SYSTEM GROUNDING (UNGROUNDED AND HIGH IMPEDANCE GROUNDED SYSTEM)

[iceworm]

correct spelling, typos

correct spelling, typos

BO - You're all over the place. Here is an example:

What do you mean sir remove the voltage if the OCPD will not trip in an UNGROUNDED SYSTEM and HRG system? How will the equipment grounding and bonding reduce risk to personnel if it will not trip the OCPD?

HRG and Un-Grounded are completely different. Grouping them up in your questions gets you responses all over the place.

Equipment Ground and Equipment Bonding are completely different. Grouping these two in your questions/discussions is getting you responses all over the place.

You never said, however your questions only make sense if you are discussing 480V, 3ph. So assuming 480V, 3ph:
Selecting between Grounded, HRG, Un-Grounded is a design decison based on operational issues, equipment requirements, system design. Selection has little, perhaps nothing, to do with personnel safety.

Bonding, as already explained, has to do with equipotential. This is a personnel safety issue. Bonding requirements have little to do with selection of G, HRG, U-G.

Purpose of system grounding is a different issue. You have access to a copy of IEEE 142, RP for Grounding Industrial and Commercial Power Systems. Recommend reading section 1.3, Purposes of System Grounding:

1.3 Purposes of system grounding​

System grounding is the intentional connection to ground of a phase or neutral conductorfor the purpose of:a) Controlling the voltage with respect to earth, or ground, within predictable limits,​

and

b) Providing for a flow of current that will allow detection of an unwanted connection between system conductors and ground. Such detection may theninitiate operation of automatic devices to remove the source of voltage from theseconductors.
The NEC prescribes certain system grounding connections that must be made to be incompliance with the code. The control of voltage to ground limits the voltage stress on theinsulation of conductors so that insulation performance can more readily be predicted. Thecontrol of voltage also allows reduction of shock hazard to persons who might come in​

contact with live conductors.

If you have specific issues in mind, now is a good time to say so. Stop jumping all over the place. Stop grouping up issues that don't have much to do with each other.

And STOP YELLING. We can all read.

ice

 

[don_resqcapt19]

The EGC brings the phase to the same potential as the boning system. Thus, the person sees no difference in potential. Difference in potential with a high enough voltage and enough available current are what harm a person.

Actually that only works for the first fault in an ungrounded or in a resistance grounded system.

With a solidly grounded system everything connected to the electrical grounding system is raised to a voltage, as measured to earth or unbonded conductive objects that are connected to earth, that is equal to the voltage drop on the fault return path. This voltage will exist until the OCPD clears the circuit and is the reason why we must have a fault return path that can conduct enough current so that the OCPD will operate in its "instantaneous" range.

 

[mbrooke]

Actually that only works for the first fault in an ungrounded or in a resistance grounded system.

With a solidly grounded system everything connected to the electrical grounding system is raised to a voltage, as measured to earth or unbonded conductive objects that are connected to earth, that is equal to the voltage drop on the fault return path. This voltage will exist until the OCPD clears the circuit and is the reason why we must have a fault return path that can conduct enough current so that the OCPD will operate in its "instantaneous" range.

Correct, but keep in mind the voltage it is being raised to. In a correctly designed system it is never 120, 230 or 277 volts. Generally it tends to be 1/3 to 1/5 sometimes less relative to the rest of the building's ground system like bonded steal. In addition to that, bonding at the service compensates for the voltage rise across the service neutral under a fault (same for normal operation). While not perfect equal potential, it gets the job done.

 

[don_resqcapt19]

Correct, but keep in mind the voltage it is being raised to. In a correctly designed system it is never 120, 230 or 277 volts. Generally it tends to be 1/3 to 1/5 sometimes less relative to the rest of the building's ground system like bonded steal. In addition to that, bonding at the service compensates for the voltage rise across the service neutral under a fault (same for normal operation). While not perfect equal potential, it gets the job done.

Typically the voltage, under fault conditions for a solidly grounded system, on everything that is bonded to the electrical system, as measured to something at "earth" potential, is ~ 1/2 of the line to ground voltage. There is a fatal shock hazard until the fault is cleared.

Under normal conditions this voltage is equal to the voltage drop of the grounded conductor between the utility transformer and the main bonding jumper.

 

[mbrooke]

Typically the voltage, under fault conditions for a solidly grounded system, on everything that is bonded to the electrical system, as measured to something at "earth" potential, is ~ 1/2 of the line to ground voltage. There is a fatal shock hazard until the fault is cleared.

Under normal conditions this voltage is equal to the voltage drop of the grounded conductor between the utility transformer and the main bonding jumper.

But how is this 1/2 value reached? It will vary for a variety of reasons. But even on average, Im curious how its determined.


EDIT: Is this what you had in mind?

http://www.electrical-installation.org/enwiki/Automatic_disconnection_for_TN_systems

 

[bobby ocampo]

BO - You're all over the place. Here is an example:


HRG and Un-Grounded are completely different. Grouping them up in your questions gets you responses all over the place.

Both High Impedance Grounding (250.36) and UNGROUDED can both operate on the single line to ground fault. How does equipment grounding and bonding work as far as personnel safety is concerned? Will it be safe even it the OCPD will not trip?

BO - You're all over the place. Here is an example: Equipment Ground and Equipment Bonding are completely different. Grouping these two in your questions/discussions is getting you responses all over the place.

What is the difference as far as protection against electrocution of Equipment Ground and Equipment bond?

BO - You're all over the place.
You never said, however your questions only make sense if you are discussing 480V, 3ph. So assuming 480V, 3ph:
Selecting between Grounded, HRG, Un-Grounded is a design decison based on operational issues, equipment requirements, system design. Selection has little, perhaps nothing, to do with personnel safety.

250.20 (B)(3) Allows ungrounded if MIDPOINT of the Delta is not used. Therefore a 240 volts delta may be allowed to be ungrounded. Since you said perhaps you are not sure about what equipment grounding and bonding can do as far as personnel safety. Please read IEEE 142-2007 Chapter 2. Equipment Grounding.

BO - You're all over the place.
Bonding, as already explained, has to do with equipotential. This is a personnel safety issue. Bonding requirements have little to do with selection of G, HRG, U-G.

Why do you think bonding has little to do with personnel safety in the selection of equipment grounding for HRG, Ungrounded system?

BO - You're all over the place.
Purpose of system grounding is a different issue. You have access to a copy of IEEE 142, RP for Grounding Industrial and Commercial Power Systems. Recommend reading section 1.3, Purposes of System Grounding:

The question I ask for is in Equipment Grounding which is in Chapter 2 of IEEE 142 Chapter 1 is for System Grounding. Industrial Power Systems Handbook of Beeman Chapter 7. IEEE 141 Red book Chapter 7.

BO - You're all over the place.
If you have specific issues in mind, now is a good time to say so. Stop jumping all over the place. Stop grouping up issues that don't have much to do with each other.

And STOP YELLING. We can all read.

ice

No one has yelled except you. Just emphasizing ungrounded not to confuse with solidly grounded. We can always be polite with our answer.

 

[iceworm]

... Why do you think bonding has little to do with personnel safety in the selection of equipment grounding for HRG, Ungrounded system? ....

Hummmm. No, I didn't say that. You're not listening. Bonding has a lot to do with personnel safety. It just doesn't have anything to do with selecting between G, HRG, U-G.

... Bonding, as already explained, has to do with equipotential. This is a personnel safety issue. Bonding requirements have little to do with selection of G, HRG, U-G. ...

You apparently have access to appropriate references. Really - you should give a some examples of what exactly is bothering you. Exactly which sections of IEEE 142, ch2, and IEEE141, Ch7 are issues?

Good catch on 240D being permitted to be un-grounded. I could have phrased that better. You are apparently discussing Low Voltage as opposed to Medium Voltage.

I didn't attempt an answer to any of the rest - they have already been answered.

ice

 

[don_resqcapt19]

But how is this 1/2 value reached? It will vary for a variety of reasons. But even on average, Im curious how its determined.


EDIT: Is this what you had in mind?

http://www.electrical-installation.org/enwiki/Automatic_disconnection_for_TN_systems

It is just based on the impedance of the path to the fault and the return path. The impedance of the two paths will be about equal giving 1/2 of the drop on the return path. The equipment at the point of the fault will have that voltage as measured to earth or conductive paths to earth other than the fault return path. Even other EGCs in the area for other equipment will still be at "earth" potential and there will be a shock hazard between the faulted equipment and other bonded objects.

 

[bobby ocampo]

Hummmm. No, I didn't say that. You're not listening. Bonding has a lot to do with personnel safety. It just doesn't have anything to do with selecting between G, HRG, U-G.

Please explain HOW equipment grounding and bonding will help personnel safety in HRG and UNGROUNDED in a single line to ground fault compared with Solidly grounded system.

 

[kwired]

Please explain HOW equipment grounding and bonding will help personnel safety in HRG and UNGROUNDED in a single line to ground fault compared with Solidly grounded system.

When an ungrounded system develops a fault in one phase - it becomes a grounded system. So if you have an ungrounded delta that first fault turns it into a grounded phase delta, but the main or system bonding jumper is at the fault location instead of at the service or source. Everything else that is supposed to be bonded together is still bonded together just like it is for a grounded system which limits stray voltage development in the premises. That first fault is supposed to be indicated by the ground detection system and steps should be taken to remedy the fault condition as soon as possible or the whole idea of the ungrounded system becomes pointless if this doesn't happen. HRG systems are very similar in their intent, but when there is a fault there will be voltage across the resistance inserted in the neutral, but everything on the "load side" is at same potential because it is all bonded together, the only place where there is a shock hazard is if you come between the "grounding system" and the X0 terminal of the source transformer.

I don't know how much simpler one can get with this answer. All the grounding and bonding are bringing associated objects to same potential whether the supply is grounded, ungrounded or a high resistance ground system. The risk of getting a shock is not there if everything you can touch is at same potential, just like a bird on a wire that can not touch anything else at same time is in no danger of electric shock. Breakdowns in bonding or improper bonding can introduce problems but it will introduce problems whether the system is grounded, ungrounded, or HRG.

 

[iceworm]

Please explain HOW equipment grounding and bonding will help personnel safety in HRG and UNGROUNDED in a single line to ground fault compared with Solidly grounded system.

Already asked and answered. See Post 41 - as well as kw's, and don's and mb and iw and ....

Time to move on.

ice

 

[paulf2k]

In an HRG system, for the conductors on the incoming and outgoing of equipment where the NGRs are installed, how is the cable insulation determined? i.e. if I have a 600V system, I would typically require no more than a 600V insulated jacket on the conductors. The line to ground voltage would be 600V and line to neutral voltage would be 347V. Would the jacket need to be 600V or 1000V? I have done a lot of research and some people say 600V*1.73 insulation and others say 347V*1.73.

 

[Smart $]

In an HRG system, ...

With a 600V HRG system, the line to ground voltage would be ~347. It will stray a little more from nominal than a solidly grounded system, dependent upon neutral to ground 'impedance" and voltage drop resulting from neutral current.

This voltage to ground or neutral doesn't matter under the NEC, at least not for 600V systems, as all circuit wiring must have an insulation voltage rating not less than system line-to-line voltage (600V).

 

[paulf2k]

With a 600V HRG system, the line to ground voltage would be ~347. It will stray a little more from nominal than a solidly grounded system, dependent upon neutral to ground 'impedance" and voltage drop resulting from neutral current.

This voltage to ground or neutral doesn't matter under the NEC, at least not for 600V systems, as all circuit wiring must have an insulation voltage rating not less than system line-to-line voltage (600V).

Thank you very much. I agree the electrical code states such and that is what I will follow, is anyone familiar with IEEE standards stating otherwise? I believe for medium voltage systems, the insulation needs to be considered differently, but there is no specific mention for low voltage systems.

 

[Smart $]

Thank you very much. I agree the electrical code states such and that is what I will follow, is anyone familiar with IEEE standards stating otherwise? I believe for medium voltage systems, the insulation needs to be considered differently, but there is no specific mention for low voltage systems.

For MV, I believe the requirement is the same. The only ease in either case is for the insulation rating of the EGC or other grounding conductor.

 

[big john]

It is just based on the impedance of the path to the fault and the return path. The impedance of the two paths will be about equal giving 1/2 of the drop on the return path. The equipment at the point of the fault will have that voltage as measured to earth or conductive paths to earth other than the fault return path. Even other EGCs in the area for other equipment will still be at "earth" potential and there will be a shock hazard between the faulted equipment and other bonded objects.

What you're saying logically makes sense, but I imagine for it to be true it would assume a near infinite available fault current and almost zero source impedance: Because that's the only way you'd be dropping full system voltage across a low-impedance ground.

I wonder if in reality it's far more likely that you'll have a very significant voltage voltage sag during the fault and that this prevents significant voltage from developing during the time it takes to clear most faults?

 

[mbrooke]

What you're saying logically makes sense, but I imagine for it to be true it would assume a near infinite available fault current and almost zero source impedance: Because that's the only way you'd be dropping full system voltage across a low-impedance ground.

I wonder if in reality it's far more likely that you'll have a very significant voltage voltage sag during the fault and that this prevents significant voltage from developing during the time it takes to clear most faults?

I agree, but in any case on top of the voltage sag on the source there is a voltage drop along the EGC.

However, bonding the neutral to say the building concrete reinforced slab will actually reduce the potential the person is exposed to since any voltage drop (voltage difference) on the neutral during the fault will also be "transferred" to the concrete slab the person is standing on. Similarly, In theory if the person was standing on metal plate bonded to the faulting appliance chassis the voltage between hand and foot would in theory be close to zero volts.


In 230 volts countries there is actually a requirement to have the breaker open within a certain amount of cycles or alternatively create an equal potential plain around the fault because the voltage drop along the EGC is more from the higher voltage.

Tony S would know better in this area.

 

[don_resqcapt19]

What you're saying logically makes sense, but I imagine for it to be true it would assume a near infinite available fault current and almost zero source impedance: Because that's the only way you'd be dropping full system voltage across a low-impedance ground.

I wonder if in reality it's far more likely that you'll have a very significant voltage voltage sag during the fault and that this prevents significant voltage from developing during the time it takes to clear most faults?

Yes, if the supply voltage drops because of the fault current the voltage drop on the circuit and EGCs will be less. I guess I should have said that the voltage drop on the EGC will be ~ 1/2 of the available supply voltage under the fault condition.