Reverse reverse polarity? (1 Viewer)

[ericonabike]

I know this has been done to death, but bear with...

The consumer unit [is that the right phrase] in our Starburst has a warning light to indicate reverse polarity. I bought an in-line reverser [right phrase again?] after a previous trip which revealed our Eberspacher heater didn't like RP. This did the trick on our latest Gallic excursion on the two occasions when the light came on. But then we reached a Belgian campsite. Hooked up, RP light came on - fitted in-line reverser - light came on again! Tried it twice to make sure I wasn't mistaken, but light resolutely stayed on whether or not the reverser was used or not. What on earth does that suggest? In the end I omitted the reverser and left it at that, but am fascinated by the physics behind it! Any suggestions?

 

[Techno]

I'm not familiar with how the reverse detector works but I imagine it reads live to earth to establish which conductor is line. If the earth was absent it would not be able to do this, did you use the rcd push to test button in your van?

 

[pappajohn]

No idea but if you find the cause let us know :thumb:

as for your heater....it will make no difference whether reversed or not.

reversed polarity is simple.....the normally live (brown or red) wire becomes neutral and the normally neutral (blue or black) wire becomes live.......it still works just the same but the normally live wire is no longer switched on and off, the normally neutral wire is instead....which is the only real danger.

switch off a 230v light and remove the bulb and accidentally stick a finger in the holder...you DONT get a belt as the switch is before the light and turned off.
reverse the polarity and you DO get a belt as the switch is after the bulb holder so the holder is still live.

but either way, the voltage still flows the same way...230+v - 0v - 230-v -0v - 230+v - 0v - 230-v, 50 times a second.

230v/12v power supply/transformer/charger polarities will still be correct, lights still light, motors still turn the correct way, heater elements still heat up.

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[pappajohn]

I'm not familiar with how the reverse detector works but I imagine it reads live to earth to establish which conductor is line. If the earth was absent it would not be able to do this, did you use the rcd push to test button in your van?

I never considered the earth Andy, especially on a foreign campsite, and very likely the reason for the light.
far better to use a plug-in tester than rely on a light...as you know, it will show both reversed and no earth faults
also, that's why you may get a reversed polarity light show when using a generator...no proper earth on a generator.

 

[TheBig1]

as you say, this is a lack of earth fault

the way that electricity is distributed generally means that the neutral and earth are at the same potential at the substation. the live is then held at 220v rms (varies in othe countries). so the reverse polarity tester should be able to see which conductor is live.

where the earth is faulty or missing, this allows the potential on the neutral to rise giving a false positive, as both would appear live with respect to earth in the van. the same as with generators, without a fixed earth held at ground or 0v then the neutral may vary whilst still remaining 220v different to line (live).


I remember my old college tutor explaining it years ago using a clock for refference. if earth is at 0v, this would place one hand of the clock to 6. the same with the neutral, as referrenced to earth would be 0v so again 6 on the clock. the live would have maximum potential difference at 220v so would be at 12. now if neutral was to drift from earth, its point on the clock would rise or fall, but the live would remain at the maximum opposite the position. in other words if neutral was at 5, live would move to 11 etc. you would still measure 220v between live and neutral, but not with reference to earth

hope I remembered and explained that ok?

 

[2657]

Another thing to remember when using a plug in tester is that most don't show more than one fault so if it is showing reverse polarity it will not show no earth. Not a problem if you correct the reverse polarity and retest, the lack of earth will then show and appropriate measures can be taken. I was a little blasé about the reverse polarity on a site in Spain and noticed a tingling when I washed the van, needless to say there was no earth and as my van has 240/110 transformer the chassis became live. I am no expert and don't know the technical reason for this but the important lesson for me was that even though I am not too worried about reverse polarity I am very worried about a lack of earth so always correct polarity and recheck for an earth connection.I now carry an earthing rod just in case.

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[Geo]

as you say, this is a lack of earth fault

the way that electricity is distributed generally means that the neutral and earth are at the same potential at the substation. the live is then held at 220v rms (varies in othe countries). so the reverse polarity tester should be able to see which conductor is live.

where the earth is faulty or missing, this allows the potential on the neutral to rise giving a false positive, as both would appear live with respect to earth in the van. the same as with generators, without a fixed earth held at ground or 0v then the neutral may vary whilst still remaining 220v different to line (live).


I remember my old college tutor explaining it years ago using a clock for refference. if earth is at 0v, this would place one hand of the clock to 6. the same with the neutral, as referrenced to earth would be 0v so again 6 on the clock. the live would have maximum potential difference at 220v so would be at 12. now if neutral was to drift from earth, its point on the clock would rise or fall, but the live would remain at the maximum opposite the position. in other words if neutral was at 5, live would move to 11 etc. you would still measure 220v between live and neutral, but not with reference to earth

hope I remembered and explained that ok?

Perfectly Clear :thumb:his van has lost 5 mins and probably needs a new battery or winding up oh:
Worst case scenario, he's locked in a time warp and the error will self correct every 12 Hrs

 

[hilldweller]

revealed our Eberspacher heater didn't like RP.

Then I'd say there is a design or installation flaw in the heater.

Unless, but why would they do this, they incorporate a reverse connection detector internally.

The way you could wire the heater to malfunction like that is to wire it to LIVE and EARTH instead of Live-Neutral. That would be A_Bad_Thing.

 

[pappajohn]

Then I'd say there is a design or installation flaw in the heater.

Unless, but why would they do this, they incorporate a reverse connection detector internally.

The way you could wire the heater to malfunction like that is to wire it to LIVE and EARTH instead of Live-Neutral. That would be A_Bad_Thing.

On a scale of 1 to 10 Brian, how bad.

1 being 'Oh dear'

10 being 'Oh F&%k'

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[hilldweller]

On a scale of 1 to 10 Brian, how bad.

1 being 'Oh dear'
10 being 'Oh F&%k'

15

If the heater is feeding 240 to earth AND there is a break in the hook up earth you have a whole motorhome sat there at 240V.

That is going to be a bit of a shock to anyone knocking on your door. Especially in the weather we've been having this year.

 

[Red Sonja]

This also happened to us at a campsite in Belgium. Camping Ter Hoeve in De Panne.

In our Van it is hooked up to a buzzer, Kevin had to disable the buzzer. Im glad we are not alone. i thought it might be because the supply was only 4 volts.

Sonja

 

[pappajohn]

This also happened to us at a campsite in Belgium. Camping Ter Hoeve in De Panne.

In our Van it is hooked up to a buzzer, Kevin had to disable the buzzer. Im glad we are not alone. i thought it might be because the supply was only 4 volts.

Sonja

thats not a supply...thats a pair of torch batteries

think you mean 4amps :thumb:

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