Equipment Grounding for Ungrounded System

[robbietan]

which is why utilities are now providing a connection to ground even to single phase customers

 

[bobby ocampo]

There must be a path from and to source for current to flow. An ungrounded system is a delta system, the “C” transformer is ungrounded and there is no XO tap or bonding jumper to the transformer “C” (C1 & C2).

In your claim why does current want to return to earth?

It is not the current wanting to return to earth but connecting the accidental energized metal piece to ground potential. In HRG and Ungrounded system there is a minimal single line to ground fault current for continuity of service but the accidental contact of one of the current carrying conductor with the metal piece will have its potential equal to the equivalent line-to-neutral voltage of the system because of system capacitance if the metal piece is not grounded or connected to earth. You can experiment this safely in a delta secondary transformer or wye transformer where neutral is not grounded or high resistance grounded system.

 

[tryinghard]

It is not the current wanting to return to earth but connecting the accidental energized metal piece to ground potential. In HRG and Ungrounded system there is a minimal single line to ground fault current for continuity of service but the accidental contact of one of the current carrying conductor with the metal piece will have its potential equal to the equivalent line-to-neutral voltage of the system because of system capacitance if the metal piece is not grounded or connected to earth. You can experiment this safely in a delta secondary transformer or wye transformer where neutral is not grounded or high resistance grounded system.

How is there a ?minimal current for continuity of service?, explain this?

 

[tryinghard]

It is not the current wanting to return to earth but connecting the accidental energized metal piece to ground potential. In HRG and Ungrounded system there is a minimal single line to ground fault current for continuity of service but the accidental contact of one of the current carrying conductor with the metal piece will have its potential equal to the equivalent line-to-neutral voltage of the system because of system capacitance if the metal piece is not grounded or connected to earth. You can experiment this safely in a delta secondary transformer or wye transformer where neutral is not grounded or high resistance grounded system.

Bonding non-current-carrying items to earth can enable path to the electrode but the earth has unknown resistance at any given moment therefore potential around and away from the electrode will be different at any given moment, this cannot be controlled.

We are not debating with you if we should ground. A journeymen electrician will ground mainly because the NEC requires it and not because they understand the physics behind it. The IEEE 142, 1.2.14 says the bonding to earth ?reduce[?s] neutral displacement from ground potential and reduce[?s] destructive high-frequency voltage oscillations.? And IEEE 142, 1.4.2 says without the bond to earth ?system overvoltages can occur during arcing, resonant or near-resonant ground faults.? But IEEE 242 reminds us ?If a ground fault is intermittent, [/b]or allowed to continue[/b] on an ungrounded system, the system wiring could be subject to severe system overvoltage.? An NEC application does not allow a fault to remain, a violating one does. I can site the above but I don?t understand it. But 250.2(A)(1) & (B)(1) tells us the purpose of grounding, this is why a journeymen grounds.

 

[don_resqcapt19]

It is not the current wanting to return to earth but connecting the accidental energized metal piece to ground potential. In HRG and Ungrounded system there is a minimal single line to ground fault current for continuity of service but the accidental contact of one of the current carrying conductor with the metal piece will have its potential equal to the equivalent line-to-neutral voltage of the system because of system capacitance if the metal piece is not grounded or connected to earth. You can experiment this safely in a delta secondary transformer or wye transformer where neutral is not grounded or high resistance grounded system.

I fully agree that a connection to earth for the HRG or ungrounded systems will do exactly that, however it doesn't work that way with a solidly grounded system. The connection to earth does not provide the same safety advantage for solidly grounded systems that it provides for HRG or ungrounded systems.

 

[bobby ocampo]

How is there a ?minimal current for continuity of service?, explain this?

In an ungrounded system because there is no connection of current carrying conductor to ground, on single line to ground fault there is very little if none current fault. There will be continuity of service because there is still a line-to-line voltage even if one of the current carrying part touches the ground or there is a single line to ground fault.

In HRG because of the impedance connected to the neutral fault current is reduced up to a maximum of 10amps only. There is still a line-to-line voltage and same with ungrounded system there will be continuity of service despite the single line to ground fault.

 

[bobby ocampo]

Bonding non-current-carrying items to earth can enable path to the electrode but the earth has unknown resistance at any given moment therefore potential around and away from the electrode will be different at any given moment, this cannot be controlled.

Connection to earth will not be used as a return path to operate the OCPD. The bonded EGC will solve this problem. What it does is reduce the potential of an accidentaly energized metal piece to ground potential.

We are not debating with you if we should ground. A journeymen electrician will ground mainly because the NEC requires it and not because they understand the physics behind it.

I am trying to explain its purpose by comparing the protection on electric shock hazard in an UNGROUNDED SYSTEM AND HRG system. Saying the connecting to a reference plane is LESS IMPORTANT is very hazardous. Both are important. BONDED EGC and CONNECTION TO A REFERENCE PLANE in this case the earth.

The IEEE 142, 1.2.14 says the bonding to earth ?reduce[?s] neutral displacement from ground potential and reduce[?s] destructive high-frequency voltage oscillations.?

Same with equipment grounding it will also reduce energized metal piece to ground potential

And IEEE 142, 1.4.2 says without the bond to earth ?system overvoltages can occur during arcing, resonant or near-resonant ground faults.?

Imagine if the arcing ground fault is touching the metal piece and not connected or bonded to earth while a personnel is touching it. What do you think will happen?

 

[weressl]

How does a connection to earth get rid of the voltage on the faulted equipment (solidly grounded system)? This is really no different than connecting a load between the hot and the neutral. The voltage on the hot as measured to the earth, the grounding conductor or any other point does not go away when you connect a load. How is a connection to earth any different?

It does not eliminate the voltage on the faulted equipment, it just makes it sure that the EARTH or whatever conductive structure there is, like the steel structure of a plant, is at the same potential. Conclusively when one stands on the EARTHED surface there is no or small potential difference between the two connecting points of the person thus the electrocution is minimized.

 

[weressl]

......the faulted apparatus was itself directly connected to the grounding grid.

-Jon

It is, for all practical purpose.

 

[bobby ocampo]

I fully agree that a connection to earth for the HRG or ungrounded systems will do exactly that,

This means that connection to earth will really reduce the energized metal piece to ground potential.

however it doesn't work that way with a solidly grounded system. The connection to earth does not provide the same safety advantage for solidly grounded systems that it provides for HRG or ungrounded systems.

What if the fault is an ARCING GROUND FAULT where the fault current is still low that the OCPD cannot sense it yet despite the connection of the EGC to the neutral? What will happen to the accidentally energzed metal piece if the bonded EGC is not bonded to the reference plane called earth in this case? Isn't it a hazard of electric shock? Is connection to earth less important in this situation?

 

[tryinghard]

...Saying the connecting to a reference plane is LESS IMPORTANT is very hazardous. Both are important. BONDED EGC and CONNECTION TO A REFERENCE PLANE in this case the earth.

Give a math example of 480v or less for your claim.

Imagine if the arcing ground fault is touching the metal piece and not connected or bonded to earth while a personnel is touching it. What do you think will happen?

The OCP will open!

 

[tryinghard]

How is there a ?minimal current for continuity of service?, explain this?

In an ungrounded system because there is no connection of current carrying conductor to ground, on single line to ground fault there is very little if none current fault. There will be continuity of service because there is still a line-to-line voltage even if one of the current carrying part touches the ground or there is a single line to ground fault.

I do not understand your answer to my question, how will there be continuity?

 

[bobby ocampo]

I do not understand your answer to my question, how will there be continuity?

There will be continuity of service because there is still line-to-line voltage available. Loads are connected line-to-line in an UNGROUNDED AND HRG SYSTEM.

 

[don_resqcapt19]

It does not eliminate the voltage on the faulted equipment, it just makes it sure that the EARTH or whatever conductive structure there is, like the steel structure of a plant, is at the same potential. Conclusively when one stands on the EARTHED surface there is no or small potential difference between the two connecting points of the person thus the electrocution is minimized.

To do that it would have to either raise the voltage of the earth or drop the voltage of the faulted equipment. It does neither. Neither bonding nor grounding changes the potential of the faulted equipment on a solidly grounded system. The only thing that does that is clearing the fault. Even with a bonded steel structure, there is still a voltage between the faulted equipment and the steel that is equal to the voltage drop on the EGC that is carrying the fault current.

 

[don_resqcapt19]

This means that connection to earth will really reduce the energized metal piece to ground potential.

On an HRG or ungrounded system it will do that, but it won't do that on a solidly grounded system.

What if the fault is an ARCING GROUND FAULT where the fault current is still low that the OCPD cannot sense it yet despite the connection of the EGC to the neutral? What will happen to the accidentally energzed metal piece if the bonded EGC is not bonded to the reference plane called earth in this case? Isn't it a hazard of electric shock? Is connection to earth less important in this situation?

The type of fault does not change anything. There will still be a voltage between the point of the fault and the earth.

 

[tryinghard]

There will be continuity of service because there is still line-to-line voltage available. Loads are connected line-to-line in an UNGROUNDED AND HRG SYSTEM.

There will not be any continuity beteen line and case frame or non current-carrying items on an ungrounded system.

 

[tryinghard]

...Saying the connecting to a reference plane is LESS IMPORTANT is very hazardous. Both are important. BONDED EGC and CONNECTION TO A REFERENCE PLANE in this case the earth.

Actually I mean give a math example scenario of 277v or less for your claim. (not 480)

 

[tryinghard]

There will be continuity of service because there is still line-to-line voltage available. Loads are connected line-to-line in an UNGROUNDED AND HRG SYSTEM.

There will be continuity through the turns in each transformer A to B & A to C & B to C on the secondary side only not the primary to secondary. But I still ask How is there a “minimal current for continuity of service”, explain this?

 

[quogueelectric]

This entire arguement lies in the basic ohms law theory that if something is electrically bonded it will be the same voltage. Zero sum. So bonding to ground has many different potential paths. Lets discuss them in detail.

 

[bobby ocampo]

There will be continuity through the turns in each transformer A to B & A to C & B to C on the secondary side only not the primary to secondary. But I still ask How is there a ?minimal current for continuity of service?, explain this?

To explain this is to first ask if you have seen a HIGH RESISTANCE GROUNDED SYSTEM. You will know what I am saying if you understand the function of HRG.