My multimeter is measuring 12v AC between the metal on the unit and the ground pin on a power strip.
In the specific case of the OP's espresso machine, it all boils down to the question:
- Are those metal parts (by design) meant to be grounded, because there is a risk that they could otherwise come in contact with "hot" mains through just a single fault in the machine? If that is the case, the tingle upon touching them suggests that the parts are not actually grounded, and that's a safety issue that needs to be fixed immediately.
In practice, I would assume that functional metal parts which are in direct contact with the heater will need to be grounded. E.g. in a typical portafilter machine, the boiler and the group head. But if the machine's outer enclosure is mostly a plastic structure, with some decorative metal parts glued on, those might well be double-insulated and not grounded.
- Or are those parts double-insulated from mains inside the machine, and were never meant to be grounded? In that case, a tingle due to capacitive coupling of some voltage is normal. The machine may still require a properly grounded plug to keep other touchable metal parts safe, but the "tingle" does not give any indication that there is something wrong with that grounding.
To tell whether specific metal parts were meant to be grounded or not, one could disassemble the machine and look for provided connection points or loose ground wires. But a judgement call "from the outside" may be good enough in some clear-cut cases. @ImpulsiveJames -- which parts specifically caused the tingle when touched? Could you share the specific brand and model, and/or a photo of your machine?
And here we have the correct answer. Usually a lot of unnecessary noise in threads like this.
Or are those parts double-insulated from mains inside the machine, and were never meant to be grounded? In that case, a tingle due to capacitive coupling of some voltage is normal.
Except, if you re-read the thread carefully, you'll find the correct answer. I also dispute part about parasitic capacitances.
You shouldn't feel a tingle from an appliance like that, which should be earthed. It's not the same as a double insulated power supply, with a Y capacitor bridging the primary and secondary sides.
Test the continuity between the exposed metallic parts and the earth pin of the mains plug.
Except, if you re-read the thread carefully, you'll find the correct answer. I also dispute part about parasitic capacitances.
Yes, you pointed out the relevant question before. But I felt that you also jumped to a particular conclusion, which may be the wrong one; hence thought that I should elaborate a bit.
Considering the boundary conditions under which the tingle was felt (barefoot on a cement floor), I would certainly not rule out harmless capacitive coupling to a metal part that is floating by design. What constitutes a "tingle" is a very subjective assessment; it might just be the 60 Hz "vibrations" which are typically felt. Let's wait whether the OP comes back with more details about his espresso machine and the specific metal parts that caused the sensation.
On a grounded device, all metal parts should be connected to the ground pin.
On a grounded device, all metal parts should be connected to the ground pin.
The reason why I doubt it's parasitic capacitance is because I can touch one side of a toroidal 1kVA transformer with one hand and earth with another and don't feel a thing and such a transformer will have far greater parasitic capacitance than a coffee maker. Mechanical vibration is a possibility, but doubt it would have raised the same level of alarm, because it would be audible i.e. the pump running.
I prefer to err on the side of caution, especially given the wording of the original post indicates it was written by a beginner..
On a grounded device, all metal parts should be connected to the ground pin.
I very much doubt that. As I said a few posts above, e.g. some decorative metal panels glued onto the plastic enclosure might well be unconnected to anything.
The reason why I doubt it's parasitic capacitance is because I can touch one side of a toroidal 1kVA transformer with one hand and earth with another and don't feel a thing and such a transformer will have far greater parasitic capacitance than a coffee maker. Mechanical vibration is a possibility, but doubt it would have raised the same level of alarm, because it would be audible i.e. the pump running.
I prefer to err on the side of caution, especially given the wording of the original post indicates it was written by a beginner..Many years ago the steel kitchen sink was giving me the tingling. The sink was electrically isolated because it had PVC drain. After some confusion I determined the sink was touching some aluminum foil which, in turn, was touching a toaster oven. The all-metal toaster oven had two heating elements which were metal tubes with, I assume, resistive wires inside, isolated from the outside metal tube which was held in place and electrically connected to the metal structure of the oven. Measuring resistance between the internal heating element and the external metal tube the reading is infinite resistance. But there was enough capacitance to give that tingling. The oven was supposed to be connected to earth and that would solve the problem but my apartment at that time did not have protective earth wire in the supply. This was long time ago. This was a 6th floor apartment and the building did not have earth wiring.
I bought some heat resistant flexible tubing and put it between the metal tube and the metal clamps which hold it in place and that resolved the problem.
I think it might be asbestos but at that time asbestos was not yet dangerous. I still have and use this toaster oven but now it is grounded.
Just an example if capacitive leak. With the oven grounded there is no problem but with the metal housing floating it does give the tingles.
On a grounded device, all metal parts should be connected to the ground pin.
I very much doubt that. As I said a few posts above, e.g. some decorative metal panels glued onto the plastic enclosure might well be unconnected to anything.That is semantics. Ofcourse this is about metal parts which are a structural part of the appliance which are close to mains voltages and where double isolation can't be guaranteed. Should go without saying. Either way, if touching an appliance gives you a tingling sensation, it is time to unplug it and have it checked / replaced.