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A case of crossed wires? A shocking situation! 

WiresIn 2014, a member reported that when in Brittany he found that about a third of the shore supply in marinas had reverse polarity.

He said the French were disinterested but felt that members should be made aware of the dangers.

So what is reverse polarity, why does it matter, how can you tell and what can you do about it?

Anyone who has wired a plug in the UK knows the importance of connecting the right wire to the right terminal and that brown insulation is used for the live wire, blue for the neutral wire and yellow/green insulation is used for the earth wire.

Furthermore a UK plug will only go into a UK socket one way; the reason for this is to maintain the correct polarity. If for some reason the live and neutral conductor wires are reversed then a ‘reverse polarity’ condition is produced.

Electrical safety

Everyone who has been abroad with an electrical gadget (hairdryer, chargers etc.) will undoubtedly have also taken an adaptor so that they can plug into the continental power supply.

You may well have noticed that many adaptors can be plugged in either way round; it is possible therefore to get the polarity right or wrong! As far as operation of our electrical appliances is concerned, most are unaffected by reverse polarity.

The reason it matters concerns electrical safety and the domestic wiring conventions used in the UK and throughout mainland Europe.

In the UK, we mostly use single-pole switches or circuit breakers which ‘switch’ the live supply conductor (brown insulation). This means that when a switch is ‘off’ electricity does not flow to the appliance.

Think about changing a light bulb, assuming a house has been wired correctly, we do this safe in the knowledge than when the light is switched off electrical power does not reach the light bulb.

If the polarity is reversed, the light switch would still switch the light off but the bulb holder would remain live – nasty if you touch the live conductor without realising and I speak from experience!

In Europe the wiring convention is that switches or more commonly circuit breakers for operating lights and sockets are double-pole which means that both the live and neutral conductor supply wires are switched off simultaneously.

Even if you hook up to a reverse polarity supply, power cannot reach an appliance when it ‘switched off’ at the socket.

Manufacturers are required to ensure that new craft that are sold with single phase 240V a.c. installations are fitted with devices that protect against or establish polarity on the craft.

Check before hooking up

But many craft are not supplied with shore power. Some may have 240V a.c. systems fitted in accordance with UK regulations at a later date; some small cruisers including those that cruise dinghies may simply run an extension lead from a shore supply to the boat to plug in a battery charger or electric kettle.

If you are unsure about the supply polarity where you ‘hook up’, check it with a plug-in polarity tester which you can generally buy from DIY stores for under £10; if you have one. It is also a good idea to check that an RCD (Residual Current Device) works properly each time you hook up to reduce the risk of electrocution.

In the UK, the shore power connection lead is normally fitted with a blue three-pin plug conforming to European Standard CEE17.

While continental marinas are changing to this system, there is still no guarantee that the live and neutral connectors have not been reversed and many still use their national plugs.

If you need an adaptor with a continental plug at one end and a CEE17 blue socket at the other to plug into shore power, check the polarity, if it is reversed it may be possible to insert it the other way round to correct it.

It is possible to modify an adaptor to deal with reverse polarity but for good reason it is not legal to sell them so unless you are entirely competent and know what you are doing do not go there!

Stuart Carruthers, RYA Cruising Manager

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