Sub-panels

[M. D.]

The threat is the same , perhaps less than that of the supply side, The NEC does not govern the utility side. It is not a safe condition either way and it is a violation of the NEC.

Requirements are changing , perhaps to slowly ....,your parents certainly must have said to you at some point "Two wrongs don't make a right " or advised not to point out a bigger "flaw" as an excuse for a smaller one. I think it is you who are misleading people ,,quite frankly.

 

[weressl]

The threat is the same , perhaps less than that of the supply side, The NEC does not govern the utility side. It is not a safe condition either way and it is a violation of the NEC.

Requirements are changing , perhaps to slowly ....,your parents certainly must have said to you at some point "Two wrongs don't make a right " or advised not to point out a bigger "flaw" as an excuse for a smaller one. I think it is you who are misleading people ,,quite frankly.

Thanks for so clearly explaining where physics were wrong. Your elaboration on HOW it represents a hazard or safety concern was also very helpful.

Repeat: I never argued that it is NOT against NEC.

My argument was that the condition is no different than it has been since perhaps the existence of the NEC. If NEC would trully be concerned about safety - if it is a safety concern in the first place - they would certainly work to eliminate the hazard by pressuring OSHA or any other Governmental body.

Perhaps a documented description of the percieved hazard created by such condition would be helpful, or if there any documented - not anecdotal - safety incident exist we can learn about it. Must be a ton of them since this condition exist at EVERY SINGLE PLACE where utility connects and that is what, in the hundreds of millions?!

Please go back to the original post and read that I argued that the statement and reasoning of HOW it creates a hazard was false and therefore misleading. That and ONLY that was my point, not that it is or isn't against NEC. I am also awaiting to be educated about how do I mislead people in this post, because if I do I certainly want to apologize for it and correct it.

 

[M. D.]

So Mike Holt is wrong ,.. there is no increase in the level of hazard from the use of electricity when impropper neutral to ground connections are made??

NEC Rules on Neutral-to-Ground Connections
By Mike Holt, Published in Power Quality Magazine

Section 250-142 - To protect against dangerous touch voltage, an effective ground-fault current path (EGFP) must be provided and it becomes complete when it is bonded to the power supply system grounded (neutral) conductor. This neutral-to-ground connection (as it?s called) is to be made at either the service equipment enclosure or at the source of the separately derived system.

Service Equipment - At service equipment (the building disconnecting means), the EGFP is established by bonding the metal service disconnect enclosure to the service grounded (neutral) conductor [250-24(b)]. This neutral-to-ground connection is accomplished by the installation of a main bonding jumper (screw or strap) in accordance with Section 250-28.

Author?s Comment: The main bonding jumper is required to be supplied by the disconnect equipment manufacturer [384-3(c)].

Separately Derived Systems - For separately derived systems, the EGFP is established by when the metal enclosure of the separately derived system (transformer, generator, UPS system, or photovoltaic system) is bonded to grounded (neutral) terminal (X0) of the power supply in accordance with Section 250-30(a)(1). This neutral-to-ground connection must be made at either the separately derived system or at the first system disconnect after the separately derived system.

DANGER: Failure to provide an EGFP for services and/or separately derived systems can create any one or more of the following:
? Dangerous touch voltage will remain on all metal part of the electrical system whenever a line-to-case fault occurs.
? Metal parts of the electrical system can have dangerous touch voltage from the normal operation of the electrical system.
? Neutral current attempting to return to the power supply can cause wood members of the building to ignite from ?pyroforic-carbonization?.

Author?s Comment: A video demonstrating ?pyroforic-carbonization? is available from my office, 1-888 NEC Code. Ask for the open-neutral video.

The NEC permits a neutral-to-ground connection at separate building and structures disconnecting means, when installed in accordance with Section 250-32(b)(2). However, this is a very dangerous practice and should be avoided.

NEC Section 250-142(b) contains two exceptions where a neutral-to-ground connection is permitted on the load side of the service or separately derived systems. Exception No.1 permits a neutral-to-ground connection for existing ranges, dryers, and ovens as are limited in Section 250-140. Exception No. 2 allows a neutral-to-ground connection at meter enclosures on the load side of the service disconnect, if the meter enclosures are located near the service disconnect and no ground-fault protection is installed at the service.


The Danger of Improper Neutral-to-Ground Connections

The purpose of the NEC ?is the practical safeguarding of persons and property from hazards arising from the use of electricity? [90-1(a)]. A neutral-to-ground connection must not be made on the load side of service equipment of separately derived systems except as permitted in Section 250-142(b). The reason neutral-to-ground connections are only permitted at service equipment and separately derived systems is so that dangerous (neutral) current will not flow on the metal parts of the electrical systems in violation of Sections 250-6 and 250-142(b).

Neutral-to-ground connection can be cause by wiring errors such as neutral-to-ground shorts in receptacles, shorted surge suppressor, ballast wires caught under ballasts or ballast covers, etc. But most commonly, improper neutral-to-ground connections are made when the neutral conductor is bonded to the metal case of a subpanel.

Author?s Comment: An improper neutral-to-ground connection can create a condition where neutral current has multiple parallel paths to return to the power supply. This condition (parallel neutral paths) creates ?ground loops?, ?net currents? and the condition of ?objections current? on the EGFP, a violation of Section 250-6.

Objectionable (neutral) current flowing on the metal parts of the electrical system can cause fires, electrocution, and power quality issues with sensitive electronic equipment.

Electrocution. Death from electric shock (electrocution) can occur when as little as 50 mA of current flows through the human body. This current flow disrupts the hearts electrical circuitry causing it to go in to ventricular fibrillation. Ventricular fibrillation (VF) is a condition where the heart no longer pumps blood through the body, particularly the brain. VF can occur when the touch voltage is greater that 30V, resulting in a current flow of more than 50 mA through the body. This can occur when the effective ground-fault path (EGFP) becomes the primary path for neutral current, and a person gets in series with this path.

Example: A 120V water filter is installed at a location where a grounded (neutral) conductor is not available (only 240V for the motor) and the installer used the EGFP for the neutral conductor. Under this condition, if a person got in series with the EGFP, they could get killed.

Fire Hazard. Fire is created when heat rises to a level that is sufficient to cause ignition of adjacent combustible material in an area that is oxygenated. In an electrical system, heat is generated whenever current flows through an object in accordance with the formula I2R. Where ?I? is the magnitude in amperes of the current and ?R? is the resistance in ohms of the object.

Improper wiring resulting in a condition where neutral current flows through the EGFP can cause the temperature at loose connections to rise to a level that can cause a fire. In addition, arcing at loose connections because of neutral current flowing through the EGFP is particularly dangerous in areas containing easily ignitable and explosive gases, vapors, or dust.

Power Quality Problems from Improper Neutral-to-Ground Connections

Elevated Ground-to-Earth Voltage. When a neutral-to-ground connection is made at more than one location (ground loop), objectionable neutral current will return to the source through much of the electrical system and building. The result will be a rise in the voltage difference between the metal parts of the electrical system and the earth.

Electromagnetic Interference (EMI). In addition to the health issue as to the effect of electromagnetic fields on the human body, EMI from ?net current? (objectionable current on the EGFP and building structure) can disrupt the performance of sensitive electronic equipment and devices, particularly video monitors, electronic microscopes, etc.

Author?s Comment: For more information about Power Quality as it related to grounding, visit www.mikeholt.com/Powerquality/Powerquality.htm
__________________
God Bless, Mike Holt

 

[weressl]

So Mike Holt is wrong ,.. there is no increase in the level of hazard from the use of electricity when impropper neutral to ground connections are made??

Yes, Mike Holt has been wrong as he is not God.

Yet it would be helpful if you would address my questions and not try to hide behind lengthy posted articles that have little and nothing to do with the question.

 

[M. D.]

Therefore, the EGC will carry current. This will cause the external metal parts of each and every component that has an EGC its to become energized.

I don't think this is a false statement. I don't underrstand you explaination of why it is false.
Current will flow, that is why it is a violation of the NEC. I think it is misleading to say it that this is an untrue statement.
I am not trying to hide I'm trying to understand , I realize Mike Holt is not God and that the NEC is not perfect . His and many other's view of the improper neutral to ground connection differ from yours,.. and I must admit I find it hard to understand your posts, perhaps due to my lack of a formal education education in physics .
If I have offended you I ask your forgiveness

 

[weressl]

I don't think this is a false statement. I don't underrstand you explaination of why it is false.
Current will flow, that is why it is a violation of the NEC. I think it is misleading to say it that this is an untrue statement.
I am not trying to hide I'm trying to understand , I realize Mike Holt is not God and that the NEC is not perfect . His and many other's view of the improper neutral to ground connection differ from yours,.. and I must admit I find it hard to understand your posts, perhaps due to my lack of a formal education education in physics .
If I have offended you I ask your forgiveness

The last two sentence read:

This will cause the external metal parts of each and every component that has an EGC its to become energized. You could not safely touch anything in the facility.

THAT is false.

No offense taken, I am just trying to engage in a dialogue. I am addressing and answering specific points and expects those specifics to be replied to, reasoned with and engaged in dispute. I think it is a disservice to take the NEC as a Bible, especially for those who do not understand the science and try to explain what the themselves do not and can not comprehend. I am not implying malice, since they can't know what is it that the do not understand. Unfortunately many of those also sit on the NEC panels with voting power and produce a document that does not always have solid science behind it.

 

[M. D.]

improper connections .​

?Breaker cabinets on floors 17 through 26 also contained
improper neutral-ground connections (Figure 6).
Compounding this Code violation, someone had added a
connection from all the N-G busses to building steel.
?As you'd expect, we found high currents on the grounding
system in several locations: 17.8 A on service #1, 8.6 A
on #2 and 23 A on #3. The 500-kVA transformer in the basement
had 33 A of current on the grounding electrode conductor,
and the 300-kVA transformer on the 27th floor registered
95 A (at 120 V) on the improper neutral-to-ground
bond."​

 

[tallguy]

The last two sentence read:

This will cause the external metal parts of each and every component that has an EGC its to become energized. You could not safely touch anything in the facility.

THAT is false.

I think what everyone is asking (and very nicely and politely, I might add) is for you to explain why exactly you believe it to be false.

No offense taken, I am just trying to engage in a dialogue. I am addressing and answering specific points and expects those specifics to be replied to, reasoned with and engaged in dispute. I think it is a disservice to take the NEC as a Bible, especially for those who do not understand the science and try to explain what the themselves do not and can not comprehend. I am not implying malice, since they can't know what is it that the do not understand. Unfortunately many of those also sit on the NEC panels with voting power and produce a document that does not always have solid science behind it.

This is.... ummmm.... more than a little bit condescending. But if it's how you feel, so be it. In keeping with that, please use small words in your explanation of what exactly is false about "THAT".

Also, because of the nature of the NEC, and IMO the sorts of people that this forum naturally attracts as a result, everyone's posts are dissected quite carefully and literally. Write accordingly.

 

[weressl]

I think what everyone is asking (and very nicely and politely, I might add) is for you to explain why exactly you believe it to be false.

Perhaps the person who stated originally can explain how is it becoming energized. Then I can explain how it isn't. The burden of explanation rest with the original statement.

But let me explain why I do not think it is correct. In case of a ground to the case, it will elevate the case to the line voltage - whatever is available at the incoming terminals of the said equipment - but since the the equipment is grounded the surrounding ground will have the same potential. Therefore no potential difference exist and no danger exist of touching that equipment. That will be the case if the EGC is bonded to the grounded conductor or not at the subpanel.

Now serve me my crow, so I can enjoy it while it is still warm.;-)

I can only condescend to people who "feel" lower than me. I certainly do not "feel " higher than anybody else. It's for others to prove differently.

 

[charlie b]

I have been away from this thread for a while, so I missed Laszlo?s invitation to explain why I think it is unsafe to bond the Neutral and Ground Bars at a sub-panel. Here goes.

First, the obvious part, the part I know you all already know. It creates a parallel path within the sub-panel?s feeder. It creates a current divider between the neutral wire and the EGC. Once again, that takes place entirely within the feeder.

Here?s the next thing that, once again, you all already know: All EGCs in the entire building are essentially bonded to each other. All metal cases are bonded internally to their respective EGCs, and are also bonded to the metal conduit surrounding all feeders and branch circuits. As I see the situation, at any point between the N-G bond in the sub-panel and the main panel, there will be multiple, parallel, current paths. Current will take all paths that are available, and all it takes for the path to be available is that it be located between one point at which current is flowing and the source of that current. If you touch anything bonded to an EGC, therefore, you will become yet again another parallel current path.

Now I will concede Laszlo?s point that the amount of current that would flow through a person?s body will most likely be very small. The driving force for this current is the voltage drop along the neutral wire, and that is not a high number. It is likely that the person would not even feel a shock. That notwithstanding, some amount of current, however small, will flow through the person?s heart, on its way from the hands to the feet to the floor to the dirt to the GES to the GEC to the N-G Main Bonding Jumper in the Main Panel, and thus back to the source. That is one reason (the lesser of two reasons) that I call it unsafe. I don?t like the idea of extraneous current flowing through my heart, even if it is a small value.

All things change, however, if a neutral wire becomes detached. The condition of the N-G bond at the sub-panel can exist for decades. During those decades, one neutral wire might become loose in one location. Once that happens, the driving force for current through a person?s body is no longer just the VD across the neutral wire. The person becomes a voltage divider, sharing full system voltage with the load that is now in series with the load.

So the primary reason that I call this connection unsafe, and that I say that all metal objects in the building are not safe to touch, is that in one building in a million, at one point in time sometime in the next 30 years, this situation is going to electrocute one person. Actually, I strongly suspect that it has happened already, but it is going to happen again.

 

[M. D.]

But let me explain why I do not think it is correct. In case of a ground to the case, it will elevate the case to the line voltage - .

What??

Not sure I agree ,.. but, I'm not sure I even understand what you are saying here either.

I can only condescend to people who "feel" lower than me. I certainly do not "feel " higher than anybody else. It's for others to prove differently.

I think your comments are clear in this regard from the lowliest to the highest of the high.

 

[weressl]

What??

Not sure I agree ,.. but, I'm not sure I even understand what you are saying here either.


I think your comments are clear in this regard from the lowliest to the highest of the high.

Should read: In case of an inadvertent phase connection(ground) to the case, it will elevate the case to the line voltage - whatever is available at the incoming terminals of the said equipment - but since the the equipment is grounded the surrounding ground will have the same potential. Therefore no potential difference exist and no danger exist of touching that equipment. That will be the case if the EGC is bonded to the grounded conductor or not at the subpanel.

 

[weressl]

To bond or double bond, that is the question!?

To bond or double bond, that is the question!?

I have been away from this thread for a while, so I missed Laszlo?s invitation to explain why I think it is unsafe to bond the Neutral and Ground Bars at a sub-panel. Here goes.

First, the obvious part, the part I know you all already know. It creates a parallel path within the sub-panel?s feeder. It creates a current divider between the neutral wire and the EGC. Once again, that takes place entirely within the feeder.

Here?s the next thing that, once again, you all already know: All EGCs in the entire building are essentially bonded to each other. All metal cases are bonded internally to their respective EGCs, and are also bonded to the metal conduit surrounding all feeders and branch circuits. As I see the situation, at any point between the N-G bond in the sub-panel and the main panel, there will be multiple, parallel, current paths. Current will take all paths that are available, and all it takes for the path to be available is that it be located between one point at which current is flowing and the source of that current. If you touch anything bonded to an EGC, therefore, you will become yet again another parallel current path.

Now I will concede Laszlo?s point that the amount of current that would flow through a person?s body will most likely be very small. The driving force for this current is the voltage drop along the neutral wire, and that is not a high number. It is likely that the person would not even feel a shock. That notwithstanding, some amount of current, however small, will flow through the person?s heart, on its way from the hands to the feet to the floor to the dirt to the GES to the GEC to the N-G Main Bonding Jumper in the Main Panel, and thus back to the source. That is one reason (the lesser of two reasons) that I call it unsafe. I don?t like the idea of extraneous current flowing through my heart, even if it is a small value.

All things change, however, if a neutral wire becomes detached. The condition of the N-G bond at the sub-panel can exist for decades. During those decades, one neutral wire might become loose in one location. Once that happens, the driving force for current through a person?s body is no longer just the VD across the neutral wire. The person becomes a voltage divider, sharing full system voltage with the load that is now in series with the load.

So the primary reason that I call this connection unsafe, and that I say that all metal objects in the building are not safe to touch, is that in one building in a million, at one point in time sometime in the next 30 years, this situation is going to electrocute one person. Actually, I strongly suspect that it has happened already, but it is going to happen again.

I buy that for a $, however the single ground/grounded conductor bond at the power source could also get loose and the same situation would occur. Given the staistical probability thatthere would be about .001% of all primary panels would have a subpanel attached to it, the problem cited in the original post would become statistically insiginficant probabilty in comparison to the neautral ground bond loosening. Following that logic, if you have double bond at the main panel AND the subpanel, the same way that one has a bond at the utility transformer AND the customers' panel, either of those bonds loosening up would still leave you a solidly grounded neutral which still provides you with protection.

I think you just convinced me that the double bonding is inherently safer, even if it is against the NEC ;-). Or did I convince my self? I am now officially confused......

 

[don_resqcapt19]

Laszlo

... but since the the equipment is grounded the surrounding ground will have the same potential. ...

That is not a correct statement. It is only correct for someone standing on top of the grounding electrode. If you are standing on earth 3' away from the grounding electrode you will be subjected to ~85% of the voltage on the equipment case as measured to "remote" earth.
Don

 

[Karl H]

I can't even express how much i enjoy watching Genius minds engage in battle. You guys keep this up and i'll miss all my football games today.

 

[ItsHot]

Neutral???

Neutral???

Just when I thought I had this all figured out, the NEC removes "neutral" from their definitions. At a continuing education class the instructor thought it was funny after a hundred years of callng the neutral the neutral ,all of a sudden we are told to call it something else!!????

 

[don_resqcapt19]

Just when I thought I had this all figured out, the NEC removes "neutral" from their definitions.

I don't think that there has ever been a defintion of "neutral" in the NEC, unless you count the wording in 310.15(B)(4). There is a defintion of "neutral conductor" in the 2008 code.
Don

 

[weressl]

Laszlo

That is not a correct statement. It is only correct for someone standing on top of the grounding electrode. If you are standing on earth 3' away from the grounding electrode you will be subjected to ~85% of the voltage on the equipment case as measured to "remote" earth.
Don

Please furnish the circuit diagram and the calculation.

If that would be the case, there is absolutely no reason to connect any part of the electrical supply system to ground, the WYE or midtap point of the supply transformer could just simply be connected to the transformer casing and that connection can be carried as the fault protective conductor and connected to the metallic casing of any supplied electrical equipment.

Step voltages only become the problem on Medium and High Voltage systems and that is why there are equipotential mats laid in such substation yards.

 

[jwelectric]

If that would be the case, there is absolutely no reason to connect any part of the electrical supply system to ground,

And just why do we connect to earth in the first place?

 

[don_resqcapt19]

Lazlo,

Please furnish the circuit diagram and the calculation.

It is based on the percent of the total resistance around a 5/8" x 10' ground rod as shown in Chaper 4, Table 9 of the 1991 IEEE Green book. That table shows ~86% of the total resistance within 5' of the ground rod (yes, I said 3' but that was from memory without checking). That would mean if you connect a 10' ground rod to a 120 volt source and touched the source and the earth 5' away from the rod you would receive a 103 volt shock.

If that would be the case, there is absolutely no reason to connect any part of the electrical supply system to ground, the WYE or midtap point of the supply transformer could just simply be connected to the transformer casing and that connection can be carried as the fault protective conductor and connected to the metallic casing of any supplied electrical equipment.

Other than lightning protection and possibly votlage stablaziation, there is no reason to connect the system to earth. It does not increase the safety of the system in any way.

Step voltages only become the problem on Medium and High Voltage systems and that is why there are equipotential mats laid in such substation yards.

They can be a problem on low voltage systems that do not have a code compliant fault clearing path. One example is where a metal parking lot light pole is installed with only a grounding electrode and not the code required equipment grounding conductor. If there is a line to pole fault anyone one touching the pole and the earth 3' away from the pole will receive ~81 volt shock, assuming a 120 volt supply. (Table 9 shows ~68% of the resistance at 3')
Don