Failed RCD in Consumer Unit??

Discussion in 'Electrics UK' started by blackbirdxx, 24 Oct 2021.

  1. blackbirdxx

    blackbirdxx

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    Throughout the last few nights the electricity supply to my house has been regularly cutting out very briefly. The smart meter has been buzzing and doing all sorts of strange things along with one of the RCD's in the consumer unit tripping.
    This morning, I contacted UKPN who confirmed they have had supply probs in my immediate area. They have now texted me to say that everything is now fixed.

    My question is why should one of my RCD's trip when the power is cut? Does it imply a faulty RCD?? Is this something I should get checked by an electrician??

    Thanking you all in advance....
     
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  3. OwainDIYer

    OwainDIYer

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    RCDs require a balance in currents between the live and neutral. There will also usually be a slight leakage to earth because the neutral and earth are connected together. If the neutral gets disconnected the imbalance may briefly exceed the trip rating of the RCD - because more current goes via the higher resistance path to earth than the lower resistance neutral - and so the RCD may trip.
     
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  4. EFLImpudence

    EFLImpudence

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    Nothing lasts for ever but sometimes RCDs do 'just trip' when something is switched off - possibly because N was disconnected before L and there is a path to earth through an appliance somewhere.
     
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  5. JohnW2

    JohnW2

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    Goodness knows. In theory, it should not happen - but it seems that occasionally it does :)
    Almost certainly not.
    Not per se. However, if you continue to get frequent 'unexplained' RCD trips (even now that the supply problem has apparently been rectified), then you would probably want to get an electrician to investigate the cause. It could, for example, be that the RCD IS faulty, and that UKPN's supply problems were just a co-incidental red herring.

    Kind Regards, John
     
    Last edited: 24 Oct 2021
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  6. JohnW2

    JohnW2

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    Indeed.
    That's all a bit back-to-front. The inbalance between L and N currents which causes an RCD to trip results from some of the current flowing in the live conductor finding a way to get back to the supply transformer other than through the neutral conductor - essentially always because of "a slight leakage to earth".
    That's one of the theories as to how these rogue trips come about, but (in the absence of a leakage to earth) it can only really only happen during the first half cycle (i.e. 10ms max) after 'disconnection', and then due to capacitive coupling to earth. Basically, I don't think anyone knows why these trips sometimes seem to happen.

    Kind Regards, John
     
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  7. blackbirdxx

    blackbirdxx

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    Thanks for the info.
    I'm asking because the RCD which fails after a power cut is the one with the freezer on it. All food in the freezer will be lost following a very short power cut which would be annoying, especially if this can be avoided with a replacement RCD which doesn't trip.
     
  8. JohnW2

    JohnW2

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    Provided you don't open the door/lid, food in a freezer should stay OK for up to 48 hours.
    That would be true if a faulty RCD were the problem, but there's no guarantee (indeed, probabaly not that likely) that that is the problem. You could ask an electrician to test the RCD but, even if it 'passes' the tests, that would not necessarily prove that it doesn't have a fault which causes it to trip occasionally/intermittently I suppose you could ask an electrician to just replace the RCD, but that could well prove to be 'wasted money' - but, as I said, if fairly frequent trips persist, it would make sense to get an electrician to investigate.

    Kind Regards, John
     
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  9. davelx

    davelx

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    The food in the freezer should be OK for quite a few hours (sometimes up to 48) as long as you don't open it!
     
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  11. ericmark

    ericmark

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    No it is not, with a chest freezer yes it will be likely OK for 12 hours, but with up right frost free it depends on where it was on the cycle when the power failed.

    I heard my freezer fail, so had a spare in garage used for brewing, so removed the thermostat used for brewing with and switched on to let it cool first before transferring food for an hour.

    I found the bottom was OK but food at top de-frosted within that hour.

    A frost free freezer has a compartment behind the food with the evaporator in and a fan, not between the shelves as with non frost free, and with the evaporator is a heater which melts any ice and allows it to drain onto a tray on top of motor which gets hot when motor runs so evaporates, while de-frosting the fan does not run so food stays cold, due to having a fan when it does cool whole of freezer cools together so no warm spots, however if the motor does not restart heat raises at back of panel and will defrost food above the vent.

    So length of time it can be without power depends where it was on the defrost cycle, my freezers show the maximum temperature reached during a power cut until the door is opened, when it returns to current temperature.

    The amount of food will also affect how long it can go without power, but I know with shop chest freezers they have alarms to alert the manager at home if they fail over night, I know my son-in-law is a shop manager and has needed to go out to sort freezers when alarm has gone off, shop opens around 8 am closes around 10 pm so only 10 hours with no one there, if the freezer could last 10 hours then there would be no point in having the alarms. Or paying my son-in-law to drive 20 miles to sort it should one fail.

    It does worry me, as my wife tends to keep three freezers full of food, in the winter if there is bad weather we don't go out, not worth the risk to car or myself driving in icy or snowy weather when we don't need to. Milk is delivered every other day, so if the milkman can deliver we can go for a month without leaving the house. However it would mean a lot of money lost if they fail, so my house all RCBO protected, and to-date in this house not lost a freezer.
     
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  12. JohnW2

    JohnW2

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    I think you are probably being unnecessarily conservative/pessimistic, particularly in relation to domestic freezers.

    In terms of chest freezers, one often sees "up to 48 hours" mentioned and my personal experience is that (with the lid closed, and freezer 'nearly full'), the contents remain 'well frozen' for well over 24 hours.

    As for 'frost free' upright ones, as I've said, I've never had one. However, I had assumed that the 'no cooling' part of the defrost cycle was relatively brief, so that (provided door remained closed) the temperature of the cavity (and contents) would rise little during that period. Is that not the case? If not, how high does the cavity temp go during the 'no cooling' part of the cycle?

    The other thing is that, even if temps do rise, the advice we are given is ultra-cautious. The reality is that even 'total thawing' (which is unlikley to happen) followed by re-freezing is extremely unlikely to cause any 'health' problems, particularly in the case of things which are going to be 'properly cooked' after removal from the freezer.

    To put this in context, when I manually defrost one of my (large) chest freezers, I leave most of the contents lying around in crates (in cellar, garage or wherever) in 'ambient temp surroundings' for probably at least 3-4 hours in many cases. It's only things like 'ice lollies' or items which will ultimately be eaten without any further cooking, that I bother to put into another freezer.
    Very much so, and many people don't seem to realise that. The more 'space' (air) there is in a freezer, the more rapidly will the temp rise when there is no active cooling. However, that's rarely an issue with our freezers, which always seem to be 'ridiculously full'!
    That's a very different world from the domestic environment. Freezers in shops don't usually have significant insulation in the doors/lids - often just sliding perspex/glass panels, and some of the chest ones don't have lids at all. Furthermore, I suspect that they may be constrained by regulations that one requires them to throw away food if the temp of the freezer has risen to some arbitrary number for even a very short period of time - although, as above, I suspect that any true risk' is usually very minimal.
    '
    Kind Regards, John
     
  13. ericmark

    ericmark

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    I am not willing to turn off freezer to test rate of cooling. But brine freezes at -18°C and so there is a demarcation mark at -18°C below all is frozen, above only some bits are frozen. So even at -12°C there may be a problem.
     
  14. winston1

    winston1

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    All very true. The only time we had a freezer fail we went around the neighbours “borrowing” spare freezer space. The other half said don’t worry about vegetables they can be refrozen with no worries. Neither of us got ill.
     
  15. JohnW2

    JohnW2

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    I didn't ask you to. However, what I did ask is how much the temperature in the cavity of a 'frost free' freezer rises during the 'no active cooling' part of the defosting cycle - do you know the answer to that?
    It is temperature, not "whether or not something is frozen" that matters - since micro-organisms know about the former, but not the latter (don't forget that some things will not be "frozen" even at -18°C, but that doesn't mean that bugs would be able to multiply in them).

    Very very few micro-organisms can multiply at temperatures below 0°C, and the vast majority can't multiply at temps below about +5°C - which is just as well, since otherwise food would not be 'safe' in a fridge.

    As I understand it, the -18°C recommendation originally arose essentially arbitrarily - when they first started having freezers, the US decided to recommend the 'very round' figure of 0°F. That (about -17.8°C) was subsequently rounded to -18°C in Europe. It seems that it was subsequently discovered/ decided/ agreed that -18°C was a pretty reasonable figure, so was essentially adopted as the global recommendation.

    I think it's more a matter of food quality and 'aesthetics' than safety, being primarily down to chemical, rather than microbiological, considerations. As I understand it, the main difference between, say, -10°C and -18°C is that many micro-nutrients (particularly vitamins) survive much better at the lower temperature. However, if one gets much colder than -18°C, although obviously still 'safe', one starts getting deterioration in taste, texture and appearance (e.g. 'freezer burn'), which can be interpreted as 'unpleasant';.

    Kind Regards, John
     
  16. JohnW2

    JohnW2

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    Indeed. However, it's extremely unlikely that vegetables (or many other things) would do you any harm even if they had been lying around at ambient temperature for days or weeks (even though they might look and taste nasty :) ). It's primarily meat and fish products which are the potential problem but, as I've said, many/most people seem to be probably excessively concerned (albeit aided and abetted by 'official advice') about the perceived risks of re-freezing after partial re-thawing of foods, particularly those which are subsequently going to be 'properly cooked'.
     
  17. bernardgreen

    bernardgreen

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    Re-freezing in a domestic freezer is a slow process at -18°C, blast freezing in the food processing factory is a very fast process at much lower temperatures -40°C.

    Slow freezing can significantly damage the texture and appearance of the food, blast freezing does less damage to the product.
     
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