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PostPosted: Sat Aug 04, 2018 10:37 am 
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So, pottery kiln.
It's a relatively small one, only 6"x6"x9" chamber heated by kanthal elements, rated at 3kw.
The lead from it is approx a meter with a 13A plug & fuse.
I'm plugging that into an extension cable, apprx 7m, into the kitchen and a normal 13a socket.

The house has, the usual RCD at main board.
Kiln had new elements recently, all connections tightened and checked.

Normally I have it on a very low setting for a couple of hours, then crank it up over 6 or 7 hours.
Control is via a sunvic 'simmerstat' or 'energy regulator' - Dial 0-5 dial which controls how long the elements come on for.


Works well, but, the plug on the kiln lead gets hot.
Was like that before and after the recent service/new elements.
I think I was ok with that, but I've also noticed when I unplug after a firing, the plug pins are really hot - like I screamed when I touched one !!
The wife also complained that she could smell a plastic/burning smell towards the end of the firing.

So, question is.... how much of a problem is this?
Is there anything I can do to minimise the heat accumulation like seperate circuit/spur ?

I'm not an electrician, but can usually understand concepts if explained!

And guidance appreciate :)


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PostPosted: Sat Aug 04, 2018 11:32 am 
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I'd love to have a little test kiln like that, but if it comes fitted with a 3 pin plug then it is designed to be used with one.

I can only speak as an amateur potter and not an electrician, but my first kiln was the same.

I taped a largish (approx 8" x 2") piece of thin aluminium to the back of the plug on mine to (hopefully) act as a sort of heat sink/dissipator. It never blew up or blew a fuse but I was always nervous about it.

As it would only fire to 1200°C I did eventually buy a larger kiln that goes to 1300°C which is 7Kw and has its own dedicated supply and uses Commando plugs (the type of plug used for caravan hook-ups).

Thinking about it, I've never actually felt those to see if they get hot, I will try next time I fire it.

Hopefully an electrician will be able to give you a technical answer.

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PostPosted: Sat Aug 04, 2018 11:41 am 
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Thanks Ajay.

Knowing that I'm not 'unusual' is quite reassuring.
I hadn't thought about the heat sink idea with the plug bring plastic, but thinking about it, no reason that it shouldn't take some heat away - good tip!

Yes im very respectfully of this kiln and my luck to have it.
If I recall, eBay £150? Is a 1965 Cromartie. I dread the day it dies as a new modern one would be between 500 and a grand ! Just for a little box and some elements !

Again, thanks for input :)


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PostPosted: Sat Aug 04, 2018 12:38 pm 
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Your plug should NOT get hot, I assume that as it came from ebay it has "any old plug" fitted.

I would suggest you change the plug to a well known brand such as MK

Also the extension lead, not really a good idea for 3kw.

Ideally you should have another socket installed closer to where the kiln is.

Most electrical fires are caused by overloading, if you must use an extension lead, get one that is rated for 3kw, as most believe it or not are NOT rated for 3kw, you could even make your own with suitable sized cable and well known brand plug and socket, and make it to the required length, as coiled up leads cause fires.

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PostPosted: Sat Aug 04, 2018 4:44 pm 
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Thanks, I've got an mk ordered now.
Will cut the extension down and I guess out mk on that too !?

If problem persists after that, maybe look at getting a sparky to quote for a socket closer.

Thanks


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PostPosted: Sun Aug 05, 2018 1:57 pm 
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A fuse works by the wire inside getting so hot that it melts, so all fuses get hot, however there should be enough material in the plug and socket to dissipate that heat, however when the socket is not fixed to a wall then all heat has to be removed by air around it.

So replace the second plug and socket for an unfused type and they will not get hot, be it a 15 amp or 16 amp plug and socket it does not matter, caravan type likely best option, the plug in house still has a fuse, and simply no need for two.


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PostPosted: Sun Aug 05, 2018 2:38 pm 
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My miss-spent middle age means I've got quite a bit of experience running 3kw appliances from a domestic mains plug & socket, though only for several hours at a time. They will (as ericmark says) always get warm, but they should not get hot as such, that is a sign of something not quite right.

Both the plug and socket need to be of very high quality to run near their maximum (official) current for long duration, cheap ones will either perform more poorly and/or will degrade more quickly; when that begins more heat is generated, so a downward spiral has begun. If domestic sockets need to be used, I too would go for the MK brand, and not plug anything else into the same socket 'even' if it is a double one.

Similarly, most extension leads aren't really up to it. For those occasions where they can't reasonably be avoided, I made my own using a metal MK socket & back-box (plus cable restraints and a somewhat over-specified flex size), but even then it increases the number of weak links in the chain. So preferably as suggested above, I would get a dedicated socket fitted; you could consider 16amp industrial plugs (e.g. cee-form or commando) or maybe a permanently wired flex outlet if the kiln is never moved, both with due consideration to fuse protection and electrical isolation as necessary.

(BTW There are similar questions asked from time to time in relation to big welders, if that helps you dig around with the forum search for additional ideas).

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PostPosted: Sun Aug 05, 2018 2:46 pm 
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At 3kW, as Kev says above you really want a dedicated circuit for it.
I've never seen anything rated at 3kW, run off a 13A socket, and left on for more than a few minutes at a time, which hasn't caused heat degradation of the plug or socket over a period of time.
As already said, poor quality plugs and sockets, sockets which have already been overheated, and extension leads will all add to the problem.


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