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  1. peterinreading
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    peterinreading Active EF Member

    Location:
    reading
    This is maybe not strictly a PAT testing question but you PAT testers might be able to help. I am renovating a set of electric cookers and start by testing them disconnected from the supply using PAT testing principles. So I test for earth continuity and insulation resistance. If OK then I connect the cooker to the supply and functionally test it. The supply is via an RCD protected circuit I set up and tested specifically for testing cookers.

    These cookers have 4 metal hot plates - two small ones and two big ones. Some of these cookers fail the insulation resistance test when a hot plate is turned on. If I put in a new hot plate in then it is OK. That's obvious but what is not so obvious is what earth continuity you would expect to the surface of the hot plate. I typically get a reading of 10-20 ohm to the surface of the hotplate but a reading of < 1 ohm to the earth tag connected to the bottom of the hot plate. What would you consider acceptable earth continuity to the surface of the hotplate? Its obviously a lot easier testing to the surface of the hotplate as then you don't need to start disassembling the cooker.

    If connected to the supply via an RCD the safe limit would be much higher than 20 ohm as all you need is enough current leak to trip the RCD but this doesnt really fit with the PAT testing rules. Any ideas?

    I am a qualified electrician but new to appliance testing!
     
  2. telectrix
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    telectrix Scouser and Proud of It Trusted Advisor

    Location:
    cheshire/staffordshire
    Business Name:
    Telectrix
    them solid hotplates are made od some type of steel. the resistance of steel is roughly 8 x that of copper ( some alloys are much more) so you will get a higher reading.
     
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