Jump to content

And now for something completely diferent....

Recommended Posts

Earlier this year, I got myself a 'race truck', a Mk6 Transit.     It's equipped with domestic three pin plugs inside, that work when you plug a cable into the side if the van is connected to the mains, as you would on an 'electric' pitch on a camp site.     I do this at home while it's parked up, and run a battery conditioner on it to stop the battery running down.

I've found that after I plug the cable in there's no power!   Because, the other end is plugged into a circuit protected by a "residual earth current relay", supposed to be the best protection from injury when working outside.   It's simple to just flip the circuit breaker on this back to normal, whereupon it all works, but why does it break?   Should I have any concerns, or be reassured that the device is doing its job?


Link to post
Share on other sites

Hi John, yes you need to be concerned and you need to get advice/help from an electrician if you are not sure what you are doing? I'm not local to you, if I was I would be happy to help out. I met you at Donington Park a couple of years back now. Good luck with the rebuild and hope to see you out on track again soon/ish. Atb



Link to post
Share on other sites

Are you saying it “trips” every time power is removed from the system? I think some RCD devices do have to be reset every time they are powered up?

Certainly one of the plug-in ones I have for my garden extension leads does, whereas the other one I have (different make) does not and only trips if I hit the test button (or cut my cable :ninja:)

Link to post
Share on other sites

if it happens when you plug the lead into the van it could be connecting the live and the earth before connecting the neutral. if you have a battery conditioner on board, that probably has a switched mode PSU then it will have capacitors between the  life, neutral and earth. If all three are not connected you could get flow from the live thru to the earth. The RCD would see this as an a fault. It is measuring current from the live to neutral, if there is a difference (30ma for 30mS) it will trip. The current flow will be thru the noise suppression capacitor on the psu.

I would have a close look at the terminals in the socket on the van and on the lead for corrosion. If  there is any then as you plug it in not all the pins will connect at the same time.

Have you got an isolator in the van? Usually there is a MCB or RCD installed. if so trip this to remove any load at the van end and then plug in and see if the house RCD trips.


(I have a campervan with similar setup, had to change the van male socket due to corrosion).


Link to post
Share on other sites

My thanks to all!    Again, the Common Room of Sideways U. come up with knowledgable advice, albeit a little conflicting!

Rog, are your concerns reflected in the later comments?

Nick and mp,   The cable I use is brand new, and iin case you're not familiar (you must be, mp) it's a hefty three pin cable, with enormous, cylindrical, industrial three-pins connectors on each end.   I have an adaptor for one end that allows me to plug it into the ordinary three pin socket.

An isolator in the van?    In the workshop in the back are these:



This doesn't trip - it's the one on my garage wall that does!


Edited by JohnD
Link to post
Share on other sites

As Mike said.

An RCD compares the current being drawn from live, with the current returning through the neutral.  If there is a difference the lost current must be flowing to earth and more than 30mA difference will trip-out a normal RCD.   There are different ranges though - you can also get 10mA RCDs for extra protection or 100mA RCDs for circuits where 'nuisance tripping'  is a problem. 

The fact that you can re-set your garage RDC after which everything works OK, shows that there is no basic wiring fault, else it would keep tripping,  and that this is probably just a nuisance trip due to inrush current - again as Mike said.  Anything with a filter capacitor in it can cause that.  

The switch panel in the photo looks a bit long in the tooth but I think the 25A switch on the left could be an RCBO as it has a test button. (An RCBO combines the function of an RCD and an MCB circuit breaker for overload currents).  The fact that this doesn't trip means either the inrush current is occurring somewhere in the circuit prior to it or perhaps it has a different range to the RCD in the garage.   It also may be stuck - you need to exercise RCDs periodically by using the test button to keep them free. 

The switch on the right is just a 16A MCB and the middle one looks to be the main contactor.

It might be worth considering upgrading the panel with more modern switchery though, as you really don't know the state of those... 

Link to post
Share on other sites

The circuit I use that trips the RCD, was fitted by a qualified electrician in my garage extention when it was built, fifteen years ago (?).  As far as I know it is earthed to water pipes that run through the original garage, to supply a "Belfast" sink in there.

Link to post
Share on other sites

Hi John,

I think you are confusing earth bonding with your supplier's provided earthing arrangement, which is what I was referring to.

Have a look at BS 7671:2018 – Section 708 (caravan/camping parks) And Section 721 (caravan and motor caravans) it will give you an idea on the, often overlooked, issue with caravans/motorhomes etc. hooked up on driveways potentially using PME arrangements.

I'm not suggesting that this is causing your issue here, but it might inform you(and other's) about safety concerns. 

The reason it trips (latched or non-latched which I think Nick might be referring to) doesn't really matter.

When were the van electrics last inspected/tested?

When were your house electrics last tested? 

Get it checked for peace of mind and that can't be done remotely hence my original reply.




Link to post
Share on other sites

campervan and sites electrics can be a bit tricky...

We stayed in a Spanish camp site a few years ago (2018). It rained and every time you touched the van, standing outside, you got a mild shock. If you were in the van it was ok as you at the same potential  as the rest of the van but different from the ground potential.. Once the rain stopped and everything dried  it was all ok.. To stop the mild shock you had to make a clean jump from the van to the ground.... This is not a recommend approach  in any of the IEE's regulations......
I think the problem was that the earth/ground connection was missing somewhere on the supply and when everything got wet there was leakage between the neutral and ground connection to the van supply point. Ideally the neutral and earth should be at the same potential but not on this site... We moved the van plugged into a different supply point and all was ok. 
Later when I looked at reviews of the site it seemed to be a common problem when the site was wet! 

As Roger says having a site test and is a really good idea to keep everything safe.


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Create New...