# The definitive explanation of "Reverse"



## pippin (Nov 15, 2007)

Have decided to post this as a new topic - perhaps it should go into somewhere permanent.

Now, let me lay to rest once and for all the confusion about AC mains. 

There are two wires, conventionally one is blue and one is brown. 

It is the voltage difference between them that provides the oomph. 

Note that I have not mentioned the green/yellow "earth" wire - yet. 

We are talking about Aternating Current but for a current to flow there must be an Alternating Voltage so let's concentrate on voltage. 

This side of the pond we have 50Hz AC (AV) mains. 

I can't draw a sinewave on here but I'm sure you all know what one looks like - a snake. 

Draw one on a piece of paper. (a sine-wave - not a snake!) 

Now draw three horizontal lines. 
One through the middle, one touching the top of the curve and the third one touching the bottom of the curve. 

Your sinewave should start on the middle line, go up to the top one, down through the middle line to the bottom one and come up to the middle one again. 

That is one Hz or cycle. There are 50 of them every second. 

Let's call the bottom line Neutral or the blue wire. 

The bottom line is fixed and doesn't move up or down. 

Draw a dot on the middle line at the left where the sinewave starts. 

Imagine the brown wire aka the Live connected to that dot. 

As time advances the brown wire follows the curve of the sinewave - rises up, down passing through the middle line and then up again until it reaches the middle line again. 

The wire has to be "flexible" to follow the movement. 

Now, just for clarity let's call the blue wire zero. 
The "flexible" brown wire is the live and by definition has an average voltage of 230V relative to the blue or neutral wire. 

You can see from your diagram that when the brown wire is touching the bottom line there are no volts between it and the blue. 

You can also see that when the brown wire is touching the top line there is a high voltage between it and the blue. 

You will have to take my word for it that for an average 
voltage of 230 (the middle line) the top line is 1.4141 times higher than that. 

(For the more mathematically minded it is called RMS) 

So to summarise: the Brown wire goes from +339V down to zero fifty times a second with respect to the blue wire to give our average of 230V. 

Now, let's factor in the green/yellow wire or earth. 

In the UK it is convention that the blue and green/yellow wires are joined together - usually by the electricity board where they enter your property. 
They are connected to earth at the substation. 

So, that is why we call the blue wire Neutral. 

Between you, it and earth there are no volts and hence no shock. 
Unless there is an earth fault somewhere. 

You don't want to touch the brown or Live wire at the same time as you are touching either the Blue or earth, especially if you are barefoot on wet earth! 

In UK we need switches only in the brown Live wire because that is the only one that has volts on it. 

So, what is different in €U-land that causes us to mither on about "reverse polarity" and "reversed leads"? 

Remember that I said that in UK we tie blue and earth together? 

Well that ain't necessarily so in €U. 

The blue wire might be connected "flexibly" to that moving point on the sinewave and the brown wire connected to earth. 
This is unlikely but can happen - in which case you can get a shock from it to earth. 

Or neither blue nor brown tied to the earth green/yellow. 

So, the blue wire could be floating anywhere between zero earth and halfway or even all the way to the top, remember that is 339V!! 

That is why in €U-land they use two pole switches, one for the blue and one for the brown. 

Your UK-sold MH (even if manufactured in €U) will almost certainly have single pole switches in the brown/Live wires only - because they are cheaper (by a few €cents!!). 

It raises complications with earth leakage trips (RCBs) too. 

We seem to have settled on the term "reverse polarity" which is a total nonsense as there is no such thing with AC (AV). 

For want of anything better I think we should adopt the term "reverse polarisation". 

So, do you need to worry about it? 

Ideally - yes. 

In practice - not really, perhaps maybe, probably yes - who knows! 

Even though I know all about it, I invariably forget to check on the odd occasions we use hook-up in foreign parts. 

I ain't had a shock yet! (touch wood - a good insulator when dry) 

We would be better off demanding that our electrics are to €U standards with double pole switches and double pole trips - the extra cost on a £50k MH would be not much more than twenty quid! 

My Hymer was built in Germany but to UK electrical standards - why?! 

So, I hope the above clarifies things a bit - if anyone needs more info please ask. 


E&OE - that's a disclaimer.


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## 747 (Oct 2, 2009)

So where does electricity come from ? :?


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## Techno100 (May 8, 2010)

747 said:


> So where does electricity come from ? :?


the lecky board who you pay every quarter :wink:


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## alphadee (May 10, 2009)

Forget all this technical stuff.

Electric cables are like water pipes but they have smoke flowing through them not water.

As long as you do not let the smoke escape from the cables then evrything will be OK.

Shocking stuff !


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## listerdiesel (Aug 3, 2012)

Some of what is written does not conform to what I have been taught and always understood to be true.

The centre (time) axis of a sine wave is zero volts, with a positive and negative peak, the lower part of the sine wave is NOT zero, so the Line or Brown wire goes from 0v to maximum positive through zero again to maximum negative and back to Zero in one complete cycle.










The true peak to peak voltage of 240V rms is double that quoted, 650V approximately, or 340V in the USA.

What we call the Neutral or Blue cable is the centre tap of a star-connected secondary winding on the street supply transformer, it is connected at the house input as part of the PME (Protective Multiple Earth system, otherwise there would be a floating voltage level of the Neutral line of a few volts which would affect many devices such as RCD's etc.

I feel that the correct figures and mechanicals should be quoted if they are going to be used as references.

As far as motorhome electrics go, the Neutral and Earth are never connected together in the electrical system, or should not be, that would defeat the whole point of having 3-pin plugs with separate earth pins. I believe also that it is is illegal to use a PME connection to a mobile caravan.

Peter

Edit: All of this stuff is readily accessed on the web, so don't take anyone's word for it, check it up yourselves.


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## tonyt (May 25, 2005)

If you're at all worried about it, why not replace your UK single pole 13a sockets with something like this - not exactly expensive!

In fact, probably cheaper than buying or making a changeover cable.

Example Double Pole


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## pippin (Nov 15, 2007)

Why not? Because they wouldn't fit in the modular fixing frames.


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## 747 (Oct 2, 2009)

All this talk of single Poles has me confused. :? 

Do they come over here to work ...... or to look for husbands/wives. 8O


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## pippin (Nov 15, 2007)

747 - If you are not careful I will ask Nuke to disconnect you permanently :lol:


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## aldra (Jul 2, 2009)

8O 8O 8O  
Aldra


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## 747 (Oct 2, 2009)

pippin said:


> 747 - If you are not careful I will ask Nuke to disconnect you permanently :lol:


I'm POSITIVE that you are too SHORT to do it yourself, if you try it, you will get a SHOCK. :lol:


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## bigbazza (Mar 6, 2008)

Stop being negative, you should try and be a bright spark.


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## Spacerunner (Mar 18, 2006)

pippin said:


> Now, let me lay to rest once and for all the confusion about AC mains.
> 
> .


You're having a laugh! :?


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## Phil42 (Apr 4, 2006)

aldra said:


> 8O 8O 8O
> Aldra


I agree.

Phil


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## aldra (Jul 2, 2009)

Thank Goodness Phil

I thought I was losing it

Not the thread 

I lost that a while ago

Aldra


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