Adding a thermal cutout to a 13amp plug?

[John Rumm]

You can get "one shot" thermal fuses that are quite small for this kind of application:

[Robin]

Sounds like hard work compared with a variation on the Jesus lead: two

13A plugs wired onto 2 short lenghts of 1.5mm flex connected in a junction box to 10m (or whatever length you think you need) of 2.5mm flex to a trailing socket into which you plug your "granny lead". Better if the plug tops were fixed to a bar so they could not be removed individually but I can't recall if BS1363 mandates the spacing of the contacts in 2 gang sockets.

JOOI are a plug and socket to make up an extension at the other end exorbitantly expensive or is there some other barrier to that?

[ARW]

and

hotter than the 18 year old secretary in her 12" skirt.

[Chris Bacon]

As you probably know, the hot bit can be felt, sometimes even painfully.

Recently I've been doing a bit of welding with my very old buzz box. Downstairs ring circuit connection to 25m extension lead to welder. Using 3.2mm electrodes on about 125A setting, likely the scale's a bit off either way though. For some reason the fuse in the extension lead's plug has blown three or four times, but never the one in the welder's plug. Not sure why. All connections seem good. The thermal fuse in the (fully unwound) extension cable's middle tripped once too, but it was in the hot sun. Oh well.

[jon]

That's a hot socket, that could also be damp.

[Max Demian]

Portable 3kW fan heaters are still available.

[charles]

Some of the probles are caused by the "socket protectors" that people plug in to stop children inserting things in the sockets. Some of them have oversize 'pins'. I had to replace one of our village hall sockets which kept overheating due to this cause.

[ARW]

At my age my best chance is her mother.

And she is probably younger than me.

[jon]

With me, it would be great-grandmother and she would have to be very helpful.

[Andrew]

For heavy loads I always use the MK plugs where you wrap the cable around a pillar and the fastener clamps down with a greater contact area.

[Tim+]

I do John, but I can?t always know the quality of the socket that I?m using if I?m away from home.

But the thermostat will be cycling regularly so that?s not really comparable to 10 amps continuously for 12 hours say.

Tim

[Tim+]

Thanks. I might try that. Something self resetting would be nice but maybe that?s to much to fit into a standard plug.

Tim

[John Rumm]

There are self resetting ones - but they tend to be bigger. I suppose you could piggy back something onto the back of a plug.

[John Rumm]

So the diy solution, have a box of good quality single and double sockets in the car, and do a free upgrade for the owner each time you find a suspect one :-)

Or as a quick fix you can also help matters by inserting and removing the plug a few times to help wipe the contacts a bit.

The main danger are shagged sockets where they no longer have the spring tension in the contacts to make a solid contact - whether through use or abuse.

If its a reheat following a bath, then it will likely be on solid for a a couple of hours[1] - that ought to get the plug to its "final" temperature whatever that might be.

[1] Say 100L with a rise from 10 to 60 degrees, and a 3kW heater - that's 100 x 50 x 4200 / 3000 / 3600 hours or ~2 hours

[John Rumm]

+1

BS1363 is very specific about pin dimensions and tolerances, also things like chamfer angles so that the pin makes good contact, but also so that it can't damage or dislodge the terminals on insertion.

Most of those socket protector things don't even come close on spec, and it's not helped by them usually being made from soft thermoplastics that are more likely to snag in the first place.

[Tim+]

But surely if it?s not *in* the plug next to the live terminal, it?s not going to offer much protection?

Tim

[John Rumm]

You would just need to adjust the sensitivity to account for the thermal resistance of whatever is between your sensor and the hot bit. So if you decide that 70 degrees at the terminal is the limit, that may translate to 45 degrees at the place you can measure.

(failing that you run a K style thermocouple into plug and have a microcontroller monitor it, while also controlling a contactor so you can disconnect the load if required)

[Jeff Layman]

Are all fuses created equal? I don't mean the difference between fast and slow blow, but within a type. I'd always assumed that if BS 1362 was on the fuse, it met a standard. But there are fakes around:

Perhaps the OP had one of these counterfeit fuses.

[Brian Gaff (Sofa]

I don't see how that can work given the mass in the materials present.I've seen plugs melt and sockets melt at apparently just warm temperatures. Seems like those polypropylene ones are particularly prone to this. Surely a current device is the best thing, so the button pops when you are getting near to the current which might warm up the contacts in either part. Brian

[Brian Gaff (Sofa]

There used to be extension cables with a simple current measuring breaker in the lead, normally about a couple of feet from the plug and when the load exceeded the current, pop goes the button. Can be a trifle irritating on devices with a high start up current though.

Brian