3kw comet kiln-plug socket renewed 3 times...

[Archibald Tarquin Blenkinsopp]

Correct, I misunderstood when reading the original.

The problem should be pretty damned obvious though to anyone with a basic idea of electrical work.

Socket burnt out means nothing until inspection, it may simply be a loose cable.

It could be a cheap nasty socket with a sliver of bent brass carrying the 13A. BS marks seem to get onto anything with square pins these days.

Current information summary, socket burnt, replaced by "professional"

Went again, Ditto

Went again, overheating, Electrician baffled

1. Inspection of the defective items should be more than enough to indicate the reasons for the problem.

2, Instead of being "baffled" if the "electrician" measured the current drawn, then it would remove one item of uncertainty.

Personally I would suggest that the major problem is the choice of electrician.

AB

[Archibald Tarquin Blenkinsopp]

Only if you buy Cheap.

The type of socket wasn't stated.

BS1363-2:1995 requires for double socket outlets that both socket outlets have loads applied via test plugs, 1 test plug having a load of 14 amps whilst the other has a load of 6 amps, making a total load of 20 amps on the cable supplying the double socket outlet. The double socket outlet is then subjected to this loading for a minimum continuous period of 4 hours or longer until stability is reached with a maximum duration of 8 hours (stability being taken as less than 1 degC rise within 1 h). The test is passed if neither the terminals / terminations, nor the accessible external surface, increase in temperature by more than 52 degC.

AB

[Dave Plowman (News)]

I've got a 3Kw one here as a standby. Is pretty old, though. Made of steel rather than plastic.

[Dave Plowman (News)]

Those original MK surface mount 13 amp sockets (and the matching plug) used to cook too. As anyone who's removed them when re-wiring will have found. Usually plenty scorch marks.

[Dave Plowman (News)]

A double socket with two plugs taking a total 20 amps might well run cooler than a single at 13 amps. More 'air' around it.

[tabbypurr]

You've not done much looking then.

[tabbypurr]

you're missing the point. They deteriorate over time.

NT

[alan_m]

This will be a one off laboratory test and not necessarily representative of the equivalent same test (operation of a kiln) repeated over regular period over years.

It's much like the mpg figures that car manufactures publish but then in small print tell you that they are not real world figures. And, just look how clean diesel cars are!

An increase of 52C from an ambient of, say, 20C takes the temperature to

72C. I would expect prolonged use at 72C to degrade the performance in a relatively short time. There may also be a problem of screw terminals and thermal cycling where the temperature regularly changes by 50C.

[alan_m]

Anyone who has done some DIY electrical work and purchased no-name plugs/sockets from the sheds probably knows that they can be vastly inferior to MK branded products. If MK can burn what hope is there for an inferior product?

[Archibald Tarquin Blenkinsopp]

On the face of it yes.

The areas of the socket dissipating power will not be the conductors, they will be the interface or the relatively high resistance between the male and female prongs.

Two plugs will dissipate more than a single unit of twice the current [generally speaking].

AB

[Archibald Tarquin Blenkinsopp]

Not really a problem to diagnose, yellowing of the surrounding area should be enough to take any "competent" electrician out of his bafflement.

My point is, that whatever the hardware in use, if the post is an accurate record, then the electrician was unfit for purpose.

3kW kilns are sold on the basis that they can be supplied via a 13A plug, they are not 3kW on a permanent basis, they are reasonably well insulated anyway.

If the thing was over 3kW even a domestic electrician should be capable of verifying the fact.

AB

[Archibald Tarquin Blenkinsopp]

They can be found, I have a few. 2kW isn't enough for an average room in winter.

3kW are around but can be expensive, the cheaper end of the range are festooned with noisy and sticking fans.

I tend to wonder if the reason that there are not so many is because of the thermal overload/ plastic shell combination.

I have overloads trip farlt often, in obstacle free surroundings. They have a limited trip life too. After half a dozen trip events, the springiness of the trip seems to go, preventing the fan heater working permanently.

I dropped a 250 degree thermal fuse across one, this blew also.

I might have to do some checks to see if a higher rating is practical.

AB

[Andy Burns]

but the test isn't 2x10A, it's 14A+6A

[Archibald Tarquin Blenkinsopp]

You know that "cheapest first" option you get in the listings on Ebay.................................. :-)

I play at PAT testing from time to time, I always strip and examine the failiures, a lot of the cheaper multiway sockets fail due to discolouration. The conductors are not exactly very generous on size or contact area.

For a 3kW heater, I would go MK or a similar known brand.

AB

[NY]

"Archibald Tarquin Blenkinsopp" wrote in message news: [e-mail]...

And ideally hard-wire it, as for a cooker. I've noticed 3-bar electric fire plugs get quite warm, even on 2 bars (2 kW). Given the high current that fires draw, I got into the habit of checking the plug every so often. On one occasion I found that the neutral wire was down to just a few strands and the insulation had melted so evidently that bit of narrower wire had got rather hot. Of course if you cut that bit of wire off and start afresh, you also have to do the other two wires to shorten them correspondingly.

When my oven stopped working, I removed it (the oven was separate from the gas hob above it) and was surprised to see that the "Cooker" switch on the wall simply switched a pair of 3-pin sockets. The oven was plugged into one and the lighting mechanism for the gas hob went into the other. I'd expected the oven to be hard-wired and that I'd have to do battle with ring-main grade cable. As it is, it was just the 13A fuse that had blown so it was a quick repair - the longest thing was working out how to unscrew and slide the oven out of the worktop/cupboards into which it had been fitted by the builders.

[Archibald Tarquin Blenkinsopp]

From my experience, with good quality kit terminated correctly, 13A isn't a problem on a domestic socket.

Any loose connection, or even crud on the pins of a plug will raise the resistance to the point where damage to conductors occur's

Indeed some plugs seem to do well where the point of contact to the fuse is merely at three spots stamped out of a sheet of copper or brass.

One dodgy connection and overheating can and does occur. The plus point is that it does not take a degree in thermodtnamics to pinpoint the source.

AB

[Dave Plowman (News)]

I didn't say it was.

Heating of a connector happens because of resistance. The same resistance will result in more heat with more current. Likely balancing things out in a twin type with the same total current.

[newshound]

Oops!

[Terry Casey]

The contact spring tension has to be a compremise between insertion force versus contact force so why can't someone devise a switched 13A socket which uses a cam arrangement to increase the contact force, reducing resistance, when the switch is moved to the on position?

(Personally, I prefer unswitched sockets but even when you find them these days, they are more expensive than the switched version!)

[dennis]

I would suggest that if you are fitting a socket like that a 32A one might be better as they cost about the same.