Is an Ungrounded Power Adapter Dangerous?

Vince - Please read the my answer above again and my comment to brrempel. While I'll agree corded appliances (desktop systems, washing machines, toasters etc...) should be grounded for safety. Laptops and other transformer connected devices are in a different class. Unlike directly connected to AC these systems have a conversion which converts the voltage and the power from 110/220 volts AC to alternating 18 volts DC within the power adapter. When using a real Apple power adapter you won't have the risk of shock. The ply risk you could have is with a fake power adapter which is what happened in China. I should also printout the Apple design has a fuse link so if the MagSafe cord where to get wet or shorted it would trip inside the adapter. In any case it shouldn't damage your laptop. ESD entering via the MagSafe is more likely the issue burning out the power FET's (a common problem).

Apple didn't put a ground wire in there for decoration. The fake Chinese power adapters don't even have ground wires, and if the 10mm stud happens to be made of metal (usually it's plastic on the fakes) it's never connected to anything inside the case. In fact, that's an easy way to tell if you have a fake or the real thing--check for continuity between the ground wire and the DC cord pins.

Yes, obviously the power adapter converts high voltage AC into low voltage DC, but what you don't seem to understand is that high voltages are still active inside the case. Damage to the power adapter, liquid spills, or anything that might accidentally bridge the gap between the internal mains lead and the outgoing DC leads would create a serious shock hazard if not for the ground. There is no fusible link inside the adapter as many owners of incinerated Magsafes can attest. This is the same type of foolishness from people who think that a GFCI is a substitute for a ground wire. GFCI only limits the time you can be exposed to a shock, whereas grounding prevents the shock from ever happening in the first place. In addition to the safety element, grounding the power supply also prevents electrostatic influence in your laptop or tablet, and Apple's power supplies have Faraday shielding inside the case which is grounded through the earth wire.

Vince your only half right here (half wrong). I think you need to do some more research (with a bit more of an open mind). I won't go into all of the this but lets clear some facts: Apple does put fuse links inside their power adapters and if you are so foolish to soak your adapter in water then you can't blame Apple for the sparks! Just like you can't take your AC powered radio into the shower. The EMI shielding (faraday cage) as explained above does not have any safety involvement. You should check your house fuse panel did you note the common side is tied to the ground side as well. So what is the difference???? Think about that. Don't get me wrong here you should use a grounded outlet and plug! The point in the OP was the cheap knock offs safe to use and We both agree NO.

1. Grounding can NOT prevent ESD discharge to your computer board. Even when power cord isn't connected to the computer (or you can say it is floating), charges can still go from your finger tip to the board when you touch components, because the board can be considered as ground (with a much larger metal area) compared to your finger.

2. Grounding can NOT prevent power surge. Power surge can be protected by a shunt diode to ground or a fuse. Fuse is in series on the hot line, not on the ground line.

Actually, you're the one who needs to do some research. Using an ungrounded plug is always less safe for you and for your device, and surges are shunted to ground using a varistor, not a diode. You can use the adapter with an open ground wire if you want, but it's stupid and dangerous, especially with a Chinese knockoff which is all the more likely to leak potentially deadly voltage into the DC output cord. People do stupid things with electricity all the time, and usually they get away with it. If you want to stick your neck out, it doesn't bother me.

The word Ground has different meanings depending on the context. Earth Ground and the White Neutral wire are bonded together at the fuse panel with 120 Volt North American house wiring. The third ground line is commonly used as a means to offer a second pathway is case a short to prevent shock in the case of a GFI outlet.

Today the function ground is to offer a means to dispel emissive noise in electrical devices.

When working on static sensitive devices ground plays a role in discharging the dangerous voltages that someone may have built up on their person (ESD).

The question here involved all three facets.

FishDrowned - Sorry guy, thats not the correct answer. Device size and current it uses, as well as international standards define what type of plug is used.

Since laptop's transformer/adapter is wrapped in a plastic case, you don't even need the ground pin (it is there only for precaution that you might break the case); which means 2 prong plug is also okay for a laptop...... Sorry Dan, which part is wrong? I think ground pin is for shielding EMI or noise is pretty nonsense.

Here's a good read on the the different plugs AC plugs & sockets. If you drop down to the NEMA standards you will see the plugs amperage dictates if the plug is grounded or not. A phone or tablet does not consume the same amount of power most laptops require which is why the MacBook Pro systems need it and the new MacBook doesn't. It has nothing to do with the construction of the device. As to ground for EMI that too is a factor! But that's a different question :-}

The majority of EMI is coupled through the wires AFTER the power adapter, because the wires behave like an antenna. And that is why you usually see a Ferrite bead at the end of the power cord. Grounding the transformer on the AC side won't reduce much EMI.

More about noise: Since there is no ground at the second stage (DC side) of transformer, the signal is balanced; which means any noise from the AC power line at the first stage of transformer will become common-mode noise at the second stage, and will be cancelled out. This is why sometimes transformer is also called balun.

Sorry guy this is not just no true! I can point you to many sources that say otherwise.

The problem you and others are facing is a problem of forgery of the power charger. People have been caught making & selling fake chargers for both laptops & phones which are junk! In India & China it is the most repent!

Many fires have been pegged on these fake chargers as well!

Apple has tried very hard to get the fakes off the market. But, we are the guilty ones here as well when we see a bargain and don't question if it's a fake or not.

I too have experienced the same small electrical shocks from a MacBook Pro using its original MagSafe power supply, which came with the computer purchased new at an Apple Store. The power cord was grounded with a three-prong fitting and plugged into a 120V grounded outlet. I believe the problem has its roots in the crappy rubber-encased cord that connects the power supply to the computer; this cord seems to suffer from internal fraying of its wires, leading to these untoward and shocking effects. Ultimately this is either due to bad design or substandard materials Apple uses in its rubber cords; I've literally had to replace half a dozen power supplies over the years at around $80 a pop.

@theophilus - There are two issues you raise Apple did have a run of bad cords and has a recall. But I don't think thats the real issue here!

If you are very sure you have a good REAL Apple MagSafe charger and you need to replace it that often then you have power line issues! Sounds like you needed a good surge suppressor or UPS. You also may need to check your outlets and buildings grounds.

You've encountered a cross-wired outlet or some device near you is leaking to the ground connection so its live (in India). This gets into proper building grounding as well as properly wired outlets.

Get a simple AC power line checker to check your outlets.

Ah! The word Transformer can get in the way in the dialog!

Let's think that device between the AC outlet Transforms the power from AC to something else. While the technology maybe different from using the older transformer method, in either design there is isolation between the AC side and the lower voltage side (AC or DC).

The real issue is the voltage and current limits of the connection that are involved here if a ground connection is required at the AC side.

Yes! Any device that 'Transforms' power can be defective! And cheap copies are the worst! As they use the least protective design! The best way to think this is I have two cups on a table one has a foam ball under it just looking at the cups you have no idea which has the ball only testing by moving the cup side to side you might feel the difference. Basically thats what you need to do here as well test the design to make sure its real and good.

@thejohndyson - Are you so sure your building wiring is good? Until you do the proper testing and make the needed corrections you are just throwing aspersions!

I bet you, you really have a power issue! You either have a crossed wired outlet or another device plugged in is mis-wired leaking power to ground or you have a poor ground circuit.

When I was based in the UK working for IBM network group I encountered many poor power setups in businesses. One bank was so bad they needed to rewire the entire building! They moved out and had over a million pounds of work done it took over a year before we got back to install the network hardware. Such a big difference! Even here in the States we have buildings which have very poor power, mostly it's dropouts and surges. One of my customers needed to put in UPS's in for almost every PC system.

Apple can't fix your power issues! A grounded cord is a good solution to remove the leakage to your system but its not fixing the root issue!

I think you're fundamentally misunderstanding how these switching power adapters work. There is no earth connection because there's nothing to earth in the laptop, since it has no connection to line voltage. In a correctly designed power supply, the line and low voltage sides are isolated. Even some devices that connect directly between the device and wall don't have an earth, because the line voltage entering is immediately isolated by the internal power supply. If there is no path where the device could become energized with line voltage, then an earth connection is redundant. The only power entering your MacBook is the ~20v DC from the power supply, so an earth connection is really pointless. The "shock" you're feeling is most likely static. The 110v you're reading (with a digital multimeter I assume) is probably "ghost" voltage, induced by proximity to live circuits. This is a very common phenomenon. You need an instrument designed to test high voltage lines to get accurate readings.

@Guy Onearth - You are very correct for a properly wired outlet!

Now what happens when the neural and hot leads within the outlet are reversed? The ground line then can become charged! While a MacBook Pro charger should be isolated from the power feeds the shielding does carry forward to the system so in some cases the metal case can become live but not by design by Apple. The failure is the outlets/buildings wiring.

However in the UK Apple seem to think we like using a laptop that doubles as a van der graaf generator!