Ground lift adapter for laptop

[garlandb]

I'm reading conflicting information in regards to the safety of using a ground lift adapter (ie converts a three prong to a two prong) to resolve a ground loop between an LCD monitor and a laptop.

Anyone care to weigh in on this?

 

[Swivelguy2]

Ok, I'll weigh in: I've never seen a laptop power supply with a grounding prong.

 

[garlandb]

You have no idea how badly I wish that was the case. ; )

 

[Mark R]

Most laptop adaptors are double insulated and do not require earthing. I've never seen one that isn't (and does require earthing), but that's not to say they don't exist.

'Earth lift' adaptors have no purpose, as they always introduce a safety hazard. If a device is built so that it is not double insulated, it must be earthed whenever it is in use. If a device is built so that it is double insulated, it must not be earthed.

If your laptop adaptor genuinely isn't double insulated, then replace it with one that is (virtually every aftermarket one is).

 

[Modelworks]

Those two prong to three prong adapters have a little green tab with a screw hole that people often ignore. That screw hole is so you can remove the face plate screw from the outlet cover , plug in the adapter, then put the screw through the tab and tighten it down. That connects the neutral side of the outlet with the ground prong on the plug which is the older form of ground before the 3rd prong was allowed. If the screw is not used then the adapter is being misused.
http://www.tangible-technology.com/power/p2/power_2.htm

[FONT=Geneva,Arial]The most common bad-practice electrical activity is the misuse of the ground adapter as a ground lifter (see Figure-3). Use it only as a testing tool, never as a fix. Nothing is more permanent than a temporary solution.[/FONT]

Ground loops only happen when there are wiring problems in the home. If the outlets are wired properly and the devices plugged in are not broken then no ground loop should occur.
The exceptions are ground loops from wires coming from the outside like cable or telephone, and those are supposed to be connected to the home ground before they enter the home.

If you want an easy truly safe way to isolate your laptop from everything it is connected to you can get isolation transformers really cheap in the size needed for a laptop. Other options are to get a 13.8vdc @4A + adapter and power the laptop off a car charger.
Just make sure the 13.8VDC is using a transformer and not a switching supply, transformers are heavy which is a good quick indicator.

 

[VirtualLarry]

Ok, I'll weigh in: I've never seen a laptop power supply with a grounding prong.

Both my mom's Compaq (Vista era, Celeron 755, 2GB, 250GB), and my HP (XP era, Sempron 3000+ 754, 512MB, 60GB) have grounding prongs on the AC adaptor plug.

 

[alkemyst]

Some laptops tranformers use a standard PC plug but really have no ground pole.

 

[Paperdoc]

Sorry, Modelworks is wrong on two significant points.
1. By connecting the prong on the adapter to the screw properly, you do NOT connect it to the Neutral side of the power supply line. And the Neutral side never was a substitute for a true Ground. It is true that most house supply systems in North America and many other places use a "Grounded Neutral" system and have done for many decades. However, it is vital to recognize that the Neutral line is ONLY at Ground potential at the breaker (or fuse) box where it is connected to a true Ground source. Anywhere else in the house the Neutral line is NOT at true zero potential (compared to Ground) because of its non-zero resistance and the current flowing in the circuit. For this reason NO house wiring system ever uses the Neutral line as a Ground substitute - unless, of course, some amateur has mis-wired the circuit. You either have a true Ground lead that carries NO current under normal operations, or you have NO Ground lead.
2. The screw in the middle of the cover plate connects to the metal frame of the duplex receptacle mounted in the device box. That frame is completely isolated from both the Hot and Neutral connections to the blade slots. (In the current wiring system with a third bare Ground lead and a third prong hole in the receptacle, the frame is connected to the Ground wire and U-shaped hole.) But by being mounted in the box with screws, it is connected to the box. HOWEVER, in older houses with only 2-wire cabling those boxes are not connected to anything electrically - they are merely mounted mechanically in the wall. So in those systems the box, receptacle frame and screw are all floating completely independent of all electrical connections. They are NOT Ground, Neutral, or Hot. Thus attaching the screw in those cases does absolutely nothing. Now, in SOME systems there has been an attempt to update by installing a third true Ground lead to each box in the wall, or by re-wiring using BX cable - the kind with a spiral-wound metal cover that is connected to the breaker box itself, and THAT IS connected to Ground. So in those cases the box MAY be Grounded, and then the screw does establish a Ground connection to the U-shaped hole in the adapter. The trouble is, you do not know about those possible updates without doing a good investigation to verify the presence of a high-quality (that is, extremely low resistance) Ground connection.

For OP's original problem, the best suggestion I can offer is to plug the computer, the monitor, and any other connected devices into ONE common power source - like, a power bar - so that all devices have exactly the same Hot and Neutral supply lines. Plugging into different wall outlets may NOT achieve that, and result in "Ground Loops" that are really circuit elements designed to operate at the same voltage levels and references, but not actually doing that because of unbalanced supply issues.

 

[Modelworks]

. And the Neutral side never was a substitute for a true Ground. It is true that most house supply systems in North America and many other places use a "Grounded Neutral" system and have done for many decades. However, it is vital to recognize that the Neutral line is ONLY at Ground potential at the breaker (or fuse) box where it is connected to a true Ground source. Anywhere else in the house the Neutral line is NOT at true zero potential (compared to Ground) because of its non-zero resistance and the current flowing in the circuit.

I knew someone would bring this up. The reason for the addition of the ground wire was because there was no protection in homes from someone touching a neutral grounded appliance and a grounded source like a metal sink. There was also the possibility of a hot wire contacting a metal part that was not connected to another wire and energizing that part. Neutral was a substitute for ground and it is why there are two different sized slots on the outlets to begin with. Many older homes depended on the neutral being wired correctly for use as a ground because it was often connected directly to the metal frame on appliances. When it comes to the choice of no ground or neutral ground at the appliance, the NEC prefers the neutral as ground.

For this reason NO house wiring system ever uses the Neutral line as a Ground substitute - unless, of course, some amateur has mis-wired the circuit. You either have a true Ground lead that carries NO current under normal operations, or you have NO Ground lead.

what about the millions of outlets that use it everyday and have for decades ?

220VAC appliance outlets continued with this practice up until 2004 and it is grandfathered in so that it only has to be changed on new construction. . Most electric dryer outlets are 3 prongs, 2 hots and 1 neutral. The neutral is connected to the metal dryer frame by a jumper that serves as the ground.

 

[Paperdoc]

I agree that many items in the past were designed with Neutral connected to the metal chassis. This is especially true of electronic equipment, but less so for heavy-current devices like heaters. It still is done today with some electronics, although it is poor design. In those systems, the chassis serves both as power supply "Return" or Neutral, and as Signal Ground. They can be a great source of noise and hum often called "Ground Loop Noise". One major reason for discontinuing the practice is that if the Neutral line has some flaw that raises its resistance, anything at the appliance end of the line is actually NOT at zero volts with respect to a true Ground (like a nearby water pipe, for example) and thus the exterior might be a source of electrical shock.

As Modelworks says, it is VITALLY important in a 2-wire system that allows Neutral to be connected to the chassis for the receptacles and the plugs to have the two different blade / slot sizes. That is the way one can be forced to ensure that the Neutral of the supply wiring IS connected to the intended Neutral of the appliance. The problem is that MANY (most??) old 2-prong wiring systems only had outlets with slots (and matching plugs with blades) of the identical (smaller) size and hence it is always possible to plug appliances in the wrong way! For designs that do NOT connect the Neutral side to exposed metal (like modern "double insulated" items) that is not a big problem. Even worse, there are sites where the original wiring work paid no attention to which slot was Hot, and which was Neutral. So when you look at a 2-prong outlet with identical slots, you have no way of knowing the correct way to plug in an appliance. As Modelworks says, the introduction of different slot sizes eliminated this problem. But it wasn't long after that until the introduction of 3-prong outlets and plugs to add the true Ground lead, and that has become dominant.

I am surprised to learn what Modelworks says about the 220 Volt 3-wire system up until 2004. Certainly I can understand that such a system in widespread use until then would be "grandfathered". It's just that in the area where I live, all new household wiring systems HAD to have Ground leads and connections since at least the late 1960's. This applied to 15 amp duplex outlets as well as to heavier outlets like those for dryers and stoves. But I can see that, if you must have no dedicated Ground in the wiring to a dryer, connecting the Neutral to the exterior chassis is better than leaving the exterior completely unconnected. If you didn't do this, any failure of the unit that allowed a Hot-connected component to touch the chassis (for example, a broken and bent heating coil wire) would create a dangerous potential for lethal electrical shock.