Grounding the neutral

T

The electron man

Senior Member
Location
Nyc
Occupation
Electrician
I know grounding and bonding is a complex subject so I'm trying to understand it better

1# I know we drive a rod to help dissipate any emf caused by outside source's like lighting and to prevent arc flashes inside

2# I know the purpose of the main bounding jumper and egc is so fualt current can make it back to the source (transform) to create a surge of current to open the ocpd

But what I'm still having trouble understanding is why do we attach the neutral to earth

Would love to hear from more experienced electricians for reference I've been an electrician for almost 3.5 year

Thanks
 
The electron man said:
I know grounding and bonding is a complex subject so I'm trying to understand it better

1# I know we drive a rod to help dissipate any emf caused by outside source's like lighting and to prevent arc flashes inside

2# I know the purpose of the main bounding jumper and egc is so fualt current can make it back to the source (transform) to create a surge of current to open the ocpd

But what I'm still having trouble understanding is why do we attach the neutral to earth

Would love to hear from more experienced electricians for reference I've been an electrician for almost 3.5 year

Thanks
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Look up corner grounded systems. We chose the nuetral because center tapping lowers voltage to ground but corner grounding is still an option.

120 years ago the pros and cons of grounding and bonding vs using entirely non bonded systems was discussed and argued and decided on. Its interesting to look into.
 
The electron man said:
But what I'm still having trouble understanding is why do we attach the neutral to earth
Click to expand...
Note, per letgomywago's post, its not always the neutral that is grounded, but 99% of the time its the neutral. But anyway, This is system grounding. In an electrical system, you have to decide whether you want the system solidly referenced to earth or not. There are advantages and disadvantages to both. Obviously we almost exclusively use grounded systems for premise wiring systems here in the states. An ungrounded electrical system will "float" with no hard reference to ground beyond what you get from capacitive coupling or high impedance faults and leakage. There are probably two major negatives with ungrounded systems. One is there is a phenomenon where arcing faults can result in voltages that exceed the regular line to line voltage. Thus ungrounded systems utilizing insulation systems typically need higher insulation levels (think mostly in the MV world here) than even the L-L voltage. Compare that to a Wye grounded system where its grounded in the "center" so everything sees much lower voltages. The second issue is if a L-G fault happens, although nothing happens other than the system now having a somewhat solid ground reference, it takes action to notice that this has happened and take corrective action. Compare this to a grounded system where faults automatically result in a breaker tripping or fuse blowing and the problem must be fixed before the system can be turned on again. Imagine ungrounded systems in houses and harry and jane homeowner knowing when a fault happens ("honey, what is that red light in the basement mean?? I dont know, Ill go put some electrical tape over it) , not to mention fixing the problem.

Disadvantages of grounded systems are high fault currents for first faults. That ungrounded system gives you one "free" fault where nothing much happens. Another big disadvantage is stray current traveling on things like piping systems, messengers, and shields.
 
electrofelon said:
Note, per letgomywago's post, its not always the neutral that is grounded, but 99% of the time its the neutral. But anyway, This is system grounding. In an electrical system, you have to decide whether you want the system solidly referenced to earth or not. There are advantages and disadvantages to both. Obviously we almost exclusively use grounded systems for premise wiring systems here in the states. An ungrounded electrical system will "float" with no hard reference to ground beyond what you get from capacitive coupling or high impedance faults and leakage. There are probably two major negatives with ungrounded systems. One is there is a phenomenon where arcing faults can result in voltages that exceed the regular line to line voltage. Thus ungrounded systems utilizing insulation systems typically need higher insulation levels (think mostly in the MV world here) than even the L-L voltage. Compare that to a Wye grounded system where its grounded in the "center" so everything sees much lower voltages. The second issue is if a L-G fault happens, although nothing happens other than the system now having a somewhat solid ground reference, it takes action to notice that this has happened and take corrective action. Compare this to a grounded system where faults automatically result in a breaker tripping or fuse blowing and the problem must be fixed before the system can be turned on again. Imagine ungrounded systems in houses and harry and jane homeowner knowing when a fault happens ("honey, what is that red light in the basement mean?? I dont know, Ill go put some electrical tape over it) , not to mention fixing the problem.

Disadvantages of grounded systems are high fault currents for first faults. That ungrounded system gives you one "free" fault where nothing much happens. Another big disadvantage is stray current traveling on things like piping systems, messengers, and shields.
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If a system is not grounded how would you test voltages with no reference to ground ?
 
Strathead said:
You test phase to phase and phase to neutral. Submarine electrical systems are ungrounded. 120 volt is actually 110 if I remember correctly. And it is 2 pole breakers for each circuit.
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an ungrounded system would often not have a neutral. Even if it did, the phase to neutral voltage would be normal and consistent. In an ungrounded system, all non current carrying metal parts still get connected together and to earth, so when we say measure to "ground" , it is to a point on that. I guess if you were standing in a field with just the ungrounded conductors, you could stick one probe of the voltmeter in the dirt and you would probably still get something but it wouldnt be very meaningful.
 
The electron man said:
But what I'm still having trouble understanding is why do we attach the neutral to earth
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Because the earth is universally (or widely, anyway) recognized to be the "absolute zero" voltage that all grounded systems use for voltage reference.
 
ggunn said:
Because the earth is universally (or widely, anyway) recognized to be the "absolute zero" voltage that all grounded systems use for voltage reference.
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But then the question is, why do we care about having a solid voltage reference? Ok there is the fact that some things like AC drives apparently have components like MOV's connected phase to ground and are "expecting" a certain voltage, so then it matters.
 
I think of it this way: first we choose if we want a bonded system or an unbonded system.

In a bonded system we make one _intentional_ connection between the electrical system and any nearby conductive (but not intended to carry current) materials. This bonding provides a path to dissipate any 'static' voltages built up by the normal movements around the electrical system, and provides a fault current path in the event of an insulation failure.

Bonding works without connection to soil. Bonding works just fine on airplanes and space craft.

For structures on the ground, I see earthing as an extension of bonding, simply extending the concept of bonding to encompass the soil beneath the structure.
 
electrofelon said:
But then the question is, why do we care about having a solid voltage reference?
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That's a different question, of course, but having a (more or less) universal zero voltage reference is the point, not, as some people seem to believe, to be an infinite sink for fault currents.
 
electrofelon said:
an ungrounded system would often not have a neutral. Even if it did, the phase to neutral voltage would be normal and consistent. In an ungrounded system, all non current carrying metal parts still get connected together and to earth, so when we say measure to "ground" , it is to a point on that. I guess if you were standing in a field with just the ungrounded conductors, you could stick one probe of the voltmeter in the dirt and you would probably still get something but it wouldnt be very meaningful.
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I am fairly well versed in fundamental theory, so we don't really need to discuss the minutia but, You say, " so when we say measure to "ground" " when was the last time you measured to ground? The OP is asking why we tie to earth, not why we bond everything together. What we measure to all the bonded metal parts has little to do with what we measure to earth. Also, a ground fault to earth is often not strong enough to trip a circuit breaker, so while I get why we bond the neutral to unenergized metal that may become energized, I don't fully understand how advantageous it is to bond to the earth. I think that is the OP's point.
 
electrofelon said:
But then the question is, why do we care about having a solid voltage reference? Ok there is the fact that some things like AC drives apparently have components like MOV's connected phase to ground and are "expecting" a certain voltage, so then it matters.
Click to expand...
Agree with you and assume you know this but for the matter of discussion, that zero reference is the bond point between the neutral and the ground, not the distance from line voltage to earth.
 
winnie said:
I think of it this way: first we choose if we want a bonded system or an unbonded system.

In a bonded system we make one _intentional_ connection between the electrical system and any nearby conductive (but not intended to carry current) materials. This bonding provides a path to dissipate any 'static' voltages built up by the normal movements around the electrical system, and provides a fault current path in the event of an insulation failure.

Bonding works without connection to soil. Bonding works just fine on airplanes and space craft.

For structures on the ground, I see earthing as an extension of bonding, simply extending the concept of bonding to encompass the soil beneath the structure.
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Why, though? Especially when the entire concept is the most misunderstood portion of the code, in my experience.
 
ggunn said:
That's a different question, of course, but having a (more or less) universal zero voltage reference is the point, not, as some people seem to believe, to be an infinite sink for fault currents.
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But, the earth in two locations 100 feet apart has a voltage potential. So, I don't agree with the term "zero voltage reference" which you also included in quotes the first time you mentioned it, so I am not in any way trying to educate you, but merely to extend the conversation.
 
Strathead said:
But, the earth in two locations 100 feet apart has a voltage potential. So, I don't agree with the term "zero voltage reference" which you also included in quotes the first time you mentioned it, so I am not in any way trying to educate you, but merely to extend the conversation.
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I have no idea how much potential you would measure between two points 100' apart or how you would go about measuring it, but that's not really relevant. In a grounded system it is the zero volt point to which all the rest of the voltages are referenced. If there are a few millivolts (or whatever) difference between two isolated systems some distance apart, that's not really relevant, either; it's a local variable. As to why a zero volt reference point is necessary or desirable, that is a question for someone else.
 
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Strathead said:
while I get why we bond the neutral to unenergized metal that may become energized, I don't fully understand how advantageous it is to bond to the earth.
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1) Since the user may contact actual earth (or unbonded metal in contact with actual earth) and bonded metal parts at the same time, bonding them together will reduce the chance of a shock. Otherwise the electrical system and bonded metal parts could conceivably float to a voltage relative to earth, e.g. charge up as a capacitor, and you might get a shock.

2) Something something lightning.

Cheers, Wayne
 
winnie said:
I think of it this way: first we choose if we want a bonded system or an unbonded system.

In a bonded system we make one _intentional_ connection between the electrical system and any nearby conductive (but not intended to carry current) materials. This bonding provides a path to dissipate any 'static' voltages built up by the normal movements around the electrical system, and provides a fault current path in the event of an insulation failure.

Bonding works without connection to soil. Bonding works just fine on airplanes and space craft.

For structures on the ground, I see earthing as an extension of bonding, simply extending the concept of bonding to encompass the soil beneath the structure.
Click to expand...

This is perhaps as good a concise summation as I've seen. It emphasizes that the actual connection to earth ("ground") is of secondary importance, just an extension of the concept where the electrical system is not on a vehicle.

One way to put it is that we bond a conductor so that when I open a panel, the conductors which pose the most danger are much more predictable. Earthing extends the concept (at least in theory) from my hands that are touching the panel to my feet that are standing on the ground.
 
Strathead said:
Why, though? Especially when the entire concept is the most misunderstood portion of the code, in my experience.
Click to expand...

A metal structure completely insulated from ground would be a shock hazard because of 'static' charging. But this would be discharged by many k of resistance.

I do not know the reason to strive for 10s of ohm resistance.
 
Strathead said:
Why, though? Especially when the entire concept is the most misunderstood portion of the code, in my experience.
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I heard Mike Holt mention in the old days there were things like side flashing and over voltage problems. I'm not sure what a side flashing is. I know capacitance can be a problem on ungrounded systems and that's why high impedance systems evolved.

There was a post on here a while back about Norway going all ungrounded because it would be safer and it turned out to be a nightmare because there would be a fault that would go undetected and would become the default grounded conductor and then somewhere down the street there would be another fault and eventually there would be fuses blowing and nobody knew where to find the problem.
 
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