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Old 12-30-2008, 10:14 PM   #1
Mike in Ohio
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Default 3 wire vs. 4 wire 220v

I did not want to hijack the previous thread on this subject but I have a question. On my well pump it is 220v on the pressure switch the the two hot wires are hooked to the switch and both the neutral and the ground are hooked to green screws on the base of the switch. Is this a situation where I did not need a neutral? I made an extension cord to hook the pump to my generator I wired a 4 prong range cord to the pump that i can disconnect from the house wiring and plug into the extension cord to the generator I wired everything as it was. The gen has a 4 prong plug for 220 and it is the only 220 item I have plugged in. It worked the one time I had to use it but now I'm wondering weather the neutral and ground hooked together at the pump is ok for the generator? Thanks alot, Mike
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Old 12-30-2008, 10:30 PM   #2
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Default Re: 3 wire vs. 4 wire 220v

Sounds like here you didn't need a neutral.... 2 hots and a ground...
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Old 12-31-2008, 08:22 AM   #3
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Default Re: 3 wire vs. 4 wire 220v

Quite a lot of misconception on this. 240V is two hots and a ground. Neutral is for 110V. You have four wires on a range or a dryer because there are 110V components (clock, lights, etc) in the appliance as well as 240V components (the heating elements).
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Old 12-31-2008, 08:23 AM   #4
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Default Re: 3 wire vs. 4 wire 220v

Spot on, Pat.

Scott
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Old 12-31-2008, 12:01 PM   #5
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Default Re: 3 wire vs. 4 wire 220v

It sounds like you have the neutral and ground connected together and this thing connected to your house. If so that is creating a hazardous situation. You cant have a neutral to ground connection anywhere other than in your main service.
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Old 12-31-2008, 11:40 PM   #6
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Default Re: 3 wire vs. 4 wire 220v

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Originally Posted by PAToyota View Post
Quite a lot of misconception on this. 240V is two hots and a ground. Neutral is for 110V. You have four wires on a range or a dryer because there are 110V components (clock, lights, etc) in the appliance as well as 240V components (the heating elements).
WOW! You ever had one of those moments where something finally just made perfect sense? This is one for me! Thanks PAT! Happy New Year.

Cheers,
Eric
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Old 01-02-2009, 04:11 AM   #7
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Default Re: 3 wire vs. 4 wire 220v

Pat, Scott,

I think you got confused. First lets have a look what a "circuit" looks like:

Inside the panel, connections are made to the incoming wires. These connections are then used to supply power to selected portions of the home. There are three different combinations:
1) one hot, one neutral, and ground: 120V circuit.
2) two hots, no neutral, and ground: 240V circuit.
3) two hots, neutral, and ground: 240V circuit + neutral, and/or two 120V circuits with a common neutral.

(1) is used for most circuits supplying receptacles and lighting within your house. (3) is usually used for supplying power to major appliances such as stoves, and dryers - they often have need for both 240V and 120V, or for bringing several circuits from the panel box to a distribution point. (2) is usually for special 240V motor circuits, electric heaters, or air conditioners.

[Important Note: In the US, the NEC used to permit a circuit similar to (2) be used for stoves and dryers - namely, three conductor wiring, with a ground wire doing dual duty as a neutral. As of the 1996 revision to the NEC, this is NO LONGER PERMITTED.] Mike, this is actualy the awnser to your original question.

This is all for typical residential 2 phase service. If you look at industrial applications you see 3 phase 208V Y / 120V and 480V Y / 277 V systems or delta systems. This could fill another book of comments so I will stop here on 3 phase systems.

Regarding a word on voltage levels like: 110/115/117/120/125/220/240


One thing where things might get a bit confusing is the different numbers people bandy about for the voltage of a circuit. One person might talk about 110V, another 117V or another 120V. These are all, in fact, exactly the same thing... In North America the utility companies are required to supply a split-phase 240 volt (+-5%) feed to your house. This works out as two 120V +- 5% legs. Additionally, since there are resistive voltage drops in the house wiring, it's not unreasonable to find 120V has dropped to 110V or 240V has dropped to 220V by the time the power reaches a wall outlet. Especially at the end of an extension cord or long circuit run. For a number of reasons, some historical, some simple personal orneryness, different people choose to call them by slightly different numbers. This FAQ has chosen to be consistent with calling them "110V" and "220V", except when actually saying what the measured voltage will be. Confusing? A bit. Just ignore it. One thing that might make this a little more understandable is that the nameplates on equipment ofen show the lower (ie: 110V instead of 120V) value. What this implies is that the device is designed to operate properly when the voltage drops that low. 208V is *not* the same as 240V. 208V is the voltage between phases of a 3-phase "Y" circuit that is 120V from neutral to any hot. 480V is the voltage between phases of a 3-phase "Y" circuit that's 277V from hot to neutral. In keeping with 110V versus 120V strangeness, motors intended to run on 480V three phase are often labelled as 440V...

Last edited by a266; 01-02-2009 at 04:16 AM. Reason: correction of typos
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Old 01-02-2009, 07:41 AM   #8
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Question Re: 3 wire vs. 4 wire 220v

Quote:
Originally Posted by a266 View Post
Pat, Scott,

I think you got confused. First lets have a look what a "circuit" looks like:
Quote:
Originally Posted by a266 View Post
3) two hots, neutral, and ground: 240V circuit + neutral, and/or two 120V circuits with a common neutral.

...............

(3) is usually used for supplying power to major appliances such as stoves, and dryers - they often have need for both 240V and 120V, or for bringing several circuits from the panel box to a distribution point.
a266:

It seems like you are saying the same thing as PA Toyota and Scott. I quoted the relevant sections of your post above. Not sure they were confused. I do not see any inconsistency. Am I missing something?

Cheers!

Jim
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Old 01-02-2009, 09:23 AM   #9
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Default Re: 3 wire vs. 4 wire 220v

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Originally Posted by a266 View Post
[Important Note: In the US, the NEC used to permit a circuit similar to (2) be used for stoves and dryers - namely, three conductor wiring, with a ground wire doing dual duty as a neutral. As of the 1996 revision to the NEC, this is NO LONGER PERMITTED.] Mike, this is actually the answer to your original question.
Actually that has nothing to do with Mike's original question. The old dryer and range circuits used two hots and a NEUTRAL. There is no ground. If it were a ground, the prong on the plug would be in the regular D shape, like all other grounded receptacles.

The code you are quoting only applies to loads that require a neutral to run 120v circuits (dryers and ranges being the most common). It requires that all new installations use a 4 wire circuit that includes a ground. Installations made before the code change are grandfathered in.

Mike's 240v well pump would not require a neutral since there are no components of a well pump requiring 120v. He only needs two hots and a ground.

Sometimes I have seen water wells with a small light bulb mounted on the well-head to signal when it is running. In that case you WOULD need a neutral, since the bulb only requires 120v. The only part of the setup that uses the neutral is the bulb.
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Old 01-02-2009, 09:39 AM   #10
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Default Re: 3 wire vs. 4 wire 220v

Quote:
Originally Posted by a266 View Post
Pat, Scott,

I think you got confused. First lets have a look what a "circuit" looks like:

Inside the panel, connections are made to the incoming wires. These connections are then used to supply power to selected portions of the home. There are three different combinations:
1) one hot, one neutral, and ground: 120V circuit.
2) two hots, no neutral, and ground: 240V circuit.
3) two hots, neutral, and ground: 240V circuit + neutral, and/or two 120V circuits with a common neutral.

(1) is used for most circuits supplying receptacles and lighting within your house. (3) is usually used for supplying power to major appliances such as stoves, and dryers - they often have need for both 240V and 120V, or for bringing several circuits from the panel box to a distribution point. (2) is usually for special 240V motor circuits, electric heaters, or air conditioners.

[Important Note: In the US, the NEC used to permit a circuit similar to (2) be used for stoves and dryers - namely, three conductor wiring, with a ground wire doing dual duty as a neutral. As of the 1996 revision to the NEC, this is NO LONGER PERMITTED.] Mike, this is actualy the awnser to your original question.

This is all for typical residential 2 phase service. If you look at industrial applications you see 3 phase 208V Y / 120V and 480V Y / 277 V systems or delta systems. This could fill another book of comments so I will stop here on 3 phase systems.

Regarding a word on voltage levels like: 110/115/117/120/125/220/240


One thing where things might get a bit confusing is the different numbers people bandy about for the voltage of a circuit. One person might talk about 110V, another 117V or another 120V. These are all, in fact, exactly the same thing... In North America the utility companies are required to supply a split-phase 240 volt (+-5%) feed to your house. This works out as two 120V +- 5% legs. Additionally, since there are resistive voltage drops in the house wiring, it's not unreasonable to find 120V has dropped to 110V or 240V has dropped to 220V by the time the power reaches a wall outlet. Especially at the end of an extension cord or long circuit run. For a number of reasons, some historical, some simple personal orneryness, different people choose to call them by slightly different numbers. This FAQ has chosen to be consistent with calling them "110V" and "220V", except when actually saying what the measured voltage will be. Confusing? A bit. Just ignore it. One thing that might make this a little more understandable is that the nameplates on equipment ofen show the lower (ie: 110V instead of 120V) value. What this implies is that the device is designed to operate properly when the voltage drops that low. 208V is *not* the same as 240V. 208V is the voltage between phases of a 3-phase "Y" circuit that is 120V from neutral to any hot. 480V is the voltage between phases of a 3-phase "Y" circuit that's 277V from hot to neutral. In keeping with 110V versus 120V strangeness, motors intended to run on 480V three phase are often labelled as 440V...
I follow everything that you wrote, but I have never heard of 2 phase service.. only single phase and 3 phase... Is this a typo or what??? Please explain to this old guy...
I did go to Wikipedia to research this question, and what I found was this....

Quote:
Three-wire, 120/240 volt single phase power used in the USA and Canada is sometimes incorrectly called "two-phase". The proper term is split phase or 3-wire single-phase.
Is the industry changing terms with the times????
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Old 01-02-2009, 03:15 PM   #11
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Default Re: 3 wire vs. 4 wire 220v

Junk,
You are correct, it really is not 2 phase. I have heard it called this but not very often. Later on in his post he also refers to it as split phase so I think it was more of a typo than anything else. No the industry terms are not changing.

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Old 01-02-2009, 04:49 PM   #12
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Default Re: 3 wire vs. 4 wire 220v

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Junk,
You are correct, it really is not 2 phase. I have heard it called this but not very often. Later on in his post he also refers to it as split phase so I think it was more of a typo than anything else. No the industry terms are not changing.

Tom
In the early days of electricity, there actually was a two phase current. It was not common, and offered in certain areas. This was before any kind of standardization, and eventually did go away. See Wikipedia for some info on it.

This is somewhat like the 25 hz current that was the norm in Buffalo, NY at one time. Lights flickered visibly on it, and with time, they went to standardized 60 cycle current (the rest of the world uses 50 cycle, and for the life of me, I don't understand why, since cycles are related to time, 60 makes more sense, anyhow, I digress) There was one machine shop company in Buffalo who did not want to change their motors out, and state laws mandated the power company continue to provide this oddball current to whoever needed it, finally the power company paid the very high price to have new motors installed on their machinery. I recall reading this in American Heritage Invention and Technology Magazine some years ago.

Charles
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Old 01-04-2009, 03:35 PM   #13
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Default Re: 3 wire vs. 4 wire 220v

Well pumps are pretty well grounded just because of what and where they are.
The nurtral vs ground argument dosn't mean much with them.
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Old 01-07-2013, 04:39 PM   #14
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Default Re: 3 wire vs. 4 wire 220v

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It sounds like you have the neutral and ground connected together and this thing connected to your house. If so that is creating a hazardous situation. You cant have a neutral to ground connection anywhere other than in your main service.
Since it appears this this thread ran its course but contains the topic I'm curious about, I'll take a chance and hijack it.

The above statement repeats something I've read in several other posts, but not seen explained - that a neutral-to-ground connection is a bad thing outside your main service. I would like to understand the hazard that this creates.

The reason I ask is that from my pole/meter, the co-op provides three wires to my main panel for my "single-phase" service. Two "hots", and one "neutral". This neutral wire - at the meter/source - is coming literally from the ground. It did not come down the road on the poles. It is this "ground" wire that the co-op hooked into my "neutral" bar in the main panel. So, at the very source, it certainly appears that we have a "neutral-to-ground" connection. As if to confirm, I also have a ground rod just outside with another stout copper wire running to that same bar.

So, at what point do these two - the neutral and the ground - become "different", or need to be treated differently? I assume it has something to do with the "return" AC that comes down the "neutral" wire from a load, but in my residence, the white and bare wires on each circuit both end up tied to that original co-op "ground". I've never encountered a service panel or sub-panel with separate bars for neutral and ground, but I understand they are available.

Forgive my ignorance - I just want to know more about what's going on.
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Old 01-07-2013, 09:35 PM   #15
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Default Re: 3 wire vs. 4 wire 220v

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Originally Posted by SaddleBronc View Post
Since it appears this this thread ran its course but contains the topic I'm curious about, I'll take a chance and hijack it.

The above statement repeats something I've read in several other posts, but not seen explained - that a neutral-to-ground connection is a bad thing outside your main service. I would like to understand the hazard that this creates.

The reason I ask is that from my pole/meter, the co-op provides three wires to my main panel for my "single-phase" service. Two "hots", and one "neutral". This neutral wire - at the meter/source - is coming literally from the ground. It did not come down the road on the poles. It is this "ground" wire that the co-op hooked into my "neutral" bar in the main panel. So, at the very source, it certainly appears that we have a "neutral-to-ground" connection. As if to confirm, I also have a ground rod just outside with another stout copper wire running to that same bar.

So, at what point do these two - the neutral and the ground - become "different", or need to be treated differently? I assume it has something to do with the "return" AC that comes down the "neutral" wire from a load, but in my residence, the white and bare wires on each circuit both end up tied to that original co-op "ground". I've never encountered a service panel or sub-panel with separate bars for neutral and ground, but I understand they are available.

Forgive my ignorance - I just want to know more about what's going on.
No, the neutral does not "come from the ground", rather, the neutral is the center tap off the transformer, right in the middle of the windings. The hots come off the ends of the windings. Thus, the neutral is a CURRENT CARRYING WIRE and is also know as a GROUNDED CONDUCTOR. Further, look at your pole where the transformer is located. If it is a single phase service, you will have a wire at the top of the pole, on insulators, which is the high voltage feed to the transformers. The lower wire, from pole to pole, is the Power Companies neutral and is grounded, and is also connected to the center tap of the transformer. It is supposed to be a pure ground. This is why, sometimes, people have everything in their house destroyed, or the house gets burned down, should the power company lose the ground to this conductor.

The ground does not carry any current, and is intended to provide a shunt to ground in case of a short, but normally, just sits there doing nothing. Indeed, it is connected to the neutral at the service entrance, but no current passes over the ground wires, while the neutral wire carries current all the time.

Grounds don't always make a home run to the connection in the panel, they are many times tied to other grounds and interconnected. In addition, metal boxes are grounded to them. Running a ground and neutral in parallel means that current is traveling on the ground circuit, and possibly thru other ground wires and boxes, before reaching the service entrance. This is a dangerous situation if someone get 'ahold of a ground that is hot, and their body happens to have a better ground than the ground rod/service entrance.

Charles

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Old 01-08-2013, 08:32 AM   #16
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Default Re: 3 wire vs. 4 wire 220v

Very well put Charles. I like that you, unlike some others, clearly and accurately got your point across without arrogance or reference to the "King James Version" of the National Electric Code. Most of all I like that there is nothing in what you said that I do not agree with. "It is truly amazing how intelligent we think a person is when he agrees with us." (quoted from unknown source).

That is why I am hoping that you can explain something to me. I am apparently blind when it comes to 3 wire dryer circuits. What is it about that third wire that makes it strictly a neutral and NOT a ground? I can clearly see what makes it a neutral AND a ground. But it has been explained to me that a current carrying ground has NEVER been allowed and that wire is NOT a ground!

Assuming there is no sub panel involved, it seems to me that, electrically, there is no difference between a 3 wire dryer circuit and any other 3 wire 240 volt circuit other than the device that is connected to it. I realize that some will insist that a neutral cannot be green and a ground cannot be white but wire color aside, physically/mechanically/electrically the connection seems very much the same to me.
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Old 01-08-2013, 12:50 PM   #17
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Default Re: 3 wire vs. 4 wire 220v

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Very well put Charles. I like that you, unlike some others, clearly and accurately got your point across without arrogance or reference to the "King James Version" of the National Electric Code. Most of all I like that there is nothing in what you said that I do not agree with. "It is truly amazing how intelligent we think a person is when he agrees with us." (quoted from unknown source).

That is why I am hoping that you can explain something to me. I am apparently blind when it comes to 3 wire dryer circuits. What is it about that third wire that makes it strictly a neutral and NOT a ground? I can clearly see what makes it a neutral AND a ground. But it has been explained to me that a current carrying ground has NEVER been allowed and that wire is NOT a ground!

Assuming there is no sub panel involved, it seems to me that, electrically, there is no difference between a 3 wire dryer circuit and any other 3 wire 240 volt circuit other than the device that is connected to it. I realize that some will insist that a neutral cannot be green and a ground cannot be white but wire color aside, physically/mechanically/electrically the connection seems very much the same to me.

I *think* I understand what you are asking, as I have struggled with a similar same question. (i.e. If both neutral and ground wires are connected to the same bar back at the main panel, why even bother with two wires?)

My understanding is as follows (and please let me know if I'm wrong charles, or anyone else that knows more about this than me, which is a lot of you)

The point of the neutral wire is to carry 120V current back to the panel. So it actually sees some current in normal operation (as charles mentioned above, it is also known as a grounded conductor)

The point of the ground wire (which should not see any current in normal operation) is ensure the safety of anyone who uses or touches the equipment by making sure that the casing of the appliance/equpipment is always electrically grounded (dead).

If a hot conductor were to come loose in your dryer for example and come into contact with the metal case of the dryer, and there were no ground wire connected, then your dryer would become energized, and if you touched it you would be shocked.

If a hot conductor were to come loose in your dryer for example and come into contact with the grounded metal case of the dryer, as in a ground wire is present and connected, then the hot conductor should arc to ground, lots of heat and a high electrical current flowing into that ground fault, but when the current reaches the max allowed by the circuit breaker, the circuit breaker should open (turn off), meaning you would not be in danger of being shocked by the dryer at that point.
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Old 01-08-2013, 01:34 PM   #18
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Default Re: 3 wire vs. 4 wire 220v

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it seems to me that, electrically, there is no difference between a 3 wire dryer circuit and any other 3 wire 240 volt circuit other than the device that is connected to it.
Larwyn, is your home wired in Romex? I think this would make more sense to you if your home were wired in conduit.

In Chicago, all homes use metal conduit (the ground). A pre 2008 dryer outlet would have three insulated wires (2 hots and a neutral in conduit. A well pump, arc welder, or air compressor would have two insulated wires (2 hots, no neutral) in conduit.

The "other 3 wire 240 volt circuit" you refer to is really a 2 wire with ground circuit. Because you are familiar with Romex, in your case the the ground is a wire. Homes with metal conduit do not always use a dedicated wire for a ground.

You would not want the metal conduit to be current carrying unless there was a short.
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Old 01-08-2013, 02:18 PM   #19
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Default Re: 3 wire vs. 4 wire 220v

Yes, I am quite familiar with what a ground is and what a neutral is. My question is "How is the third (neutral) wire in a 3 wire dryer circuit NOT a ground?"

Yes my home is wired with Romex. But I have run several miles of EMT, Rigid and Flex conduit in my life. In some cases the conduit was the only ground but in most cases a ground wire was called for by the engineers on the job. I wired my shop with EMT and THHN, but I did run ground wires too. I had the wire and there was plenty of room in the 3/4" EMT that I used so why not. The 240 volt circuits that I ran in the shop are for power tools so I ran two hots and a ground to them from those receptacles.
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Old 01-08-2013, 03:54 PM   #20
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Default Re: 3 wire vs. 4 wire 220v

http://www.stayonline.com/reference-...ght-blade.aspx


This is the proper 30 amp 250 volt receptacle for 250 volt only loads.

NEMA 6-30

This is the receptacle that was previously code compliant for dryers in earlier code implementations.

NEMA 10-30

This is the receptacle that is currently code compliant for clothes dryers.

NEMA 14-30


When a 120 volt appliance is in use, equal current flows on both the hot (Ungrounded Conductor), and the neutral (Grounded Conductor). The Equipment Grounding Conductor (Ground) will have no current flowing in a properly operating piece of equipment. If the appliance is NOT operating, and the wire gauge for all three conductors is the same, the Neutral and the Ground are at the same potential, with reference to the Hot Conductor. If the appliance IS operating, the neutral and the ground are no longer at the same potential (Half of the time) in reference to the Hot Conductor. As there is current flow in the neutral, its impedance is higher, with reference to the hot conductor, than the EGC ground conductor. As the ECG (Ground) has lower impedance referenced to the hot conductor, than the neutral during equipment operation, its capability to provide a fault path to trip a breaker or blow a fuse is more robust. The only place that the Neutral and the Ground are always at the same potential is at the main service where they are bonded together. At any other user device location, they are never at the same potential while equipment is operating.

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