Equipment Grounding for Ungrounded System

[bobby ocampo]

Not really...the first ground fault on an ungrounded system turns that system into a grounded system. It may or may not be solidly grounded but it becomes a grounded system.

While it is true that an ungrounded system will become corner grounded in a single line to ground fault, the issue is on the purpose of the EGC during the instant that one ungrounded conductor touches the metal enclosure. Will the EGC serves as the return path to trip the OCPD? Or will te EGC serve as the connection to the earth to make the energized metal enclosure equipotential with the earth or ground?

 

[bobby ocampo]

Grounded, or ungrounded, I'll stand with my statement!

IF you truely feel I missed the mark then send a note to the Moderator and ask my thread to be removed! The ! in the upper right corner will do it, Have at it...

Dear Sir,

We are here to discuss based on technical facts of our answers to the different opinion in the thread. Our objective is to clarify things so that we will not misinterpret technical information given in the forum.

Please provide your justification for your answers. I am here to listen and learn too.

Our discussion in the thread I hope should be purely objective and not personal.

 

[iwire]

Even the first ground fault, there is a danger of electrocution even if there is no return path for the current to the source.

There is no 'return path' with a single ground fault on an system that was installed as an ungrounded system as there is no main bonding jumper. The EGC connection to earth is not a 'return path'.

The first fault to ground on an ungrounded system basically acts as the systems main bonding jumper, if a second fault on an opposing phase happens then the enclosures and the EGC work as a fault path between the two phase conductors.

I do agree with Peter, it appears you are not reading the replies.

 

[infinity]

Please explain as an UNGROUNDED and HIGH RESISTANCE GROUNDED system operate differently from a SOLIDLY GROUNDED SYSTEM. This is a totally different topic.

You're correct they are different but this thread previously made no mention of resistance grounding until you brought it up. An ungrounded system which has a one phase fault to ground doesn't become a resistance ground system, but for the reason of correctness you could add the word solidly to my first post.

The short answer is that an ungrounded system with one phase to ground fault will operate the same as an intentionally solidly grounded system.

 

[don_resqcapt19]

...
Even the first ground fault, there is a danger of electrocution even if there is no return path for the current to the source. ...

There is no way to have a path back to the source with a single ground fault on an ungrounded system. You can as you say make everything that is connected to the EGCs at an equal potential for a single ground fault on an ungrounded or high resistance grounded system, something that you can't do on an ungrounded system, but you can't make a path back to the source on an ungrounded system until you have the second ground fault on a different phase.

 

[bobby ocampo]

There is no way to have a path back to the source with a single ground fault on an ungrounded system.

If the equipment grounding/and bonding is not a return path to the source then what is the purpose of equipment grounding? Isn't it to reduce the potential of the energized metal part to ground potential and not as a return path to the source?

You can as you say make everything that is connected to the EGCs at an equal potential for a single ground fault on an ungrounded or high resistance grounded system, something that you can't do on an ungrounded system, but you can't make a path back to the source on an ungrounded system until you have the second ground fault on a different phase.

Does it mean that EGC is NOT ONLY as a return path to the source but as a means to reduce the potential of the metal part to ground potential for safety specialy in UNGROUNDED SYSTEM and HRG SYSTEM?

 

[roger]

Or will te EGC serve as the connection to the earth to make the energized metal enclosure equipotential with the earth or ground?

For this discussion you will be better off forgetting earth all together in that it plays no part here.

With that said, go back and read the replies with an open mind and things will be clearer.

Roger

 

[don_resqcapt19]

If the equipment grounding/and bonding is not a return path to the source then what is the purpose of equipment grounding? Isn't it to reduce the potential of the energized metal part to ground potential and not as a return path to the source? ...

With a single ground fault on a system that is not solidly grounded there is no possible way that the EGC can provide a path back to the source as there is no second connection to the source. A current carrying circuit requires two connections to the source and you only have one in this case. On an system that is no solidly grounded the EGC can, in this case, act to reduce the potential between the faulted equipment and other conductive items that are directly or indirectly connected to the EGC. We need to be careful here as the types of systems you are talking about here are somewhat rare and behave differently than solidly grounded systems. The EGC does little to provide equal potential on a solidly grounded system under fault conditions...in fact it actually raises the potential of all of the items connected to the equipment grounding system by a voltage equal to the voltage drop on the grounded conductor between the main bonding jumper and the system source. At the point of the fault the equipment will be energized with a voltage that is the sum of the voltage drop on the system grounded conductor between the main bonding jumper and the source and the voltage drop on the EGC between the point of the fault and the main bonding jumper. This voltage will often exceed 50 volts and can be a shock hazard. This voltage will exist until the fault is cleared.

 

[bobby ocampo]

With a single ground fault on a system that is not solidly grounded there is no possible way that the EGC can provide a path back to the source as there is no second connection to the source.

This is exactly the point. The Equipment grounding conductor now for an ungrounded system is to reduce the accidentaly energized metal piece to GROUND POTENTIAL to prevent electrocution to person who may accidentaly touch the energized metal piece. EGC is not always a return path to operate the OCPD.

A current carrying circuit requires two connections to the source and you only have one in this case. On an system that is no solidly grounded the EGC can, in this case, act to reduce the potential between the faulted equipment and other conductive items that are directly or indirectly connected to the EGC.

Therefore Equipment grounding for UNGROUNDED and HRG SYSTEM serves to reduce the potential of the accidentaly energized metal piece to ground potential or earth potential and not as a return path to the source to operate the OCPD.

We need to be careful here as the types of systems you are talking about here are somewhat rare and behave differently than solidly grounded systems. The EGC does little to provide equal potential on a solidly grounded system under fault conditions...in fact it actually raises the potential of all of the items connected to the equipment grounding system by a voltage equal to the voltage drop on the grounded conductor between the main bonding jumper and the system source. At the point of the fault the equipment will be energized with a voltage that is the sum of the voltage drop on the system grounded conductor between the main bonding jumper and the source and the voltage drop on the EGC between the point of the fault and the main bonding jumper. This voltage will often exceed 50 volts and can be a shock hazard. This voltage will exist until the fault is cleared.

Therefore for SOLIDLY GROUNDED, EGC serves as a return path to the source for the operation of the OCPD. However for UNGROUNDED and HRG SYSTEM, the EGC serves to reduce the accidentally energized metal piece to ground potential or earth potential.

 

[roger]

or earth potential.

No, it has nothing to do with earth or earths relative potential difference to any part of a transformer winding.

 

[don_resqcapt19]

This is exactly the point. The Equipment grounding conductor now for an ungrounded system is to reduce the accidentaly energized metal piece to GROUND POTENTIAL to prevent electrocution to person who may accidentaly touch the energized metal piece. EGC is not always a return path to operate the OCPD.
Therefore Equipment grounding for UNGROUNDED and HRG SYSTEM serves to reduce the potential of the accidentaly energized metal piece to ground potential or earth potential and not as a return path to the source to operate the OCPD.

While the EGC does reduce the potential to other grounded conductive objects and the earth on an ungrounded system with a single fault, it is also a return path when there is a second fault and it must be sized to operate the OCPD.

I don't understand the point you are trying to make in this thread.

The main purpose of the EGC is as a fault return path no matter what type of system you are talking about. It does a better job of reducing the potential when there is a single fault on a high resistance or ungrounded system, but its main purpose is to clear a fault.

 

[bobby ocampo]

While the EGC does reduce the potential to other grounded conductive objects and the earth on an ungrounded system with a single fault, it is also a return path when there is a second fault and it must be sized to operate the OCPD.

It is important for most of us to understand that equipment grounding is a protection against hazard in the use of electricity. Reducing the potential of the accidentally energized metal piece to ground potential is the main purpose of Equipment grounding. It is very hazardous that an Enclosure is not equipment grounded in a single line to ground fault specially on UNGROUNDED SYSTEM AND HRG SYSTEM.

I don't understand the point you are trying to make in this thread.

The point here is that EGC is NOT ONLY for the return path to trip the OCPD. EGC is also to make sure that metal enclosure is at ground potential for the safety of personnel specially in a single line to ground fault for UNGROUNDED AND HRG SYSTEM.

The main purpose of the EGC is as a fault return path no matter what type of system you are talking about. It does a better job of reducing the potential when there is a single fault on a high resistance or ungrounded system, but its main purpose is to clear a fault.

The first objective in IEEE Std 142-1991 page 52 is "Reduce electric shock hazard to personnel." The third objective is "To provide a low impedance return path for ground-fault current necessary for the timely operation of the
overcurrent protection system."

You can verify this in experiment on a Delta secondary ungrounded system. Measure metal enclosure to ground without equipment grounding connected and measure metal enclosure to ground with EGC. This experiment will prove the value reducing electricl shock because the potential of the metal enclosure will be reduce to ground potential.

 

[bobby ocampo]

IEEE Std 142-1991

"2.1.2 Electric-Shock Exposure
Electric shock injuries result from contact with metallic components that are unintentionally energized [10].7 Effective equipment grounding practices can minimize these personal injuries.

A breakdown of insulation can cause accidental contact between an energized electrical conductor and the metal frame that encloses it. Such contact tends to energize the frame to the voltage level of the conductor. Avoiding shock-hazard voltage requires nullifying this tendency. The equipment-grounding system should do this by forming a low impedance path to ground."

 

[enteng14]

EGC is important for all electrical systems whether it is grounded (solidly or impedance) or ungrounded.

Solidly Grounded System
EGC provide low impedance path for ground fault current back to the source. Ground fault current will flow in two parallel path from the main bonding jumper (1) Grounded Service Conductor and (2) Earth through the Grounding Electrode System. The OCPD will facilitate (open) because of the high magnitude of the ground fault return to the source.

View attachment 2153

High Resistance Grounding
EGC will provide low impedance path for ground fault current back to the source. Ground dectectors and alarm will be trigger that there is a ground fault in the system but it will not facilitate the OCPD because of low magnitude of ground fault current.

View attachment 2154

Ungrounded System
First be reminded that there is no grounding connections at the source. There is still grounding electrode system at the service equipment and also EGC.

When first ground fault occurs, the ground fault will not return to source as there is no return path to earth (source is not grounded). With EGC bonded all the metallic parts/enclosure that will likely to be energized, all of bonding connections will now be energized by the first ground fault. Any person touches the energized parts will not be electrocuted since there is no complete circuit back to the source.

View attachment 2155

When the second ground fault occurs, there will now be a line to line fault and there is a complete circuit back to the source through one of the ungrounded phase conductor and will facilitate the OCPD.

View attachment 2156

Importance of EGC in ungrounded is system is to have all metallic parts/enclosure to have same potential when there is a ground fault.

Grounding electrode will limit the voltage imposed by lightning and surges and limit the voltage to ground on service equipment (grounding electrode conductor is bonded at the service equipment).

EGC is size differently in each system.

 

[bobby ocampo]

EGC is important for all electrical systems whether it is grounded (solidly or impedance) or ungrounded.

EGC should always be connected to ground.

Solidly Grounded System
EGC provide low impedance path for ground fault current back to the source. Ground fault current will flow in two parallel path from the main bonding jumper (1) Grounded Service Conductor and (2) Earth through the Grounding Electrode System. The OCPD will facilitate (open) because of the high magnitude of the ground fault return to the source.

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?

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

View attachment 2153

High Resistance Grounding
EGC will provide low impedance path for ground fault current back to the source. Ground dectectors and alarm will be trigger that there is a ground fault in the system but it will not facilitate the OCPD because of low magnitude of ground fault current.

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

View attachment 2154

Ungrounded System
First be reminded that there is no grounding connections at the source. There is still grounding electrode system at the service equipment and also EGC.

When first ground fault occurs, the ground fault will not return to source as there is no return path to earth (source is not grounded). With EGC bonded all the metallic parts/enclosure that will likely to be energized, all of bonding connections will now be energized by the first ground fault. Any person touches the energized parts will not be electrocuted since there is no complete circuit back to the source.

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

 

[don_resqcapt19]

IEEE Std 142-1991

"2.1.2 Electric-Shock Exposure
Electric shock injuries result from contact with metallic components that are unintentionally energized [10].7 Effective equipment grounding practices can minimize these personal injuries.

A breakdown of insulation can cause accidental contact between an energized electrical conductor and the metal frame that encloses it. Such contact tends to energize the frame to the voltage level of the conductor. Avoiding shock-hazard voltage requires nullifying this tendency. The equipment-grounding system should do this by forming a low impedance path to ground."

If that statement from the IEEE is intended to apply to grounded systems, then they have no idea of what they are talking about. A path to ground does nothing to provide shock protection on a grounded system.

 

[bobby ocampo]

If that statement from the IEEE is intended to apply to grounded systems, then they have no idea of what they are talking about. A path to ground does nothing to provide shock protection on a grounded system.

HRG and LRG are also considered grounded system. This can be verified in an experiment by measuring the potential of the metal enclosure to ground in a single line-to-ground fault if the enclosure is connected to earth and then measuring potential of metal enclosure to ground when the enclosure is NOT connected to earth. We can verify from this experiment the importance of the connection of the EGC to ground.

Justification of importance of connection to earth of EGC may also be verified by vector diagrams on a single line to ground fault. It is difficult to say that electrical engineering experts in IEEE have no idea of what they are talking about. IEEE Color books are considered American National Standard.

IEEE Recommended Practice for
Grounding of Industrial and Commercial
Power Systems

Sponsor
Power Systems Engineering Committee
of the
IEEE Industry Applications Society
Approved June 27, 1991
IEEE Standards Board
Approved December 9, 1991
American National Standards Institute

 

[don_resqcapt19]

EGC should always be 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?

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

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. 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. 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.

 

[don_resqcapt19]

HRG and LRG are also considered grounded system. This can be verified in an experiment by measuring the potential of the metal enclosure to ground in a single line-to-ground fault if the enclosure is connected to earth and then measuring potential of metal enclosure to ground when the enclosure is NOT connected to earth. We can verify from this experiment the importance of the connection of the EGC to ground.

Justification of importance of connection to earth of EGC may also be verified by vector diagrams on a single line to ground fault. It is difficult to say that electrical engineering experts in IEEE have no idea of what they are talking about. IEEE Color books are considered American National Standard.

IEEE Recommended Practice for
Grounding of Industrial and Commercial
Power Systems

Sponsor
Power Systems Engineering Committee
of the
IEEE Industry Applications Society
Approved June 27, 1991
IEEE Standards Board
Approved December 9, 1991
American National Standards Institute

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.

 

[weressl]

Generally there would be ground fault indicating lights or alarm to notify maintenance personal to start looking for the ground fault.

(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.
​

(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.​

(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.

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.​

​