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A couple of Reversed Polarity points
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userBrian Kirby
Posted: 21 November 2015 7:07 PM
Subject: RE: A couple of Reversed Polarity points
 


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Location: East Sussex. Motorhome: Knaus Boxstar 600 Street


Dave225 - 2015-11-21 5:25 PM

I am not a qualified electrcian but would make the following comments.

I agree that the majority of outfits these days will have EU certified systems which mean that the mains circuit is protected on both live and return so polarity is not such an issue. I have noted that some mains units are rated at 20 amp for the mains circuits which is high so do not really use this as a primary safety device. However, I would take issue withe comments regarding earthing. Even Schoko plugs all have earth connections and if there is none then if an item is faulty it is possible that by touching it you will become the earth path with disastrous effects. I know we have 13 amp fuses in most items here in the UK but do note it takes a huge surge to blow it, which if you are in the path, will revert to you. If your polsrity teste shows no earth to the mains bollard then please do not use it. If it just shows reverse polarity but still has earth, then there should be no problem at all.

If you have any concerns at all then use a safety trip socket between the socket in the van and your electrics. Always remember electricity is an invisible killer. It has no sound, smell or visual identity. 230 volts at 13 amps will fry you.


Apologies Dave, but as another non-electrician , I think you may be confusing two things. The fuse to which you refer (be it an actual fuse as in a plug, or an MCB as in all consumer units), is not your protection against electrocution. It is there to protect the wiring from overload, not the person from electrocution. Fuses/MCBs are to eliminate the risk of overloaded circuits overheating, possibly to the point at which they catch fire.

Your protection against electrocution lies at the mains switch which, since the 1970's, will incorporate some form of earth trip.

These are Residual Current Devices (RCDs), which compare the current flowing in to your system (on the line, or live wire) with that flowing out (on the neutral wire). The logic is that if there is a difference between the two currents, the difference must be flowing to earth (possibly via an external conductor, such as that person), and the supply should be interrupted, so providing protection against electrocution.

They respond in milliseconds and, with their sensitivity usually set at about 30mA, they should interrupt the supply before you are aware of much more than a tingle. They are mechanical devices, but are easily tested via the test button on the switch, which simulates a fault (how many of us, I wonder, do that regularly?), though I understand anyone with a pacemaker may still be at risk under certain circumstances. But, they are infinitely safer than any of the electrical systems most of us will have grown up with, with individually wired fuses and only an "on-off" switch alongside the fuseboard.

I agree, as I said above, that it is sense to check for an earth - but an earth alone does not protect against electrocution. It will provide a partial belt for the wiring, but that far more important braces against electrocution are provided by the RCD.
userDerek Uzzell
Posted: 23 November 2015 3:51 PM
Subject: RE: A couple of Reversed Polarity points
 


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Location: MODERATOR - 2015 Rapido 640F LHD 2.3ltr 150bhp


Returning to the Eberspacher Airtronic+Airlectric system’s reaction to a reverse-polarity power supply, I’ve now emailed a UK firm advertising the system about this.

I said

"Your website advertises the Eberspacher Airlectric 230V unit that can be added to an Airtronic D2/D4 heater.

I have been given to understand that the Airlectric unit fitted with the automatic diesel/230V switching option is polarity sensitive and requires a UK-standard 230V power-supply to function. Users of the Airtronic+Airlectric system have said that If the power-supply has 'reverse-polarity' (ie. the supply's live and neutral cables have been swapped over as is commonly found to be the case at campsites outside the UK) the system will not switch automatically from diesel to electric heating. Experiments have shown that, if a reverse-polarity 230V supply is encountered and the system will not switch from diesel to electric heating, using an adapter that modifies the supply's polarity to the UK-norm causes the system to switch automatically between diesel and 230V.

Are you aware of this reverse-polarity limitation, please?”

The very prompt reply was

“...I have spoken to Eberspacher technical and they have said that if you were to plug into a supply with reverse polarity then nothing would happen at all and it wouldn't switch over. So they said to carry another lead that is the opposite just in case.”
userCharles
Posted: 23 November 2015 11:34 PM
Subject: RE: A couple of Reversed Polarity points
 
Pillar of the forums

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Location: Derbyshire Elddis accordo 105


You could install a 230v relay (coil) between neutral and earth to automatically correct the polarity. But the van would fail an earth leakage test. Better (but still not perfect) would be a solid state high impedance circuit... I can look into it if if anybody's interested
userDerek Uzzell
Posted: 24 November 2015 8:25 AM
Subject: RE: A couple of Reversed Polarity points
 


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Location: MODERATOR - 2015 Rapido 640F LHD 2.3ltr 150bhp


A commercial product to ‘correct’ a reverse-polarity mains power-supply (and check the supply’s general functionality) has been marketed in the UK for a good many years, and a GOOGLE-search on “mains polarity changeover switch” will show that versions are available (for £40-£50) from several suppliers. Examples are here

http://www.homesteadcaravans.co.uk/accessory-shop/caravan-motorhome/electrical/230v-electrics/nova-mains-polarity-changeover-switch.htm

http://www.marcleleisure.co.uk/store/mains-polarity-changeover-switch-with-audible-alarm-p-3419.html?osCsid=6dc43ec764c57a462c662a38723c36f5

http://www.marcleleisure.co.uk/store/pdf/polarityswitchinstructions-02.pdf?osCsid=6dc43ec764c57a462c662a38723c36f5

with the last link providing fitting guidance.

The changeover switch (apparently the asking-price was cheaper then) is mentioned by Dave Newell in this 2009 forum discussion

http://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Reverse-polarity-adaptors/14639/

I’ve no idea how many of these switches are sold nowadays, but an owner of a motorhome with an Airtronic + Airlectric heating system who travels a lot abroad might find the switch a useful, safer modification to his/her vehicle rather than needing to use the traditional cable reversing adapter.
userGeorge Collings
Posted: 18 December 2015 9:05 PM
Subject: RE: A couple of Reversed Polarity points
 
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Location: South Devon A/Sleepers Medallion on VW LT


Mains sparks are not really my subject although like Derek I have in the past installed ring main in a dormer conversion.( I had a full test and eventual professional rewire four years a go and the only part that was up to scratch was my work).

About 6 years ago I was in an electrical factors where three near retirement sparkies were talking about the latest Electrical Regulations. One said they are falling into line with continental practice and some of the changes lower UK standards. all three intended to work until retirement without requalifying on the principle that they had not killed anyone so far and could not afford the four figure sum for the required course and test.

Personally having an 18 year old van that had its mains wiring rattled about for 80,000 miles I always test for polarity and correct if necessary but above all never use a post with no earth.

HU is became quite rare since fitting a 150w solar panel.
useraandncaravan
Posted: 2 March 2016 12:12 AM
Subject: RE: A couple of Reversed Polarity points
 
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Location: Conwy, North Wales


The fact that an appliance like a Kettle has a reversed polarity plug, is not a danger in itself. Only should you carry out maintenance while it is still plugged in and switched on.

There is no real danger with mains 230v electrics being reverse polarity, unless you remove the cover to an appliance and stick a metal object into the wiring, which clearly most sensible people are not going to do. Therefore the risk is, and has always been, almost zero.


The primary issue is with Electronics. Some of the older British Caravan and Motorhome Charger electronics did not work on reverse polarity, and some popped.

As late as early 2000's British Motorhome builders were pressing the need to check for reverse polarity rather than build reverse mains polarity protection into the units. This preservation of the 'Electronics Warranty' by the industry led to some statements which were at best, exaggerated.


Most of the Continental built charger units (indeed almost all continental built electronics) from 30 + years back are generally ok.
Most of the stuff coming out of China is also ok, because they design and build for a World market, which includes the Spanish.

Better explanation here : http://www.aandncaravanservices.co.uk/reverse-polarity.php



Edited by aandncaravan 2016-03-02 12:15 AM
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