EV charging

It's all bollocks. The 13A ring main is very carefully specified and is very safe.

It has far fewer problems than any other system

It is rather dependent on how they are made. In theory there is slightly more surface area but if the sockets are just curve brass sheet its crap,.

"Assume maximal contact along the outer cylinder" That is the point I was wondering about.

The (round) pins have to be less than an interference fit into its socket, or you would never manage to plug or unplug it.

Hence assuming the pin is 7.06mm in diameter, the socket into which it fits must be larger than that. The actual surface area of contact is then difficult to quantify. On a 13 amp plug, there is a wiping contact which is pressed against the sides of the pin. I don't believe it covers the full surface area of the (non-sleeved) pin

I think this is really the point. UK chose square (rectangular) pins for a reason... It is extremely hard to get a round socket to work reliably after a hundred pluggings..but a spring leaf contact works pretty well.

Unless they've been deformed by the nylon 'safety' plugs.

Well, in the 1940s when they were designing these things, what loads did they have that needed to take power continuously? Even electric fires would have had a bimetallic thermostat. The one thing that was a continuous load, the hot water cylinder, was hardwired.

Perhaps with 80 years of hindsight they could have chosen differently. But 13A plugs were fine for most of those 80 years.

Theo

Um, only fan heaters. We never had a radiant heater with a stat of any kind. You just selected 1, 2 or 3 bars.

Seen immersion heaters connected to a three (square) pin plug. Obviously not a good idea but it did happen.

Tim

I found this about 13A plugs and sockets: "Key details regarding the contact area: Plug Pins: The live and neutral pins are 6.35mm wide, 4mm thick, and

I can't find the equivalent information for 15A round-pin plugs. But the live and neutral pins are about 7mm in diameter and mate with close-fitting cylindrical sockets over a length of (I estimate) 10mm. This gives a potential contact area of around 200 mm^2 per pin.

But they're not. The cylindrical sockets have two longitudinal cuts along part of their length, with the strip between them pushed in a bit

- effectively making the pin an interference fit in the socket.

BS 546, it was updated last year and does now include sleeved pins.

The contact area is nothing like that, which is why these things get to an elevated temperature.

Even the materials they are made of, can be an issue. The metal selected for the job. Typically, you need different characteristics, that might be satisfied by plating up a base metal. Something has to maintain the K constant of the spring that helps make the contact reliable. Then you need metals that are particularly conductive.

You can look at the evolution a bit here, and see how shaped female bits attempt to provide a reliable contact over a relatively small area. Like 11 and 13.

Paul

I've an old fan heater fitted with a 13a plug (and fuse) of a vintage that didn't have sleeved pins. it also uses 2.5mm cable and doesn't run noticably warmer than ambient at 3KW. I've found more modern plugs always run hot at

In my testing of plugs and sockets for a home-made extension cable for temporary EV charging I found the best 13A plug to be an old MK, the type with the terminals where you wrap the cable around a threaded post and clamp down with a nut with captive washer.

nib

The cable clamps on many modern 13A plugs struggle with 3-core 18 awg cable (i.e sub 1mm^2) let alone 2.5mm^2.

Yep, these?

do note that MK are now made in China!

I bought a 13A plug and trailing socket, both described on CEF website as "Rubber"

which both turned out to be hard thermoplastic, no better than what was on offer in B&Q :-(

:(

There is nothing wrong with Chinese manufacturing *IF IT'S DONE TO SPEC*.

I buy a LOT of s*it from china.

Some of it is total crap, but mostly it isn't