On the UK granny lead box there is a button on the rear where you can set 6,8,10 Amps. It defaults to 10 Amps (~2.3kW).

 

I believe there's a button on the back of the granny lead control unit to step through 12 - 10 - 8A. It's 10A by default in the UK. Plugs can get quite hot with extended use. How hot is worryingly hot, though? I've only noticed hot plugs when using an extension lead and I'm not sure whether that was the plug or a dicky 13A socket. Your charging losses might be even greater at 8A, though.

 

Thank you, I've found it now - you have to press and hold the little black button in the back.

I will try out 6A and 8A to see if it makes any difference.

 

HAVE YOU HAD ANY JOY WITH YOUR CHARGER XIRO21

 

The "how hot is too hot?" question is a good one. The maximum allowable internal temperature of the plug will be around 70°C, as that's the max temperature for most PVC cables. The external temperature when the inside is this hot will be a lot lower, and I'd start to get worried if the surface temperature reached about 40°C. 40°C is roughly the temperature of a hot shower, so if the surface of the plug is around that temperature then I'd take action.

Perhaps most importantly, the temperature of the plug should not get anywhere near that hot if the plug and socket are in good condition. If any plug is getting much over 30°C at its surface then the thing to do is not to turn down the current, it's to stop using it and find out where that heat is coming from. First thing to check is the terminations inside the socket (after safely isolating the power), making sure the wires are fully home and that the screws are torqued up correctly. The torque required on socket terminal screws is higher than some may think, typically around 2 Nm.

 

i had this found the extension cable was too thin to carry a high load for long periods of time, I made a 10m cable with 3x2.5mm rubber flex, heavy duty plug an single trailing socket. the plug no longer gets hot or even warm to the touch.

 

From your description I get the impression you are plugging the "granny" cable into an extension lead. Firstly this lead should be rated for use at 13A load. Many extension leads on the market are rated at less than this. Secondly the lead should be fully uncoiled to prevent it representing an inductive load that will in itself cause the lead to heat up when loaded. The lead should be kept as short as possible. Again as said above check the wiring in the plug, and if possible the socket, to make sure all connections are secure and tight. It might also be worth plugging in to a different 13A socket in case there is a problem with the socket you are using.

 

Good advice, but coiled cables don't have any appreciable inductance, and the current flowing in the line and neutral conductors cancel each others fields out. The problem with coiled cables is that the cable cannot dissipate heat as well, so under a high load the heat builds up in the cables that are touching each other within the coil. The Toughleads extension cable being used is one that is fine for the 10 A current a portable charge point needs, and one that several here (me included) have recommended. That's why I suspect that there may be something awry with the terminations at the socket, or. perhaps, a fault in the granny lead plug, as these leads use 1.5mm² H07RN-F cable that is plenty big enough for a constant 10 A load (it's rated at 15 A).

 

What he said, 100%. It’s nothing to do with inductance whatsoever. Everyone says that but it’s a myth. It’s resistive heat generated which builds up in the reel. When cable is extended, the exact same heat is dissipated, but it’s spread out across the length of the cable.

Back to the OP. I bet the Very hot pin he was referring to was not the one on the actual granny plug itself but the one on the extension lead plug? Also, I bet it was the L pin?
Its very often caused by crap (resistive) connection to the 13A fuse end caps. It can be due to old oxidised fuse caps, or fuse holder clips. Also the fuse holder clips often have inadequate tension onto the actual fuse. What happens then is they can heat up, which then causes even less tension and even more contact resistance and even more heating. Before you know it the plug can self destruct with a kind of thermal runaway.

Another cause of heating pins is lack of contact tension in the wall socket, possibly combined with old oxidised mating surfaces on plug pins and contact clips in the socket. Then add to that gradually self loosening screw terminals and even solder tinned stranded wire ends which is a really big no no, yet often seen. Even an ageing or poor quality 13A fuse can cause heating on its own.

Sadly our so called 13A plug and socket system isn’t great, and often cannot safely handle it’s rated current continuously. This is then made even worse with lots of inferior imported units and a complete lack of proper type approvals or regulation. I’ve seen lots of heat damaged 13A plugs, sockets and adapters etc in my time.
With a bit of TLC they can be made to work ok at full load, but need regular checking and maintenance which they rarely (if ever) get. Peter

 

...even solder tinned stranded wire ends which is a really big no no...

Just out of interest, what's the problem with tinned copper terminations?

I only ask because years ago I had to use a specialised LV PSU (nothing to do with EVs) which ran at around 100A max. It sometimes gave problems, but never the connection block which used tinned copper connections internally. I assume it left the factory this way.

 

Yes, it was the L pin in the extension lead that was very hot. The extension lead is less than a month old so while possible I don't think it is the issue.

I suspect the wall socket is the issue - when I took the plug out it came out too easily. When the kids are at school tomorrow I'm going to check the socket to see if there are any visible signs of damage but I don't think I'll be using that socket again until it's been checked by a qualified professional.

If the socket should be replaced, are there any brands that cope better with the consistent high load?

 

Make sure the 13A fuse is securely held in the clips in the plug. If needed, remove the fuse and pinch the clips together to increase the contact tension. Even though the extension may be brand new, sadly it doesn’t guarantee good quality. There's a lot of quite tacky stuff around, even when new!

Regarding best socket brand, IMHO MK is probably the most trusted make and as good as they get. It’s very possible sometimes to tighten up the socket spring contacts if you know what you’re doing. However, please don’t attempt this yourself, unless you are really experienced and knowledgeable in such things. Peter.

PS. The best way by far is to not use the plug in granny lead at all. Get a properly installed EV charge point If possible.

 

Very likely that the socket has lost some of the tension in the springy brass contacts, something that is often caused by heat from the fuse travelling down the pin of the plug. Over time the contact resistance increases, which makes the socket get warmer around the line pin, and that in turn tends to reduce the force the springy contacts apply, which in turn makes the contact resistance higher, so increasing the heat further.

Burning around the line pin of a plug/socket is a pretty common problem, partly caused by heat from the fuse, partly caused by running loads that are greater than the 10 A continuous current rating of the plug and socket (the 13 A rating in BS1363 is not a continuous one, it's a short duration maximum).

 

Thanks Jeremy. I agree the tough leads extension looks like top quality gear. Peter.

 

Issues with plugs becoming warm can occur with EVs and other higher power equipment such as hot tubs. We created this guide to try and explain the various different causes, and what can be done to reduce the chance of an issue occurring Why does my plug get warm? – Tough Leads

 

Nothing at all wrong with tinned copper conductors, or tinned copper or brass terminations. The problem is if someone decides to solder stranded flexible cable, as this is pretty much a sure fire way to result in a broken conductor, as a consequence of fatigue. It's why crimps, spring or screw clamp terminations must always be used on stranded flex cables, as if soldered the solder will wick up inside, under the insulation, and reduce the ability of the flex to flex, resulting in a fatigue fracture from vibration or flexing.

 

All true, but actually it’s rather more than that. Soldering a multi strand cable end leaves the gaps between the copper conductors filled with a soft and very maleable metal (solder). The solder is in essence virtually a viscous fluid and over time it compresses, flows and exudes. So screws that were initially correctly tightened virtually always become loose. Not because the screws unscrew themselves, but the clamped wire ends slowly squish and move thus leaving no force on the screw end. In electrical approvals institutions such as BEAB and BSI, tinned stranded wire ends in screw terminals is strictly forbidden for this reason. Any product safety inspection using this termination technique is classed as an immediate fail. Crimp on brass ferrules is the way considered acceptable. Peter

 

OK - I see your point - it's a mechanical one.

 

I accept that soldered terminations on flex is not acceptable for several reasons, as already mentioned. However, tinned copper wires are extremely commonplace in flexible cables, and have been in common use for decades. Of course, tin and solder are not necessarily the same thing, and tin plated stranded conductors are absolutely fine in any type of termination, including screw types.

Edited to add:

Just for the avoidance of confusion, this is what I have been referring to as tinned copper stranded conductors (literally just grabbed the first roll of heavy duty flex off the rack and stripped a bit to illustrate this):

 

I accept that soldered terminations on flex is not acceptable for several reasons, as already mentioned. However, tinned copper wires are extremely commonplace in flexible cables, and have been in common use for decades. Of course, tin and solder are not necessarily the same thing, and tin plated stranded conductors are absolutely fine in any type of termination, including screw types.

Edited to add:

Just for the avoidance of confusion, this is what I have been referring to as tinned copper stranded conductors (literally just grabbed the first roll of heavy duty flex off the rack and stripped a bit to illustrate this):

View attachment 146142

100% agree. Individual tinned wire strands, that is fine. I was referring to the entire stranded wire end bundle being soldered (often referred to as dip tinning) to effectively make one solid conductor for screw terminal clamping. That is the very big no no. Peter.

EDIT: For further clarity, I just solder tinned just the N end of this multi stranded cable. Clamp that end into a screw terminal in a plug and it’s sure to come loose over time. It’s a common practice that causes no end of issues.

Cheers Peter.

 

Charging at 6A helped but I think the plug socket just couldn't take the load.

Luckily I've had my 7kw charger installed and don't need to use the granny now.