Reverse Polarity

[Thornebt]

I've read posts on this forum about reverse polarity and can see that it seems to be a 'non-issue' and that just a couple of people disagree.

When I have EHU connected my reverse polarity light is illuminated. Can I take it that this is definitely not a problem? I probably won't understand any technical explanations. I just wonder about the point of having a warning light if it's not an issue.

 

[Lenny HB]

Shouldn't happen in the UK if everything is wired correctly but you will find it a lot over the channel. Not something that I worry about.

 

[Thornebt]

I am in the UK so something must be wired incorrectly? Is it best to check my hook up lead as a starting point?

 

[Richard n Ann]

I am in the UK so something must be wired incorrectly? Is it best to check my hook up lead as a starting point?

Could be reverse polarity or a missing earth.

 

[Phill D]

I am in the UK so something must be wired incorrectly? Is it best to check my hook up lead as a starting point?

it could be the hook up lead. a multimeter to check that the pins in the cable are correctly wired to the relevant pins. check the earth is connected in the lead.

but as has been said its not a significant issue (unless ) you are going to strip things withe the EHU cable still connected. Then it could be a problem.

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[Thornebt]

I've checked the EHU lead (3 pin plug to EHU adaptor) and the earth is connected. Not sure if the live and neutral are right way round as there's no markings on the EHU end to identify live or neutral. It should me a quality item as I bought it from large motorhome dealer, not on EBay. Manufactured by Maypole.

 

[Lenny HB]

Could be reverse polarity or a missing earth.

Won't be a missing earth the polarity light is a neon connected between earth & neutral.

 

[NigelNovice]

This may help with pin layout

 

[Thornebt]

Thank you very much NigelNovice. Your diagram shows me that the live and neutral are transposed in my adaptor lead. It's manufactured by Maypole.ltd.uk. it's very surprising to me that they can manufacture the lead incorrectly. I will email their sales dept (email address is on plug) to see what they say.

 

[Madcaravanner]

I am in the UK so something must be wired incorrectly? Is it best to check my hook up lead as a starting point?

YES
a friend had this and it destroyed his Sargent turned out his socket in the wall outside had a faulty connection

in a foreign van a real reverse polarity doesn't matter
in a UK van a real reverse leave the electric item Live but inoperable except if it get an earth via something else then you're fried

start with your cable make sure there are no short circuits

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[RustyRuss]

Nigel make sure that the SOCKET end is wired in a corresponding fashion, your post #8 shows the PLUG connections. Live should be a BROWN conductor (wire), the terminal will DEFINITELY be marked L, you might have to look really hard for it as the mouldings are often poor quality, The Neutral should be marked N and the conductor (wire) should be BLUE, the Earth should be marked E or have a symbol like this

and be GREEN/YELLOW.

It is illegal for the terminals not to be marked, as per BS7671 Amendment 2 2022 Electrical Installation Regulations.

Cheers! Russ

 

[NigelNovice]

Nigel make sure that the SOCKET end is wired in a corresponding fashion, your post #8 shows the PLUG connections. Live should be a BROWN conductor (wire), the terminal will DEFINITELY be marked L, you might have to look really hard for it as the mouldings are often poor quality, The Neutral should be marked N and the conductor (wire) should be BLUE, the Earth should be marked E or have a symbol like this View attachment 634573View attachment 634573and be GREEN/YELLOW.

It is illegal for the terminals not to be marked, as per BS7671 Amendment 2 2022 Electrical Installation Regulations.

Cheers! Russ

Yes I know, I recently made a domestic/household plug to 16amp blue socket so as to hookup on the drive at home, merely trying to help a fellow Funster

 

[Old Gibber]

in a foreign van a real reverse polarity doesn't matter
in a UK van a real reverse leave the electric item Live but inoperable except if it get an earth via something else then you're fried

This is just scaremongering, what you have written is hopelessly incorrect. Electrical mains is alternating current so in reality there is no "right" live, and of course, reverse polarity will work just as well as normal polarity. Technically it is the neutral which is tied to earth back at the substation.

As has been said the only danger is if you decide to take an appliance apart and it is still connected to the mains, though even if the mains polarity is correct this is still dangerous.

 

[Thornebt]

I can see now that I didn't look at Nigel's diagram properly. I confused the socket / plug connections! I've removed the cover on the van end of the lead and it is correctly wired.

Thanks for your help everyone. Everything seems to work perfectly with my van electrics so I will just mention it when I eventually get a hab service done.

 

[pappajohn]

Maypole are a budget supplier/manufacture.
There's every chance the hookup lead was made in China.

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[RustyRuss]

Most funsters are at best “have a go” amateurs, providing them with electrical theory, is, in my opinion as a time served electrician, at best irresponsible, and at worst, downright dangerous. Telling a fellow funster what colour and signifying letter or symbol a conductor should be is just enough information provided to make sure they don’t hurt themselves or others. As a colleague once said…. “As a plumber the worst you can do is flood the place, as an electrician the worst you can do is kill yourself, and as a gas plumber the worst you can do is kill yourself and everybody else in a quarter mile radius!!”

Cheers!

Russ

 

[autorouter]

It's a good idea to carry one of these socket testers, available from any DIY store. Plug it into a MH socket to check whenever you connect up to EHU. It will tell you if polarity is reversed (live/neutral reversed) and a few other possible faults like missing earth. Quick and simple.

If there's a problem, or if there's no mains coming through, you can investigate further if you have one of these:

You can plug in your tester, and check the hookup post, then the MH end of the hookup cable, to give you the approximate location of the fault.

From your picture I can see the MH mains box has an RCD - the left-most circuit breaker, the one with a 'Test' button on it. That means you are protected against electric shock anywhere inside the MH. There should be a similar device on the hookup post too.

 

[autorouter]

Maypole are a budget supplier/manufacture.
There's every chance the hookup lead was made in China.

One big benefit of our new freedoms is it doesn't need to be CE marked any more. Thank goodness that bit of red tape has gone on the bonfire...

 

[Nedge68]

I have seen some very bad equipment with CE marking, it appears that some manufacturers regard printing CE on the box and a label on the goods as enough, I regard it as meaning “Check Everything“ mark.

 

[Odd-no-more]

This is just scaremongering, what you have written is hopelessly incorrect. Electrical mains is alternating current so in reality there is no "right" live, and of course, reverse polarity will work just as well as normal polarity. Technically it is the neutral which is tied to earth back at the substation.

As has been said the only danger is if you decide to take an appliance apart and it is still connected to the mains, though even if the mains polarity is correct this is still dangerous.

This is not quite correct, alternating current is not alternating between line and neutral, it alternates above and below zero in the live supply. In an older van the MCB will be on the live only, so with reverse polarity although the circuit will be disconnected the live wire will still have power. If you touch it you could be saved by the RCD but they often fail especially if they are not tested regularly. If you are not sure what you are doing get it checked by a professional.

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[Richard n Ann]

This is not quite correct, alternating current is not alternating between line and neutral, it alternates above and below zero in the live supply. In an older van the MCB will be on the live only, so with reverse polarity although the circuit will be disconnected the live wire will still have power. If you touch it you could be saved by the RCD but they often fail especially if they are not tested regularly. If you are not sure what you are doing get it checked by a professional.

There isn't a zero volts reference point though.. Just L and N as said, earth is tied to N

 

[Odd-no-more]

earth is tied to N

This is only with a PME earth which is not acceptable for a MOHO. An EHU post should have a TT earth (earth rod)
The zero point is only visable on an oscilloscope

 

[autorouter]

This is not quite correct, alternating current is not alternating between line and neutral, it alternates above and below zero in the live supply. In an older van the MCB will be on the live only, so with reverse polarity although the circuit will be disconnected the live wire will still have power. If you touch it you could be saved by the RCD but they often fail especially if they are not tested regularly. If you are not sure what you are doing get it checked by a professional.

That's true, it's nothing like correct, but there's always someone who comes out with it whenever reverse polarity is mentioned. And what you say is not the whole story either.

Non-UK MHs have double-pole MCBs, double-pole switches and unfused plugs. They rely on the MCB for overcurrent protection. They also have an RCD like UK MHs. It makes no difference which wire the live and neutral are connected to, because both wires are protected and switched.

UK MHs should also have double-pole MCBs, but as you say some older van or even newer self-conversions have single-pole MCBs like the ones in domestic consumer units. But they all have fused plugs on appliances. Fuses are by definition single-pole protection, and there's nothing you can do about that apart from ditching 13A sockets and fitting non-UK sockets.

The fused plugs are a consequence of the UK 'ring main' system, where the sockets are supplied on a ring which has a 32A MCB protecting it. That means individual appliances need to have their own fuse, in the plug, either 13A or 3A for example, depending on the connecting flex thickness. This system is never used outside the UK, all the circuits are 'radial' not 'ring', and they have 16A MCBs. That's why the round blue plugs and sockets are rated at 16A.

This inherent single-pole protection is the reason that the correct 'polarity', ie connection of live and neutral, is important for UK MHs but not for non-UK MHs. But having an RCD will protect you from almost all electric shocks.

 

[Odd-no-more]

That's true, it's nothing like correct, but there's always someone who comes out with it whenever reverse polarity is mentioned. And what you say is not the whole story either.

Non-UK MHs have double-pole MCBs, double-pole switches and unfused plugs. They rely on the MCB for overcurrent protection. They also have an RCD like UK MHs. It makes no difference which wire the live and neutral are connected to, because both wires are protected and switched.

UK MHs should also have double-pole MCBs, but as you say some older van or even newer self-conversions have single-pole MCBs like the ones in domestic consumer units. But they all have fused plugs on appliances. Fuses are by definition single-pole protection, and there's nothing you can do about that apart from ditching 13A sockets and fitting non-UK sockets.

The fused plugs are a consequence of the UK 'ring main' system, where the sockets are supplied on a ring which has a 32A MCB protecting it. That means individual appliances need to have their own fuse, in the plug, either 13A or 3A for example, depending on the connecting flex thickness. This system is never used outside the UK, all the circuits are 'radial' not 'ring', and they have 16A MCBs. That's why the round blue plugs and sockets are rated at 16A.

I'm retired and out of it now, but I believe under 18th edition it has gone back to radial circuits and ring mains are out.

 

[Lenny HB]

there's nothing you can do about that apart from ditching 13A sockets and fitting non-UK sockets.

You could change the so jets for double pole switched ones. Quite a few UK manufacters sockets are double pole switched, MEM, Volex, Contatum are some of them.

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[autorouter]

You could change the so jets for double pole switched ones. Quite a few UK manufacters sockets are double pole switched, MEM, Volex, Contatum are some of them.

You could also swap the 13A fuse in the plug for a neatly cut piece of six-inch nail, it would be safer because most MH MCBs are 10A rather than 32A. But then it wouldn't be safe to use the appliance in a house, so not a good idea overall

 

[Old Gibber]

This is not quite correct, alternating current is not alternating between line and neutral, it alternates above and below zero in the live supply. In an older van the MCB will be on the live only, so with reverse polarity although the circuit will be disconnected the live wire will still have power. If you touch it you could be saved by the RCD but they often fail especially if they are not tested regularly. If you are not sure what you are doing get it checked by a professional.

My post was completely correct.

Firstly I never said that alternating current is alternating between line and neutral.

Secondly, the MCB will only trip when it detects a significant current overload. This will happen whether polarity is correct or reversed, and all it does is stops any current flowing through the circuit.

Also I made it quite plain that opening up a live electrical appliance is dangerous.

 

[Odd-no-more]

But having an RCD will protect you from almost all electric shocks.

As long as it works OK, I tested many of these when installing new circuits several didn't trip at all and most were slow until they had been tripped a few times. We are all supposed to push the test button once a month, nobody does that, including myself.

 

[Odd-no-more]

he MCB will only trip when it detects a significant current overload. This will happen whether polarity is correct or reversed,

Yes but with reversed polarity, although the circuit will carry no current it will still be live and could have a short to earth in which case the RCD should save you, but as I have said in a previous post, many RCD's I have tested either didn't work at all or were very slow. The RCD is an electro-mechanical device and if not moved regularly they can stick, this makes them slow or inoperable. By using a circuit without overload protection on the live supply you are in effect removing one of the main safety devices and relying on the secondary device only.

 

[Old Gibber]

Yes but with reversed polarity, although the circuit will carry no current it will still be live and could have a short to earth in which case the RCD should save you, but as I have said in a previous post, many RCD's I have tested either didn't work at all or were very slow. The RCD is an electro-mechanical device and if not moved regularly they can stick, this makes them slow or inoperable. By using a circuit without overload protection on the live supply you are in effect removing one of the main safety devices and relying on the secondary device only.

Not at all. All the MCB does is is protect against overcurrent which it will do whatever the polarity. You are not removing overload protection with reverse polarity. Also most, if not all, appliances will have a fuse in the plug or internally which protect against overcurrent situations. Fuses and MCBs work wherever they are placed in a circuit.

I will make my point again, "As has been said the only danger is if you decide to take an appliance apart and it is still connected to the mains, though even if the mains polarity is correct this is still dangerous."

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