Replacing oven...help

Discussion in 'Electricians' Talk' started by Ban90, May 12, 2019.

  1. peter palmer

    peter palmer Well-Known Member

    There are exceptions to that reg about fusing required, I think its if the cable is less than 3M, is clearly visible and is supplying a fixed load then no fuse is required if you reduce the cable for that section.

    I get the idea that if the only fuse protecting the oven is 32A then although there is no way to overload the cable because its a fixed load if the element was to go short circuit then the MCB would still trip within the allowed time there is a greater risk of the selector switch welding together when its turned thus making the oven not worth repairing, where as if there was a 13A fuse in the plug then it may save the switch, but I'm not so sure there would be much difference between the two, fuses don't blow especially quickly, they are more for overload.
     
  2. robertpstubbs

    robertpstubbs Active Member

    Irrespective of the regs, connecting the two appliances separately now may help if a fault develops in the future. Eg you could just unplug a faulty oven and the hob would continue to work.
     
    Last edited: May 15, 2019
  3. unphased

    unphased Screwfix Select

    Protection for what? Everyone keeps banging on about protection. The only protection that needs to be afforded is overload, short circuit, earth leakage (RCD), and that is purely for circuits. Anything that gets plugged in or attached or connected to a circuit doesn't need any protection. Protection from what exactly? BS7671 is about distribution, and circuits and safety against shock. A fuse in a plug is doing nothing to contribute anything to that other than protecting the flex it is attached.
     
  4. peter palmer

    peter palmer Well-Known Member

    Why do boilers specify a 3A fuse and not the size of the supply cable. Or an extractor fan for that matter.
     
    dobbie likes this.
  5. Lucky13

    Lucky13 New Member

    because the size of the supply cable isn't based on only the load requirements.
     
  6. Lucky13

    Lucky13 New Member

    Isn't that the point. its protecting the item of equipment. its also not tripping out the entire circuit just because little Timmy has been has been using a fork to get his toast out the toaster
     
  7. unphased

    unphased Screwfix Select

    I may have to read the code of practice for in-service inspection and testing of electrical equipment again. I cannot remember where it states that fuses don't protect equipment. I may be corrected on that. :p
     
  8. peter palmer

    peter palmer Well-Known Member

    I agree, the fuse is to protect the cable supplying an appliance, but as I mentioned above people like boiler manufacturers insist on a 3A fuse in the spur to try and protect the PCB inside the boiler. Also with extractor fans, the issue was they were seizing up and getting hot/melting the 6A MCB wouldn't trip because obviously the current melting the fan was below 6A but above 3A - so there is an instance of a fuse designed to protect the appliance and not the cable supplying it.
     
    dobbie likes this.
  9. unphased

    unphased Screwfix Select

    Thank you Peter, that does make sense.
     
  10. Coloumb

    Coloumb Well-Known Member

    I would be surprised if there wasn't some form of protection in a fan, like a heat fuse or resistor. I can't see any BS standard for electrical equipment with a motor would really on another standard to provide protection. Most boiler's I've looked in have their own QB. fuse.

    Sounds like another variation on the DNO not understanding the 3m rule theme.
     
  11. Alster

    Alster Member

    Cooker hoods have a thermal protector built in to the motor but this won’t help when the bulb blows and takes out the pcb- A 5 a fuse nearly all ways prevents this. 13a and normally the pcb is blown.
     
  12. Alster

    Alster Member

    For some reason white goods manufacturers hardly ever fit internal fuses these days (probably so more stuff gets written off!!!)
     
  13. robertpstubbs

    robertpstubbs Active Member

    In my experience a lot of electrical equipment (AV etc) comes with 5A fuses in the plugs.
     
  14. Coloumb

    Coloumb Well-Known Member

    3a, 5a, 13a what does it matter? None of them will protect a pcb.
     
  15. Alster

    Alster Member

    Does for me!!! I’ll get me coat now.....
     
  16. Bazza-spark

    Bazza-spark Well-Known Member

    BS 7671 is a whole mish-mash of other documents, mainly the 60364 series of documents. They are listed in the preface.

    Section 110 lists the scope of the document, which is mainly installations.

    One of the regulations to apply here is

    113.1 The Regulations apply to items of electrical equipment only so far as selection and application of the equipment in the installation are concerned. The Regulations do not deal with requirements for the construction of assemblies of electrical equipment, which are required to comply with appropriate standards.

    Toasters, cookers, washing machines etc have their own product standards that they must comply with and are outside the scope of 7671.

    7671 also only applies to machines up to the main isolator. From that point onwards BS EN 60204 applies.

    Kind regards
     
  17. unphased

    unphased Screwfix Select

    Yes I know, but the predominant fuses are 3A and 13A. There are a whole range of fuses 1A, 2A, 3A 5A, 7A, 10A and 13A from the top of my head, I can't be bothered to find the total list.
     
  18. Comlec

    Comlec Well-Known Member

    @unphased I have looked in the book and you are sort of right.

    "Although the fuse in the plug is not fitted to protect the appliance, in practice it often does this. The fuse in the plug protects the flex against faults and can allow the use of a reduced csa cable....
    .... For the convenience of users, appliance equipment manufacturers have standardised on two plug fuse ratings (3A and 13A) [blah blah blah]
    .... However, note that for some IT equipment, manufacturers fit 5A fuses.

    Although two standardised plug top fuse ratings have been adopted, the fuse recommended by the manufacturer should be fitted. "

    Source P 101 15.13 - Code of practice for the in-service inspection and testing of electrical equipment. IET
     
    unphased likes this.
  19. peter palmer

    peter palmer Well-Known Member

    IMHO fuses in plugs were designed when circuit protection was via 3036 re-wireable fuses. Obviously a 13A fuse in the plug top would blow well before a 30A re-wireable fuse that may well have a piece of 1mm copper cable across it anyway.

    Nowadays even a 32A MCB is so sensitive to trip current I would say the fuse in the plug is practically irrelevant. The only purpose it serves is in things like multi way extension leads. If I found a 13A fuse in a table lamp plug I wouldn't even bat an eyelid.
     
  20. robertpstubbs

    robertpstubbs Active Member

    When I threw some stuff away recently I kept the fuses. I’ve just counted them:
    3A x7 =29%
    5A x9 =38%
    13A x8 =33%
     

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