Morrisman
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- Staffordshire, England
I do have a separate consumer unit box that powers just my workshop, with its own RCB etc, so I may experiment and try the microwave out in the workshop and see if anything changes. At least I’ll know if it is the old RCB on the way out or definitely the microwave.Hi @Morrisman
Sadly, you can’t diagnose a mains powered appliance insulation resistance problem with a multimeter.
As others have mentioned, you need a “megger” test instrument that would apply twice the nominal supply voltage (500V) during the test.
Metallic elements such as those used in cookers or immersion heaters are notoriously unreliable when supplied via a 30mA RCD.
The RCD can be tested if you can find someone with an RCD tester that includes the ramp facility but in all honesty, it’s more likely that the element is faulty and will need to be replaced.