reverse polarity

[3.0ghia]

I seem to be getting mixed comments from fellow caravaners and dealers regarding the above, we are going to France in June and as a precaution i have bought two- two pin conectors ( one with the blue and brown reversed which i done myself) and have made a short cable up with the blue connectors with one end reversed, i also bought a plug in tester which lights up to let you know how the electric is wired, we recently upgraded our van at the back end of last year and have used the van a dozen times since, at the weekend i plugged the van into the supply in my garage to charge the battery i then plugged the tester in and was amazed it was incorrect, thinking it was the wiring in the garage i plugged the tester into the socket and it was fine i then plugged in a spare cable from the socket to the van and it was also ok, so seems i have been using a reversed polarity cable for several months without knowing, when i contacted the previous owner he had know idea either as he hadnt travelled abroad and had never tested the polarity, so my question is does it really make any difference ? and is there no warning visual or audiable in the van to let you know of this ?
thanks in advance for your time

chris.

 

[ProfJohnL]

Hello Chris,
Most mains applainces will work quite happily with the live and nuetral wires crossed and generally you wont be exposed to any danger unless an appliance actually developes a fault, or you start to to tinker with the system.
The danger starts to arise where equipment has a fuse or single pole switched only in the live conductor. This means that if the supply is reveresed if the fuse or the switch is apparently off, internal parts of the applaince will still be live and thus potentially (no pun intended) dangerouse.
Modern Caravan systems utilise double pole RCD,s and doublel pole isolators,trip both the live and nuetral conductors are isolated. The majority electrical applainces designed for caravans also have to use double pole switches.

So in most cases reversed polarity will not cause a probelem, BUT there are a few where it may, so it is still a good safety precaution to check the polarity and to correct it.
such that if either .

 

[ProfJohnL]

Hello Chris,
Most mains applainces will work quite happily with the live and nuetral wires crossed and generally you wont be exposed to any danger unless an appliance actually developes a fault, or you start to to tinker with the system.
The danger starts to arise where equipment has a fuse or single pole switched only in the live conductor. This means that if the supply is reveresed if the fuse or the switch is apparently off, internal parts of the applaince will still be live and thus potentially (no pun intended) dangerouse.
Modern Caravan systems utilise double pole RCD,s and doublel pole isolators,trip both the live and nuetral conductors are isolated. The majority electrical applainces designed for caravans also have to use double pole switches.

So in most cases reversed polarity will not cause a probelem, BUT there are a few where it may, so it is still a good safety precaution to check the polarity and to correct it.
such that if either .

 

[John_374564913]

The most simplistic way to explain this is the following
Imagine your house is running on the correct polarity your wife asks you to change the light in the kitchen so you switch of the light switch which stops the current going to the light as it breaks the feed.

However if the polarity in your house is revered the light swith will still work but in the off position it has only cut the return so when you go to change the light fitting it is still live and you get the electric shock.
If you cravan has fuses that cut both the feed and the return then you would not have a problem as in both cases the feed would be cut as proffesor john stated

 

[emmerson]

Prof John, will reverse polarity affect things like laptops, tvs, battery chargers, etc?

 

[Lutz]

If you will permit me to reply on behalf of Prof John, no, reverse polarity does not affect the function of any of those pieces of equipment. Living here on the Continent where it is possible to plug my laptop both ways round I can confirm that it works both this way and that.

 

[emmerson]

Many thanks, Lutz and Prof.I thought it didn't really matter, but a friend says RP blew up his TV.
Anyway, I'll now have no problems on that score.
This is me now leaving home for our Euro-jaunt, so I'll see you all in August. Have a great summer.

Emmerson

 

[Surfer]

Many thanks, Lutz and Prof.I thought it didn't really matter, but a friend says RP blew up his TV.
Anyway, I'll now have no problems on that score.
This is me now leaving home for our Euro-jaunt, so I'll see you all in August. Have a great summer.

Emmerson

Highly unlikely as most of the circuits in the old analogue TVs are powered by DC and not AC. I would imagine the same applies to all new plasma and LCD TVs. RP should have no effect as in many countries the TV comes standard with a 2 pin plug anyway.

 

[bopeep]

I was in a camp site here in spain where we have just a two pin plug, but the caravan has english sockets, I plugged into the site and plugged in my tester to find reversed polarity. I just turned the plug up the other way in the camp electrics and it solved the problem.
I have to add that it was a two pin adapter I was using in the camp site box to be able to do that.

 

[ProfJohnL]

Hello Emmerson,
Lutz has given you the correct short answer,
I stated in my first sentence - "Most mains applainces" for good reason beacasue it applies only to mains powered appliances. mains supplies are rated at 230V ac where ac stands for alternating current. In essence the neutral line is a reference, and live condutor will change from +230V to -230V realtive to the neutral 50 times a second The wave form a is a sinewave. This causes the current in the circuits to change direction also at 50Hz. Most mains applainces cannot tell if the phase and neutral lines are reversed as it still sees ac current

The other type of current we have in cars and caravans is 12V dc where dc stands for Direct Current - here the voltage always stays in the same polarity +12V relative to 0V. The systems are always designed to work with this unipolar current, and if you reverse it then at best the appliance wont work, orworst it may be permanantly damaged.

All applaicnes you mention ultimately use or produce dc power they do it by first transforming the 230V ac ( and thsi can be polarity reversed) down to a more appropriate level (e.g. 12Vac) and then rectify the ac wave form to produce a lumpy dc. Smoothing is them applied to prduce a nice smoothe direct current or unipoalr supply.

 

[ProfJohnL]

Correcting revers polarity is still as sensible thing to do just in case an appliance you use does not use double pole switching (many older UK appliances only used single pole switching).

The reason that in the UK older appliances may only have single pole switches, is that there was a much greater certatntiy of the supply being correct due to the quite stringent installation practices and certification for wiring used in the UK. Also our 3 pin plug (BS 1636) prevents inadvertand incorrect connection to the local supply. With such a high certanty of supply polarity, single pole switching was seen as more than adequate for safety.

It is only since we have became part of the EEU and that 'free trade between member states means that appliances need to cater for older and less stringent istallation regulations elswhere in the EU. It becomes a particular problem for caravans and other mobile electrical installations that connect to many different supplies, which is why all current new caravan must have double pole RCDs and MCB's

 

[Dustydog]

which is why all current new caravan must have double pole RCDs and MCB's

Prof John
If I have double RCDs and MCBs do I really need to bother checking the polarity when abroad? I was under the misapprehension polarity was important until I read this thread.
Learn something every day!

 

[ProfJohnL]

Hello Dusty,
The caravans consumer unit may well be DP (Double Pole) switched but some of the equipment fitted ot some of the items you take with you may not be. You can still get faults on appliances that wont cause either the RCD or the MCB's to trip.

All UK (BS1636) plugs contain a fuse, for some appliance the fuse may be a low as 3A where as the MCB for the circuit in a caravan is likely to be 10A. The principal behind a fuse is to automatically disconnect the live condictor if the appliance overloads thus reducing any risk that live parts may be exposed. It is quite possible for the 3A fuse to blow without causing teh 10A breaker to throw. Now if the supply is reversed, then the fuse will still blow, but it will only disconnect the neutral leaving the appliance technically Live.
It is not always possible to easliy identify what appliances use douple pole switching or fusing, consequently it is far safer to assume that one or more appliance is only single pole and thus you must check and correct any reversed polarity supplies.

 

[Lutz]

Although Continental plugs are reversible, allowing appliances to be connected either way round, I have not come across any piece of household electrical equipment anywhere that is double pole switched, not even potentially dangerous things like hair dryers. In fact, some low current items, such as the power pack for my latptop computer, for example, are not switched at all. Besides, Continental plugs are not fused. I therefore feel that the Prof may be a little over-concerned on this issue.

 

[Beehpee]

I work with 12 volt systems on cars and that's how I like it, the big difference with 12 DC and 240 AC is 12 DC doesn't bite you quite so hard if you get it wrong, it will damage the car but not the owner, the point I'm making is why take any chances with mains electrics? If there is a chance it's going to damage a piece of equipment in your caravan then ok you can go out and buy a new item, you may or may not be quite so lucky if the 240 volts then decides to give you a jolt as well, and all this for the sake of using a polarity checker and doing it right in the first place, I haven't used my caravan abroad yet but I think I know which way I would go if I did.

Beehpee

 

[Lutz]

Maybe we take a more relaxed attitude towards mains current here on the Continent. I've received a mains jolt at least half a dozen times over the years while working on circuits which were thought to be switched off or circuits which couldn't be switched off for one reason or another.

 

[Surfer]

The caravans consumer unit may well be DP (Double Pole) switched but some of the equipment fitted ot some of the items you take with you may not be. You can still get faults on appliances that wont cause either the RCD or the MCB's to trip.

Can you name some of the items that not DP so that we are all aware and give a reason why they will not trip out the RCD or MCB if a fault develops? Thanks.

 

[ProfJohnL]

Hello Surfer,
No.! I will not name or identify any specific products for the simple reason that I do not know all of them, and by providing a list and being human it may not be accurate or complete so it may give someone the wrong impression about a particular product and suggest they can be less carefull than they should. - Always assume you have single pole equiepemnt and check your supply polarity accordingly.

The RCD straddles and monitors both the live and nuetral conducors of the incomming supply. It works on the basis that the current flowing in any circuit will be the same at all points in that circuit. In other words what you push in on the live conductor you should get out on the neutral condiuctor. If there is a difference then some of the current is leaking and finding its own way back to the generator by another route. That is a fault condition, and it may be the current is finding its way back to earth through someone giving them an electric shock. The RCD will detect any difference in the current between L and N of up to 30mA at which point it should trip and shut the supply off.
The MCB's monitor the current flowing in a circuit and their purpose is to protect the wiring from excessive current. Hence they only opertate when the current rises abover ther preset threshold (E.g. 6A 10A 16A depending on which model you choose)
Products can develope many different types of faults, for example a heater element may go open circuit, No current flows so neither the RCD or the MCB will respond to that.
A small apppliance like a pair of curling toungs may go partialy short circuit across part of its element, the appliance may get hotter than it should but it may still be drawing less current that its plug fuse needs to trip and as ther is no leakeage of current the RCD is un affected.
The tounges may go partially short circuit where the current flow increases enough to cause the plug fuse to blow but it still may not have been enough to trip the MCB.

These are just a few of the ways that applainces my become faulty without causing either the RCD or MCB's to trip.

And Lutz,
I am very much aware that many continantal systems lack some of the protections we have traditionally used in the UK, That under some circumstances may make them less safe than the equivelent UK systems. If you received shocks form applainces when they were notionally turned off, then in the UK if an employee or memebr of the public received a shock, then clearly there is a danger, which the HSE would investigate.

I assume that when you got your shocks that caused the RCD(or the continental equivelent) protecting the supply to operate? Even though the energy required to trip an RCD, is relatively small It can still be enough to seriously harm youngsters or people with pacemakers or some other medical conditions.

maybe I am being over cautious, but when it is so relatively simple to check and correct for reversed polarity the added protection is very cost effective, and gives peaceof mind.

Logically if the one of the puposes of a single pole switch is to isolate a product, then the only way it can provide that function is to break the live supply. Connecting that device to a reversed supply negates the isolation and reneder it ineffetive.

 

[David_L]

I realy do not know why this thread is getting so heated.
The simplest way is for caravaners to carry a polarity tester as standard with a reversing cable connector ,check the polarity when on site and fit the reverser or not, then everone is safe problem solved

 

[Lutz]

And Lutz,
I am very much aware that many continantal systems lack some of the protections we have traditionally used in the UK, That under some circumstances may make them less safe than the equivelent UK systems. If you received shocks form applainces when they were notionally turned off, then in the UK if an employee or memebr of the public received a shock, then clearly there is a danger, which the HSE would investigate.

RCD's have only been legally required here since 1984 for new installations in rooms where high levels of damp are likely to be encountered, such as bathrooms, cellars, etc., and since 2009 on all new circuits likely to be used by a layman. It is therefore more than likely that the circuits where I got a shock from were unprotected as nothing was tripped as a result.
Like I said, I don't know of any household appliances that are fitted with a double pole switch.
By the way, I have never got a shock from an appliance. These are normally well enough isolated that no surface that can be touched by hand can get into contact with any current-carrying leads unless the appliance is opened up or wet.

 

[ProfJohnL]

Hello David,
I do not get the impression the topic is getting heated - good honest dicussion yes, but I dont detect any downward spiral into mire of personal abuse etc.

If someone asks" why should I care about reversed polarity" then it needs some explination to explain some of reasons and dangers.

I agree with you that the matter is usually simply resolved.

Hello Lutz,
One houshold product that does uaually have a DP is the electric kettle, but there are still plenty of other applainces that don't. adn I agree that the majority of household applainces are designed to provide protection from shock usually by insulation and barrier, but under some fault or damaged conditons I have seen instances of where electrical circuits could be touched, but the wors tcase is usually tehhandy man trying to fix an applince and exposing electrical circuits.

 

[Gafferbill]

…….for once I agree with most of what the Prof says on this particular subject particularly in relation to lower rated fuses fitted to some appliances under the UK system.
The UKs wiring system and its rules are probably the best in the world.
In Australia for instance, it is common to have power sockets in bathrooms and often within 30cms of a sink!
The science of electricity is factual and the same the world over, however the language and practices of wiring and circuitry are not.

Correcting reverse polarity is no big deal, indeed a simple indicator device and correction switch can easily be contained in a small unit and wired into the caravans circuitry.
Such units exist and are available on the market for around £30.00 retail.
Why these cannot be specified on new UK caravans is a surprise to me.
Many new UK caravans come with an indicator only, leaving it up to the owner to decide what action to take.

My view is that a caravan is a leisure vehicle and as such why take any risks if they can be avoided
……. I would always correct reverse polarity.

I use a self made up lead that is identical to the common EHU lead except it is only 1 metre long
and has the brown and blue wires reversed in either the plug or socket end.
This correction lead is placed at the caravan end of the supply wire if needed.
The length is such that the extra join can be placed under the caravan off the ground for protection against the elements.
This method leaves the supply post end of the EHU free to accept a Continental 2 pin adapter if it is needed.