Reverse Polarity is nothing to do with your compass pointing in the wrong direction! It is something that can happen when you plug into the Electrical Hook Up (EHU) on a caravan site. It is unusual for it to happen in the UK, it is more likely to happen when touring on the continent. So what is it and how does it affect you?

Reverse polarity is quite easy to understand and once you know about it, it’s fairly easy to correct. Simply, it is the live and neutral wires are the wrong way round on the EHU bollard.

“Wow… that was some mistake by the electrician that wired it up wasn’t it?” Well, not quite. To understand how the situation comes about we need to go back in history a bit. When electricity was first started to be distributed and sold on a commercial-scale, all the switches had two poles… a live and a neutral, so when you switched something on, both live and neutral were connected at the same time. Conversely, when you switched something off, both live and neutral were disconnected. Quite simple really and quite safe. So we and the rest of Europe carried on switching both wires. At some point, some bright spark (excuse the pun) said… “Hey, we can save some money here on switches. Lets make them so they only have to switch the live on and off… leave the neutral connected” To make sure we got it right, we coloured our wires Red and Black so everyone knew which was live and which was neutral. Meanwhile in Europe… they said “…Pfft….” and carried on using ‘two pole” switches and their cables stayed black and grey or white and grey or black and white.

We became obsessed slightly and said “what if someone wires it wrong?… we better put another cable in there” so we suddenly gained an ‘earth” cable… coloured green for our protection. The electricians in Europe liked the idea of an earth cable so they had a yellow one… or green depending in which country you were in. Now, the cable manufacturers were up in arms… “can we please agree on a colour for this earth“… no agreement was made, so the manufacturers got smart and made the earth cable stripey… green and yellow stripey to be exact. We saw the new stripey cable and thought “this is good” so we went stripey too, and not to be out done we decided that Brown was the new Red and Blue was the new Black!

Now I may have just re-written history slightly there… but I think you can grasp what went on. So here we are… Brown, Blue and Green & Yellow cables and switches that only operate on the live (Brown) cable, While our continental cousins still use White and Grey and Black… with a Green & Yellow striped earth but importantly switch both the live and the neutral.

So what goes on when you plug your caravan into a bollard?. Well, the current flows down the brown wire to your circuit breaker, then on to your socket and in to your appliance… lets say a toaster. It returns up the Blue wire and back to the EHU bollard. When you switch off your toaster, it turns off the Brown wire and stops the current flowing. If you turn it off at the socket on the wall, it still stops the current flowing down the Brown wire. If you turn it off by flipping the little switch on the circuit breaker, it still stops the current flowing down the brown wire to all the sockets.

Now, if we plug into a continental bollard, that has the live and neutral the wrong way round and we look again at our toaster we see there is a problem. We turn the toaster off and this time the switch is on the neutral or return path, so when we switch it off, the element ‘may’ still have a voltage present on it. If we turn it off at the wall socket, again we switch off the neutral side of the circuit, so the toaster still might have 240 volts going to it. Even if we switch it off at the circuit breaker… it will still might have 240 volts going to it.

Now 99% of the time, this is not a problem…. until that is, someone decides to put their fingers into the toaster for what ever reason…. they can touch a live element. So the toaster doesn’t even need to have a fault with it. It can still be potentially dangerous.

Keep Calm and Carry On

Don’t get too panicky though! Modern caravans are fitted with and RCD (Residual Current Device)… It’s the job of this little device to check the current flowing in on one wire and out on the other. If it detects that more current is flowing in than out because it’s leaking out somewhere – it switches off. The RCD doesn’t really care what colour the wire is that the current flows in and out on, it just wants to see the same on each wire.

Now how can we correct it? Well, checking for reversed polarity is easy and simple. All you need is to buy a “socket tester”.  You can get them from various outlets, I have listed a few links at the bottom of the page. They are simple to use and will usually have three lights on the front. Just look at the lights that are lit and they will have a label on the front telling you what each light means. If it indicates anything that is not “normal”, switch off your van’s master switch and unplug from the bollard. If necessary, consult the site warden before you do anything else. I prefer to use a Martindale CP201 tester, so I can check the bollard before plugging my van in. If on the continent and you use one of the continental adaptor leads, you can check that before you plug your van in. I’ll assume though you are using one that plugs into the normal 13 amp household socket in your van.

Now, if it indicates reverse polarity, you must switch off and unplug from the bollard. Now we can correct a reverse polarity bollard. The best way is to have a short lead, like your 16 Amp EHU lead with the blue plug and socket. This one only needs to be about a foot (30cm) long. The plug is wired up in the correct way… brown to live, blue to neutral and green/yellow to earth. The socket at the other end however needs wiring up the wrong way… Brown to Neutral, Blue to Live and Green/Yellow to Earth. If you are unsure about this, please go to your local qualified electrician, they will be able to make it for you for a small charge. It’s better to pay to have it done correctly than attempt it yourself and get it wrong. It is vitally important that you mark the lead “Reverse Polarity Correction Lead” clearly and make sure it stands out.

A note of caution. There are some of these leads available via on-line sellers at a well-known trading site. The ones I have seen are made with 1.5mm cable and are not really safe to use at 16 Amps. They won’t catch fire or melt, but they might warm up a bit at the full 16 amps.  Any EHU lead that is supplied with a new caravan must be made out of 2.5mm cable. I don;t see any reason why reverse polarity leads are any different. It is actually illegal to sell these “reverse polarity correction leads” in the UK. It is however, not illegal to make one for your own use.

If you are unsure about any aspect of reverse polarity and using a “reverse polarity correction lead” Ask a qualified electrician. If you have any doubts about your ability to make one… don’t… get your local qualified electrician to make it.

Testers can be bought from these and other places: Maplin  |  Amazon  |  PASS  |

 

Post updated June 2012

Copyright © 2011 – 2013 Simon P Barlow