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Immersion Heater & 13 Amp socket.

Zoomup
We were discussing the rating of 13 Amp sockets recently, both double and single types. The rating seems to be 13 Amp. as indicated on the back of the accessories. Yesterday I had to replace a 13 Amp. single socket that became faulty. It supplied a 3000 Watt water heater. Did the 13  Amp plug burn out? No. Did the socket burn out? No. But the socket switch terminals welded together and would not switch off. So I fitted a 20 Amp double pole switch instead. So, even if a 13 Amp. socket is marked 13 Amp. it may not deliver 13 Amps. reliably, perhaps the makers apply "diversity" when calculating the load current and sizing the contacts for their 13 Amp sockets.


Z.
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    Zoom ,

    When ring circuits and 13amp outlets were first designed it was decided that immersion heaters

    could conveniently served by a 13amp socket in the airing cupboard.

    A large number of fires later, the idea was abandoned.

    Pulling the plug on load might have been one cause but I have had a few plugs/sockets run hot

    on 3kW loads.


    Terence.
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    BS1363 sockets were made of sterner stuff back in the 60s and 70s, at 240V


    the continuous full load current was 12.5A, for a heating element designed to operate at 240V, theoretically


    and many appliance power ratings are not the same as the attached label.


    Legh
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    I think that there is a growing acceptance that 13 amp plugs and sockets can not safely and reliably carry a full 13 amps other than briefly.

    My view is that 10 amps is the sensible upper limit for continual loading.

    Apart from electric kettles which are fine in view of the very short term use, almost no modern domestic appliances use more than 10 amps.


    In my view a 13 amp plug and socket SHOULD be able to survive long term use at 110% of the nominal loading in order to allow for manufacturing tolerances of the connected load and variations in the supply voltage. AND should also be able to survive loading to 20 amps for the time that it takes for the 13 amp fuse to operate.

    In practice though this is not the case.


    I would consider it to be very poor practice to connect a 3Kw immersion heater via a 13 amp plug and socket. A 2 Kw immersion heater should be fine, but I am not very keen on the idea due to risk of a 3Kw replacement being fitted.
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    What is the rated current of a BS 1363 socket and plug if it is not the current that may safely be handled continuously; and if it is a switched one, made and broken?


    The type testing requires that the switch still works after being cycled 15,000 times on the full rated load. It is also interesting to note that the combination must also survive insertion and withdrawal on load 15,000 times.


    The caveat is that the circuit should be "substantially non-inductive".


    Perhaps there is a quality-control issue at some manufacturers?
  • 0

    Did the 13  Amp plug burn out? No. Did the socket burn out? No. But the socket switch terminals welded together and would not switch off. So I fitted a 20 Amp double pole switch instead. So, even if a 13 Amp. socket is marked 13 Amp. it may not deliver 13 Amps. reliably, perhaps the makers apply "diversity" when calculating the load current and sizing the contacts for their 13 Amp sockets.



    There's more to consider than just load current - the ambient temperature will also influence how hot a conductor will run - so too anything else that reduces heat dissipation (e.g. clothes piled up against the accessory). If it was in an airing cupboard it could well have overheated at its nominal rating, even if the same accessory would have performed perfectly in more normal circumstances.


      - Andy.
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    I agree that the old type of 13 Amp. sockets were better made than some modern ones. The old M.K. 60s solid cream coloured sockets were used for 3kW electric fires for hours in the evening when folk were watching t.v. using their coal effect electric fire with the rotating propeller. They lasted for many years.


    The location in question for me was in an airing cupboard, but it has a small well insulated pressurised unvented bomb water heater, not a copper cylinder with ill fitting insulating jacket and lots of hot pipes. The bomb is very well insulated. The airing cupboard does not get very hot at all.


    I do believe that modern wiring accessories are of a poor quality these days in many cases.


    Z.
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    With regard to the testing requirements, 15,000 make break cycles may be all very well.... but was the accessory allowed to roast for 10+ years in an airing cupboard with the poorly insulated jacket described above...at full load because the thermostat was shorted and had been for a while, between each one of those cycles?


    IMO, manufacturers back in the old days used to use worst case scenarios such as the above, to design to.


    Now it's how can we get past this specific test in the cheapest manner?


    Even MK themselves have fallen victim
  • 0

    MHRestorations:

    ... but was the accessory allowed to roast for 10+ years in an airing cupboard with the poorly insulated jacket described above...at full load because the thermostat was shorted and had been for a while, between each one of those cycles.




    I can probably count on my thumbs the number of times that we have used the immersion heater during the 20-odd years that we have lived here, but yes, in some circumstances it could be overloaded. However, (a) wouldn't the boiling water alert you to a problem, and (b) wouldn't the leccy bill be a little concerning after a few months let alone 10 years?

  • 0

    MHRestorations:

    With regard to the testing requirements, 15,000 make break cycles may be all very well.... but was the accessory allowed to roast for 10+ years in an airing cupboard with the poorly insulated jacket described above...at full load because the thermostat was shorted and had been for a while, between each one of those cycles?


    IMO, manufacturers back in the old days used to use worst case scenarios such as the above, to design to.


    Now it's how can we get past this specific test in the cheapest manner?


    Even MK themselves have fallen victim




    Of course the big difference between electric fire use and the immersion heater is the ambient temperature of the plug and socket.

    Personally I've seen (in my youth) far too many round pin plugs burnt out because they were used with a continuous heavy load.

    The fuse used to be the Achilles heel in the early 13 amp square pin plugs. 

    They'd overheat quite badly in some cases, probably because the clips did not hold the fuse well but also because they were confined in a lot of plastic and couldn't dissipate the heat fast enough... and made worse in an airing cupboard. 


    I totally agree about modern manufacturing of electrical fittings being extremely poor and cable so stiff.

    Quality has completely fallen through the floor.

    I hate working with it now.

    How anyone can do a decent job these days rather surprises me.

  • 0
    Chris Pearson‍ Yes, agreed, 99.99% of the time the bill or water temp would alert someone. But I was doing 'worst case scenario' for overheating of accessories. I agree with you that it would be unusual at the very least, I drive my colleague mad by doing the 'what if this, that and the other happened at the same time' <grin>

    Potential‍ It's possible to do decent work these days, but you have to pay 'over the minimum'. We for example will only use Prysmian (formerly Pirelli) or Doncaster cable. And we feed back to the wholesaler if there's an issue with a batch. (prysmian for example could do with hiring someone to check that the drum ends are at least slightly concentric lol).


    With accessories, the gap between the worst and the best is enormous. I suspect it was probably similar back in the 'good old days' but only the best has survived for 40+ years? The cable stiffness however, is definitely an issue

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