Electric shocks from macbook Pro + Laptop stand

Laptop: MacBook Pro (Retina, 13-inch, Early 2015)

Power Source: non-GFCI NEMA 5-15R Outlet tested with Sperry GFI6302 Outlet Tester

Outlet test result: Correct wiring, with grounded third prong

Inline Surge Protector: Tripp Lite SUPER7B Tripp Lite - 7 Outlet Surge Protector Power Strip, 7ft Cord, Right Angle Plug, 2160 Joules

Grounding Procedures used:

Laptop stand: is grounded by attaching alligator clips to exposed metal on stand using the following

• Wire: 10AWG Solid Copper Core, UL Listed, Satellite Antenna Grounding Cable (yes, this is heavy duty grounding wire)
• Plug: Qube Q007-Duo ESD Grounding Cube (this is a plug where AC prongs are plastic and only the third grounding prong is metal)
• Fasteners: Alligator clip x1, Banana plug x1 (both secured to 10AWG grounding wire leads)

Macbook Pro: AC Adapter is grounded by using official Apple Power Adapter Extension Cable

Grounding Validation: Ground connectivity was testing using RadioShack 46-Range Digital Multimeter in Continuity Testing mode.

Grounding Testing Results:

• Qube Q007 ESD Grounding Cube + 10AWG Copper Wire: Correct grounding, continuous connection from laptop stand to third prong of power outlet was verified.
• Macbook Pro AC Power Adapter + official Apple Power Adapter Extension Cable: No pins, nor metal case of of MagSafe 2 Power Adapter, nor metal body of macbook Pro were found to be actually connected to third prong ground of power outlet!

Test Scenarios:

• non-grounded Macbook Pro on non-Grounded Odyssey LSTAND:
  • macbook Power Adapter: Using 2-prong "duck head" plug on Apple Magsafe 2 60Watt power adapter
  • Placing wrist on stand: no shock felt. This scenario is with floating ground of stand, human, and laptop body. Thus, no circuit is connected (e.g.: by standing on grounded surface). Hazard still present if user is standing on or touching a grounded surface!
  • Voltmeter measurements: 600 mV ~AC RMS up to 1.62 V ~AC RMS measured from metal macbook body casing to laptop stand's exposed metal
• grounded Macbook Pro on Grounded Odyssey LSTAND:
  • macbook Power Adapter: Using 3-prong grounded plug Apple Extension Cable on Apple Magsafe 2 60Watt power adapter
  • Placing wrist on stand: small to little shock felt. This scenario is with laptop stand fully grounded and macbook body attempted grounding with Apple supplied adapter plug.
  • Voltmeter measurement: 161.1 mV ~AC RMS up to 460 mV ~AC RMS measured from metal macbook body casing to laptop stand's exposed metal
• non-grounded Macbook Pro on Grounded Odyssey LSTAND:
  • macbook Power Adapter: Using 2-prong non-grounded "duck head" type plug on Apple Magsafe 2 60Watt power adapter
  • Placing wrist on stand: medium to very sharp shock felt. This scenario is with laptop stand fully grounded and macbook body no attempted grounding with Apple supplied 2-prong "duck head" adapter plug.
  • Voltmeter measurement: 733 mV ~AC RMS up to 55.2 V ~AC RMS measured from metal macbook body casing to laptop stand's exposed metal

Observations:

All measured AC voltage potentials are in RMS (root mean square). The voltages would fluctuate widely over time, indicating a ground fault with variable characteristics.

Conclusions:

Based on the fact that no continuity to ground is observed on any magsafe pins, nor on macbook body, nor magsafe 2 adapter metal casing when using the official Apple 3-prong Extension Cable, there is an internal AC ground fault from power circuits inside the laptop to the metal chassis / body. There is some voltage drop from mains voltage levels, and the measured voltage potential from chassis / body to third prong home AC ground wire is variable when using Apple 2-prong vs 3-prong adapter plugs.

N.B.> Do not anticipate a direct connection to the computer: 
There is an extremely small logic board with a green/amber LED inside the distal end of the DC power cord. It has a bi-directional data connection to the computer, and turns on the LEDs on that board and/or permits charging-level power to flow ONLY on command from the computer.

@Grant Bennet-Alder: Thank you for this information, it's very helpful! This explains why I was unable to measure connectivity to earth ground while the distal end of this MagSafe 2 connector was not plugged into the side of the macbook. I suppose it's similar to computer power supplies that are switched by pins 4 and 5 on the ATX 24-pin connector.

I still wonder about the measured voltages and tingling to barely sensible shock sensations on the chassis in scenario 2 where the official 3-prong Apple Power Adapter Extension Cable was used to try and properly ground the macbook's chassis, and the laptop stand and all other equipment was verified to be properly grounded. Assumptions made here were:

1. Third prong should provide direct path to earth ground from some pin on distal end of MagSafe 2 adapter
2. macbook chassis should be connected to earth ground through MagSafe 2 adapter GND pin(s)

Based on your information, one or both of these assumptions may be false. Possibly #1 is only true when the charge control pin activates the power supply? However, I did just test that assumption by plugging in MagSafe 2 adapter and doing the connectivity test between chassis and earth ground. No detectable current could flow while the laptop was verified to be charging (~80% battery), and orange charging LED was lit on MagSafe2 plug. Assumptions here would be both #1 and #2 while charging pin has activated the other pins on MagSafe 2 plug. I suppose either the DC GND pins are not connected to earth ground, or the chassis is not connected to DC GND pin inside the laptop.

It's understandable that the other scenario results are to be expected given that the two prong NEMA 1-15P "duck head" connector has no way of providing a true earth ground. The floating ground scenario seemed to be less sensed than scenario 3, most likely due to no true path to ground from any of the contact points. I wonder also about how much the shock sensation is potentiated by the very small surface area of contact with the laptop stand, where the paint had chipped off. It's possible that this amplifies the sensation of pain due to the "skin effect" of how the electrons flow under and around the larger painted metal surface area of the stand, and then forcing more concentrated current through the small exposed contact point to a small surface area of skin.

Shouldn't the design of MagSafe 2 connector include an "always on" direct path to ground the chassis properly? Also note that this assumption that any ground pin actually provides a direct path to the third-prong ground may not be true, as I said earlier: I tried testing chassis connectivity to ground _while the laptop was charging_. Also note that all prior measurements were made while the laptop was charging, thus confirming that the charge control pin was activated during this time, as power was flowing to charge the battery.

What is electricity

When a Atom looses (or gains) a electron it become electrically active (called Ion).

There are two type of electricity

Conductive (metals) electrons flow from positive to negative

Non Conductive also know as Static Electricity (occurs in non conductive materials).

Grounding would do nothing to Static Electricity (no flow), the charge remains till discharged.

Grounding conductive surfaces will lead surplus electors to the ground (no static charge build up)

So I'm not sure you read my original post, as I mentioned that I'm an EE major and as such understand static electricity and other physics principles pretty well ;-)

😆

However, this consideration of electrical principles reminds me to reconsider something that I recently had to dive deeper into when trying to test a gas fireplace's thermocouple: the Seebeck Effect!

Now that I reconsider the setup and the voltages measured... I'm wondering how much the Seebeck effect is in play here. The macbook body is made of aluminum, and the grounding wire I'm using is copper. I'm not sure what metal the laptop stand is, but it's probably not copper either, possibly a different metal than aluminum also. The conductors used in the Apple power adapter + MagSafe 2 connector are unknown but I'm assuming there's at least 2 or more different metals involved in that connection.

When the laptop starts charging the battery, it does heat up...

So, we have all the environmental factors necessary to generate small voltages via the Seebeck Effect in this laptop charging & grounding scenario: 2 (or more) different metals connected together, and a temperature differential!

@Grant Bennet-Alder: You seem pretty knowledgeable about the laptop and electrical circuits involved here, I'd be curious to hear your thoughts about the possibility that this voltage measured could be from the Seebeck Effect.

@Grant Bennet-Alder Thanks for your quick and well thought out responses! Agreed that a metal stand may not be the best option due to the unexpected voltage differential phenomenon that happened here. I can do some touch up to the paint job to avoid contacting the conductive metal of the stand.

I'd expect that the stand does absorb some heat from the charging laptop, which I've noticed does occur while the charge light is amber. I also have noticed that the measured voltages do fluctuate, and start increasing towards the maximum end of measured values when the laptop has been charging for a longer time. It seemed to stabilize at the higher values after more time elapsed. I did inspect the laptop during this time, feeling that it and the stand were heating up. This suggests to me that perhaps it is something dependent on temperature or some other related condition as battery charge increases. I didn't measure temperature, as I did not even think of it being a factor at the time.

Anyway, I think we've thoroughly explored the issue and I've got enough information to mitigate the problem now.

Marking solved!

Thanks for all your help and expertise!

I should also mention that the measured voltages for all scenarios were not constant over long spans of time. There was a lot of fluctuation, and the max voltages measured did correlate with feeling tingling or shock, while the lower voltages were lower intensity or not detectable.

It seemed to take some time while charging for the macbook chassis to build up enough voltage potential to produce a sensed shock, but once it charged up it was very reproducible. If I waited long enough to see the larger voltages appear on the multimeter display, and then placed my hand across to complete the circuit it did produce a sensed shock.

What's your point? My finding is that the miniscule number of people 
experiencing "buzzing" when touching their plugged in computer are not 
using a correctly configured grounded outlet with a grounded plug and 
power brick.

Yes, this is true for most cases and the un-grounded adapter 2-prong scenario did produce the higher voltages and shock. However, the assumption was: when properly grounding all equipment with a 3-prong plug, the macbook chassis should not have any voltage, and continuity from earth ground to chassis should be detectable. This wasn't the case in any scenario, and fluctuating voltages were detected in all of these.

Ah, that's a bit more complex than I had originally thought. Really interesting that it's actually able to receive digital data and commands. Also really helpful to know that data can be sent and read from that MagSafe 2 connector data pin and viewed in the system report! Really cool!