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Ovens on cooker ccts

Farmboy
In domestic kitchens, what do you think of the practice of connecting ovens to 32/40A cb cooker ccts via dual cooker connection outlet plates? For example, along with a 6kw hob, a 2.5kw oven is connected via a 1.5mm2 3 core h/r flex? One view is that it's acceptable because the flex can't be overloaded and the cb provides s/c protection for the flex, nor would it be coded on an eicr.


F
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    As we've recently discussed in another thread, it depends on the manufacturer's installation instructions - the manufacturer has a right to demand an appropriate circuit protective device is used to facilitate fault protection in their appliance - perhaps even the type and rating, e.g. I've heard of B25 mcb or RCBO being specifically stated by one manufacturer.
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    Poor practice in my view, unless the oven manufacturer states that this is acceptable. The oven is almost certainly intended to be connected to a circuit protected by a 15 amp or 16 amp OCPD, and to connect it to 32 amp or larger circuit is unwise. Any internal fault or failure in the oven is liable to be more destructive and possibly dangerous with an oversized OCPD.


    The practice is very common, but that does not make it sensible.
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    The oven, and the extractor fan above, might be considered to be luminaires and therefore the circuits would need rcd protection :)
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    The cover all base solution is a single 13 amp unswitched socket wired from, and adjacent to, the low level cooker outlet, though only if space permitting if you are retrofitting and the new box has to go surface. Then to the flex on the 2.2 or 2.5 kW Oven fit a tank top , plug top?

    coded on an eicr.



    But would you necessarily be dismantling fixed equipment [the Oven screwed into the base unit] to find out how it was connected?
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    gkenyon:

    As we've recently discussed in another thread, it depends on the manufacturer's installation instructions - the manufacturer has a right to demand an appropriate circuit protective device is used to facilitate fault protection in their appliance - perhaps even the type and rating, e.g. I've heard of B25 mcb or RCBO being specifically stated by one manufacturer.




    If I get an oven, extractor fan or other appliance for a customer I check the installation instructions for odd instructions that will be difficult or impossible to comply with, if there are potential issues I get another manufacturers product.


    Andy Betteridge 

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    gkenyon:

    As we've recently discussed in another thread, it depends on the manufacturer's installation instructions - the manufacturer has a right to demand an appropriate circuit protective device is used to facilitate fault protection in their appliance - perhaps even the type and rating, e.g. I've heard of B25 mcb or RCBO being specifically stated by one manufacturer.




    I disagree with that fundamental statement, but:


    Why has the manufacturer the right to make products that cannot safely be connected to known standard circuits?


    Is the internal wiring of an oven any larger that that of a cooker?

    It is not, so should a cooker be connected with two (or three) separate 16A circuits? If so, why in the UK do they come with the links between the two (or three) cooker terminals?


    The internal wiring of an oven will safely cope with the fault current with a 32A OPD, therefore 433 and omission of overload protection may be applied.



    Do you think manufacturers of, say, a 70W television set have the right to demand a 300mA fuse?

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    geoffsd:




    gkenyon:

    As we've recently discussed in another thread, it depends on the manufacturer's installation instructions - the manufacturer has a right to demand an appropriate circuit protective device is used to facilitate fault protection in their appliance - perhaps even the type and rating, e.g. I've heard of B25 mcb or RCBO being specifically stated by one manufacturer.




    I disagree with that fundamental statement, but:


    Happy to discuss, but you don't say why you disagree - it's a basic requirement in Chapter 13, i.e. a fundamental part of BS 7671  plain and simple


    Why has the manufacturer the right to make products that cannot safely be connected to known standard circuits?


    The appliances CAN be connected to a standard circuit (15, 16, 20 or 25 A radial) - just not one protected by a far higher rating of protective device. It's like saying "Not fair, I didn't know I couldn't supply my TV using a polo wrapper in place of the plug fuse".


    Is the internal wiring of an oven any larger that that of a cooker?

    It is not, so should a cooker be connected with two (or three) separate 16A circuits? If so, why in the UK do they come with the links between the two (or three) cooker terminals?


    That is the manufacturer's design, NOT the designer of the electrical installation to consider.


    It's a fundamental requirement of BS 7671 that the designer of the electrical installation considers manufacturer's instructions.

    The internal wiring of an oven will safely cope with the fault current with a 32A OPD, therefore 433 and omission of overload protection may be applied.


    433 applies to wiring of the fixed installation, not internal wiring in appliances.


    As per previous thread ... we may not be talking about protecting wiring only, but of course ovens do include smaller wire than that used for the heating elements. The wiring for the heating elements might be OK for adiabatic at ambient temperatures of 20C, but the temperatures inside parts of the oven exceed this. Finally, BS 7671 doesn't contain tables for the wiring used inside ovens.


    Why should we in the UK expect the rest of the world to capitulate to our vain hanging on to the 30/32 A ring final circuit, when mush of the rest of the world provides dedicated circuits for major items of fixed equipment. If we're not talking about an RFC, then what's the problem with swapping the B32 for a B16, B20 or B25 as necessary? (Of course from an appliance installers perspective , Part P becomes an issue, but that's merely another knot that's been tied for us that the manufacturer won't care about)



    Do you think manufacturers of, say, a 70W television set have the right to demand a 300mA fuse?


     




    No, these are designed as "pluggable type B" equipment in the product standards, and the use case of standard plug (perhaps without a fuse, but in that case on a 15, 16 or 20 A circuit) is considered in the standards, and by manufacturers.


    If the equipment is to be permanently wired, then, EVEN IN THE SAME PRODUCT STANDARDS the manufacturer is required to state the acceptable installation method and protective device(s) that are acceptable, if this is important for installation. So I'm not sure where this part of the argument is coming from?

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    I picked an oven randomly on the Currys website.

     
    This product requires hardwiring to a 13 Amp fuse and should be installed by a qualified installer, such as one of our Team Knowhow experts.



    That sounds fine, but experience shows that they expect the FCU to already be in place for them to connect to.


    As Graham says the existing circuits that people have in UK homes are not actually designed for modern cooking appliances, so when a customer buys high end modern appliance made by an European manufacturer they may have to have to pay an electrician to update the circuit that was installed for a freestanding cooker that was designed to be connected to a 30-amp circuit.


    Unfortunately the modern appliances are often just connected into a socket circuit in a haphazard way.


    Andy Betteridge
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    Well, I disagree because I do not think you are correct.

    If there is no difference between the internal wiring of ovens and cookers then demanding lower OPD ratings for ovens is not valid.


    Nothing to do with polo wrappers, the ovens are sold in the UK therefore the manufacturer knows about 32A circuits for cookers.

    Why do you not suggest cookers should be on two 16A circuits as they would be in Europe?

    To design a cooking appliance that cannot be connected to a standard UK 32A circuit without extra protection is negligent.


    If we are talking about ring circuits then they know it will have a 13A plug; to demand a 16A OPD is also negligent.

    If we are talking about cooker circuits then they know it might be 32A which is apparent by the terminal links and instructions for cookers.


    You seem to be confusing the fixed wiring and appliance wiring and clutching at straws - I thought the problem was affording 16A protection on 32A circuits.

    If a cooker is alright on a 32A circuit then so is an oven. If you think a larger flex on the oven is required (it likely isn't) then that is a lot easier than down-fusing a cooker circuit - especially for two ovens.


    The OPD is for protecting the fixed wiring, not the appliance. If a manufacturer demands a lower rated OPD than the normal circuit OPD for the product  then it is not fit for purpose.


    There is also the point that the manufacturer's instructions often state what they believe are the regulations in the UK rather than actually required for the product.

    The mention of 3A fuses and isolators which are not required for the same products in Europe being an example.

    The mention of an RCBO in your previous post is also obviously not definitive - unless you think an RCCB would be unsuitable.
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    So you want appliances specifically manufactured for the UK market. Because people in the UK don't want to upgrade outdated electrical installations in their homes. 


    Andy Betteridge

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