Exactly why is it wrong (aside from code) to replace a two- wire outlet recepticle with a three-wire recepticle in a 45 year-old house that did not require ground wires everywhere, and simply connecting the neutral side to the green ground wire screw? What is the danger it poses--for safety and to protect, say computers?

 

It would take 10,000 words to properly address your question, so let me just give you one example. Suppose you did what you said. Then you plugged in something like a refrigerator that has a three-pronged plug. Then further suppose that at some time in the future, perhaps months or years in the future, the neutral connection opens up (which, by the way, is a very common failure). At that point, the case of your refrigerator is now energized to a full 120 volts. When your daughter grabs the handle of the refrigerator to get a glass of juice, she's very dead instantly.

And the sad thing is that this type of ground doesn't protect your computer anyway.

 

Country, first take what John says to heart you dont really need to know anymore than what he says. I'll spend a little time to answer some of the why of your question. But as John said it is a long subject.
I dont know how many times Ive been drawn into arguments with people who think the neutral is a ground wire and doesnt carry current. Hopefully these people never work in the electrical field under that understanding, they wont be alive very long.
The neutral is a current carrying wire, more properly called the grounded conductor. It provides the path for the current to return the central tap of the utility transformer after it goes thru the load (light bulb, kitchen mixer motor etc..). The ground wire that connects to that green screw you mention is a non current carrying wire. It is only meant to carry current in the event of an electrical fault, under normal everyday conditions this wire does nothing. It is there for safety reasons only. Now take a look at that three wire receptacle. Notice the "D" hole (ground) is electrically connected to that green screw. Notice also that the ground screw is not connected to the neutral nor is the ground hole of the receptacle. Now think about a kitchen mixer lets say a Kitchen Aid metal cased mixer. The cord to the mixer has three wires. A hot wire bringing electricity to the mixer a neutral wire and a ground wire. If you could follow the cord inside the mixer you will find that ground wire terminated to the metal case of the mixer. Now think about what you have asked. Now think about what happens when you plug this mixer into this receptacle and turn it on. Current passes thru the windings of the motor then out the neutral wire of the cord to the receptacle then thru the neutral wiring in the house back to the house main panel neutral bar then to the transformer center tap. If a wire as you ask is installed on this receptacle connecting the current carrying neutral to the non-current carrying green screw you have just provided a path for the current to travel right up the cord in the metal case of the mixer via the ground wire in the cord. The metal case of course is the part you touch. Now here is how you get killed. As John said sometime down the road your neutral comes apart on the branch circuit serving this Kitchen Aid mixer. Now the electricity has no way to flow back to the center tap of the transformer. Now you walk up, plug the mixer into the receptacle you have intalled this wire joining the neutral and ground. You then turn on the mixer while of course touching its metal case. Your body has just provided the path to ground the circuit didnt have because of the open neutral and your dead. Do you see? Without this "bootleg ground" beween the neutral and ground screw the electricity will stay inside the walls where it cant hurt you. By installing it you provide another path for the current to come out of the walls to the metal case of your mixer and create a potentially fatal event.
Now one last thing as John is probably pulling his hair out by now. Doing what you ask is a very common misconception in order to fool an inspectors receptacle tester. Those who do it, thru lack of knowledge, think since the white wire (neutral) goes to the neutral bar which is grounded, then it will act as a ground or a false ground. They dont know they are connectiong to a current carrying wire. By the way it might fool the tester but it wont fool the inspector, they have seen it a thousand times. There is a proper way to install three wire receptacles on two wire ungrounded wiring. If you need to know this start a new thread and someone will tell you how....GL....Roger

 

Now I will address the computer issue.

Your computer generates power that it can use. The integrated circuits and other components need various DC voltages. These voltages are generally in the -12 volts to +12 volts range. Your computer generates this power with a power supply, converting the incoming AC to the required DC voltages.

The voltages generated are all with respect to some value. While that value can be anything, it generally works best if that value is 0 volts, often called ground. Your computer gets that ground from the ground prong. Since it is a reference voltage, this is not a problem.

However, if that ground deviates, which it will if it is incorrectly connected to the current carrying neutral connector, the voltages in your computer fluctuate. Generally speaking your computer can handle this without a problem.

However, if you have a computer, a printer, and various other devices, then you MAY end up with communication problems because the voltages vary from each other.

Finally, there is the issue of a surge suppressor. To properly function a surge suppressor needs to be grounded. The ground path is used to safely route the surge away from your electronic equipment. Without a ground, your surge suppressor won't work. With a bootleg ground, the surge is put on the same wire that all of your other household electric appliances are connected to.

 

The ground pin on your plug has little or nothing to do with the ground used to reference the DC voltages in your pc. The only reason you need the ground pin is for surge protection. Almost all surge protectors shunt the spikes to the ground pin.

 

Joe, if that were true, then PC plugs wouldn't even have a grounding pin, would they?

 

I neglected to include the standard saftey reason you have a ground on any eletrical appliance.
My main point is that the ground pin is not relevent to the DC voltages inside your pc. The DC voltages are referenced from a ground point created inside the power supply. That point could be connected the ground pin but it is not required to operate the PC.

 

Joe, I never said that a PC wouldn't operate properly without a ground. It will operate just fine, especially by itself. However, when you begin to interconnect devices together that each create their own ground, and when a ground is necessary for transferred signals, you begin to have problems.

Now, most communications these days are done without the need of a ground. They use a serial connection of some sort, but there are still some older computers and systems that will be effected by lack of a ground.

My father and I had just this very problem about 20 years ago with his first computer. There was no problem when he used a properly grounded receptacle, but when he moved his computer and printer to a different portion of the house with ungrounded receptacles, the problem appeared. At first he thought he damaged the cable somehow. We solved the problem by manually connecting the ground pins for the printer and for the computer. He did eventually install a grounded receptacle.

 

If the “hot leg”, due to a problem internal to the mixer, comes into contact with the mixer’s metal frame, is the safer condition a bootleg ground (neutral connected to frame, fuse blows) or is the safer condition to allow the frame to remain energized?

In one assumed fault condition we’re safer with the bootleg, in another fault condition we’re not.

IMO, in an environment that does not support wiring to present code requirements, the GFCI is the only answer, even for the fridge.

 

Slow down. You should never end up with a three prong plug on an ungrounded and non-gfci protected circuit. The two slot receptacle won;t accept the plug, and the user will have to find another receptacle.

 

Good point!

 

Yes, there are some conditions in which the bootleg ground is conceivably safer than no ground, and you identify one. However, such faults are less common than open neutrals. So it's an issue of playing the odds. And the odds are heavily against the bootleg ground. The GFCI combined with no bootleg protects against both. No contest.

 

This shouldn't be about how it could work out better under ONE circumstance, it should be -> Just don't do it and fix it if you did. Since then it will be ok all the time.

 

I want to thank all of you for your most helpful explanations.
Could you also tell me how to test for a genuine ground in a three-wire receptacle and one with the neutral and ground connected? Would a GFCI tester alert me to the dangerous condition, or do I have to take the receptacle out and look at it?
Countrymusic

 

Even taking out the receptacle and looking at it may not tell you. The receptacle you look at may look just fine, but the neutral and grounding wire may be interconnected in the next box over, the box from which the wires to this box run. So maybe you need to look in all the boxes. Even that won't tell you if somebody made a flying splice in the wall. And it won't tell you about other stupid things such as somebody grounding a receptacle to a grounding rod or plumbing pipes (other dumb things to do).

There's a reason why electrical installations must have a first inspection before the drywall goes up.

 

Just been reading this thread with interest, im from the uk as many know in this forum but i love reading you electrical questions. Anyways do your houses have earthing setup already as standard installation via earthing rod etc..
Just interested as it seems crazy that anyone would even consider jumping together the neutral and earth wires. Does anyone know any good books for electrical installations in Us and Canada.
Im an electrician in Uk at present and im moving to Canada next year and hopefully will be continuing my career over there just would like to brush up on some stuff before i get there.

Thanks

 

All new construction has our receptacles wired with three wires, a hot wire a neutral or return, and a ground.

However, most electrical devices only use the hot and neutral. It is only appliances (washer, dryer, refrigerator, microwave oven, etc.) and some electronic equipment (mainly computers) that use the ground.

The problem is that years ago houses were not wired for grounded receptacles, except for the kitchen and sertain other places. Sometimes the houses were wired with ground wires, other times just two wires were used.

Unfortunately people sometimes to replace their receptacles. Sometimes this is for color, or simply because they have worn out, other times it is to allow them to accept a three wire cord and plug. However, the homeowner does not always look for old style receptacles (with no ground) and they do not check to see if the outlet box is properly grounded and/or contains a ground wire.

 

The house I'm about to purchase has the same problem, i.e. old two-prong outlets everywhere (and even worse, 3-prong outlets that aren't grounded!).
I of course will do the job right, but I'm not sure I understand the safety hazard of the bootleg ground.

If I have two wires coming into my recepticle, and I attach the neutral wire to both the neutral post on the recepticle and the grounding post, and then I have an open neutral, how does the metal case of the appliance get energized? Obviously, a wire could come loose inside the appliance, but assuming the appliance is otherwise in good repair, I don't see how an open neutral will cause a problem. You'd simply have the hot wire coming into the appliance, with no path for current to leave. You still need some kind of failure in the appliance to have a problem, right?

Bottom line, I don't understand how a bootleg ground is worse than having no ground at all.

I drew up a diagram to illustrate this. The picture is too big to include here, but if you click on this link it'll pop up. Click Here As I drew this, condition 1 is a normal, healthy, 3-wire grounded circuit, and condition 2 shows what happens when the hot wire gets loose and energizes the case - current is diverted along the ground, and the breaker trips.

Conditions, 3, 4, and 5 show a bootleg ground. As I see it, the only dangerous condition is when the appliance case is energized, and there is an open neutral (condition 5). But this is just the same as if there was no ground. John Nelson's answer made it sound like a bootleg ground is worse than no ground at all. Please clarify. Thanks!!

 

Here is one problem.

The neutral wire in a circuit carries current. Normally the neutral goes back to the panel and then to the utility company. It normally does this through the white neutral wire. However, if you incorrectly connect a ground wire here, and that ground wire finds another path to ground, then some current will flow that way. An example of this would be washer. If the washer has a bootleg ground, then the metal shell of the washer gets connected to ground, say a cold water pipe, through some other means, say a human body, then some of the return current on the circuit will flow through the other means (the human body) to the ground. Ouch.

 

Racraft

Still, doesn't that require the hot wire to somehow come loose and touch the washing machine shell? Ordinarily, the hot and neutrals are isolated from the shell, and the shell is grounded in case of a failure inside the washer, right? I still can't understand why a bootleg ground is more dangerous than no ground, because in the example you provided, the person who touches the washer shell and a cold water pipe at the same time is still screwed, bootleg ground or no ground.

Arnie

 

I realize that this is a hard concepot to grasp. The neutral wires carries current. In my example the human body and the appliance would be in series with 120 volts across both items. Current would flow. Would it be enough current to kill you? Possible, depending upon where it went across the body..

 

The problem occurs not so much when one receptacle has a bootleg ground but when all or many do in a household that have metal cased appliances plugged into them. A phenomenom called neutral loading occurs over time on these metal cases. The ungrounded conductor is regulated at a given voltage say 120 volts. But the grounded conductor (neutral) is not regulated under these conditions. Its sort of like a balloon, blow it up tight and then release it and the air flows out in a regulated manner. Now blow up the balloon tight not letting the air out and poke it in the side with a pin....Bam!! This is the effect of neutral loading. When the neutral comes apart and you touch any metal appliance and neutral loading has occurred massive amounts of current will flow somewhat like a discharging capacitor because you gave it the ground it needed thru the bootleg to your body.
Also the hot wire does not need to touch the the metal case for the bootleg to be dangerous. If the neutral on the circuit the mixer is plugged into comes apart then simply turning the switch on will not operate the mixer because there is no return path to the panel neutral bar and center tap of serving transformer. But with the neutral bootlegged to the ground screw and in turn this is connected to the green wire in the appliance cord and that green wire is terminated to the metal case of the mixer, it only needs a path to ground to complete the circuit loop. You provide this once you touch the metal case trying to figure out what is wrong.You might even hear the mixer start to operate as you are electrocuted.
Now look at your diagram number #4. In your head visualize you turning on the mixer, while touching the metal case, at the same time reaching over and grabbing the kitchen faucet, you have just become an extension of the green wire attached to the metal case making a path to ground thru you to the plumbing because the neutral is open and you provided another path with the bootleg.

 

The problem is with a boot leg ground the shell of the washer is NOW connected to the neutral. It is not isolated. Now it has a potential on it and if you touch the metal and a water pipe or other ground the current can/will flow from the shell though you to the pipe. It become even worse if the neutral becomes disconnected somewhere. Because now the ONLY path for the current is though whoever touches the shell.

 

Because of my previous post I feel responsible for some of the confusion re: a “bootleg ground”. My post was only to advocate the use of GFCI’s, not to suggest using a bootleg ground. To make my position clear, NEVER, ever use a bootleg ground! I’ll not bother providing reasons as the experts have already provided them.

As far as computer performance, there are several safe, effective, and “legal” means to effect proper performance, none of which require a bootleg ground or any code violation. For electronic systems, one should think in terms of providing an “equipotential environment” rather than using contrived, unsafe grounding techniques.

 

I get it now... I kept trying to think in terms of what would happen if the hot wire broke loose inside the case, I never realize the implication that if you bootleg ground an appliance, it's like you're splicing a wire into the neutral wire on your appliance cord, and then holding onto that wire every time you touch the appliance!

I realize on my diagrams, what I was missing was the effect of bonding the neutral and ground at the recepticle, was basically to un-isolate the internal machinery, and include the metal shell of the appliance as a part of the electrical wiring.

Thanks for everyone making it clear to me!