Immersion heater on a plug?

[EFLImpudence]

I would use a circular 16A plug and socket.

Connected where?

 

[bkenn]

To the back of the nearest accessible power point. I wouldn't draw more than 10A sustained, through a 13A socket, or even pair of sockets. Pairs get their power through one screw-terminal.

 

[wundaboy]

I'll most likely get flak for this but what the hell... I wouldn't feed a 3kW immersion off a 13 amp plug and socket for any length of time as I don't believe they can cope with the continuous full load.

However, with 1.5mm2 flex feeding the immersion I'd feel quite happy, even on a ring final circuit, to temporarily swap a 13 amp plug and socket to a BS546 15amp plug and socket. Non-standard, yes, but it's a fixed load and any fault will clear on a 30/32A protective device if the circuit is within spec. And these days, when appliances exclusively have 13 amp plugs, it's not as if there's a risk of an apppliance with a puny flex being unknowingly plugged in and not adequately protected.

I'm quite a fan of the BS546 plug and think there's still a place for it in domestic / light commercial. I think its potential is under-exploited.

 

[JohnW2]

I'll most likely get flak for this but what the hell... I wouldn't feed a 3kW immersion off a 13 amp plug and socket for any length of time as I don't believe they can cope with the continuous full load.

Some certainly don't cope. However, as I imagine is the experience of others, I've seen 3kW immersions that have been fed via a 13A BS363 plug/socket for years, without any signs of a problem.

However, with 1.5mm2 flex feeding the immersion I'd feel quite happy, even on a ring final circuit, to temporarily swap a 13 amp plug and socket to a BS546 15amp plug and socket. Non-standard, yes, but it's a fixed load and any fault will clear on a 30/32A protective device if the circuit is within spec.

Yes, in reality, probably OK as a temporary measure. Indeed, using your logic, why bother with a plug/socket at all when 3 Wagos would do the job?

Don't forget that, provided he is telling the truth, we're only talking about an arrangement which is going to be in service for "6-8 weeks".

And these days, when appliances exclusively have 13 amp plugs, it's not as if there's a risk of an apppliance with a puny flex being unknowingly plugged in and not adequately protected.

I'm not sure that I would put too much money on that

I'm quite a fan of the BS546 plug and think there's still a place for it in domestic / light commercial. I think its potential is under-exploited.

There's quite a it to be said for them, the main problem obviously being the lack of a fuse,particularly on 32A circuits.

Kind Regards, John

 

[ScottishGasMan]

I'm going over at the weekend so will take everyones suggestions into account. Consensus seems to be not to use the 13A plug/socket, In my own house as a temp measure I'd just do it, but this is at my sisters and she will switch it on and forget to turn it off, so will need to see if they can get cable back to CU without lifting floors, otherwise they will be having showers at my folks for the next month or so until the combi can go back in.

 

[ericmark]

May seem odd, but often better if not switched off, reason is time the immersion is switched on for, clearly we use kettles every day with 13 amp plugs and 3 kW elements, but with the immersion it can take a few hours to heat the water, and a fuse is designed to melt, so must get hot, that's how they work, so must be a way for that heat to dissipate, so black plugs are better, and the larger the plug the better, but once the water is hot, the time the immersion works to re-heat water is shorter, so plug heat wise leaving on is likely better.

If plugged in where there is free air not so much of a problem, the problem is were inside an airing cupboard.

 

[JohnW2]

May seem odd, but often better if not switched off, reason is time the immersion is switched on for ..... once the water is hot, the time the immersion works to re-heat water is shorter, so plug heat wise leaving on is likely better.

Indeed. People tend to forget that when we're having these discussions about the potential problem of having an immersion fed via a plug socket, when many people seem to think of it as a 'continuous' 3kW (about 13A) load.

The reality is, as you say, that, particularly if one never switches the immersion supply off, the immersion will never be powered for a very long continuous period. Even in my case, with the (admittedly very well lagged) immersion only powered ('continuously') for 7 hours per day (the E7 off-peak/cheap period), it is not usually 'on' for much more than an hour, and only on for a total of a couple or so of those 7 hours (so, roughly less than one-third of the time). Even if the cylinder starts off totally cold (very rare), it only takes about 2.4 hours. Here is a particular day, picked at random:

If plugged in where there is free air not so much of a problem, the problem is were inside an airing cupboard.

... which, of course, is a very common location.

Kind Regards, John

 

[EFLImpudence]

I think the problem is just that the individual socket and plug might be faulty (loose) rather than any complicated physics, locations, calculations or anything else.

 

[JohnW2]

I think the problem is just that the individual socket and plug might be faulty (loose) rather than any complicated physics, locations, calculations or anything else.

That is undoubtedly very often the case.

However, it does seem that there may also be some design issues in terms of what service plugs/sockets can actually 'reliably cope with'. As you will recall, an oft-quoted extract, allegedly from a pre-2010 MK catalogue, said of their double sockets ..

Research by ourselves and third party organisations has shown that all MK double sockets can safely withstand a continuous load of 19.5A for an indefinite period. Increasing the load slightly will begin to cause heat and mechanical stresses on the components in a relatively short period. Testing showed that a load of 22.3A was sufficient to cause heat stress that would cause a browning of the faceplates and sufficient heat to cause insulation damage to cable cores. A load of 24A for 43 hours was sufficient to cause significant heat damage to the material in which the socket-outlet was situated and within 75 hours sufficient to cause significant damage that would lead to the very real potential of fire.

Kind Regards, John

 

[EFLImpudence]

I was thinking more of a single socket for the immersion - but - apart from that -

surely manufacturing a product, into which a quite reasonable unsuspecting person can attach two 13A devices and loads, which cannot cope with that load (not to mention the extra current until a protective device would operate) is a negation of duty and a deception on the public.

So, in view of the quote, then it is not surprising that some sockets and plugs fail because they were not made well enough.

 

[JohnW2]

I was thinking more of a single socket for the immersion - but - apart from that -

I realised that, but I was just making the point that the capabilities of plugs/sockets may not necessarily be what one would (I would say 'reasonably') expect. As you go on to say ...

surely manufacturing a product, into which a quite reasonable unsuspecting person can attach two 13A devices and loads, which cannot cope with that load (not to mention the extra current until a protective device would operate) is a negation of duty and a deception on the public.

Quite so - and I would say that applies to a socket with two "13A outlets", which one certainly would not expect to suffer "... significant damage that would lead to the very real potential of fire." whilst carrying 24A total (even if for 75 hours), doesn't it ?

So, in view of the quote, then it is not surprising that some sockets and plugs fail because they were not made well enough.

Exactly -as above.

Kind Regards, John

 

[EFLImpudence]

Quite so - and I would say that applies to a socket with two "13A outlets", which one certainly would not expect to suffer "... significant damage that would lead to the very real potential of fire." whilst carrying 24A total (even if for 75 hours), doesn't it ?

Yes, indeed.

It is rather strange that the manufacturers are allowed to get away with it.

Is there anything similar - something apparently obvious but not?

We think (know) cable rated at 27A will not only be able to carry 27A 'for ever' but also cope with the over-current caused by the fusing factor of protective devices.
Yet sockets will cause a fire.


Better have only metal sockets.

 

[JohnW2]

Yes, indeed. It is rather strange that the manufacturers are allowed to get away with it.

As you say, "yes, indeed".

I suppose to some extent it might come down to the age-old question of "what is the 'rating' of an MK double socket". Given that the general public could be excused for assuming that it was 13A x 2, it really ought to be able to cope with that - but, as we know, opinions about the 'rating' vary between 13A, 20A and 26A. MK have always said "13A per socket outlet", but even the tech support guy I spoke to wasn't absolutely certain of what it meant!

IF the 'rating' were 20A (which, as above, I don't believe it should be), then the text I quoted does say:

all MK double sockets can safely withstand a continuous load of 19.5A for an indefinite period

... which would 'almost' be OK. However, as many of believe, it is (or should be) 26A then, as you say, in view of what they have written, I don't understand why they are "allowed to get away with it" - apart from anything else, it would sound like a Trading Standards issue to me.

Is there anything similar - something apparently obvious but not?

None 'as bad as' this one come immediately to my mind.

We think (know) cable rated at 27A will not only be able to carry 27A 'for ever' but also cope with the over-current caused by the fusing factor of protective devices. Yet sockets will cause a fire.

I can but agree.

Better have only metal sockets.

Even that might not be a total solution, if the metal socket got hot enough 'to start a fire'!

Kind Regards, John

 

[Harry Bloomfield]

Even if the cylinder starts off totally cold (very rare), it only takes about 2.4 hours.

I would judge it might only take an over-heating 13amp plug and socket, 15 minutes to hit their peak temperature, so I personally would be quite wary of leaving such an arrangement unattended until it had proved itself.

 

[JohnW2]

I would judge it might only take an over-heating 13amp plug and socket, 15 minutes to hit their peak temperature...

That obviously depends upon the degree of ventilation and other means of heat loss. In the absence of means of 'getting rid of the heat' as fast as it was being produced, the temperature would continue to rise 'indefinitely' - so by no means guaranteed to reach a peak in 15 mins.

I think you're really talking about a situation is which the plug and/or socket and/or connections are 'faulty' - and if that fault is bad enough, the plug/socket could reach a 'dangerous temperature' much sooner than 15 mins.

, so I personally would be quite wary of leaving such an arrangement unattended until it had proved itself.

That's reasonable enough, but would you say the same if the immersion was connected via, say, a DP switch - which, if the connections were loose enough, could get very hot very quickly? ... and what about cooking appliances?

Kind Regards, John