Polarity problems with hookup

Pollik

Guest
I often read that in some, perhaps many, euro countries, there are warnings that some hookups have reversed polarity and that that can be an issue. A couple of reports even claim that polarity testers won't detect the problem.

I only have O-level physics, but this surely cannot be right.

Mains hookup runs on alternating current, which means that 50,000 times a second, the polarity of the electric supply reverses itself...polarity simply can't be the issue.

I can think of many other reasons to be wary - issues with earthing, stability of supply, different voltages, different frequencies, but polarity is wrong, sure.

Isn't it?

Can anyone comment usefully? I haver avoided hooking up in Scandinavia and Estonia, but sometimes it would be useful if I could.



Polly
 
Polarity is a slight misnomer.

At the supply feed, one side is connected to earth the neutral whilst the live is not, so you measure the voltage between the Live and neutral and get 230-240 ish volts. Measure between Live and earth and you get the same.

The issues come that many switched outlets only switch the Live cable so if the supply is reversed, there is a potential issue.

Most MH's have RCD breakers that basically look at the current passing through each power wire and make sure that they are equal. So if 1 amp passes through the live cable and returns through the neutral cable all is well. If a fault develops and the cable is shorted to earth, then there is an imbalance in the cables and it switches off the supply

So a reversal in Live and Neutral could potentially lead to issue, ie if a cable has frayed exposing a conductor, even if it is switched off at the plug, it could still be live.
 
PS Mains in Europe is 50 Hz or 50 cycles per second and in the US 60 Hz

At 50 thousand cycles per second, thats ultra high frequency sound or very low frequency radio waves!!
 
polarity in Italy

Hi traveling in Europe came down through Belgium Germany Austria and now in Italy,All the sites I have stayed on have
had the three pin like home but I still plug in my polarity tester the little one looks like 3 pin house plug, cost £9.00p
from camping shop back home have not blown up yet

cheers snowbirds


Pollik said:
I often read that in some, perhaps many, euro countries, there are warnings that some hookups have reversed polarity and that that can be an issue. A couple of reports even claim that polarity testers won't detect the problem.

I only have O-level physics, but this surely cannot be right.

Mains hookup runs on alternating current, which means that 50,000 times a second, the polarity of the electric supply reverses itself...polarity simply can't be the issue.

I can think of many other reasons to be wary - issues with earthing, stability of supply, different voltages, different frequencies, but polarity is wrong, sure.

Isn't it?

Can anyone comment usefully? I haver avoided hooking up in Scandinavia and Estonia, but sometimes it would be useful if I could.



Polly
Click to expand...
 
Bigpeetee said:
The issues come that many switched outlets only switch the Live cable so if the supply is reversed, there is a potential issue.
Click to expand...
I agree with this. All being well, there is no problem with what is termed 'reverse polarity'. It is just that switched sockets in the UK generally only switch what is thought to be the live cable. If the polarity is reversed, then the socket will switch the neutral instead. This actually makes no difference to the apparent behaviour of the socket, providing you dont go rooting around in the wiring assuming that the live has been switched off. Your mains appliances will work just the same regardless.

I think that generally switched sockets on the continent will switch both poles, so people dont care so much about the polarity.
 
During the afternoon, I realised I had overstated the frequency more than somewhat....thanks for pointing it out though.

I still can't figure out the polarity issue though. I have never tried it, but I would have expected live and neutral to be interchangeable - at any one time, one will be positive and the other negative, but it changes 50 times per second. And earthing takes the current to ground in the event of a short circuit.

What I am reading here suggests strongly that my understanding is wrong. Think I need to talk to my friend Google.

Thanks for the replies.



Polly
 
In a floating system, ie neither side of the generator is connected to earth, then you are correct, it wouldn't matter, however as one side of the generator is connected to earth, voltage measurements are made with respect to earth. The neutral cable is connected to earth at the generator (slightly simplifying the process), so that results in the live cable being 240vac with respect to earth.

Without any RCD protection, you can earth the neutral cable any where and not notice. The earth is separate to provide protection. If you had a floating system, then an earth connection would do nothing.

It is true that an appliance will work with the two supply cables reversed. Many items such as laptop chargers, are double insulated so don't use the earth.

Take a table lamp, a simple lamp doesn't care on the supply connection. If you knocked it over and broke the glass, if you switched it off at the plug and the supply was reversed, then the neutral cable in the lamp would still be connected to the live of the supply circuit. If you touched the remaining exposed element, you could still get a shock.

It only matters when things go wrong.
 
Thanks Pete - at least I am not going mad.

I need to learn some more......


Polly
 
I have recently had a couple of weeks in Spain & France and took my polarity tester and a spare plug & socket flying lead to correct any incorrect live & neutral issues found but found on numerous sites that the live & earth was reversed & so had to keep swapping the wiring around. I will be making up a flying lead to correct this live / earth crossed wiring issues for future use.

Look on ebay for 3 pin polarity testers, just a few £'s - well worth it.
 
Bigpeetee said:
Polarity is a slight misnomer.

At the supply feed, one side is connected to earth the neutral whilst the live is not, so you measure the voltage between the Live and neutral and get 230-240 ish volts. Measure between Live and earth and you get the same.

The issues come that many switched outlets only switch the Live cable so if the supply is reversed, there is a potential issue.

Most MH's have RCD breakers that basically look at the current passing through each power wire and make sure that they are equal. So if 1 amp passes through the live cable and returns through the neutral cable all is well. If a fault develops and the cable is shorted to earth, then there is an imbalance in the cables and it switches off the supply

So a reversal in Live and Neutral could potentially lead to issue, ie if a cable has frayed exposing a conductor, even if it is switched off at the plug, it could still be live.
Click to expand...

Hi Pete, Although I have never (knowingly) had a problem with polarity I am tempted to get a tester off fleabay just to be on the safe side. Would I be right in thinking that I can use a UK spec plug into one of the MH sockets or should I test it diest at the power supply point?

I just wondered if modern vans maybe have the technology to deal with the problem of reversed polarity automatically, or not.

Graham

PS By the way, that wifi signal extender you recommended - excellent! Thanks.
 
I have no idea how much they are, but we use martindales to test for reverse polarity.

They also tell you other useful bits of info too.

Always test in the van, and make up a flylead to reverse wires between the end of your cable and the entry to the campsite box;

Flickering lights btw are a telltale sign of reverse polarity.

Channa
 
An alternative is to wire a "Double Pole Changeover" switch rated at 15A inline with the feed to the consumer unit.

If you wire a socket next to the consumer unit for the tester or leave it on all the time in the habitation area, you can see if it changes.

I've had it where people have very kindly swapped my connection, to one that is correct.

A switch inside is quick, less likely to go wrong, you don't get wet and you can't loose it!

If you leave the tester in the power outlet all the time, it casts a gentle glow around the MH, enough to see your way to the loo in the night, or for kids who don't like the total darkness.
 
fairytooth said:
Thanks for the info, I've ordered one now.
Click to expand...

No idea which one you have bought we use the EZ150 which is around 55 pounds.

A useful tool around the house too if you have a problem socket;

I have mobile homes to look after and it certainly helps speed up the fault diagnosis. Whack a travel adaptor on it and you are away with french sockets. Be mindful the euro sockets (earth pin in the centre) Your travel adaptor in effect plugs in upside down which means it will flash red showing rp. the reality of course is everything is fine. I made up a fmy lead to test these so the results are always correct;

On our campsites hook up can be fine and then Pierre comes along plays with the campsite box and reverses the polarity; So always worth checking a source which was previously correct.

On that note if you get rp rather than start fitting fly leads try another socket on the campsite box and often that will be fine.

Channa
 
Reverse polarity posts go on for ages. Provided you are not tampering with the electrics and your electrical circuits are "healthy" then reversed polarity presents no problem. Only when there are faults in the system or you are working on live circuits can danger occur.
 
In Spain last winter on the same hookup without anything being touched the polarity kept switching from time to time. It must have been changed somewhere back along the supply line. Occasionally earth would also disappear only to reappear again later without intervention. Funny electrics in Spain. My German vans wiring coped well though.

It you disconect before doing anything with the wires it is ok. I was brought up in a 2 wire, no earth house, two pin plugs went in both ways in the UK then and we came to no harm.
 
shortcircuit said:
Reverse polarity posts go on for ages. Provided you are not tampering with the electrics and your electrical circuits are "healthy" then reversed polarity presents no problem. Only when there are faults in the system or you are working on live circuits can danger occur.
Click to expand...
I agree

Channa
 
Great, thanks for all the advice! I have just ordered a basic plug with a red light. I figure that will do for now. Good point about using upside down in a euro adaptor - so that means any device attached the same way would have R/P too - hmm, not ideal but as you say nothing to get worried about normally.

Many thanks.
 
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