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Reversed polarity on EHU?

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If the polarity is reversed, the fuse in a UK plug will be in the wrong phase.  The RCD should operate in the event of a short to earth but you have lost one layer of protection against fire.  Presumably RCDs do fail occasionally.  How do you know whether your RCD operates quickly enough?

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1 hour ago, Lost in France said:

 

I really wish people wouldn't use the term 'reverse polarity' with regard to continental mains supply, as has been said most mainland European sockets aren't polarised and they were not designed to be.

 

But some EHU's are reversed polarity to UK caravans where the systems have a design specification to the position of the positive and negative poles, so to them 'reverse polarity' might be encountered.

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Is anyone aware of UK equipment that does not work if the polarity is 'wrong'?  I read of washing machines that ere fussy.

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11 minutes ago, kelper said:

If the polarity is reversed, the fuse in a UK plug will be in the wrong phase.  The RCD should operate in the event of a short to earth but you have lost one layer of protection against fire. 

 

UK caravans manufactured since the mid 90's have had to have double pole MCBs, so there are already 2 levels of protection.

 

13 minutes ago, kelper said:

How do you know whether your RCD operates quickly enough?

 

Press the test button ?

 

I see more of a problem with an additional (IMV unnecessary) often home made, external plug and socket in the mains supply.

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16 hours ago, kelper said:

In a French marina the boat indicated polarity incorrect but swapping phases made no difference.  Both phases were live!  It was a 55-0-55 supply.  Caravan sockets really ought to be double pole switched.  So unplug stuff not in use!

 

I thought that after a certain date UK caravans were double pole switched as well, so there would be no need to check for reverse polarity. I can't understand the issue then as they would be same as their Continental counterparts.

 

 

Edited by Lutz
I see Lost in France has already mentioned a date so why does this issue continue to come up?

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35 minutes ago, Lost in France said:

Press the test button ?

But you still won't know if itvtripoed within the required time.

RCDs don't protect against overload. 

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6 minutes ago, kelper said:

But you still won't know if itvtripoed within the required time.

 

While you might not be able to tell between 30ms and 35 ms, I would have thought most could tell between 30ms and a second or if it worked at all.

 

A couple of weeks ago I bought a socket tester that had an adjustable time RCD tester, which wasn't much more expensive than a good quality tester without that facility.

 

8 minutes ago, kelper said:

RCDs don't protect against overload. 

 

That's what the MCB is for.

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19 minutes ago, Lost in France said:

A couple of weeks ago I bought a socket tester that had an adjustable time RCD tester

That's interesting.  Can you post details please?

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The AWS guy who does my servicing says he now has to test the trip speed of the board in the caravan. Ok it's not at the start of every trip but it is annually.

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8 minutes ago, kelper said:

That's interesting.  Can you post details please?

 

Sorry, it was adjustable trip current.
https://www.amazon.fr/Testeur-prises-différentiels-Multimetrix-VT35/dp/B00D826CZO

 

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1 hour ago, kelper said:

 How do you know whether your RCD operates quickly enough?

Apparently a couple of years ago, our AWS mobile guy said its part of the service to check how quick the RCD trips, as I have sold the vans the service and test was done I can not find the service sheets but I do remember the trip timing was written on them. 

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1 hour ago, kelper said:

If the polarity is reversed, the fuse in a UK plug will be in the wrong phase.  The RCD should operate in the event of a short to earth but you have lost one layer of protection against fire.  Presumably RCDs do fail occasionally.  How do you know whether your RCD operates quickly enough?

 

Regular testing of the electrics - the RCD time is tested.

 

Reminds that back in the '80s when few caravans had mains electrics, I bought all the bits from a caravan dealer and installed it myself and then paid an electrician to test it all - he rejected the RCD as too slow so I took it back, got a refund and bought one from an electrical wholesaler.

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8 hours ago, kelper said:

Is anyone aware of UK equipment that does not work if the polarity is 'wrong'?  I read of washing machines that ere fussy.

 

I cannot imagine any domestic electronic equipment where it matters in the slightest. Mains electricity is alternating current.

 

8 hours ago, kelper said:

If the polarity is reversed, the fuse in a UK plug will be in the wrong phase. 

 

Noooo! A fuse will work just the same anywhere in a circuit.

 

This topic has had me in stitches. It is so funny. As for carrying 6 leads to have all permutations, that is simply classic.

 

Quite frankly, with most modern caravans reverse polarity matters not a jot.

 

While you are panicking about reverse polarity, ask yourselves the following questions first:

  1. Have you tested every socket in your own house for reverse polarity. There's a fair chance you have at least one.

2. How modern is your house wiring? Has it got a modern consumer unit with RCDs covering all the circuits. If not why all the angst about your caravan. Surely your home needs to be safe too.

3. How many examples of people being electrocuted on caravan sites have you ever heard of?

4. Have you checked the consumer unit on your caravan. Does it have an RCD, and does it have double pole MCBs.

5. Is your caravan a continental model?

6. Have you considered that continental models electrical systems are designed for reverse polarity situations.

7. Have you considered that modern UK caravans are designed to be taken abroad and thus (6) also applies.

 

 

 

 

 

Edited by thebriars

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2 hours ago, thebriars said:

1. Have you tested every socket in your own house for reverse polarity. There's a fair chance you have at least one.

2. How modern is your house wiring? Has it got a modern consumer unit with RCDs covering all the circuits. If not why all the angst about your caravan. Surely your home needs to be safe too.

4. Have you checked the consumer unit on your caravan. Does it have an RCD, and does it have double pole MCBs.


 A fuse will work just the same anywhere in a circuit. 

 

1 Yes. 2 Yes. 4 Yes. 

 

If polarity is reversed and the "neutral" is shorted to earth, the fuse won't blow.

Edited by kelper

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If polarity is reversed and the "neutral" is shorted to earth, the fuse won't blow.

 

Kelper

 

Yes the fuse will blow in your statement above.The fuse is still part of the circuit.So much is made of RP that we have to sit here and read peoples understanding of electrical theory.I still cannot work out in your previous reply about being on a different phase.

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9 hours ago, borrowdale said:

If polarity is reversed and the "neutral" is shorted to earth, the fuse won't blow.

 

Kelper

 

Yes the fuse will blow in your statement above.The fuse is still part of the circuit.So much is made of RP that we have to sit here and read peoples understanding of electrical theory.I still cannot work out in your previous reply about being on a different phase.

Think about it; perhaps I did not explain.  If your hookup is reversed neutral becomes live.  If a wiring fault in an appliance shorts neutral to earth, fault current flows in the neutral wire and the earth.  No current flows in what was the live.  So the fuse won't blow.

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1 hour ago, kelper said:

Think about it; perhaps I did not explain.  If your hookup is reversed neutral becomes live.  If a wiring fault in an appliance shorts neutral to earth, fault current flows in the neutral wire and the earth.  No current flows in what was the live.  So the fuse won't blow.

The RCD will trip.

Reverse polarity is not a problem in a caravan unless its old enough to not have double pole MCB or RCD.

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21 minutes ago, AndersG said:

The RCD will trip.

 

and a lot faster than a fuse will clear.

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5 hours ago, kelper said:

Think about it; perhaps I did not explain.  If your hookup is reversed neutral becomes live.  If a wiring fault in an appliance shorts neutral to earth, fault current flows in the neutral wire and the earth.  No current flows in what was the live.  So the fuse won't blow.

 

You've just said your caravan has a double pole MCB which is essentially a double pole fuse, and one which is much more responsive than the fuse in the plug.

 

Common sense should tell you that this MCB will trip in the situation you describe above whatever the polarity if the RCD hasn't already tripped as has been stated above.

 

 

Edited by thebriars

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Think the problem is that with reversed polarity you can still have power to the appliance even if the fuse blows.  Shouldn’t be a problem unless you are going to delve inside the item but it’s a possibility.  And yes it has happened to me although not in a caravan.

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4 hours ago, AndersG said:

 

Reverse polarity is not a problem in a caravan unless its old enough to not have double pole MCB or RCD.

 

And THAT IS A PROBLEM. We all have to remember that there are some folk out there who know NOTHING about electrics and who have old caravans so for people to say "No-one needs to carry a reverse lead on the continent" may be correct for most of us but be careful who you say that to. 

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46 minutes ago, thebriars said:

 

You've just said your caravan has a double pole MCB which is essentially a double pole fuse, and one which is much more responsive than the fuse in the plug.

 

Common sense should tell you that this MCB will trip in the situation you describe above whatever the polarity if the RCD hasn't already tripped as has been stated above.

 

 

Often fuses in plugs have a lower rating such as 3 amps which is lower than the mcb trip of maybe 10 or 16 amps or even higher in houses.

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43 minutes ago, thebriars said:

 

You've just said your caravan has a double pole MCB which is essentially a double pole fuse, and one which is much more responsive than the fuse in the plug.

 

Common sense should tell you that this MCB will trip in the situation you describe above whatever the polarity if the RCD hasn't already tripped as has been stated above.

 

 

I agree 100%.  I just wanted to correct the statement that a fuse works anywhere in a circuit.

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17 minutes ago, kelper said:

I agree 100%.  I just wanted to correct the statement that a fuse works anywhere in a circuit.

 

A fuse does work anywhere in a circuit. Its job is not to prevent a short circuit to earth- you have an RCD for that, but to prevent too much current passing through the circuit.

20 minutes ago, Paul1957 said:

Often fuses in plugs have a lower rating such as 3 amps which is lower than the mcb trip of maybe 10 or 16 amps or even higher in houses.

Quite, but as I pointed out above, a fuse is there to protect against too great a current flow.  Cartridges fused do not blow straight away anyway, they are quite slow, and thus a far higher current will flow for a time, as they will for an MCB.

Edited by thebriars

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Why is this only an issue among UK caravanners, even though by now most caravans now have double pole MCB's. I don't understand it. I've never come across anyone on the Continent even giving it a thought.

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