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Kettle earth - why?

Stephen Biddle
Hi guys, just curious.  I have a plastic electric kettle that has an earth lead in the flex.  I can't see much point in it.  It will trip the RCD in the event of an element insulation breakdown so there's some use there.  Any thoughts?
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    The Kettle element has a metal casing which when compromised will short to earth (L-PE or/and N-PE), hence trip the RCD. It may well produce a short circuit (L-N) in which case the MCB will also trip.


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    Stephen Biddle:

    Hi guys, just curious.  I have a plastic electric kettle that has an earth lead in the flex.  I can't see much point in it.  It will trip the RCD in the event of an element insulation breakdown so there's some use there.  Any thoughts?




     That assumes that there is an RCD in the circuit that the kettle is plugged in to, and that the RCD trips when required to do so.

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    My first thought would be that this is a standard element that can also be fitted to a metal bodied kettle in which case the earth would serve a purpose.


    It will also offer protection in case of a major element failure by tripping the overcurrent protection.


    It may also be "we always fit earth connections to kettles but never thought why".


    The first reason is the most likely.


    Best regards


    Roger
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    Just a comment that's not specific to kettles, but goes to illustrate a point.


    Many appliances contain components which, individually, might have different methods of protection against electric shock. The kettle you cite may well comprise a Class I element, with Class II (probably reinforced insulation) for the terminals and switching elements.


    Similarly, a washing machine may well have a Class I element, Class I motor, Class II pump, and have an overall Class I construction with earthed metal body, although the bezel area being plastic may comprise various forms of Class II construction.


    These consideraions are important for those inspecting the appliance for safety after repair or during regular workplace inspection and/or testing that we have in the UK.
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    Well, an appliance with an earth terminal should be firstly inspected and tested as a class I appliance as at least some metalic part is likely to be accessible to human touch. It may also comprise of parts offering class II specifications but as for the reinforced plastic bezel this seems to suggest both mechanical, scrape and scratch protection for the machine and for those who come into contact. It may also include a certain level of aesthetics. -  however, I'm just pleased to get a hot cup of tea when I boil a kettle ....
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    Well, an appliance with an earth terminal should be firstly inspected and tested as a class I appliance as at least some metalic part is likely to be accessible to human touch.


    Yes, for appliances with heating elements and / or higher current components, this is often (although not always necessarily) the case.


    For appliances containing electronics, we need to be very careful about the liberal application of "Class I Earth Test" at a few A up to say 25 A (depending on the test kit), as not all PCBs have to be rated to take the whole appliance fault current.


    In addition, some devices have an earth conductor included for funcitonal purposes for either suppressors etc for EMC purposes, or for earthing the otherwise isolated d.c. (PELV)  - laptop power supplies are a prime example of this.
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    Yes, I agree class I appliances such as desk top PCs  would use a lower test current such as 100mA.

    It would still be a class I item and in need of verification of cpc plug to case continuity. I think we are saying the same thing. I would add that inspecting and testing relies on the expertise of the inspector to make the correct judgment call.
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    Yes, definitely the expertise and relevant knowledge of the inspector is key.


    It's not just PCs that have these circuit boards these days, and if you are doing say an 8 A or 25 A a.c. earth test, it's sometimes knowing where you should (and should not) put the test clip. Easy to make the judgement with a washing machine or dishwasher, easy to make a mistake with some other appliances.


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    leakage current can go through water up handle  strip  it will harmful to the user, leakage current level should match sensitivity tripping level of RCD, most element current leakage level buildup little by little at the time, at the beginning of current leakage it will sense user if it tuch the water 

     My experience -if change the N& L wire from plug top of  current leakage element,it can use the element without tripping RCD 

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     My experience -if change the N& L wire from plug top of  current leakage element,it can use the element without tripping RCD 

    Are you suggesting that reversing the L. and N. conductors at a 13 Amp plug is safer? I do not recommend that as the fuse should always be protecting the L. (brown)  conductor only.

    Z.

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