Motorhome Mains Polarity Tester (1 Viewer)

[ymfb]

Do folks carry a Mains Polarity Tester and use it ?

I ask as there is an article in Ask Jack practical magazine delivered today.

 

[Richard n Ann]

I do, just out of interest but never done anything about it. It's reversed about 50% of the time.

 

[Zigisla]

I bought one when I started MH ing, as I was told it was one of the "things to have" and also a reverse polarity lead. Well 18 months on and numerous Funster threads on the subject, my tester is somewhere and the reverse polarity lead is still only half made as I found it recently in the back of the garage during my "must clear this mess up" days.

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[ymfb]

I do, just out of interest but never done anything about it. It's reversed about 50% of the time.

presumably this when you are abroad where they have two pin plugs ?

 

[Lenny HB]

Nope, our van has unswitched sockets can be a problem in UK vans if the sockets only switch the live but you have an RCD in the van and one on the site outlet and most items you use are double insulated.

 

[Lenny HB]

I bought one when I started MH ing, as I was told it was one of the "things to have" and also a reverse polarity lead. Well 18 months on and numerous Funster threads on the subject, my tester is somewhere and the reverse polarity lead is still only half made as I found it recently in the back of the garage during my "must clear this mess up" days.

Surprise, surprise, you are still alive, if the doom & gloom brigade had their way you would have been dead years ago.

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[LesW]

I carry one..!

 

[rosalan]

I do carry one and love to observe some of the Johnie foreigners miss-wired sockets but not too concerned.
I am possibly mistaken but think that not too much equipment on my van is worried by polarity, I did hear once that compressor fridges would not always smile at such niceties and there was an occasional chance of performing a version of St Vitus dance.

 

[vwalan]

yes i carry one . and the leads and ehu lead but in 17 yrs have never used it .
fitted an rcd etc when converting the trailer but never had ehu since . solar works for me .
cant see as i will ever use it all. but better keep it in the seat base might one day.

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[davidbaldam]

I carry a tester and ways use it, even in this country and if needed use my reverse polarity lead. It only takes a couple of seconds and in my mind it's better to be safe than sorry.

 

[Wagoneer]

I have one - wouldn't be without it. Good for checking you've got power at the EHU post (with suitable adaptor).

 

[autorouter]

I am possibly mistaken but think that not too much equipment on my van is worried by polarity

Correct, it's not a function problem at all, it's a safety problem.

Continental plugs do not have a fuse inside. Continental sockets are protected by 2-pole circuit breakers, that switch off both live and neutral.

UK plugs have a fuse. A fuse can only protect one wire. The wire with the fuse should always be connected to live, not neutral. If it's connected to neutral, and if there's a fault, the fuse will blow but the appliance will still be live.

UK electricians are usually very careful to wire the live and neutral correctly, because it is important. Continental electricians are more cavalier in this respect, because it is not important to them. Some continental plugs are even reversible (Germany, Spain, Italy, but not France and Switzerland for example).

If you plug your UK-wired motorhome into a continental system, it's a good thing to know this. With a polarity checker and polarity reversal adapter, it only takes a minute to check and correct it.

Sure, the pitch hook-up has an RCD as well. Carefully wired up by the expert professional that just got the polarity reversed...

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[Camping Gaza]

Nah... but I got a multimeter and that's handy.

 

[JeanLuc]

I bought one when we got the van 10 years ago and I made up a reverse polarity cable link. Only used the cable link once and I 'raided' it for the plug and socket ages ago.
Now I occasionally use the polarity tester but not really to check polarity, just to ensure there is a good earth at the hook-up point. I tend to do this on small site power supplies rather than those at Club Sites for example.

 

[tonyidle]

Sure, the pitch hook-up has an RCD as well. Carefully wired up by the expert professional that just got the polarity reversed...

You cannot wire up an RCD (or anything else) with L / N reversed when L / N are irrelevant or don't exist as in some or all of Continental Europe. If a system is designed for double pole switching it is inherently safer than one that isn't and allows for the possibility that neither phase wire is earthed ('L' / 'N' don't exist scenario). The UK took the cheaper (and arguably less safe) route with an earthed neutral and single-pole switching.

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[Two on Tour]

Our control panel has a polarity indicator and it lights up if the polarity is reversed plus the 240v gets no further than the control panel until the polarity is correct.

 

[2657]

I am certainly no electrician but this information is from experience and advice from an electrician, if you have an American or Japanese import with a mains voltage transformer it is important to have an earthed supply, I do not know the technical reasons for this.

I found out when on a site in Spain when getting a tingling in my fingers while washing the wheels,I had checked the polarity before hooking up but my tester showed only reversed polarity, which after reading various articles and posts decided to ignore, after many years of rigorously correcting reversed polarity.

After the tingling incident I corrected the polarity and tested again which showed no earth, this showed me that my tester, a basic 3 light plug in, will not show up a lack of earth until the polarity is correct.

 

[bigtwin]

Correct, it's not a function problem at all, it's a safety problem.

The wire with the fuse should always be connected to live, not neutral. If it's connected to neutral, and if there's a fault, the fuse will blow but the appliance will still be live.
...

For those that understand the issue, it's a non issue for two reasons:

1 - They're the only people likely to start dismantling a product when a fault occurs, and
2 - They're fully aware of the precautions that need to be taken under such circumstances.

For those inclined to test for 'negative polarity'/use an adaptor lead, it's clear that they don't have an understanding of the issue and, consequently, would never expose themselves to the potential hazard.

For the balance of the population, they are potential candidates for the Darwin awards!

Ian

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[Deleted member 29692]

Have one in the van somewhere but never use it. Also had a polarity correction lead but that was cannibalized ages ago.

Like others have said if you understand electricity then you understand how much of a non issue it is on an RCD protected system.

If a fault develops and you start poking around investigating it with the supply switched on then you deserve everything you get.

 

[Two on Tour]

If a fault develops and you start poking around investigating it with the supply switched on then you deserve everything you get.

At least it helps to freshen up the gene pool.

 

[two]

You cannot wire up an RCD (or anything else) with L / N reversed when L / N are irrelevant or don't exist as in some or all of Continental Europe. If a system is designed for double pole switching it is inherently safer than one that isn't and allows for the possibility that neither phase wire is earthed ('L' / 'N' don't exist scenario). The UK took the cheaper (and arguably less safe) route with an earthed neutral and single-pole switching.

I've not stopped to think about this before but how would a polarity tester show anything if the supply is 'floating'?

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[Lenny HB]

I've not stopped to think about this before but how would a polarity tester show anything if the supply is 'floating'?

It will confuse it.
You get this problem with generators (sorry didn't mean to swear) if they haven't got a true earth, you can make a true earth with a metal stake driven 1 metre into the ground and if it's dry water it.

That also reminds me of when we first started going to france over 30 years ago some of the sites in small villages had 2 phase supplies. When they upgraded from 110v the 220v was 2 phases of 110v, that used to throw a wobbly on polarity testers.

 

[mitzimad]

i use one but mainly becase i can see it from the hookup point and it tells me theres power there

 

[autorouter]

Like others have said if you understand electricity then you understand how much of a non issue it is on an RCD protected system.

RCDs give excellent protection against most common fault scenarios, but they are not magic.

Some, particularly the older unreliable electromechanical type, or the single-pole type, need to be wired by someone who knew what he was doing. On many pitch hookup boxes, you can only test the RCD by switching several other pitches off at the same time. So when is it ever tested?

I'd have some trust in a nice modern hookup, but what about that old wobbly box on a post with the missing door?

If a fault develops and you start poking around investigating it with the supply switched on then you deserve everything you get.

We're talking about faults here, not workbench fault-finding. Toaster in the washing-up, cable trapped in a metal folding table, that kind of thing. The fuse blows but it's all still live. A working RCD will save the day, of course. Bet your life it will.

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[The Wino]

As we have a French motorhome I have never bothered as I assume ours is made to cope!

 

[pappajohn]

Many years ago as an experiment, and to prove myself correct, I reverse wired my garage mains supply by simply swapping the incoming wires to the double pole main switch....live to neutral/nuetral to live
I intentionally introduced a short to the sockets to see if the 32amp garage RCD would still trip or if the normally wired 40amp RCD in the house fuse box feeding the whole garage would trip if the garage one didn't.
Note I was protected either way.
I proved my point, the garage 32a RCD still tripped under reverse polarity conditions and the higher value supply RCD in the house remained live.

 

[Deleted member 29692]

RCDs give excellent protection against most common fault scenarios, but they are not magic.

Some, particularly the older unreliable electromechanical type, or the single-pole type, need to be wired by someone who knew what he was doing. On many pitch hookup boxes, you can only test the RCD by switching several other pitches off at the same time. So when is it ever tested?

I'd have some trust in a nice modern hookup, but what about that old wobbly box on a post with the missing door?



We're talking about faults here, not workbench fault-finding. Toaster in the washing-up, cable trapped in a metal folding table, that kind of thing. The fuse blows but it's all still live. A working RCD will save the day, of course. Bet your life it will.

Former electrical engineer here so I don't need the beginner advice thanks

You worry about nothing if you like.

I won't.

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[Don Quixote]

I carry one, however never used it but you have it ask? when was the last time you read about a problem............ enough said.............

now lets move on to talking about grey waste again..........

 

[The Wino]

About as much use as a breathalyser when touring France then!!

 

[Lenny HB]

Many years ago as an experiment, and to prove myself correct, I reverse wired my garage mains supply by simply swapping the incoming wires to the double pole main switch....live to neutral/nuetral to live
I intentionally introduced a short to the sockets to see if the 32amp garage RCD would still trip or if the normally wired 40amp RCD in the house fuse box feeding the whole garage would trip if the garage one didn't.
Note I was protected either way.
I proved my point, the garage 32a RCD still tripped under reverse polarity conditions and the higher value supply RCD in the house remained live.

Either RCD could have tripped first as it will be the responce time of the RCD that determines which one trips first. If both had 30ms trip times they are built to a tolerance so unlikely to be identical one will always have a shorter time than the other and that will be the one that trips first.

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