Polarity Changeover


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Intro: When plugging your EHU into random services, it is important (IMO anyway) to make sure the service that is coming into your vehicle is wired correctly.
I am not going to get into discussions about how it doesn't matter in Europe. I believe that the inside of a UK Campervan or Motorhome should be wired (and supplied) with the same convention as a UK House as the 240V devices used within it are the same.

Basically you want to make sure the Live, Neutral and Earth on the incoming EHU match the Live, Neutral and Earth wiring in the vehicle.

I have one of these Testers which is nice (and it also has an RCD function tester to confirm that your RCD works, which is useful to know, especially if you are doing a new build with new untested components)
Advanced RCD Electric Socket Tester Automatic Neutral Live Earth Wire Testing Circuit Polarity Detector Wall Plug Breaker Finder Electric Leakage Test with Voltage Backlight LCD Display
This is a very handy device, but what do you do if you find the incoming supply IS wired wrong? Well, assuming the issue is limited to reversed Live and Neutral, which is the most likely issue, especially in Europe where less care is taken on that due to the way European wiring is done (which is different to the UK, hence why this is important), you can fix the problem either OUTSIDE the vehicle, or INSIDE.

Outside, you can make a little Polarity Crossover Cable with a 16A Plug and a 16A Socket, delibrately switching over Live and Neutral, so you are effectively making two wrongs into a right :D. This works well and I have one of those. Now I believe that while it is perfectly fine to make these yourself, it is actually illegal for anyone to sell them commercially (and maybe even provide them?) as they would be providing a knowingly incorrectly wired product.

Inside, you can get crossover/changeover switches to do the same thing with a flick of a switch, and this is what this post is about :)
There are different styles available. I am going to show the style I installed, which is a DIN Rail mounting, the same that is used in Consumer Units as I like that style and it would kind of blend with my existing Consumer Unit.
This is the Changeover Switch I bought -
125 Amp Changeover Switch with Busbar, Generator / Mains Transfer, Single Phase, Din Rail Mount

This is the Consumer Unit Housing I bought to fit it inside -
Surface-Mounted Small Distribution/Fuse Box/Distribution Box Surface-Mounted

I have an existing 8-way Consumer Unit, but decided against swapping it out for a 12-Way so I can fit all these switches together as the bigger boxes tend to be much bigger all around as well as being quite pricey. So having an 8-way and a 4-way next to each other was neat enough for me (you will see a photo and be able to decide for yourself ;) )

This is how I wired up the Changeover Switch in the CU -

Polarity Changeover
by David, on Flickr
At the top of the switch, you can see the "Mains In" Side has the right colours going in, but on the "Gen In" Side, they have been swapped over.
And the output is at the bottom.
So when the switch is up, it is using the "Mains In" Side as the supply; and when the switch is down, it is using the "Gen In"Side as the supply, which of course is now the same as the Mains In but with the Live and Neutral swapped over :geek:
I am using a WAGO lever conductor to join up the incoming and outgoing Earthes, plus sending earths to the RPIs.

I also added a couple of "RPIs" - or "Reverse Polarity Indicators" to the Box. These are wired to the output of the switch (the blue wire going to Neutral, the brown wire going to Live, and the yellows going to the Earth)
At the left is an Amber light that comes on if the output is reversed (i.e. the Neutral Out is actually Live); and on the right is a Green Light that comes on if the Output is correct. They work this way as there should only be a voltage present between Earth and Live and never between Earth and Neutral.
And of course, if neither light is on, it means there is no supply.
I actually used a pair of 20mm NEON AC Switches rather than buy lights specifically as I had them already. I also wired in a 2.7 Mohm resistor in series with the power in wires to the lights as a safety precuation (not sure if this is mandated at all in the UK, but is a requirement for Yachts in the US, so I thought I would add this in).

And this is the switch fitted next to the existing Consumer Unit

240AC CUs
by David, on Flickr
The existing CU has its own Power Indicator which is handy as well as confirmation that power is being fed in AND it is correct.

As it happens and a slight aside, I have also standardised on Double-Pole MCBs here so when an MCB is turned off, both Live and Neutral are disconnected as a further precaution on EHU supplied Sockets and also the supply to the Multiplus. (the Outlet from the Multiplus I am just using Single Pole MCBs)

As mentioned, other switches are available and even with a changeover switch built in, it is still always worth carrying a plug-in tester as a quick double-check when plugging in to somewhere new.
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Far more easy to have this like me,mains change over with warning led on incoming cable before fuse box.

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