WHAT EXACTLY IS REVERSE POLARITY AND WHY IS IT POTENTIALLY SO DANGEROUS?
WHAT ARE WE TALKING ABOUT?
SHORE POWER POST
SHORE POWER LEAD
ELECTRIC HOOK-UP POST
ELECTRIC HOOK-UP LEAD
In brief it's a situation caused by human error when connecting the 220v/240v mains brown wire to where the blue neutral wire should attach within the socket. This can happen in the pontoon fitting, campsite hookup or the leads that plugs into them.
The PCE plug is used in the UK, Europe and most of the world for marine use, caravans, motor homes and camping to name a few. Therefore the potential for it to be wired in reverse are statistically very high and so are the dangers connected with it! When visiting the many marinas and campsites both in the UK and abroad you would expect to find a reliable, safe power supply which is essential for welfare on the boat, vehicle or in a tent.
However it is also quite normal for owners to perform DIY emergency repairs when damage has happened to their shore power leads or hookup power supply leads.
If unaware of the wiring protocol or marking nomenclature, then reversing the wire connections in poor visibility would be a real probability. So unless tested afterwards by a qualified electrician, it could be endangering the lives of everybody on the boat, vehicle or tent. Unfortunately this is not mere speculation it's a fact that could cost lives and be responsible for expensive repairs over time.
WHY IS IT DANGEROUS?
ALL mains devices are designed to turn off the live (brown wire) side of the switch and NOT the neutral (blue wire). However if these wires are reversed on the mains input cable, every 240v device will be a potential point of danger.
UK wall sockets, marine, vehicular or otherwise are designed to switch the live wire off. In a reverse polarity situation these will now be live all the time and the neutral will be switched off, this allows the earth to become the return path should a fault happen. For example the humble toaster may now become constantly live, so by touching the heater element to clear it, despite turning it off at the switch, could be fatal. Another is the hot water heater you switched off at the plug, it will still be live all the time. Should a fault occur, which is common with marine calorifiers (water tanks) the heater element may now come into contact with the water within the tank including the connected earth bonding system. You may not receive a large shock, however the leakage current to the bonding system (0volts) will erode the anodes rapidly causing long term damage to the engine and drive components.
WHAT ARE THE DANGERS ON A BOAT OR CAMPSITE?
If you were to switch off the 240v breaker for a circuit so you or an engineer could work on the 240v main electrics, you may assume it would be safe. However if the neutral wire was reversed it would now become un-switched live and if touched whilst holding any bonded metal object (0v, engine, seacock etc) you would receive a serious shock.
The ship's negative is connected to the 240v earthing system so any metal part touched ie. engine, toaster, kettle, shroud, etc. will complete the circuit with you in between. There are many cases where the polarity has been wrong for years without the owner knowing and it only takes one piece of 240v equipment to fail and the consequences could be devastating.
On boats with euro plugs fitted (round prongs) the polarity issue can be more confusing because the plug can go in the socket two ways, plus euro sockets don’t have an off switch.