Reverse Polarity


A lot of 'scaremongering' surrounds the topic of Reverse Polarity on Caravan/Motorhome websites based on data that is no longer current.

Can I start by talking about Reverse Polarity in General, as it can, and does happen in the Home, not just a Caravan/Motorhome.
Reverse Polarity is a term usually used to describe where a 230V device, like a household appliance, e.g Toaster,  has been wired incorrectly at the plug so that the Live/+ power travels down the Neutral/- wire of the 3 wire cable.

Normally the Live/+ voltage would pass down the Brown wire which is where most Appliances have the On/Off switch. 
The Blue wire is used for Neutral and the Yellow/Green wire for Earth. (This is the colour code for the UK, other countries have different colours).
It is not an uncommon situation in the UK where somebody fits a 13A plug to, for example, a Kettle they have purchased and accidently reverses the wiring so that the 230v Live/+ comes in down the Blue neutral wire in the cable. 
This is reversed Polarity.
Something like a Kettle will continue to function if connected this way. Unless a fault develops with the appliance.

However, even when the device works correctly there can be a 'perceived' safety issue as the On/Off switch is sometimes only located in the Brown/cable.
If the Polarity is reversed much of the cable in the device would still be 'live' when 'switched off'. If someone then opened the Case and put their fingers into the wiring, they might be injured. 
Which is why 'standard practice' suggests removing the power supply plug from the wall socket before opening a 230v device and touching live wiring. 

Much is made of this 'danger', yet it quite clearly isn't a safety risk as few sensible people are going to open up any 230v device while it is still connected to the wall 230v socket and put their fingers on the bare wires!! 
Even less people are likely to do this in a Motorhome. 
Fewer still are likely to be stupid enough to expose an Appliances wiring while still 'live', in a Motorhome at exactly the same time as the Bollard has been wired 'reverse Polarity'. 
Even back in the 1980's the likely hood of that combination of 'disasters' happening all at the same time has got to be a million to one, yet some sources suggest it is more likely than getting a Green Bannana from Asda's fruit section. 

While a Kettle, Toaster and many other devices may function and be perfectly safe with the Polarity/Wires reversed, some electronics will not.
Older technology Electronics/Electrics expect the +/Live current to be coming in on the Brown wire. Some older Electronic units (like Chargers) will fail to operate properly if the wiring has been mismatched with the Live/Neutral wiring been reversed. 
This can stop some older technology chargers from working correctly. 

To combat this issue of 13A plugs being incorrectly fitted in the Home, new UK regulations were introduced (around 1990?) that specified all Appliances being sold in the UK, had to be pre-fitted with a 13A plug so that purchasers are less likley to fit a 13A Plug with wires/Polarity reversed
Around the same time Appliances began to be 'Double Insulated' and 'double pole' switched, i.e. a switch in both the Live wire AND the Neutral wire. 
UK quality Electronic devices (from say 1999 onwards) began including features to cope with Reverse Polarity by having 
Double Pole switches and Polarity protected Electronics, following the mainland Europe practice started many years before.   

So with 'Double Pole' switching and 'Double Insulated' adding even better protection, it makes our million to one example above, now a one trillion to one risk. 
I therefore don't understand why it is even mentioned any more? 

In France and Spain, they had long ago realised that even when good standards were in place, people did not always follow them in the home. So the majority of French and Spanish manufactured 230v Appliances of the 1970's and 1980's took account of Voltage Polarity reversal and generally worked/were safe on both.

Any Camping Site Electric Hook-Up (EHU) bollard should follow the European 230v wiring standards on all camp sites.
But in the 1980's some French and Spanish camp sites were slow to adopt the more rigidly enforced standards. It had never been a problem before, so some viewed it as unnecessary bureaucracy.
But with growing International travel it was soon discovered that the electrics/electronics in British Motorhomes and Caravans were not as tolerant as the French, German and Spanish items.
Up until about 2002, some British built chargers (TV's, etc) would explode if the polarity was reversed.

The situation is now very different. Double Insulated, Double Pole switched and Polarity Reversal proof appliances are the norm. 
Chargers from Schaudt, Toptron, Nordelettronica, Reich, Arsilicii, CBE, etc will all function on either 230v polarity.
A modern, quality Motorhome like Burstner, Hymer, Dethleffs, N&B, Knaus, etc. will happily function on any Polarity and has for about 20 years. 

Talk to a native of Germany, Spain, etc about 'Reverse Polarity' and they won't have a clue what you are talking about, because for many years everything in their countries has been built around it being a potential daily occurrence so not a safety issue. 
However, some British built Motorhomes had a 'Polarity Detection/Reversal' device right up until about 5 years ago rather than focus on 'safety with ANY polarity'

So while the issue in the 1980's with 'Reverse Polarity' was significant, it is now not the problem it was with a quality, modern Motorhome/Caravan
Much of the advice you will read will be old and no longer so relevant.

However, if you are still concerned, focus on making your Motorhome Polarity resilient, just as the continental's do, rather than going around looking for EHU Bollards that are not wired the 'UK' way.

12v Reverse Polarity is where the Battery is connected the wrong way around, potentially more expensive than 230v Reverse Polarity.
Camper Van/Motorhome Technicians sometimes connect a 12v battery the wrong way around creating a 'Reverse 12v Polarity' situation, usually with lots of Sparks and Pops.

Not many electronic devices will escape that without damage so make sure the battery leads are clearly marked up with Red and Black Tape before you remove them.
Use Red tape to mark the Positive Lead, sometimes a Blue or Black wire, and mark the Negative cable, sometimes a Brown wire, with Black Tape. 
And yes I have got that the correct way around, some Caravans/Motorhomes will have Blue or Black wires for the 12v Positive/ + feed and Brown for 12v Negative/ -. 
Even though the same Motorhomes may then use Brown for 230v Live and Blue for 230v Neutral, the International standard for 230V, there is no International standard for Motorhome Habitation low voltage (12 or 24volt DC). 

If you are not sure which is which on 12v circuits, most Battery terminal Clamps have a +/P or -/N sign cast on to them or onto the casing near the terminal.

German motorhomes generally have the following wiring Colour codes :

Habitation battery 12v
          Positive :  Black
          Negative : Brown
                The Cable running between the Power Control unit and the Starter battery is usually Red
230v Mains (as per the UK)
          Live  : Brown
          Neutral: Blue
          Earth      : Yellow/Green

Engine compartment (Starter) Battery (as per the UK)
          Positive :  Red
          Negative : Black

Most Motorhomes (but not all) have a 'Test' button on the mains RCD, this should be tested on a regular basis, like so :  
                     With the EHU connected and the switches in the Up/On position, Press the test button and the RCD should flick                      Down into the 'Off' position.    
Your Home should also have a test button in the Mains input Fuse/RCD box which should be tested on a regularly basis to ensure it is protecting the Home. 

Note the test is only relevant with Mains connected, as it uses the 230v supply to trip the switch Off/Down. 
The RCD will not 'trip' down if there is not 230v power at the RCD unit. 

This is a useful way of testing if there is 230v applied to the vehicle when issues arise. If you press the RCD test button when on EHU and it doesn't trip off, there is a 230v supply issue up to the RCD, usually outside the vehicle, possibly the EHU cable.