[niggle]

After 6 months of charging our 24kWh Nissan Leaf nearly every night using a genuine Nissan EVSE 3 pin plug 13A charging brick, via a 13A rated extension lead, we suddenly had a near disaster. My wife's keen sense of smell saved us from a serious fire: at 11pm, when we were about to retire to bed, she said she could smell a slight smell of electrical burning. The smell was in the kitchen area of our open plan house, and my wife's nose led her to the corner where the extension lead was plugged in, behind the microwave:

As you can see, the live pin overheated, melting the plug around it. I had to pull the pin out of the wall socket with pliers. The house is less than two years old, there is an MCB on the ring main circuit. The car had been charging for about 45 minutes and was at about 60% when I plugged it in. The extension lead is otherwise fine, I have fitted a heavy duty MK brand plug on it after cutting a few cms off the lead and this plug is only getting vaguely warm. I checked inside the old plug and the live wire was still firmly attached to the plug terminal, the plug was inserted fully and the cable was not under any strain. I have now also installed a surge protector adapter, which has a thermal cutout, between the wall socket and plug.

 

[cah197]

It could also be an issue with the socket causing a poor connection. This can happen if they're old or slightly corroded.

Any reason why you can't install a proper charge point?

 

[husoi]

As above, you should have a wall unit.
make sure you change the socket you will be using for charging to a decent quality, those ones you have are the cheapest in the market and they barely take 10A. Their rating just makes them legal.

Evists should know by now that granny charger should be a last resource method not a day-to-day charging station.

 

[E Geeza]

Glad things got no worse and house occupants ok. Short term, replace the wall socket with a quality replacement, with appropriate checks to the wiring behind.
But mostly sort a dedicated ev charger, as others have already suggested.

 

[Richtrash]

The socket outlet is probably poor quality, fit something like an Mk or BG, put a cheap plug on a 3kW heater and see how hot the plug gets compared to a quality product, the Leaf was probably drawing around 10A so it should have been well within the capability of a quality 13A outlet and plug, I was charging my i3 for over 3 years before I installed a CM 32A charger I scored off EBay.

Another thing that is often overlooked is the actual house wiring, I only found that I only had one ring main when I lifted the floorboards to drop in some additional sockets in my kitchen which then turned into a rewire, I now have 3 ring mains plus separate cooker circuit and the garage has it's own dedicated supply.

I use a laser thermometer if I'm plugging into an unknown socket and monitor for 10-15mins as that should reveal any abnormal heat build up.

 

[Spiny]

As others have said glad everyone is fine.
The cause is probably a poor quality wall socket and possibly the wiring behind it not being clamped properly in the socket. The extension does not not help as the plug on it is thermoplastic, see previous thread, and probably has poor ventilation for the fuse. Use the older style high quality thermosetting (Bakelite!) type from someone like MK

This is why you see comments on here about having a dedicated wallbox, these are simply high power sockets designed for continuous use day in day out. They also contain electronics to detect the car and set the power level. As a nice addition they charge cars faster

 

[Jeremy Harris]

The problem seems to be the near-standard one of the fuse having overheated the L pin in the plug. I'm not at all sure that the cable on that extension lead is up to running at 10 A continuously, either, as it looks a bit on the thin side.

The probable sequence that caused this failure is the L pin of the plug getting hot from the fuse, which then overheats the contacts in the wall outlet and causes them to lose temper, so they are no longer making such good contact. This may then exacerbate the overheating, as the L pin and outlet terminal have to deal with the normal fuse heat plus additional heat from the increased contact resistance.

Although some will say that the fix is to never use the granny charger and never use an extension lead either, the reality is that both can be used OK provided that the outlet is in good condition, any extension lead is suitably rated for at least 10 A continuously and that there is good ventilation around the plugs.

As someone who used a granny lead for around 3 years and over 1000 charges, I can say that it can be adequately safe, but it does need to be done with care, and with regular checks to ensure that nothing is getting a bit too warm. A cheap hand-held IR thermometer is a good investment. They only cost a few pounds, and if you get into the habit of regularly pointing the thing at the plug, after the car has been charging for an hour or so, you should be able to spot any early indications of a sudden temperature rise, that would indicate that there may be a potential problem. I'd also suggest that anyone using a granny lead ensures that the outlet that they are using is both in good condition and a reputable make, and not suffering from any signs of abuse. It's a sad fact that there are some pretty dire electrical fittings on the market, many coming from the Far East, which may well be less well made.

Ask any electrician and you will hear tales of some makes that have poorly constructed terminals etc, and sadly it seems to be these cheaper makes that often get fitted to mass produced houses. I have a personal aversion to the LAP stuff sold by Screwfix, for example, as I've seen far too many fittings with very poor terminals. A few years ago I'd have said the same about MK, but I recently fitted loads of MK stuff and found that it was pretty good, much improved from the last time I used the stuff (which may well have been 20 years ago). One problem seems to be that some of the well known "British" brands switched to overseas manufacture, to reduce costs, and that doesn't always seem to have been a good thing in terms of quality.

 

[niggle]

Thanks all. Yes I will replace the wall socket with a quality one, probably an MK. Seems odd that it happened when it did, I frequently felt the plug to see if it was getting hot and it never got above luke warm. As I said the house was built less than two years ago so the wiring should be perfect, but as suggested maybe not fitted with the highest grade sockets. Re getting a 'proper' wall charger, this was the plan but ill health leading to lack of work/income had interrupted that, though happily I'm now much better and back in work, first pay day is Friday.

 

[husoi]

You would apply for an OLEV grant so the charger will be free

 

[Matthew Knott]

Couldn't someone make a 13 amp fuse with an integrated thermal fuse?

 

[mikeselectricstuff]

I have now also installed a surge protector adapter, which has a thermal cutout, between the wall socket and plug.

Thats probably not a great idea, as every additional connection is a potential point of failure.

 

[freddym]

Whilst apologists for BS1363 will blame a poor socket or a Chinese plug or operator error etc, the statistical reality is that failures of BS1363 plugs, operating at RATED loads of 10 amps are very common.

If one has to use a "13A" plug/socket combination to charge an EV, then a recent post by JH did make the very good point that use of well ventilated thermoset plug material was once more common than thermosplastic.

MK make a 646 plug in Urea Formaldehyde thermoset material which might be an option to give the plug better temperature capability, up to in excess of 100degC, without plug melting, fire, general failure etc as seen here.

MK646 plug image - Google Search:

 

[niggle]

Extension cable labelling:

 

[Jeremy Harris]

1.25mm² PVC flexible cable is rated at about 13 A continuous, but as the plug that's failed has screw terminals, I wonder if these were tight?

A loose screw terminal is a pretty sure fire way to get overheating, and is one of my biggest gripes with some cheaper makes of fittings. Some outlets barely have enough capacity in the screw terminals to get two 2.5mm² wires in, and some seem to use steel screws in a brass terminal, which isn't (IMHO) a very sensible idea.

FWIW, my extension lead that I use for occasional charging is made up from 2.5mm² H07RN-F cable.

 

[DBMandrake]

The problem seems to be the near-standard one of the fuse having overheated the L pin in the plug. I'm not at all sure that the cable on that extension lead is up to running at 10 A continuously, either, as it looks a bit on the thin side.

I was surprised to see so many people so quick to blame the socket in the wall when from the photo the triggering cause of the problem is clearly the fuse holder in the plug overheating, a very common problem, so thanks for pointing it out.

Of course as you say the socket will now be damaged from overheating as well and must be replaced - personally I would put some tape over those sockets and not use them until they are replaced.

I charged for over 6 months using an extension lead as well, and although it was fine at first (the plastic of the plug cool to touch and the pin just warm when the plug was removed after an hour of charging) towards the end of that 6 months I started to notice the plug on the extension lead getting warmer - now I could feel warmth on the plastic top of the plug towards the end of a charge and the Live pin would be bordering on "hot" after a few hours charging. (At a guess maybe 40-50C) The Neutral pin was still cold.

I removed and refitted the fuse a couple of times turning it around as well to try to improve the contact and that fixed it again for a while - clearly a bit of oxidation between the fuse and the contact occurs over time increasing the resistance, and this susceptibility of the fuse socket to develop a high resistance connection over time seems to be a design flaw of all British 3 pin BS 1363 plugs due to the inclusion of a fuse.

I come from NZ where plugs do not have fuses in them and fuses are mandated in the chassis of equipment instead, (and from memory ring main circuits are not used - which is the main reason British plugs need their own fuse, due to the high current breaker supplying a ring) and I don't ever recall seeing plugs melting down in this way despite high power electric heaters being commonly used. I don't even remember noticing the pins getting hot.

To the original poster - if at all possible get yourself a dedicated EV charge point installed, it's definitely worth it. Not only is it much safer, (as you have discovered) your car will charge faster as well and it will be a lot more convenient to plug in and unplug. I couldn't go back to a granny charger and extension lead now - except in an emergency!

 

[niggle]

The new plug is an MK 655 Toughplug:

 

[DBMandrake]

The new plug is an MK 655 Toughplug:

While some plugs are better quality than others and may last longer, the fundamental issue is that all BS 1363 plugs have fuses with spring loaded contacts which add two extra contact points where excess resistance can develop.

A combination of heat cycling of the contacts and oxidation will inevitably cause the resistance to go up over time until the plug can no longer sustain 10 amps continuous without overheating. It's a matter of when not if.

A dedicated EV charge point is totally different - the Type 1 or Type 2 connector on the car is far more rugged with contacts specifically designed to run at full power for hours on end, there is no fuse holder to heat up and there is a direct run back to a dedicated circuit at the consumer unit, so it is not placing stress on the ring circuits in the house either. It's definitely the way to go.

 

[proddick]

I am relieved for you that nothing more serious occured. I had a similar experience a few years ago using the Ampera granny at 10A directly into a garage socket at a rented house. It was replaced under warranty.

I do hope other people thinking of using indoor sockets and extension leads see your photos and take note.

For regular charging, If people do not want the cost or inconvenience of a proper charging point, then IMO the minimum requirement is a dedicated, external, weatherproof 13A socket.

I do occasional granny charging using a high quality (not coiled) RCD protected extension lead at family and friends. As I can't reduce current in Zoe I only do this if they have an external or garage socket. I won't normally plug into an inside socket and would certainly avoid high use circuits like a kitchen

 

[niggle]

Actually it is an old plug from a mini grinder I bought in the 1990s, cannot be sure what the material is, but the white base is hard/rigid whilst the orange cover is flexible.

A wallbox charger installation would not be free as a) we will need an external fuse box fitting and b) the parking place is at the end of a 10m long garden. Quotes were around £375 or more with the government grant deducted.

The extension lead is fully unwound and the socket end with EVSE plugged in is inside a dry shed. It is going to be a few weeks until we can pay for a wall charger but I will get the ball rolling on that now. Meanwhile I will do everything I can to mitigate risk with the current set-up. So what is the consensus re the surge protector? I thought the built in thermal cut-out was a good thing but as mentioned it does add to the amount of contact points that might cause a problem.

 

[mikeselectricstuff]

So what is the consensus re the surge protector? I thought the built in thermal cut-out was a good thing but as mentioned it does add to the amount of contact points that might cause a problem.

What is the cut-out actually doing? - it's possible that it only protects the surge protection device ( which can fail to a resistive state after a surge) and doesn't actually isolate the load.