Equipment Grounding for Ungrounded System

[iwire]

Laszlo, I have no idea why that post was aimed at me, I am aware of the rules.

I said 'generally' as the systems not required to be grounded by 250.20(B) are not required to have fault indicators.

 

[enteng14]

EGC should always be connected to ground.

EGC are always connected to ground. I didn't post that it was ungrounded. My post was "EGC is important for all electrical systems whether it is grounded (solidly or impedance) or ungrounded." It is basic that EGC are connected to ground.

What is the purpose of the neutral being connected to the ground? Will the accidentally energized metal enclosure become hazardous because it has a different potential as the ground if the neutral is not bonded to the ground?

If the neutral is NOT connected to the ground, will the accidentally energized metal enclosure be still safe even if the OCPD operate because of the return path to the source?

Maybe the first question would be "what is the purpose of grounding the electrical system?" second is "what is the purpose of grounding the metal enclosure of the electrical equipment?" and third is "what is the purpose of bonding the metal enclosure/frames of electrical equipments?"

What will happen if the EGC is not connected to the ground? Isn't it that the OCPD will still operate?

For solidly grounded system, connecting the EGC to ground has nothing to do in facilitating the operation of OCPD as earth does not provide low impedance path that's why we bonded the grounded service conductor at the service equipment to the EGC to achieve the effective ground fault path in order to facilitate the OCPD.

View attachment 2153

The EGC will provide a low impedance path to the GROUND and NOT ONLY TO THE SOURCE.

Look at the illustration, it has only a single grounding electrode. In HRG, the grounding electrode can be located at the transformer or at the service equipment. During ground fault, EGC will provide the low impedance back to the source and there is no current flowing in the ground because of single point grounding.

View attachment 2154

Maybe the question to clarify things would be "what is the purpose of connecting the EGC to the ground?."

EGC should be connected to the grounding electrode to have same potential to the ground and not just same potential with all of the enclosure because of bonding

View attachment 2155

EGC has the same potential at the ground only at the service equipment where the grounding electrode conductor is bonded. Earth is not a zero impedance that's why at different points, EGC has different potential with respect to earth.

 

[weressl]

Laszlo, I have no idea why that post was aimed at me, I am aware of the rules.

I said 'generally' as the systems not required to be grounded by 250.20(B) are not required to have fault indicators.

I was trying to be supportive of your assertion that there usually is a GF indication by posting where the current Code actually requires it.

The other highlights were just summing up the issue.

Let go of your paranoia,,,I am not after you.......:wink:

 

[iwire]

Let go of your paranoia,,,

Then what would I have?

 

[weressl]

Then what would I have?

Scizophrenia still remains a viable option.........

 

[iwire]

I will investigate that option. :grin:

 

[weressl]

I will investigate that option. :grin:

Talk to Bob about it....

...and if I am talking to to Bob at this moment, please contact Iwire ASAP........

 

[bobby ocampo]

With a solidly grounded system, the connection to earth does not mean that the energized metal will be at the same potential as the earth. You can say that all bonded conductive parts, with the exception of the part where the fault is located, will be at the same potential as the other bonded parts, but they will not be at the same potential as the earth.

If all bonded enclosure will be connected to the earth then why can't it have the same potential with the earth? If in ungrounded and HRG is connected to the earth and will have the same potential with the earth during a single line to ground fault, then why can't a solidly grounded system have the same potential to the earth if the EGC is connected to the ground rod? Any techical justification that it will not be approximately the same potential with the earth to REDUCE electric shock to personnel?

I will develop an experiment for a 21Y/12 volts secondary transformer to determine the characteristics of Ground fault on solidly grounded system. In HRG and Ungrounded we have already verified it on a single line-to-ground fault.

The connection to the earth and the earth itself is not of a low enough impedance to make that happen. The part with the fault will have a voltage, when measured to other bonded parts, equal to the voltage drop on the EGC that is carrying the fault current. These are the reasons why the EGC, for a solidly grounded system, has to be sized to make the OCPD open quickly.

I respectfully agree that the EGC should be sized in accordance with the zero sequence fault due to a very high line-to-ground fault in a solidly grounded system. However bonded EGC is still connected to the ground to make sure that accidentaly energized enclosure are still with the same potential with the earth.

With this type of system, the hazard is there until the fault is cleared. The connection to earth has very little to do with the opening of the OCPD and in reality does little to provide equal potential in the event of a fault on a solidly grounded system.

It is true that for solidly grounded system there are two conditions that should be met. First, reduce the electric shock hazards to personel that may accidentaly touch the accidentaly energized metal piece. This is done through the connection of the bonded low impedance EGC to the EARTH. Second and I respectfully agree that the fault should ALSO be cleared immediately because of the very high current that can cause ARC FLASH HAZARD if the OCPD will not operate. IEEE Std 142-1991.

 

[bobby ocampo]

EGC are always connected to ground. I didn't post that it was ungrounded. My post was "EGC is important for all electrical systems whether it is grounded (solidly or impedance) or ungrounded." It is basic that EGC are connected to ground.

I respectfully agree then sir.

Maybe the first question would be "what is the purpose of grounding the electrical system?" second is "what is the purpose of grounding the metal enclosure of the electrical equipment?" and third is "what is the purpose of bonding the metal enclosure/frames of electrical equipments?"[/quote}

What is your answer sir?

For solidly grounded system, connecting the EGC to ground has nothing to do in facilitating the operation of OCPD as earth does not provide low impedance path that's why we bonded the grounded service conductor at the service equipment to the EGC to achieve the effective ground fault path in order to facilitate the OCPD.

I agree that connecting the bonded EGC to the ground will have not effect on the fast operation of the OCPD. What the bonded EGC can do is it will REDUCE (not eliminate due to impedance even how low the EGC has) the electric shock hazard to personnel.

Look at the illustration, it has only a single grounding electrode. In HRG, the grounding electrode can be located at the transformer or at the service equipment. During ground fault, EGC will provide the low impedance back to the source and there is no current flowing in the ground because of single point grounding.

I respectfully agree that grounding electrode is connected at the transformer neutral after the impedance or thru the service equipment. However the low current flowing to the low impedance EGC goint to ground is being limited by the resistor connected and not because it is grounded.

Maybe the question to clarify things would be "what is the purpose of connecting the EGC to the ground?."

What is your opinion sir on this question?

 

[bobby ocampo]

My post should have read solidly grounded systems and I stand by my statement that if the IEEE thinks that is what a connect to earth does for a solidly grounded system then they have no idea what they are talking about.

I respect your opinion sir if you think that IEEE have no idea on what they are talking about. While my opinion is otherwise. I respectfully agree to disagree. Hope we can have technical explanation on why it is so for all of us to learn including me on the purpose of equipment grounding.
Basic objective of equipment grounding based on IEEE 142-1991 American National Standard.
1) To reduce (NOT REMOVE) electric shock hazard to personnel.
2) To provide adequate current carrying capability, both in magnitude and duration, to accept the ground-fault current permitted by the overcurrent protection system without creating a fire or explosive hazard to building or contents.
3) To provide a low impedance return path for ground-fault current necessary for the timely operation of the overcurrent protection system.

 

[bobby ocampo]

(B) Ungrounded Systems.​

(1) Grounding Electrical Equipment.

Non?currentcarrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected to earth in a manner that will limit the voltage imposed by lightning or unintentional contact with higher-voltage lines and limit the voltage to ground on these materials.

In other words when there is a single fault to the conductive case of an electrical equipment of an ungrounded system a person approaching and touching the equipment would expreience a voltage difference of line voltage between the case and ground he is standing on.
​

This is the reason why the bonded EGC is connected to ground or earth to reduce electric shock hazard to personnel.

(2) Bonding of Electrical Equipment.​

Non?currentcarrying conductive materials enclosing electrical conductors or equipment, or forming part of such equipment, shall be connected together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying the maximum fault current likely to be imposed on it.​

I respectfully agree sir specially on SOLIDLY GROUNDED SYSTEM where there is a very high line-to-ground fault current.

(3) Bonding of Electrically Conductive Materials and Other Equipment. ​

Electrically conductive materials that are likely to become energized shall be connected together and to the supply system grounded equipment in a manner that creates a low-impedance path for ground-fault current that is capable of carrying the maximum fault current likely to be imposed on it.​

I respectfully agree sir specially on solidly grounded system.

250.21 Alternating-Current Systems of 50 Volts to 1000 Volts Not Required to Be Grounded.​

(A) General. ​

The following ac systems of 50 volts to 1000 volts shall be permitted to be grounded but shall not be required to be grounded:​

(1) Electrical systems used exclusively to supply industrial electric furnaces for melting, refining, tempering, and the like

(2) Separately derived systems used exclusively for rectifiers that supply only adjustable-speed industrial drives
(3) Separately derived systems supplied by transformers that have a primary voltage rating less than 1000 volts, provided that all the following conditions are met:
a. The system is used exclusively for control circuits.
b. The conditions of maintenance and supervision ensure that only qualified persons service the installation.
c. Continuity of control power is required.
(4) Other systems that are not required to be grounded in accordance with the requirements of 250.20(B)​

​

​

(B) Ground Detectors.​

Ungrounded alternating current systems as permitted in 250.21(A)(1) through (A)(4) operating at not less than 120 volts and not exceeding 1000 volts shall have ground detectors installed on the system.​

​

[/quote]

The code should be clear that this systems are not required to be SOLIDLY GROUNDED because of a very high arc flash hazard in this type of system. Acceptable system should be UNGROUNDED OR HRG SYSTEM. HRG is considered a grounded system with manageable fault current of 10amps or less.

 

[don_resqcapt19]

I respect your opinion sir if you think that IEEE have no idea on what they are talking about. While my opinion is otherwise. I respectfully agree to disagree. Hope we can have technical explanation on why it is so for all of us to learn including me on the purpose of equipment grounding.
Basic objective of equipment grounding based on IEEE 142-1991 American National Standard.
1) To reduce (NOT REMOVE) electric shock hazard to personnel.
2) To provide adequate current carrying capability, both in magnitude and duration, to accept the ground-fault current permitted by the overcurrent protection system without creating a fire or explosive hazard to building or contents.
3) To provide a low impedance return path for ground-fault current necessary for the timely operation of the overcurrent protection system.

Even the document that you are citing has a table that shows how ineffective the connection to earth is to reduce the shock potential. The bonding of the conductive objects is what reduces the potential, and not the connection to the earth. The only way that the earth could make the potential equal is if it was a good enough conductor to raise the voltage of the earth to the potential of the fault. It can't do that and the table in the green book says that at 5' from the grounding electrode you will have about 86% of the total voltage. And just because the green book is an peer reviewed document does not mean that everything in it is correct. Many engineers do not have a good grasp on what grounding and bonding is all about.

 

[don_resqcapt19]

The information on this slide is based on the table in the green book. While this is a single light pole, the same thing happens on a building system. The grounding electrode only reduces the potential in the area very close to the grounding electrode.

 

[tryinghard]

An ungrounded system is devoid of any transformer bonding.

In premises wiring the sole purpose of an ungrounded system is to allow critical machinery to operate with a short, indication and or annunciation warns of this short for repair. The second short will actually be a phase short between the first - A, B or A, C or B, C.

If a warning, indication and or annunciation, does not exist this will eliminate the only purpose for an ungrounded system.

An effective ground fault current path has exactly the same importance on grounded or ungrounded systems.

The earth has no role in allowing the operation of protection devices; it also has no role in causing zero potential because its resistance is unknown at any given moment.

Again an ungrounded system allows one short to literally just sit there on conductive items, this short is not returning to source or earth. A second will be a phase short.

Check out: Grounding & Bonding: The Big Picture Post

 

[bobby ocampo]

Even the document that you are citing has a table that shows how ineffective the connection to earth is to reduce the shock potential. The bonding of the conductive objects is what reduces the potential, and not the connection to the earth.

It is not ONLY connection to the earth and NOT ONLY bonding but BOTH should be done. If the bonded EGC will not be connected to the earth then the solidly grounded will be ungrounded and it will have a different potential such that personell touching the accidentaly energized metal piece will have a shock.

The only way that the earth could make the potential equal is if it was a good enough conductor to raise the voltage of the earth to the potential of the fault.

Because earth resistance is variable and earth is not a good conductor most of the time, we realy have to bond using EGC or other exemptions allowed by the code. However this does not mean that the EGC will not be connected to ground.

It can't do that and the table in the green book says that at 5' from the grounding electrode you will have about 86% of the total voltage. And just because the green book is an peer reviewed document does not mean that everything in it is correct. Many engineers do not have a good grasp on what grounding and bonding is all about.

The table is the justification why it is both important to connect to ground and to bond. Both should be done to prevent electric shock to personnel. There is a big danger if the EGC will not be connected to the Ground.

 

[bobby ocampo]

The information on this slide is based on the table in the green book. While this is a single light pole, the same thing happens on a building system. The grounding electrode only reduces the potential in the area very close to the grounding electrode.

The picture shows the importance of bonding and I respectfully agree that because of the resistance of the ground and the high current there is a voltage drop that may cause electric shock even if the pole is connected to the earth. This same principle is used why several grounding rod are installed in a substation and are interconnected (bonded together) to reduce the step potential as shown in the illustration. A mesh is installed in the substation to have the same purpose. However it can not be denied that still all this interconnection and bonding are still connected to the ground.

Based on our experience on UNGROUNDED SYSTEM and HRG without equipment grounding and if Bonded EGC is not connected to earth there is a potential from the metal enclosure to ground. You can also do this experiment to verify. This shows the importance of connecting to the earth.

It is very dangerous to say that connection of the bonded EGC to earth is not important. It is as important as the bonding and bonding without connection to earth is dangerous. Not connecting to earth the bonded EGC will result in an increase potential and vector diagram can prove this. Industrial Power System Handbook by Beeman.

 

[bobby ocampo]

it (The earth ) also has no role in causing zero potential because its resistance is unknown at any given moment.

This is a very dangerous statement and may cause electrocution. You can experiment on this on an UNGROUNDED SYSTEM and HRG. Not connecting to earth bonded EGC will be very hazardous. Connection to earth either in the source or in the service equipment is very important. In the source meaning metal enclosure of the transformer is connected to earth and this is where all EGC should be connected.

Again an ungrounded system allows one short to literally just sit there on conductive items, this short is not returning to source or earth. A second will be a phase short.

Check out: Grounding & Bonding: The Big Picture Post

Try to measure the potential from enclosure to ground if the EGC is not connected to the ground rod. Hope nobody gets electrocuted. I have verified this in my experience. You can verify it also for yourself.

 

[don_resqcapt19]

The table is the justification why it is both important to connect to ground and to bond. Both should be done to prevent electric shock to personnel. There is a big danger if the EGC will not be connected to the Ground.

That is still a minor player in preventing shock, especially under fault conditions. The bonding is much more important, however even that does not remove the hazard. If you have two pieces of equipment next to each other and one has a fault, there will a voltage between them, assuming that they each have their own EGC. This voltage will be equal to the voltage drop on the EGC for the faulted equipment. The only way to remove that voltage is to clear the fault.
I have never said that the system should not be connect to earth, however that connection does very little to prevent shock, for a solidly grounded system, under fault conditions.
All of my comments are based on the much more common solidly grounded system. There is a big difference on what the connection to earth does for a single fault on a resistance grounded system. It does, for the most part, remove the hazardous voltage when a single fault occurs on those types of systems.

 

[don_resqcapt19]

Try to measure the potential from enclosure to ground if the EGC is not connected to the ground rod. Hope nobody gets electrocuted. I have verified this in my experience. You can verify it also for yourself.

Under fault conditions for a solidly grounded system, you will find very little, if any difference, with or with out the connection to earth.

 

[tryinghard]

This is a very dangerous statement and may cause electrocution. You can experiment on this on an UNGROUNDED SYSTEM and HRG. Not connecting to earth bonded EGC will be very hazardous.

It's a code violation if its not grounded! Nobody here is advocating avoiding grounding!

Your original post asks a clear question about equipment grounding, but you are now trying to prove the purpose of earth connection. These have different functions/purposes.