Mains extension lead diameter

The thicker the better MR H. Voltage will drop over long distances. When I was a ‘hook up ‘ caravanner I bought a 50 metre yellow cable which I still have - lovely and thick capable of carrying the voltage over that length. ( for sale🤣)  I also still have my 25 metre orange lead which is almost a museum piece now although I do use it once in a blue moon when I take the ‘van up to my daughters farm in Scotland. Certainly running the cable in straight lines will help. Never leave it coiled  as you end up with a big resister! 

I'd say go for the 2.5 as the 1.5 has a lower current carrying capacity and will likely suffer greater voltage drop.

If you are using Club sites then all pitches are generally within 25mtr of the electrical bollard, as for cable size you need 2.5mm.

To be honest it would be better and a lot safer left looking untidy, the plugs and sockets are IP44 rated (splash Proof ) so not much good lay in a pool of water or wet grass and it does state in the C&MC rules " joints and splitters " cannot be used 

Of course, if the plug and socket between the two cables is supported off the ground then the IP rating is appropriate.  After all, there are tens of thousands of plugs stuck into matching sockets on bollards throughout the country.

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Likewise 'Mr H', I also run mine parallel to pitch and right angles where possible, a bit OTT maybe but it looks right 

Long runs always benefit with less voltage drop the bigger the cross sectional area, so agree with 2.5mm.

Thank you  for your responses. I would use the additional cable mainly in France where the pitches we use are much larger than our standard ones. For some reason, the water, electricity and waste points are often not located together. So this can force you into an unusual caravan location. However, the first time I experienced this was at the club site near Folkstone where the cable had to go diagonally underneath the caravan to reach. This was a possible trip hazard.

Following your advice I will buy a 10m x 2.5mm cable.

Thanks again

If you are joining cables I would strongly recommend doing the job properly and using IP67 connecters, a bit pricey but a one off purchase and peace of mind.They also connect to standard plugs/sockets.

Socket

Plug