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When cleaning my ceramic hob yesterday (wet, but not excessively), I noticed some voltage going through my wet finger when touching the shaft of one of the knobs (I had removed the knobs before). I immediately stopped the work and used the circuit breaker. (And that is what you should do, too, if feeling even the most gently voltage. Really)

  • The knobs are mounted right above on the hob, where it does get wet sometimes
  • The hob was installed by a professional electrician, but it is an old one.
  • The casing is connected to protective earth, but the knob shaft isn't (measured when the circuit breaker was open)

I cannot measure any voltage on the knob shaft, presumably because it has had enough time to dry. But I am wondering: Isn't it supposed to be connected to protective earth, just like the casing?

Because the plastic knob will not always provide good isolation: it's easily detachable, and even when attached, the 1/2 " it provides as a distance from the shaft sometimes gets really wet when cooking.

Should I replace the whole hob?

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For those trying to follow along at home, a hob is a cooktop. –  Aaron May 16 at 14:25

2 Answers 2

You say the hob is old so I would get an estimate to replace all 4 or 5 controls (the others may not be too far behind the one in question in wear and tear) along with an assessment of the hob's overall condition and compare that against buying a new one.

My Mom has a ceramic cooktop and I'm going to take a meter with me when I see her later today. Now I'm curious.

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I just checked my Mom's Whirlpool ceramic cooktop with a meter. I do not get continuity from the housing underneath to a control knob stem, but I do get continuity to the controls' casing. It looks like they're made so that the stem is isolated, but in your case probably a water short is causing a small voltage potential on the stem. –  Rand May 16 at 20:37
    
Good time to have a look at the wiring insulation when you open it up. If any of the insulation looks suspect, go for replacing the whole unit. And yes, if the element control has a plastic case, the switch shaft is supposed to be completely insulated. Any voltage appearing on it means it's permanently past its service life. It would have to be filled with water to leak voltage to the shaft. –  Fiasco Labs Jun 15 at 15:10

If you can isolate which component is faulty on the hob, you could just replace that without needing to replace the whole appliance.

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