# RCD and reversed polarity



## Webby1 (Mar 11, 2012)

Perhaps someone more technically minded can advise on a little query.

At first I was really concerned reading about reversed polarity on some European sites (well it sounds so dramatic) but after reading some posts on here I concluded that if I tested the RCD each time then I would be protected, should I ever mess around with the electrics when on EHU (why would anyone ever do that anyway?)

However I am sure that I read recently that some RCD are not double pole but only switch off the live connection............which if it is reversed means the neutral is switched off but the other one is still live.

Anyone shed any light on this or do all modern RCD switch off both poles when tripped.


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## rayc (Jun 3, 2008)

Webby1 said:


> Anyone shed any light on this or do all modern RCD switch off both poles when tripped.


A RCD works by comparing the flow through it on the Live and Neutral conductors and trips both legs if an imbalance is detected.
http://greenbrook.co.uk/pdf/pbcatpg21-22.pdf


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## Evs54 (Mar 11, 2013)

However I am sure that I read recently that some RCD are not double pole but only switch off the live connection............which if it is reversed means the neutral is switched off but the other one is still live.

Anyone shed any light on this or do all modern RCD switch off both poles when tripped.[/quote]

Never come across a single pole RCD used as a main switch in a motorhome or dwelling .


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## rosalan (Aug 24, 2009)

My confidence in campsite electrics is based on the simple three light testing device. It 'knows' live, neutral and earth and where they should be. If it shows three red lights the system is correct for your vehicle. 
If it shows reversed polarity:- Unless you are doing anything with the electrics you should be safe and most things should work. This however is not advisable.
IF you are in Spain, or on occasions in France, you can sometimes turn the plug upside down in the campsite socket and the polarity will then be 'Ok!'
The other alternative is to wire up a short extension piece to your cable with the negative and positive wires reversed in one of the two ends.
I recently bought a new extension cable that came with + & - wrongly fitted.

Alan


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## Penquin (Oct 15, 2007)

There are very many threads about the non-problem of reversed polarity on here - the search feature - for me that brings up 240 hits....

An RCD is a protective device that should be tested frequently - it cuts the current and effectively breaks the circuit if there is an imbalance as said above. 

The reversed polarity only becomes a problem if you try to dismantle electrical items with them still plugged in - not advised under any circumstances.

If the RCD trips, there has to be a reason and that is why I carry a plug in tester so that the combination of lights gives me a clue what the problem may be due to, but even then I am not going to start disconnecting things while they are still plugged in and attached to the EHU, even if the power appears to be off.

Reversed polarity will not affect any electrical items AFAIK, certainly in France the alignment of the positive and negative is not considered critical for safety - our house appears "wrong" for the EHU for the MH, but the RCD works superbly as we demonstrate whenever there is a minor fault such as a bulb going......

Dave


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## Zebedee (Oct 3, 2007)

And just to be a pedant - how can polarity be an issue (_or even a meaningful description_) when the direction of the current flow changes 50 times per second??

OK - got me coat! :roll:

Dave


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## Agilityman (Aug 17, 2009)

Reversed polarity is a real problem. If any device you have has an earth fault and an internal fault allowing the neutral to touch say a metallic housing, then when switched off the casing will be live!

In Europe, if a device is switched the switch disconnects the live a neutral whereas is Britain only the live is switched, hence Europeans are not concerned about polarity. Also most electrical items for Europe are double insulated.

With an earth fault, I.e. Lack of earth connection, an RCD will not see the fault.

Regardless of what others may say take Rosalan's advice, I do the same.


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## Yaxley (Jul 25, 2008)

I carry a short connection with the polarity reversed plus the tester.
Ian


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## listerdiesel (Aug 3, 2012)

Look at it logically.

What you have is an AC supply with one leg hopefully tied to ground at the Neutral point on the site supply. That is where the 'Polarity' thing comes from.

So your 'Line' connection is 240V above Earth and Neutral.

As far as almost everything in your motorhome is concerned, it doesn't matter. Almost all small gadgets are 2-wire double insulated and don't have an earth connection, so you can happily ignore 95% of things that are plugged in.

The remaining 5% WITH an earth connection couldn't care either, they will work with the supply connections reversed.

The only significance is during a fault condition, and then you could have the 'Line' connection shorting to the earthed body, in which case it will blow the fuse, trip the MCB or trip the RCD or a combination of these things.

If the 'Neutral' connection touches the earthed casing there will normally not be enough voltage to trip an MCB or blow a fuse, but the RCD should be tripped.

If there is an earth fault in the actual device, fix it. It isn't the supply's fault if you are using something that is electrically faulty, and would be as much of a hazard on regularly 'polarised' supplies as well.

So, none of these conditions are significantly affected by which way the supply is 'polarised', there is equal opportunity for the user to be protected.

The last two significant factors are:

a) Wrongly connected supply with the earth not present or on the wrong pin.

b) Motorhome electrics wrongly wired, earth in the wrong place as above.

In these conditions it WILL be a hazard, but that applies whether the input is reversed or not.

If a motorhome is correctly wired and protected, there is no hazard from a 'reversed' AC supply connection, only if the actual wiring is faulty can a hazard exist, and that goes for 'normal' supplies as well.

In our experience of supplies in Europe, most faults are on the motorhome side, either internally or in the EHU cable. Sad to say that, but it's true. 

Peter


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## tonyt (May 25, 2005)

This thread took a long time coming - It's January 14 already :lol: 

Where's the gassing one? :lol: :lol:


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## Zebedee (Oct 3, 2007)

Agilityman said:


> Reversed polarity is a real problem. If any device you have has an earth fault and an internal fault allowing the neutral to touch say a metallic housing, then when switched off the casing will be live!


Yes, but the casing will also be live when the appliance is switched on, so this is largely irrelevant to a discussion about the incorrectly named "_reversed polarity_".

And what is the likelihood of having and earth fault, and internal fault and a metallic housing all at the same time?

Of course it's better to be 100% safe and take all the precautions, but how big is the risk - really? I would be very interested to find out how many (if any) accidents have ever been genuinely caused by "_reversed polarity_".

Driving the van a mile up the road is far more dangerous. 8O

Dave

P.S. As with all such discussions, it's entirely up to the individual to make the choice, and in this case it only costs a tenner or so to buy a tester and a cross-over connector. I do still wonder however if this is not another case of exaggerating a danger so something can be sold to alleviate it.

Anyone want to buy a narcotic gas alarm?? :roll:


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## listerdiesel (Aug 3, 2012)

I think that the danger is grossly overstated, but testers give some sort of peace of mind to motorhome owners and if nothing else gets tested, at least the electrics are.

What we use is a flash tester, 2000V AC or DC and then you know if you have insulation breaking down or not. Test the AC side once a year.

Electrics are the most misunderstood part of motorhomes and caravans.

Peter


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## tonyt (May 25, 2005)

Reversed Polarity - dangerous?

Well that explains why so many motorhomers and caravanners have been killed and injured by it.

The biggest risk to life and limb when plugging into to an EHU post is tripping over the cable and breaking your neck.


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## Gary1944 (Feb 21, 2009)

I may be wrong but I think my van's Nordelettronica system sees any fault, including an earth fault, as a reversed polarity. I don't rely on that but use a plug in tester to check. I would be much more worried if the earth was faulty!

One thing I have noticed is that the system switches off the 12v system after a few hours, as we came back to the van to find lights, fridge, heating etc off. No danger but it could be inconvenient. Much easier to carry a spare "reversed" european adapter which can easily swapped over.

Gary.


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## Suenliam (Mar 22, 2006)

I see the original poster has an Adria. According to my motorhome electrician, european MHs have a gizmo where the electricity comes into the MH which trips if there is a fault in any of the electrical equipment. He explained it to me and I understood what he said, but I am not technical enough (at all  ) to describe it to anyone else.

Accordingly we do not worry about reversed polarity. Actually we didn't worry about it before either as we didn't know about it until I started to read about it on the forum :roll: 

Sue


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## Terryg (Jun 18, 2009)

Hi,

For me its simple remove the risk, I have a plug tester and short clearly marked reversed polarity lead. Part of connecting EHU to the van is testing the supply every time, and testing all leads once a year.

I also use a surge protector to protect my ELB99, a costly bit of kit to replace or repair.

Small risk or no risk its your call.

Terryg


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## rosalan (Aug 24, 2009)

Do not underrate the possibility of problems.
I was parked next to an English VW camper in France who had to disconnect his hook-up, for as he stepped out of his vehicle without shoes, he got a shock as he stepped onto the grass and it was not static!
I forget if it was the hook-up or his vans fault but it scarred the **** out of him.

Alan


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## tony50 (Oct 16, 2007)

Not knowing much about electrics, but had heard about Reversed polarity , so we bought a "reverse polarity checker " it's a small unit that you wire in between the Motor home mains connection and the main RCD box , this unit has a green and red light , I switch off the motorhome main switch , hook up the mains lead , if the unit shows red ( which is "Reversed Polarity ") I flick the switch on the unit and it changes the Polarity ,at this point as long as is nothing else wrong, the Green light shows and its safe to switch on Main switch . 

Tony A.


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## Webby1 (Mar 11, 2012)

*Poles apart*

I was not going to take the bait but then I thought about any other posters/newbies who do not ask their questions for fear of snide comments or being ridiculed.

Although it is indeed January 14th this was not one of those repeat posts about reversed polarity or gas attacks that get the more informed members hot under the collar. And I do know how to use the search facility.

You will see my initial post stated that I was not worried about reverse polarity (although this thread shows there are still people who have concerns) but rather was asking a question about the operation of the RCD.

But thanks for the informative discussion........my view about these forums is that if you find people's questions tedious or repetitive ...............don't read them.................don't respond .....................don't make unhelpful comments.


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