A/C unit earth leakage

[andyB2022]

Hi, I've just installed my new A/C Hisense QG35XV0E split unit. The unit is working fine. However, while I was looking at it operating, I touched the metal case of it and the balcony's railing and got a little shock. Nothing too scary, my RCD didn't trip. Then I got my Fluke meter and measured from the case straight to the railing and got a value of ~2mA.

What can be the cause of this? I will ground the unit properly; it was initially connected for testing purposes. However, I don't think it's good for the unit to leak 2mA to ground permanently.

[Gyro]

It sounds like general leakage current from interference suppression caps, motor winding insulation etc. HOWEVER it does imply that the unit isn't properly grounded which is very important for something that big, metal, and touchable. It could also be that your balcony rail isn't particularly well grounded if it is supported by dry brickwork or whatever (although it is probably more structurally anchored).

Try the Fluke on AC volts - if there is any significant voltage (more than single digit) then it indicates that it isn't properly grounded, rather than some small difference in ground potentials. Don't leave it without investigation though. It will be a Class-I appliance which could become lethal if something fails and there is no solid case ground! (although the RCD would hopefully catch it).

[indeterminate]

I don't think it's good for the unit to leak 2mA to ground permanently.

It is normal
The mains filter network in the AC unit is just doing its job and removing noise from the supply

[perieanuo]

little shock means usually dozens volts, for correct grounding it's too much, doesn't matter if it's coming from static or functional leakage current.
there are people feeling 12Vdc/Ac, but normally you should feel discharge of a lot more voltage potential in respect to earth.
what i'm saying, your earth circuit doesn't respect the ohmic maximal value in your country (ie, you felt 50volts, earth must be below 4ogms for example, added with your earth connection to earth central connection, divide those 50V by resistance you should have between your AC earth terminal upto earth of power distribution box, the value is not ok for sure).
lot of theory, bad earth connection for sure. with correct earth equivalent resistance (ohms, no more), you shouldn't feel a thing

[SteveThackery]

My brand new Microsoft Surface laptop feels distinctly "live" when I touch it plugged in. It's more noticeable when sliding a finger across the case - I can feel a 50Hz "buzz" through the finger.

I'm not concerned - I assume it is current flowing through the capacitors at the input of the separate PSU. I don't think the protective ground is carried through to the DC output.

[Gyro]

Yes, your Microsoft Surface has a Class II double insulated PSU (no mains wire), what you are feeling is just the normal low AC current through the Class Y noise suppression capacitor between primary and secondary sides. It's a different situation from a Class I appliance, there should be zero leakage current on touching the (grounded) case.

[SteveThackery]

Thanks, @Gyro. I wasn't clear in my mind about the differences between Class 1 and Class 2, nor that the OP's AC unit was Class 1.

Just to clarify for a newbie (me), doesn't the OP's report suggest two faults?  Firstly, he can feel a tiny shock, so the metal case is not grounded. Secondly, there is 2mA of leakage onto the case from somewhere. Or could that second one be down to the suppression capacitors?

[wasedadoc]

Thanks, @Gyro. I wasn't clear in my mind about the differences between Class 1 and Class 2, nor that the OP's AC unit was Class 1.

Just to clarify for a newbie (me), doesn't the OP's report suggest two faults?  Firstly, he can feel a tiny shock, so the metal case is not grounded. Secondly, there is 2mA of leakage onto the case from somewhere. Or could that second one be down to the suppression capacitors?

Yes, first one is a fault.  Second one is probably not a fault, just normal for that suppression method.

[Gyro]

^ What he said. Probably suppression caps, maybe a little normal capacitive leakage from things like compressor winding to chassis etc. Well within the normal 30mA trip threshold for an RCD. Everything leaks a bit.

P.S. It's worth reading up on the whole Class I / Class II thing, X and Y caps etc. It's not that complicated and useful to know. You can even have Class II products in metal cases - I used to design lots of high volume consumer A/V products that were like that (they do get a bit more complicated to get right though).

[Uup]

... I will ground the unit properly; it was initially connected for testing purposes

Edit: I somehow misunderstood this part of the OP, now realising that he meant that it wasn't grounded. So my reply below is redundant. Sorry!


The issue may not necessarily be related to your AC unit. I would imagine that if it were installed correctly that the metal casing of the unit should be properly grounded. I presume you checked the ground connection at the AC unit as a first-order of things?

The issue may be due to your railing not being grounded correctly, or it may be at a different potential to the ground at your AC unit.

Check for any voltage between ground at your AC unit and your railing, with both the AC unit running and with the circuit breaker for it switched off.

If there is a voltage present, regardless of if the AC unit had power/running or not, then there is likely a ground issue with your railing.

If there is only a voltage present when the AC unit is running, then there is likely a ground issue for your AC unit - which could possibly be somewhere in your switchboard.
 
I once had to investigate a peculiar issue on a site, where two multi-story buildings were next to each other. There was a piece of metal (from a mast) on one building that was flapping in the wind and was hitting a metal rail on the building next to it.

The ground connection on the buildings connect with neutral (PME/MEN) and one of the buildings had an issue with that junction. It caused a voltage difference of about 2V between the buildings ground connections. However, every time the flapping metal touched the other building's metal rail a significant amount of current was flowing causing a surprisingly large amount of spurious emissions.

[Gyro]

...
I once had to investigate a peculiar issue on a site, where two multi-story buildings were next to each other. There was a piece of metal (from a mast) on one building that was flapping in the wind and was hitting a metal rail on the building next to it.

The ground connection on the buildings connect with neutral (PME/MEN) and one of the buildings had an issue with that junction. It caused a voltage difference of about 2V between the buildings ground connections. However, every time the flapping metal touched the other building's metal rail a significant amount of current was flowing causing a surprisingly large amount of spurious emissions. [/i]

Yes, PME / TN-C-S, is increasingly raising issues of when is ground actually ground, particularly where there is a large unbalanced Neutral current (3-phase). It has come more to the fore with EV charger protection and there have been several documented cases of lost Neutral (between the substation and houses) which have severely tested the current carrying capacity of gas meters and associated metal pipework.

[themadhippy]

PME / TN-C-S, is increasingly raising issues of when is ground actually ground, particularly where there is a large unbalanced Neutral current

which is why ,in the uk at least ,were not supposed to extend such supplies outside the ole equipotential zone,but then who goes to the bother of converting the circuit for the air handling unit hanging on the outside wall to TT

[LatvianOnJuice]

Just make sure that is really is the A/C and nothing else, ground it properly, and you should be good.

[Stray Electron]

...
I once had to investigate a peculiar issue on a site, where two multi-story buildings were next to each other. There was a piece of metal (from a mast) on one building that was flapping in the wind and was hitting a metal rail on the building next to it.

The ground connection on the buildings connect with neutral (PME/MEN) and one of the buildings had an issue with that junction. It caused a voltage difference of about 2V between the buildings ground connections. However, every time the flapping metal touched the other building's metal rail a significant amount of current was flowing causing a surprisingly large amount of spurious emissions. [/i]

Yes, PME / TN-C-S, is increasingly raising issues of when is ground actually ground, particularly where there is a large unbalanced Neutral current (3-phase). It has come more to the fore with EV charger protection and there have been several documented cases of lost Neutral (between the substation and houses) which have severely tested the current carrying capacity of gas meters and associated metal pipework.

   Geez, in the UK are they still using water and gas pipes to ground electrical systems?  All homes in the US are required to have a copper plated ground rod driven into the ground immediately next to the incoming power line and connected to electrical panel and the ground wires of the home wiring.  That's been required since sometime before 1963 when we built a house.

[SeanB]

   Geez, in the UK are they still using water and gas pipes to ground electrical systems?  All homes in the US are required to have a copper plated ground rod driven into the ground immediately next to the incoming power line and connected to electrical panel and the ground wires of the home wiring.  That's been required since sometime before 1963 when we built a house.

No, more a result of old metal water and gas lines, and the need to have equipotential bonding to them for protection. Does mean that a failed neutral in the supply to the street can result in the return current being passed thorugh those pipelines, as they join all the houses together, and thus act as a neutral when combined with the TNCS supply, or even with a separate ground conductor and a connection for safety to a ground rod at the transformer. TT systems are very rarely found in most countries, unless you are living on a massive basalt and granite rock, which is a poor conductor, so grounding is hard, or are in one of the few countries with it.

[SteveThackery]

Geez, in the UK are they still using water and gas pipes to ground electrical systems?

You say "still", but I don't think water and gas pipes have ever been used to provide a protective earth here in the UK, have they?

Anyway, the answer to your question is no, of course not. Rather, all such piping must be bonded to the protective earth at the point of entry so that internal metal piping and appliances cannot float to a dangerous voltage (eg due to a fault condition either in, or outside, the house).

[Gyro]

Geez, in the UK are they still using water and gas pipes to ground electrical systems?

You say "still", but I don't think water and gas pipes have ever been used to provide a protective earth here in the UK, have they?

Anyway, the answer to your question is no, of course not. Rather, all such piping must be bonded to the protective earth at the point of entry so that internal metal piping and appliances cannot float to a dangerous voltage (eg due to a fault condition either in, or outside, the house).

No they haven't, (and as you say) of course not. It wouldn't be safe, especially for gas pipes, hence the concern about accidental lost Neutral incidents in TN-C-S neighborhood power distribution locations. I don't think @Stray Electron understood the 'subtleties'.

[bte]

No, more a result of old metal water and gas lines, and the need to have equipotential bonding to them for protection. Does mean that a failed neutral in the supply to the street can result in the return current being passed thorugh those pipelines, as they join all the houses together, and thus act as a neutral when combined with the TNCS supply, or even with a separate ground conductor and a connection for safety to a ground rod at the transformer. TT systems are very rarely found in most countries, unless you are living on a massive basalt and granite rock, which is a poor conductor, so grounding is hard, or are in one of the few countries with it.

What may happen in case of failed neutral in a TNCS system is discussed in these videos (part 2 is a demo with low voltages):

Part 1:
Part 2:

[andyB2022]

Update: Got the unit grounded to some 2m deep metal pipes, not under 4  for sure, (how it should be, old house) but I can't feel a thing now. The railing is definitely NOT grounded directly by any means, it just connects by metal rods to earth via other rods of the house construction.

Before the connection to ground, I've had 111Vac from the railing to one external screw of the AC unit. While the compressor was running at 100%, the current leaking from the case to the railing (via my Fluke meter) was 10.8mA...  Between railing and any terminal of the unit I've got +80 MegaOhms (including ground terminal). Unit not grounded at this point of test.

Anyway, now however I touch the unit I can't feel a thing. Basically, the unit is wired in a TT system and not in a TN-C-S as it is supposed to be in my country.

My brand new Microsoft Surface laptop feels distinctly "live" when I touch it plugged in. It's more noticeable when sliding a finger across the case - I can feel a 50Hz "buzz" through the finger.

I'm not concerned - I assume it is current flowing through the capacitors at the input of the separate PSU. I don't think the protective ground is carried through to the DC output.

My iPad does the same thing, didn't ever understood how is that possible since the charger is a class II, isolated SMPS.
I am wondering why is the need for that Class Y cap from primary to secondary side... in my vision it's just a path for current to flow.