Reverse polarity.

BouncyBoatFolk

BouncyBoatFolk

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Hi all, I have just connected a test lead to my allocated electric bollard and got a reverse polarity warning on my plug in circuit tester, how is that overcome or can it not be?
Mike.
 
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Don't worry about it, everything still works the same.
Just don't poke a knife in your toaster or dismantle your microwave without UNPLUGGING first
Theoretically our AC mains supply is reversed 25 times a second anyway.

Look at the +v & -v on the left.

sinusoidal_waveform-768x560.jpg
 
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My understanding is that the on-off switch and the fuse of an appliance are on the live wire; therefore, if the polarity is reversed, the appliance remains live, bypassing the fuse and switch - it will still work but you loose the protection offered by the switch and fuse should short circuit for example. That said, an RCD should save the day if it all goes wrong.
 
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Thanks all, I tested the bollard next door and it was fine. The one given to me had a fault, (no electric, but showing as a fault). Site attendant said to use the working one as its not needed tonight. All sorted thanks. He did say to use any of the others so perhaps he thinks the English %#&$ will probably blow another couple while he's here:giggle::giggle:.
 
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slowcoach65 said:
My understanding is that the on-off switch and the fuse of an appliance are on the live wire; therefore, if the polarity is reversed, the appliance remains live, bypassing the fuse and switch - it will still work but you loose the protection offered by the switch and fuse should short circuit for example. That said, an RCD should save the day if it all goes wrong.
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Not quite true. It does not matter where a fuse is in the circuit. Yes part of the appliance will remain live, but the protection offered by the fuse, limited though it is these days, will still be there and the appliance will stop working.
 
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Old Gibber said:
Not quite true. It does not matter where a fuse is in the circuit. Yes part of the appliance will remain live, but the protection offered by the fuse, limited though it is these days, will still be there and the appliance will stop working.
Click to expand...
If the neutral is live ("reverse polarity") and the fault is to earth then the flow of current will bypass the fuse.

It can also bypass the single pole RCD fitted to some British vans which is why this fault can be potentially dangerous in some vehicles.
 
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Old Gibber said:
Not quite true. It does not matter where a fuse is in the circuit. Yes part of the appliance will remain live, but the protection offered by the fuse, limited though it is these days, will still be there and the appliance will stop working.
Click to expand...
The fuse is to protect the appliance and if you are worried about reversed polarity fit sockets wit double pole switches.
 
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BouncyBoatFolk said:
Hi all, I have just connected a test lead to my allocated electric bollard and got a reverse polarity warning on my plug in circuit tester, how is that overcome or can it not be?
Click to expand...
As pappajohn says, everything works the same. There is a possible safety problem in the event of a fault. If your motorhome mains inlet box has an RCD, that will give you protection against possible safety problems due to reverse polarity or anything else.

You can tell if you have an RCD in the mains inlet box, because it is one of the circuit breakers that has a 'Test' button. Other circuit breakers don't have a test button. Only one RCD is required.

If you have an RCD, don't worry about reverse polarity. If you don't have an RCD, that is something you need to have fitted as a priority.

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DBK said:
If the neutral is live ("reverse polarity") and the fault is to earth then the flow of current will bypass the fuse.

It can also bypass the single pole RCD fitted to some British vans which is why this fault can be potentially dangerous in some vehicles.
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If the neutral is live ("reverse polarity") and the fault is to earth then the flow of current will bypass the fuse, but then cause the RCD to trip, so no problem.

Frankly in 30 years of owning caravans and motorhomes I've never had one with a single pole RCD. The much more sensible solution if one does have a single pole RCD it to get it replaced with a double pole one rather that worrying about reverse polarity.
 
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Spriddler said:
Wasn't there a thread about a chap who thought his toilet had reversed polarity as he could pee only when sitting down?
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You beat me to it! But mine was an image of a lady standing up……..
 
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Old Gibber said:
Yes, easy. Single pole:
1651862202648.png

Double pole:

1651862277103.png
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Let's be clear about this. The 'Single Pole RCD' is a type of RCBO, in fact a double pole RCD, combined with a 'Single Pole and Neutral' (SP&N) MCB. Because that's a bit long-winded, it gets abbreviated misleadingly to Single Pole RCD.

It functions fine as a double-pole RCD, in terms of shock protection. If it senses overcurrent in the live wire, it disconnects both live and neutral. The only thing it doesn't do is sense an overcurrent in the neutral line, flowing to earth. But as Old Gibber says that will cause the RCD to trip and disconnect both live and neutral anyway.

That Double Pole RCD in the picture is a simple RCD, with no overcurrent protection at all, as found in most MHs and house Consumer Units. It needs MCBs on the circuits for full overcurrent protection.

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This is my box, can you tell what this is? How safe is this? Apologies for the poor photo angle.
Screenshot_20220506-223222.png
 
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Have you tried reversing your motorhome onto the allocated plot ..... It might reverse the reverse, making two negatives into a positive ... :unsure: :unsure: :unsure: :unsure: :X3: :X3: :X3:

- it's ok, I've ordered my own taxi thank you ..:getmecoat:
 
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ctc said:
The fuse is to protect the appliance and if you are worried about reversed polarity fit sockets wit double pole switches.
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Or fit ones without a switch. None of the UK sockets in my motorhome have a switch which makes it clear that to be safe you need to unplug appliances. I am surprised that single pole switching is ever allowed, it assumes that no one ever makes a mistake with wiring.

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Itsmcb said:
This is my box, can you tell what this is? How safe is this?
Click to expand...
Looks fine to me. On the left is an RCD: double pole, trip current is 0.03A, ie 30mA, which is low enough to avoid serious electric shock. It's a Type A, which is fine for this usage. It's amp capacity is 40A (not visible on the photo) which means it can be used in installations up to 40A total current.

On the right are three MCBs which provide overcurrent protection. B10, B6, B6 means 10A, 6A and 6A maximum working current, and Curve B relates to how fast the circuit trips if the amps is too much. The squiggly diagram shows they are Single Pole and Neutral types, which means if it senses overcurrent in the live wire it disconnects both the live and neutral.
 
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Old Gibber said:
Not quite true. It does not matter where a fuse is in the circuit. Yes part of the appliance will remain live, but the protection offered by the fuse, limited though it is these days, will still be there and the appliance will stop working.
Click to expand...
Thank you for the correction, thinking about it, that makes sense.
 
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There is NO SUCH THING as a Single Pole RCD!

An RCD monitors the current in both phase (live) and neutral, and if it detects any imbalance of 30mA or more, disconnects the supply in no more than 40 milliseconds. That is vastly quicker than any type of fuse/mcb & is what saves lives.

It will NOT detect reversed polarity - which may or may not cause damage to your electrical system, but can easily be corrected by making yourself a simple "reverser" using male & female blue 16A fittings, with the linking cable crossed over at one end.

I have carried one of these for years & used it many times, especially in Italy, where the natives have a somewhat casual attitude to electrics.

Cb.
 
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ChesterB said:
There is NO SUCH THING as a Single Pole RCD!

An RCD monitors the current in both phase (live) and neutral, and if it detects any imbalance of 30mA or more, disconnects the supply in no more than 40 milliseconds. That is vastly quicker than any type of fuse/mcb & is what saves lives.

It will NOT detect reversed polarity - which may or may not cause damage to your electrical system, but can easily be corrected by making yourself a simple "reverser" using male & female blue 16A fittings, with the linking cable crossed over at one end.

I have carried one of these for years & used it many times, especially in Italy, where the natives have a somewhat casual attitude to electrics.

Cb.
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Not true. Yes an RCD may monitor the current in both wires but a single pole one (SP) only disconnects one connection and if the polarity is reversed it disconnects the wrong one. A double pole one will disconnect both connections.
This one is single pole (SP)
2CDBC86D-C0B4-4AA0-B4C6-F8F8FD10ED13.jpeg

and this one is dual pole (DP)
90B98667-0C41-461D-92AD-B66F31943D15.jpeg
 
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ChesterB said:
There is NO SUCH THING as a Single Pole RCD!
Click to expand...
This is a Single Pole RCBO. It is a single-pole RCD combined with a single-pole MCB. This can be fitted in UK domestic circuits, and it is vital that the live and neutral are not interchanged. They should not be fitted to mobile units like motorhomes and caravans, where there is the distinct possibility that incoming live and neutral can be interchanged (ie 'reverse polarity').

It's a case of, just when you think you've made it idiot-proof, somebody invents a better idiot.
 
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