying. I'll crawl into my hole now totally confused. I was so convinced!! but was basing that on all european sites not having neutral bonded earths, I now realise that was a wrong assumption. Jon.

[Brambles]

Philman. That's interesting some chargers do not work. I can only imagine it has something to do with electrical noise filters or safety circuits connecting to the earth, and the supply will not power up because of some internal safety circuit. Do you know the make of any of these supplies? Jon.

[Brambles]

KiethT. Risk of reverse polarity on UK sites. The risk is small because they are tested, but mistakes can happen. So in reality very unlikely but possible. What is more important is to test just to make sure you have a good earth indicated once you have hooked up. Hope that clarifies it for you. Jon.

[John H]

Dave Newell does a "polarity change over switch" if anybody's interested. £35.00 mail order, £65.00 fitted. It also checks for earth faults etc. John.

[Philman]

Hi Brambles the original one in my van was a Plug-In-Systems and if it had inadvertantly been left on from a previous site and I connected to a supply which was reversed the charger would trip. I have read on other forums posts which suggest that mine was not an isolated case ( No pun intended ). It never tripped if the supply was 'correct'. Phil.

[Bill]

[QUOTE]mom - 2006-11-05 7:28 AM

.  My original question (and apologies to Bill as it was his thread), was on the "practical" consequences. 

[/QUOTE] Don't worry mom - I don't feel proprietorial about it! And anyway the real "owner" should be Michael Durrant, whose letter in MMM kicked off the whole thing. A big thank-you to all who have responded. My take on it is that there are basically two ways in which bad electricity (be it caused by reverse polarity or anything else) can harm us: 1. It can give us a shock - which may be fatal 2. It can wreck expensive appliances If (1) were happening then French caravanners - motor and trailer alike - should be dying like flies. In which case it is inconceivable that we would not have heard of it. If (2) then angry French caravanners would be up in arms. The French are famously less tolerant of idiots in authority than we are, and by now they would probably have dusted off Madame la Guillotine for the benefit of the (ir)responsible site-owners. The whole thing is vaguely reminiscent of the council which banned hanging baskets of flowers on the basis that one might fall on somebody's head and kill him.