EHU quandary - Polarity

[Minxy]

In our Globecar the UK socket near the sink/worktop is upside down and this is very useful as the cable does not then have to loop to reach the kettle, toaster etc.

I'll have to check the socket in our new Campscout, in our Familyscout it's the right way round.

 

[Dave and Ginny]

Hi Dave, this is not something we've ever concerned ourselves with so can't really help you I'm afraid, however I think @Lenny HB's explanation sounds plausible.




As you know, we bought the van from Edgehill and they had imported it. Maybe when they fitted the UK sockets, they did exactly as described above. You could always try asking Lee Broadhurst via HOG's.

Thanks Kim, have to agree that @Lenny HB the most plausible reason. Even more reason to leave it until I get home when I can properly check the polarity of all the 230v run equipment and not just the sockets. If it's been like it the past 13 years then no real need to panic and as pointed out doing no harm either.

 

[Chas17]

Let's make it simple......

We expect live to be on the right but on European posts it can be on the left (our neutral side)

Let's say incorrect live is on the left and neutral is on the right.
correct is live right, neutral left.

Plug in your short lead to correct it and that takes the posts neutral (left, which is actually live) and transfers it to the vans live(right).

Nothing wrong with your van unless you reverse an already correct supply which will then make it reversed.

But why anyone bothers is beyond me.
Ever wondered why so many European posts are reversed... .because it doesn't matter and they don't care.

Surely it doesn't matter to Europeans and they don't care because their switches are double pole and break both Live and Neutral, whereas UK breaks only the live.
Having said that then it shouldn't matter to UK users unless you are diving into the internals of your item while still plugged into a socket.

 

[Panda-will]

I get the double-pole switch safety point and as our van has European sockets that's probably a good thing. But I still don't get why polarity doesn't matter. All the circuits in our van are protected by fuses and as far as I know the fuses are on the live wire for protection in case a device pulls too much current. If the fuse is on the neutral wire it won't offer the same protection will it?

 

[Dave and Ginny]

I get the double-pole switch safety point and as our van has European sockets that's probably a good thing. But I still don't get why polarity doesn't matter. All the circuits in our van are protected by fuses and as far as I know the fuses are on the live wire for protection in case a device pulls too much current. If the fuse is on the neutral wire it won't offer the same protection will it?

Interesting point

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[scotjimland]

All the circuits in our van are protected by fuses and as far as I know the fuses are on the live wire for protection in case a device pulls too much current. If the fuse is on the neutral wire it won't offer the same protection will it?

Don't think you will have fuses on 240v ac equipment , (other than the appliance plug top,) all AC circuits should be protected by DOUBLE POLE Circuit breakers.. not fuses .. that is the 17th edition regulation for caravans and motorhomes .. you should also have a DOUBLE pole main switch with an RCD

12v DC circuits polarity DOES matter and they are generally protected by fuses on the positive line..

 

[Panda-will]

Thanks, that makes it a bit clearer. We have a main rcd switch but everything else seems to be routed through a Schaudt Electroblok and that is loaded with fuses.

 

[two]

A fuse or MCB protects the wiring, should an excessive amount of current flow around the circuit. If the flow is to earth, the RCD should cut in first.

If you choose to poke around the internal contacts of a mains device, without removing the plug, you may get a shock but a double pole RCD will prevent you from being electrocuted.

 

[autorouter]

If you choose to poke around the internal contacts of a mains device, without removing the plug, you may get a shock but a double pole RCD will prevent you from being electrocuted

There seems to be a myth that the only way you can be exposed to live mains from a faulty device wired with 'reverse polarity' is to deliberately poke around inside. There are plenty of other situations, including faults and accidents. Of course they are unlikely. But you have a fire extinguisher, CO monitor, and airbags, for equally unlikely situations.

 

[pappajohn]

I get the double-pole switch safety point and as our van has European sockets that's probably a good thing. But I still don't get why polarity doesn't matter. All the circuits in our van are protected by fuses and as far as I know the fuses are on the live wire for protection in case a device pulls too much current. If the fuse is on the neutral wire it won't offer the same protection will it?

There seems to be a myth that the only way you can be exposed to live mains from a faulty device wired with 'reverse polarity' is to deliberately poke around inside. There are plenty of other situations, including faults and accidents. Of course they are unlikely. But you have a fire extinguisher, CO monitor, and airbags, for equally unlikely situations.

An overload MCB won't trip if it's on the neutral wire but the RCD main switch will.
I proved this to myself a few years ago by deliberately reversing the incoming live and neutral conductors to my garage consumer unit RCD main switch then introducing an earth fault to a socket then a light fitting.
The RCD main switch tripped in both cases.

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[autorouter]

We have a main rcd switch but everything else seems to be routed through a Schaudt Electroblok and that is loaded with fuses.

All the Electrobloks I've seen have many fuses, but they are all for the 12 volt circuits, not the mains 240 volt circuits. The mains RCD and circuit breakers are in a separate box by the mains inlet connector.

 

[tony dellar]

Only uk plugs worry most other countries one can plug in any way round so its random .

 

[autorouter]

Don't think you will have fuses on 240v ac equipment , (other than the appliance plug top,) all AC circuits should be protected by DOUBLE POLE Circuit breakers.. not fuses .. that is the 17th edition regulation for caravans and motorhomes .. you should also have a DOUBLE pole main switch with an RCD

The 17th Edition regs came into force about 10 years ago. Any house wired before then is likely not to have any RCDs.

Any motorhome or caravan wired before then is likely not to have an RCD.

Any DIY motorhome converter, even nowadays, is likely to use single-pole MCBs. I've never seen double-pole MCBs in B&Q, Wickes or any other British DIY store.

All British appliance plugs have a fuse, which is a single-pole protection device.

It's very easy for someone with a nice modern motorhome on a professionally wired campsite to lose sight of the danger, but it hasn't gone away.

 

[two]

An overload MCB won't trip if it's on the neutral wire but the RCD main switch will.
I proved this to myself a few years ago by deliberately reversing the incoming live and neutral conductors to my garage consumer unit RCD main switch then introducing an earth fault to a socket then a light fitting.
The RCD main switch tripped in both cases.

An MCB will trip if the circuit it is in is overloaded, no matter where it is fitted in that circuit. An earth fault is a different situation, and will cause an RCD to trip in milliseconds. Even if the current is above the threshold of the MCB in that circuit, the RCD should trip before the MCB has time to respond.

 

[Panda-will]

Thanks all, I'm feeling much more informed. So one final question on the RCD. If the campsite connection has no earth will the RCD still protect me?

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[pappajohn]

An MCB will trip if the circuit it is in is overloaded, no matter where it is fitted in that circuit.

Only if the MCB is before the appliance causing the overload.
In the case of reversed phase/neutral it would effectively be in the neutral (normally live) conductor after the fault.

 

[Richard n Ann]

RE post 75

It probably wouldn't trip, but you wouldn't get a shock either, if you touched a live wire and an 'earth' (that isn't an earth) your body would be at mains voltage but you wouldn't feel anything, the 'earth' would also be at mains voltage with no current flow.

If you were stood in a puddle with bare feet outside the van and touched a live wire from the van you may feel a shock but the RCD would then trip.

 

[scotjimland]

Only if the MCB is before the appliance causing the overload.
In the case of reversed phase/neutral it would effectively be in the neutral conductor after the fault

are you sure about that ?

the current in any circuit is the same in both L and N .. so no matter where the CB is, it will trip if the circuit is overloaded.. but a single pole breaker in the N would leave the appliance live, hence regulations requiring two pole CBs

 

[Richard n Ann]

Only if the MCB is before the appliance causing the overload.
In the case of reversed phase/neutral it would effectively be in the neutral conductor after the fault

How does the MCB know where it is?

 

[pappajohn]

Thanks all, I'm feeling much more informed. So one final question on the RCD. If the campsite connection has no earth will the RCD still protect me?

If the hookup has no earth don't use it.....simple.
No earth is extremely dangerous as you, touching a faulty appliance, become the earth.

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[pappajohn]

How does the MCB know where it is?

It doesn't, it's an inanimate object.
The faulty appliance will absorb the excess current and convert it to heat.
If the MCB, which is only a fuse, is before the appliance then it will sense the high current being drawn by the fault and trip.
In a 12v scenario if a short circuit is between battery and fuse the fuse won't blow but the wire will melt which is why a fuse should be as close as possible to the supply source.

 

[autorouter]

Thanks all, I'm feeling much more informed. So one final question on the RCD. If the campsite connection has no earth will the RCD still protect me?

In a word, yes.

A residual current device (RCD) monitors the difference between the current flow in the live and neutral wires (called the residual current). If this exceeds a pre-determined amount, it trips and disconnects both the live and neutral. The pre-determined amount is usually 30 milliamps, but may be lower, especially in a medical context.

It doesn't need an earth connection to do its job. If you touch a live part, then congratulations, you ARE the fault to earth that makes it trip.

 

[tonyidle]

It doesn't, it's an inanimate object.
The faulty appliance will absorb the excess current and convert it to heat.
If the MCB, which is only a fuse, is before the appliance then it will sense the high current being drawn by the fault and trip.
In a 12v scenario if a short circuit is between battery and fuse the fuse won't blow but the wire will melt which is why a fuse should be as close as possible to the supply source.

Only in the case of a L-E short. If the appliance itself is shorted, or if the appliance causes an L-N short then the MCB will operate.

 

[pappajohn]

Only in the case of a L-E short

Agreed, and what I meant.

But regardless of that, it should have tripped the RCD anyway.

 

[two]

A circuit describes the route of the passage of an electric current. In a simple circuit the current is the same all the way round and a fuse/MCB would blow, wherever it is placed in that circuit, when its rated threshold is exceeded.
A short-circuit describes the condition when an intended route is somehow by-passed. If that circuit’s fuse/MCB was in the remainder of the circuit, it would not blow when it should because it was also by-passed.
Fuses are normally slow to blow, however, and are unlikely to spare you electrocution if you touched a live wire. RCDs have been introduced to cut off the supply as soon as the tiniest leak is detected (when the returning current does not match what went in). Double pole RCDs cut off both incoming wires (L & N) in the circuit and thus it does not matter which way round they were connected. A single pole RCD only disconnects one of the incoming wires and the other part of the circuit remains connected. So it becomes important, then, to ensure that the incoming wires are not reversed and that the Live wire is connected to the switched part of the RCD. Most RCDs are double pole nowadays.

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[Linda18]

The first thing that I would check is the wiring on your short 'correcting' lead.

I bought one a few years ago and reversed the wires to, in theory make a correcting lead, took me quite a while to figure out that the lead was actually wired incorrectly from new and in reversing the live and neutral I had actually put the lead into the correct unreversed polarity, of course this had the effect you describe when connecting to a reversed polarity socket.

I decided, after 11 years of the same EHU cable, to change the connetor that is plugged into the van, as it was worn. The cable had been wired incorrectly the whole time! Also, I just turn my 'foreign' two pin plug upside down in the mains post and check the reading on the plug that I use when abroad, and that shows me that everything is correct.

 

[pappajohn]

I decided, after 11 years of the same EHU cable, to change the connetor that is plugged into the van, as it was worn. The cable had been wired incorrectly the whole time!

And oddly enough, you're still here to tell us about it.

I think 11 years is long enough to prove reversed polarity is a crock of crap.

 

[Lenny HB]

Just waiting for you lot to tell me I have to label all my sockets & all my plugs so I always plug them in "the so called correct way round". Well it ain't going to happen.

 

[two]

We are surrounded by idiots. Indeed, there are regular reports of them everywhere, particularly regarding other drivers and politicians. They regularly conspire to challenge the safety precautions placed to protect them and, in spite of their persistence, very few (the experts) ever succeed in killing themselves.

Sleep soundly, just respect electricity (especially if you think you understand it all)!

 

[The Wino]

I decided that as there is often reversed polarity on supplies abroad and there are thousands of motorhomes that if it was a big problem it would be reported even more than gassing!!!!

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