# Reverse polarity - am I simple ??



## 108777 (Dec 17, 2007)

Hi all' We are off to Spain the end of March on our first foreign foray. I have been reading up on the perils of reverse polarity/special leads etc and have come up with a theory that I would like someone far more knowledgeable than me (That means you ALL can have your four penneth !) to shoot down or confirm. 
My Hymer is the German model and consequently has the two pin continental sockets fitted. When using electrical appliances from the uk I use an adapter. Now, supposing I connect up to a site with reverse polarity. Before plugging in the appliance I check the polarity using a plug in mains tester and , lets say it shows reverse polarity. What is to stop me simply pulling out the uk adapter that has the two pins on the end and turning it round 180 degrees. Wouldn't that in effect reverse it back the right way. If I take this precaution on any socket I use, wouldn't this do away with the need for a 'blue' modified lead. 
O.K. I'm braced - fire away !! 

Mike


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## androidGB (May 26, 2005)

Have a look at this THREAD and you will see that someone has the same idea as you 

Andrew


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## zulurita (May 9, 2005)

Yes it will mostly work that way.

However some of the two pin plug have the wire coming out at an angle rather than out the back/central like. I have on occasions found the 2 pin angled plug will not always fit when trying to reverse it. 

Hence I bought another 2 pin plug where the wire is central and so easy to turn the other way if it is reversed polarity. Having said that I have also made up my own reversed polarity plug using the blue 3 pin set up as they are using these more and more on the continent.


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## Zebedee (Oct 3, 2007)

Don't bother.

Unless it's quite an old model your van will have double pole switches so there's no problem at all.


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## pippin (Nov 15, 2007)

Adaptors are never a really good idea.

If at all possible/practicable do away with them.

They introduce an unnecessary extra level of complication and possible danger.

A UK plug has a fuse in it (max 13A) - this protects the appliance and the cable from it to the plug.
A UK socket is generally connected up to a circuit fused at 30A.

Continental plugs do not generally have fuses as the circuit provides the protection.

You could thus use a 13A appliance via an adaptor into a circuit that is fused at a lower value, say 10A.

A fuse will not blow instantly if subjected to that small oveload - it might overheat and fail after a period of time.
Unfortunately that period of time could be enough for the adaptor, socket and wiring to overheat - and they are not in a protected ceramic tube like a fuse.

That is a recipe for fire.

I know that motorhomes are not wired with a ring-main but I still would not want to risk it.

Just compare the solid construction (electrical and mechanical) of a UK 13A plug and socket with the much lower capabilities of the average continental plugs and sockets and you might just see my point.

The use of power adaptors that plug in to mains sockets is even more hazardous.
They are bulky enough without being used with an adaptor. They are heavy enough to gradually degrade the mechanical tightness of the socket into which the pins are inserted.
Loose mechanically means a higher resistive connection.
A higher resistive connection implies heat generation.
Need I continue?

So, for me, if I had a motorhome with €U sockets and most of my appliances were fitted with UK plugs then I would be replacing the €U sockets with UK 13A types AND I would be checking the capabilities of the van wiring and fuseboard.

AND I would be checking if there are double-pole switching and tripping arrangements which address the initial question behind the post.

E&OE


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## 108777 (Dec 17, 2007)

Thanks to everybody for the replies. Taken all in all it would seem that yes, the idea is plausible, but replacing the sockets and inspection of the breaker board etc would be the more sensible (and safer !) way to go. I will have to have a closer look behind the panels tomorrow to see how big a job it would be.
Again, thanks all

Mike


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## wilse (Aug 10, 2007)

just my 10 pence worth...

I posed this question to an electrician at HYMER (blackpool/preston wherever they are), our Hymer Van 572 & 522 doesn't have this double pole malarkey (yours might??)

The electrician also told me to get a surge protector... as reversed electrics could damage some board in the truck... I didn't bother, I bought a reverse polarity tester £10 and made a reverse cable... £5.

PS I've never used either, but I've only been to France.

wilse


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## Waleem (Nov 1, 2006)

What you need is these:
http://tinyurl.com/2le7bx
A bargain ! And I'm not just saying that because it's me selling them!


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## Rapide561 (Oct 1, 2005)

*Reverse polarity*



wilse said:


> just my 10 pence worth...
> 
> I posed this question to an electrician at HYMER (blackpool/preston wherever they are), our Hymer Van 572 & 522 doesn't have this double pole malarkey (yours might??)
> 
> ...


Hi

Where can I get hold of a polarity tester for about a tenner?

Russell


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## Sargent (Feb 1, 2008)

Hi Russell, Maplin have one for 4.99 the code is WD53H it is basic but it should do the job.

Regards

Ian S


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## 108777 (Dec 17, 2007)

wilse said:


> just my 10 pence worth...
> 
> I posed this question to an electrician at HYMER (blackpool/preston wherever they are), our Hymer Van 572 & 522 doesn't have this double pole malarkey (yours might??)
> 
> ...


Sounds like the easier path to go, thanks wilse. However this is still making my poor brain ache ! Let's say, armed with my trusty mains tester and adapter lead, where do I start ? If I connect up to the van as per normal then stick my tester in a van socket fitted with 3 pin adapter, how do I know if the adapter is the right way round and giving a true reading ? I assume there is no way of testing at the hook up point. I am sure that once I have purchased/manufactured these items all will become clear, but at the moment every scenario I run through my mind comes up with another big question mark ??

regards
Mike

PS Russell, Towsure at www.towsure.com do the round plug in tester at £8.95, plus £4.95 postage. Stock code M56 should take you to the item (unless you live near one of their 3 stores) Also they take off 5% for CC members with card. (Forget that last bit, I just noticed your location)


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## 108777 (Dec 17, 2007)

Waleem said:


> What you need is these:
> http://tinyurl.com/2le7bx
> A bargain ! And I'm not just saying that because it's me selling them!


Thanks for the link John, they look promising,but being a born pessimist I am sure that the van will be amongst the .01% that they don't fit and time is getting a bit tight for restarted projects !
Mike


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## 108777 (Dec 17, 2007)

Zebedee said:


> Don't bother.
> 
> Unless it's quite an old model your van will have double pole switches so there's no problem at all.


Just been out to the van armed with the camera and this is what's under the seat !! To my ignorant eye it would seem to be a double pole switch as you mention Zebedee - anyone confirm this, please ? If so does 'no problem' mean I don't worry what polarity the hook up is ? Sorry the flash bounced, but the bit on the left looks like a couple of music notes joined by a bar (is that a hint ?) with a -2 above it - Just had a look magnified and all the markings are clear 
In hope

Mike


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## TR5 (Jun 6, 2007)

That's a double pole tripswitch!


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## Zebedee (Oct 3, 2007)

Only you can decide whether to bother or not Mike, but having taken the advice of my neighbour who is both a caravanner and a consultant electrician, I don't worry any more.

The only potential problem you are likely to encounter is if you use auxiliary equipment such as a fan heater - but only then if you are a complete berk!! (No offence   ). When switched off only by its own integral switch it will still be "live" inside the casing - but no more so than when it is running!

Just don't take it apart and firtle about inside unless you have switched off, and preferably also unplugged at the socket. (Only complete Berks do that! :roll: :roll: )

For complete peace of mind without tearing the van apart as it's not long until your holiday, take Wilse's suggestion and get a polarity tester (£7 or £8 ) and make up a reverse cable. That way it takes only a moment to make absolutely sure you are on the correct polarity.

_If you don't know how to make a reverse cable, post the question. Nobody will mind and you will get a quick response._

Hope this helps


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## wilse (Aug 10, 2007)

well I'm confused, I've the same switches in my Hymer Van 572, and was clearly told by Hymer that a reverse polarity tester was needed, as there was no facility for the 'truck' to work it out itself.

So I don't know who to believe,??

ChilliK what I would say... if you can stretch to £15, you can get all the bits you will need...

here's the tester this has lights on to show you whether the polarity is reversed or not, just plug into a socket in your truck and when the hook-up goes on it will tell you what's what.

IF you have reversed polarity, then you need a hook-up convertor, you can make your own...

You need a male hook-up connector

You need a female hook-up socket

And finally 1 foot (more or less, up to you) of 16A cable (3 core, L,N & Earth)

Wire up (like a plug) one connector.
The other end, swap the live and neutral over.

I'm no expert, but this is what I was advised to do, and I made the cable in 10 mins, on my first trip. Like Sargent says, towsure also sell the tester. And as Russ said (now I've scrolled down) maplins sell it cheaper.

Hope this helps. It's very simple

Wilse


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## 108777 (Dec 17, 2007)

Thanks TR5 for the confirmation and thanks Dave for the advice which I will follow. The more I go into what I thought was a common sense topic ie basic electricity, the more I find out how wrong I was !! Another silly thing has popped into my head while thinking about all this, namely : If my telly -working on mains voltage via the supplied transformer, to the usual 12v jack at the telly end - is supplied with a reversed polarity mains supply, does the transformer automatically swap it back the right way round at the jack, or god forbid does it shove 'back to front' DC electricity in to the TV with profound results :evil: 
Hopefully there is someone else out there that is as daft as I am that will be learning along with me !

Mike

Nice to know you are as confused as me wilse, your post came while I was typing this. I've got most of the bits, just need the tester and conversion lead


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## Zebedee (Oct 3, 2007)

ChilliK said:


> . . . does the transformer automatically swap it back the right way round at the jack, or god forbid does it shove 'back to front' DC electricity in to the TV with profound results :evil:


Fret not. It didn't blow mine up on the last two or three occasions I was on a reverse polarity hook up. I had the reverse lead with me as well, but couldn't be bothered to look for it - come to think of it I have never used it!  :roll:



ChilliK said:


> Hopefully there is someone else out there that is as daft as I am that will be learning along with me !
> Mike


Fret not for a second time Mike. We all started this game knowing nothing about anything. I wish this forum had been around when I started - it would have saved me a lot of time, effort and many, many mistakes. 

Just a tiny point about Wilse's reverse lead, and no criticism of him of course.   His version should be plugged into your long lead and effectively reverses the polarity, but still leaves you without a suitable plug for the continental hook up socket, so you will need another short conversion lead.

My reverse lead has a "British" socket (female) on one end and the continental plug reverse wired on the other end. It also has some red insulating tape wound round it so I can tell it apart from the identical, but "correctly" wired conversion lead. 8O

(_Although there are at least two different plugs in use on the continent, the common one (available at all accessory shops) will be OK in most places, and if it isn't you can buy the right one locally. It only takes a few minutes to swap the plug._)

Cheers - hope this makes sense.


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## pippin (Nov 15, 2007)

We need to sort out this "polarity" missconception.

Do NOT think of it as plus or minus polarity. That really only applies to DC.

There is NO connection between this topic and anything that happens to your 12V DC van supply,

There is NO connection between this topic and to what comes out of any mains to low-voltage DC adaptor or charger or anything else like it.
There is NO effect on whether one terminal output has + or - from your DC adapter

The use of the phrase "reversed polarity" is technically nonsensical when applied to AC.

The trouble is, what other description does one use?

Here we are talking about a single phase AC supply.

As long as 230V AC appears between two wires then we will get power.

In the UK we generally tie one wire (the neutral) roughly to earth which can be regarded as zero potential.

The other wire has a varying voltage on it. 
It varies 50 times a second between two voltages.
We call it the live or more accurately the line or phase wire

It does so with a (hopefully) sine-wave pattern.

The lowest voltage is zero volts and the highest voltage is something like 325V.

The average voltage due to the sine-wave is 230V.

In the UK because we always tie one wire to earth then we do not need to switch that wire as on its own it is never has a dangerous voltage on it.
We only switch the wire that has the (potentially - pun!) dangerous voltage on it - the live/line/phase.

Enter most other countries in €U and they do things a bit differently.

They too may try to tie one wire to earth potential (zero) but with varying success and diligence. 
Or they may not even bother.

Instantaneously one wire may go down below earth potential to say 162V and the other to 162V above earth potential. 
Or one wire may even go all the way to 325V below zero while the other stays at zero. 
Or any variation between all those limits!

As far as your appliance is concerned as long as it sees a total of 230V between the wires it will work.

Even if they do tie one wire to earth potential they might not bother to tell you which one!

Which is why they ALWAYS (should) have double pole switches/trips so that any potentially dangerous voltage is isolated from your appliance when it is switched off or the trip fails.

Come back to your motorhome that was designed for UK mains. 
The mains switches and trips will probably be single-pole. 
In the UK - no problem.

Cross the water and you may have the single pole switches/trips connected up to the safe wire. 
But you may not!

Switch something off and it will still have 325V inside it!

Get a fault and the trip will still trip due to over current but the gear will still have instantaneous 325V lurking all the way from the plug through the wire into the appliance to wreak its havoc.

That is why you need to check and if necessary reverse the L & N wires so that the single pole switches/trips are switching the dangerous side.

Don't even get me started on what happens to Earth Leakage Curent Breakers in this scenario!

So, shall we try and get away from the confusing term of "polarity reversal"?

We could try

PHASE REVERSAL

but even that is not quite right.

Even better is

*LINE REVERSAL*

PS some of this is simplified but in essence that is what we all need to know.


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## wilse (Aug 10, 2007)

hahaha

a little clearer, although no conclusion.... 

pippin, so have by having a cable with the live & neutral swapped, is this the correct thing to have? for LINE REVERSAL...


Nice post by the way.

wilse


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## hilldweller (Mar 8, 2008)

pippin said:


> Instantaneously one wire may go down below earth potential to say 162V and the other to 162V above earth potential.
> Or one wire may even go all the way to 325V below zero while the other stays at zero.
> Or any variation between all those limits!


I wonder what happens to the plug in polarity tester when the earth is not close to one of the lines ??????


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## 108777 (Dec 17, 2007)

Just back from Towsure clutching my two blue plug/sockets and plug in mains tester and thought I would check the forum for any updates - was there ever !! Thanks pippin for a very learned discourse on this LINE REVERSAL problem. I think it will take a few readings for it to sink in however ! I never fully followed the man at college when we went into alternating current and sinusoidal curves etc. , probably it was in the early afternoon after a lunch at the local pub !
I already have the two blue plug to uk and contintental plug leads, wilse, do I understand right from what you say that the hook up points on the Continent are ordinary two pin sockets and not the uk blue one ?
Think I'll just settle for candles and a camping barby !!
Mike


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## Zebedee (Oct 3, 2007)

Happy wiring Mike - Towsure are good aren't they?

Wilse is not on just now so I might have the answer. You do get the "UK blue" hookup points on the continent, and sometimes there are both sorts on the same bollard. It's always wise to have both however, as the continental ones are, unsurprisingly, more common.

Hope it all works out OK - you should have total peace of mind now, and that's worth a lot.

Cheers


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## pippin (Nov 15, 2007)

Yes wilse, that is the correct thing to do and to have and to hold!


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## 108777 (Dec 17, 2007)

Many thanks, dave, wilse, pippin and everyone else for the advice and best wishes. Just have to lock myself in the kahzie with the Spanish phrase book now and it will be all systems go !
Best regards to all

Mike


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