Immersion Radial circuit

[Owain]

Or use a BS546 15A round-pin plug and socket (shuttered but not interlocked)

Owain

[James Salisbury]

Dear Harry,

1. You say your 3Kw Oven is connected via a plug and socket, may I suggest due to the action of the thermostat that there may be 100% load for the first 5 to 10 minutes as it heats to temperature, but after that the thermostat may be on for say only 10% of the time.

In the case of the domestic immersion heater then then 3Kw load may be presented for several hours.

1. The plug and socket for the oven is probably in a well ventilated space and is so at 20 deg c. The airing cupboard is probably at 30 to 40 deg c, and often items cover the plug and socket.

Regards

James Salisbury

[js.b1]

Oh course, BS546. Much cheaper. Funny how you forget those brown bakelite surface sockets on skirting boards you used to trip over and fly up the hall on the rug covering an optically polished floor only for the magic carpet experience to be brutally terminated by the front door.

15A shuttered is fine, still popular with lighting people re "rather french" fuse at the board (drivel will be along in a minute).

Ambient may still be an issue and it comes down to duty cycle.

[Harry Bloomfield]

James Salisbury was thinking very hard :

Which is long enough to bring a plug and socket up to its maximum temperature - they have very little thermal mass.

and the socket for our 3Kw oven is (unsurprisingly) at the back of the oven - no contest on ambient temperature :-)

[alexander.keys1]

BS1363 (13A square-pin) plugs & sockets are a flawed design, as I've said in a recent post they were designed for cheap mass-production in the war-damaged economy of the 1940's. IME they are fine for loads up to 10A, more than that and the trouble starts. The problems are the socket and fuse contacts, the proportions make it difficult to provide enough pressure over time.

If you need a domestic-type socket for an appliance that draws more than 10A continuously, use 15A round-pin types to BS 546, with a non- switched socket and a seperate switch if needed (the small switches in a socket plate tend to melt and jam if heavily loaded, due to the square plate being originally intended for non-switched sockets only). The tubular socket contacts and lack of fuse contacts in the plug make them less prone to overheating. BS 546 plate sockets are available from several manufacturers, ask at an electrical wholesaler, and Lewden make a superior metalclad surface-mount version, available in black or bare metal finish with matching plugs, and with a large combined switch.

In the 2A and 5A sizes, MK make circular ones which mount on a conduit box, cat. nos. 312 WHI and 315 WHI.

[Andrew Gabriel]

1 Watt max.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Harry Bloomfield saying something like:

Yep. And plenty of other places. So that's why I won't run 13A through a 13A socket.

Notice the way to ducked out of the challenge.

[js.b1]

I thought it was 8 watt... perhaps that's for the Naff-R-Us fuse with split pin fuse contats? :-)

MK SFCU fuse holder gets plenty hot after 7hrs on an immersion.

[Harry Bloomfield]

Grimly Curmudgeon has brought this to us :

At the last count the socket count here ran to almost one hundred, whilst the vast majority of them are lightly loaded, we do have some which carry full load. All are good quality and fitted by me, never has any of them failed or over heated. That is not to suggest that I have never come across over heated 13amp sockets and plugs - I have come across numerous examples, but always explainable by poor installation or poor quality accessories.

I really do have better things to do with my time than respond to such silliness.

[John Rumm]

Agreed about the ambient de-rating - that and the tendency for some immersions to drift up in current demand as they age being the argument against a plug/socket arrangement rather than doubs about the ability of a plug to carry 13A under normal circumstances.

What I don't understand is why the desire to take a working hardwired immersion and tit about with it. Leave it alone.

If you want to add something else to the circuit, then by all means do so assuming the cable is up to it, and you label it at the CU. The cable will be adequately protected by the CU MCB, The worst that will happen is you trip the MCB if you draw too much from your extra socket when the immersion is also on.

[John Rumm]

Agreed.

I would not do it on the grounds that the high temperature of the airing cupboard may push the maximum current carrying capacity of the plug to below the required level. Remember that maximum currents for anything are really dictated by temperature budget.

[John Rumm]

I feel your fear is misplaced. Decent accessories will handle 13A without major issue. Yes a plug will get warm, but that is expected. If its getting hot enough to char, then something is wrong. IME, plugs that get seriously hot are either dirty, or have poorly tightened screws, or are inserted into a tired old socket that has weak springs and dirty contacts.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember Harry Bloomfield saying something like:

So, you're not putting your money where your mouth is? Thought so.

[Andy Wade]

But only for an ambient temperature not exceeding 35 deg. C, which could be exceeded in some airing cupboards.

The idea used to be strongly deprecated in IEE guidance as burnt plug pins and socket fronts were once quite a common sight. Admittedly this advice pre-dates pre-insulated HW cylinders and mandatory approval of plugs & sockets.

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember John Rumm saying something like:

Exactly. And that never happens.

[Andrew Gabriel]

It happens often with immersion heater wiring terminations when no plug and socket is used, so it would be amazing if using a plug and socket somehow solved that problem.

About 30 years ago, the Wylex switch for my parents' immersion heater burned out. I replaced that with a good quality (MK) 13A plug and socket. I just checked that, and no sign of overheating.

[Dave Plowman (News)]

Burned out highly loaded fittings are quite common in my experience and often caused by pro electricians not tightening the connectors properly. I can offer no explanation as to why. Perhaps they have limp wrists. ;-)

[Harry Bloomfield]

Andy Wade brought next idea :

When was this? I have seen many more burnt 13amp plugs and sockets recently, than I ever saw in the 1960's. My personal opinion is that there are a lot more poor quality examples of both about now, than back then and the standards of install workmanship has also fallen due to poor training.

I would not expect the ambient within a reasonable range, to make that much difference to the rating of accessories.

[Harry Bloomfield]

Grimly Curmudgeon formulated the question :

How's about you waste YOUR time and kwh proving me wrong, such a test could take years?

[Harry Bloomfield]

Andrew Gabriel has brought this to us :

But was the problem due to the switch, or simply due to poor termination?