Neutral and ground

[jmattero]

Hello:
I am not an electrician, but would like to learn an answer to a question that has been bothering me. In my area, it is "code correct" to have a 2 prong duplex receptacle in homes where there is no ground wire. I have also heard of people using a GFI receptacle in such situations in order to have a 3 prong receptacle, even though there is no separate ground wire. I believe, but am not sure, that this is also allowed by the code.

My question is this... I have heard guys who have "jumped the neutral" on a GFI, in order to fool the tester, which otherwise would show an open ground. I know this practice is unsafe, but I am not sure why. In other words, since the ground wire and the neutral wire both connect to the neutral bus bar in the service panel, why is jumping the neutral unsafe? I have heard people say that, if there were a short in an appliance that was plugged into a normal 3 prong outlet, the electricity would go to the ground via the ground rod or the bonding to the copper pipe. The same would, as I see it, be true with a short in an appliance plugged into a 2 prong receptacle. It seems to me that a "jumped neutral" would take the same path if a short were to occur in an appliance plugged into it, since both the neutral and ground go to the same bus bar. Can someone explain this to me? I simply wish to educate myself. Thanks in advance.

 

[normbac]

Re: Neutral and ground

Ther is to much explaining read this book by mike holt Grounding versus Bonding Textbook

05NCT2 $39.00 Grounding versus Bonding textbook is loaded with detailed color-coded graphics so you can easily differentiate between grounding and bonding. This text gets to the root of all problems associated with grounding and bonding. Subject includes: Circuit . . .

 

[celtic]

Re: Neutral and ground

Originally posted by jmattero:
... it is "code correct" to have a 2 prong duplex receptacle in homes where there is no ground wire.
...people using a GFI receptacle in such situations in order to have a 3 prong receptacle, even though there is no separate ground wire.

'BOTH of these methods ARE code compliant.

See:Code Check
Also see:How does a GFCI work?

Originally posted by jmattero:
My question is this... why is jumping the neutral unsafe?

Can someone explain this to me?

There are reasons..the first being parallel paths:

There is no "short answer", but rather a lengthy answer..here is part 1 of 12:
Grounding-vs-Bonding @ Mike Holt(you will need the Adobe reader to view the .pdf file ~ free at adobe.com)

...and it can be technical to a lay person.

While it may "seem" that the neutral and ground are the same, their purposes are entirely different and must be addressed/installed as such.

Simply put, a ground to neutral connection on the load side (after metering/1st disconnecting means) CAN allow for an undesirable potential to be applied to the ground should the neutral become lost (ie, energizing the ground system)

 

[jmattero]

Re: Neutral and ground

How does the power know which path to take once it reaches the neutral bus bar? If you are saying that the neutral and ground are redundant for each other, I understand. Someone who was supposed to be an electrician said that the power company did not want the power back, and that a short would send power back up the pole in a jumped neutral situation. That is where I am confused. Thanks.

 

[bphgravity]

Re: Neutral and ground

This is one of the biggest contradictions in the NEC. Rules change depending on what side of the service disconnect your on. Normal operating current is not permitted to flow on non-current carrying metal parts of the system, but only on the load side of the service disconnecting means. When current flows on the line side of the service disconnecting means, they call it "objectionable" yet it in no way can be avoided.

To worsen the problem, the code permits the return current path (service neutral) to be reduced in size which in effect increases it's impedance while at the same time requiring you to establish the lowest impedance grounding system as possible. The effect is even more objectionable current flowing over grounded parts.

 

[charlie b]

Re: Neutral and ground

Originally posted by jmattero: How does the power know which path to take once it reaches the neutral bus bar?

The problem takes place before the current reaches the neutral bar. Here is a not-too-lengthy-or-too-technical-(I hope) explanation that I wrote some time ago. Let me know if this helps you understand.

- - - - - - - - - - - - - - - - - - - - -

Why is it not safe to connect ground to neutral in a receptacle?

The third pin, the "ground pin," is connected to the external metal parts of whatever you plug into the receptacle. The other two pins (or "prongs"), the "hot" and the "neutral" as they are sometimes called, are only connected to stuff that is inside the case. But if one of them were to break and come into contact with the case, it might give a shock to whoever next touches the case.

The purpose of the ground pin is to take that shock current from the case and send it directly back to the source. This current will be high enough to cause the circuit breaker to trip. In other words, the ground pin will save the life of the person touching the energized case.

If you have only a 2-prong receptacle (no ground pin), the protection you lose is the ability of the system to trip the circuit breaker. So whatever shock a person might get from the case will not be stopped, unless they are lucky enough to be able to pull their hand away, or perhaps they might fall on the floor (thus causing their hand to be pulled away from the case).

So what happens when you connect the ground and the neutral within a receptacle? You cause the case of whatever is plugged into that receptacle to become energized. How? By virtue of the fact that there is current flowing in the neutral wire, the fact that the neutral wire is connected to the ground wire, and the fact that the ground wire is connected to the case of whatever item you have plugged in.

Every time anyone touches that case, they will receive a shock. But that shock is usually very slight ? so slight that the person might not notice. Therefore, the person might continue to operate that equipment for years, and still not know they are in danger. In other instances, the person will not be so lucky. The amount of the shock might be low one day and higher the next day. It cannot always be predicted.

An extreme danger comes into play, when a neutral wire becomes loose or is disconnected. In that case, the only path current can take from the equipment back to the source is along the ground wire. That means that the person touching the case will get a much greater shock, and this type of accident has been known to be fatal.

NOW HEAR THIS: If you plug something into an outlet that has the neutral and ground tied together, and if that something has metal parts on the outside, then as soon as you touch the thing there is going to be some current flowing through your heart. Might not be much, but it will happen. Every time. No exceptions.

Would you be happy about that?

 

[don_resqcapt19]

Re: Neutral and ground

How does the power know which path to take once it reaches the neutral bus bar?

The power takes all paths back to the power source.
Don

 

[celtic]

Re: Neutral and ground

Originally posted by jmattero:
How does the power know which path to take once it reaches the neutral bus bar?

It doesn't "know" - but it will take the least path of resistance.

(Image from Mike Holt)

As illustrated, the path will be one of least resistance. In this instance, it would be the unfortunate individual.

It is for this reason that neutral-to-ground connections be made on the LINE side of the disconnecting means. Additionally, the NEC does not cover power on the LINE side (ie, from your utility co.).

From our code books, we know that:

90.1 Purpose.
(A) Practical Safeguarding.
The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity.

The purpose of this Code is the practical safeguarding of persons...
People FIRST, equipment and property second.

 

[charlie b]

Re: Neutral and ground

Originally posted by celtic:. . . but it will take the least path of resistance.

As an industry, we really have to get out of the habit of saying that. It's not true.

Current will take all available paths, as Don said in an earlier post. The path of least resistance gets the lion's share of the current. But every available path will get some of the current.

 

[celtic]

Re: Neutral and ground

Originally posted by charlie b:

Originally posted by celtic:. . . but it will take the least path of resistance.

As an industry, we really have to get out of the habit of saying that. It's not true.

Current will take all available paths, as Don said in an earlier post. The path of least resistance gets the lion's share of the current. But every available path will get some of the current.

Initially, I thought this was a "splitting hairs" response (all paths vs. lion's share)...

I stand corrected and thank Charlie for bringing it to my attention ("...get out of the habit...").

For any other people who were/are of the same train of thought/theory as I am, here's a very short article over at EC&M (actually, it's an article from Mike Holt): The Path of Least Resistance

Briefly, the article states:

Electricians thought ...?electricity takes the least resistive path, and it bypasses high resistive paths.? Unfortunately, such thinking resulted in several deaths

Thanks again Charlie.

EDIT:Spelling

[ October 28, 2005, 05:50 PM: Message edited by: celtic ]

 

[jmattero]

Re: Neutral and ground

Ok, thanks to all who replied. I still have one question... is a 2 prong receptacle allowed in the code? Why would this be allowed if there is such a danger with a short in an appliance shocking the person who next touches it (since it would not trip the breaker)? It would seem to me that that danger would make a 2 prong receptacle illegal, but, since they sell them at Home Depot, I would guess that they are, in fact, allowed by code. Am I still confused???

 

[George Stolz]

Re: Neutral and ground

Originally posted by jmattero:
I still have one question... is a 2 prong receptacle allowed in the code?

Yes, when replacing a two-prong receptacle, you may install a two-prong receptacle in it's place (406.3(D)(3)(a)).

Why would this be allowed if there is such a danger with a short in an appliance shocking the person who next touches it (since it would not trip the breaker)?

That is true, but there would be more of a danger if the old defective receptacle were not replaced.

It would seem to me that that danger would make a 2 prong receptacle illegal...

But the code isn't retroactive. If the installation was legal when it was installed, then it can't be required to updated every time the code changes.

 

[jmattero]

Re: Neutral and ground

George:
Thanks for the quick reply. Now, if I may ask one more thing... wouldn't it be safer to allow people to connect an UNGROUNDED GFI in place of a 2 prong receptacle? I am not sure, but it seems to me that if there were a short in an appliance plugged into such a GFI, the GFI would trip, and stop the person from getting a shock.

For a little history, I am a rehabber of low income properties. In one of my properties there is a switch in the kitchen, which was ganged with a 2 prong duplex receptacle (more than 6 feet from the sink). Since I wanted the tenants to have the ability to plug in a three prong appliance, I changed out the 2 prong duplex and installed a GFI. The inspector came in, and plugged his tester into the GFI, and, of course, it showed an "open ground", which he told me to correct. I had two choices... jump the neutral, or go back to a 2 prong duplex. Since I have always heard that jumping the neutral was dangerous, I chose to go back to a 2 prong duplex. However, it seems to me that a GFI with an open ground would be a safer option. Am I wrong? Would a "jumped neutral" GFI be safer than a 2 prong receptacle? Thanks in advance.

 

[George Stolz]

Re: Neutral and ground

Originally posted by jmattero:
wouldn't it be safer to allow people to connect an UNGROUNDED GFI in place of a 2 prong receptacle?

Yes, which is covered in 406.3(D)(3)(b & c).

I am not sure, but it seems to me that if there were a short in an appliance plugged into such a GFI, the GFI would trip, and stop the person from getting a shock.

The person would still receive a shock, but once it exceeded 4 milliamps the GFI would trip, preventing it from being a lethal shock.

The inspector came in, and plugged his tester into the GFI, and, of course, it showed an "open ground", which he told me to correct.

And now you know you were correct: hand him the old 2-wire receptacle and show him the sections I mentioned above.

I had two choices... jump the neutral, or go back to a 2 prong duplex.

Jumping the neutral was never an acceptacle option.

...I chose to go back to a 2 prong duplex. However, it seems to me that a GFI with an open ground would be a safer option. Am I wrong?

Perhaps safer in the short run, but GFCI's don't last forever. It's a no-win situation, and the NEC understands that. One isn't safer than another, IMO. It's unfortunate if there isn't a EGC present. But it's not the "end of the world."

Would a "jumped neutral" GFI be safer than a 2 prong receptacle?

No. Get "jumping the neutral" out of your vocabulary. Get it out of your head. It doesn't exist, it lives with the boogeyman and the Loch Ness Monster.

All that does is violate code, cause a plug in tester to "work" (I say "work" because now it's lying to everybody, claiming there's grounding present).

It also causes neutral current to flow on all exposed metallic paths. See Charlie's post above.

 

[George Stolz]

Re: Neutral and ground

One thing to add: the "small amount of current" these guys are talking about when an illegal jumper is installed becomes all the current if the neutral opens in the circuit. With the circuit's neutral open, the least resistance is through the human, which means the lion's share of the current could kill the person when the neutral is jumpered to the grounding terminal of the receptacle.

 

[jmattero]

Re: Neutral and ground

OK, thank you all very much for a very informative thread. I think I now understand the logic. I will NEVER jump a neutral, and will now be able to explain to others why this is unsafe (I think!!!). I now only have to convince the inspector that a GFI with an open ground is allowed in the code.

Again, thanks to all of you.

 

[hurk27]

Re: Neutral and ground

Here is a good link all about GFCI's and how they work:
All About GFCI's

Three main reason's not to bootleg the grounds to the neutral in a receptacle.

1. Voltage drop in the neutral will be on all the grounding connected to this receptacle

2. A lost neutral to this receptacle will result in the grounding having 120 volts to earth or other grounding.

3. If the hot and neutral conductors was accidentally reversed (easy to do in old cloth wiring) all the grounding connected to this receptacle will have 120 volts the same as reason #2 But a plug in 3 light tester will falsely show to receptacle correctly wired.

Just don't do it!

I think you should hire an electrician to make sure this work is done right. We are not sposed to be giving advice here if a person is not in a related trade. I understand you want it done right but these are the forum rules.

* This NEC? Forum is for those in the electrical and related industries.
Questions of a "How-To" nature by persons not involved in the electrical industry will be removed without notice.
Please read our rules and disclaimers.

 

[George Stolz]

Re: Neutral and ground

Whoops! Missed that!

 

[charlie b]

Re: Neutral and ground

Originally posted by georgestolz:Who reads the first five words of a thread, anyway?

I did. When I did, I judged that this was not a DIY situation. I still think that is true. The original discussion was about safety and about electrical theory. We can even give that type of information to a homeowner. Then the discussion evolved into what is and what is not permitted, and why it is or is not permitted. That is more information than we should give to a DIY, but we can give it to anyone who makes a living in some aspect of electrical design, installation, or inspection.

This person makes a living doing things that are related to the question. That does not violate the Forum rules. We have answered more detailed questions along the lines of "how do I . . . ," when the person asking the question was a "maintenance technician." That is essentially equivalent to this case.

 

[hurk27]

Re: Neutral and ground

Sorry Charlie,
When I saw this "I am not an electrician"
and this "For a little history, I am a rehabber of low income properties. In one of my properties " In his post

It sent a red flage up