SYSTEM GROUNDING (UNGROUNDED AND HIGH IMPEDANCE GROUNDED SYSTEM)

[Smart $]

The question is what will this bonding do for the safety of personnel if if this bonding will not operate the OCPD in an UNGROUNDED AND HRG SYSTEM on a single line to ground fault?

You can't base the merits (and dismerits) of an ungrounded system and bonding the non-current-carrying metal parts simply on a the first line-to-ground fault. The first line-to-ground fault on an ungrounded system that has non-current-carrying metal parts bonded is actually safer than the first line-to-ground fault on a grounded system.

An ungrounded system, ground detector combination has the merit of not tripping any OCPD on line-to-ground fault (even more than one if the same phase). Industry uses this to an advantage, to keep machines running and other "important to keep energized" loads while tracking down the fault(s). Safety procedures mandate the faulting subsystem be de-energized to repair any fault.

However, when a second 'phase' has a line-to ground fault, the bonding system functions in the similar capacity as a grounded system, but in this case acts like a conductive bridge to establish a line-to-line fault. With the potential for high currents and voltage gradients during such fault, this is where the requirements put emphasis on the safety of personnel.

 

[bobby ocampo]

You can't base the merits (and dismerits) of an ungrounded system and bonding the non-current-carrying metal parts simply on a the first line-to-ground fault. The first line-to-ground fault on an ungrounded system that has non-current-carrying metal parts bonded is actually safer than the first line-to-ground fault on a grounded system.

An ungrounded system, ground detector combination has the merit of not tripping any OCPD on line-to-ground fault (even more than one if the same phase). Industry uses this to an advantage, to keep machines running and other "important to keep energized" loads while tracking down the fault(s). Safety procedures mandate the faulting subsystem be de-energized to repair any fault.

However, when a second 'phase' has a line-to ground fault, the bonding system functions in the similar capacity as a grounded system, but in this case acts like a conductive bridge to establish a line-to-line fault. With the potential for high currents and voltage gradients during such fault, this is where the requirements put emphasis on the safety of personnel.

I am more concerned on a single-line-to-ground fault in UNGROUNDED SYSTEM AND HRG. Why will it be safer in UNGROUNDED SYSTEM as compared with a SOLIDLY GROUNDED SYSTEM if non-current carrying metal parts are bonded? What makes bonding safer if the OCPD will not trip in an UNGROUNDED SYSTEM?

 

[bobby ocampo]

Remove voltage. An ungrounded system is coupled to earth via capacitance. There is no way to get rid of it. Yes Peterson coil systems can reduce that value as well as limited system size, but in an average system capacitive coupling will yielded several hundred milliamps if not several amps. So if a hot wire did touch the case or one was to touch a hot wire voltage and current potential would exist and it would most likely be dangerous.

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?

 

[kwired]

I am more concerned on a single-line-to-ground fault in UNGROUNDED SYSTEM AND HRG. Why will it be safer in UNGROUNDED SYSTEM as compared with a SOLIDLY GROUNDED SYSTEM if non-current carrying metal parts are bonded? What makes bonding safer if the OCPD will not trip in an UNGROUNDED SYSTEM?

It isn't any safer for electrocution hazards. When an ungrounded system has a ground fault it simply becomes a grounded system. The main reason to have an ungrounded system or a HRG system is for processes that may introduce more hazards when suddenly shut down like they would be if on a grounded system that experiences a ground fault. This gives operators the chance to shut the process down in an orderly fashion instead of having sudden interruption when a ground fault occurs. Now if a second phase happens to fault you still get immediate shutdown - so it is wise to take care of the first ground fault as soon as possible after it is indicated.

 

[mbrooke]

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?

Faraday cage effect. Same way an open neutral may force reading of 230 volts to remotve earth but everything bonded in the structure will be closer to zero.

 

[bobby ocampo]

It isn't any safer for electrocution hazards. When an ungrounded system has a ground fault it simply becomes a grounded system.

1.Please explain why will it NOT BE ANY SAFER for electrocution hazards? Do you mean that even with equipment grounding and bonding it is unsafe for a person to touch a non-current carrying metal part on a single line to ground fault in UNGROUNDED AND HRG? Please explain why?

The main reason to have an ungrounded system or a HRG system is for processes that may introduce more hazards when suddenly shut down like they would be if on a grounded system that experiences a ground fault. This gives operators the chance to shut the process down in an orderly fashion instead of having sudden interruption when a ground fault occurs.

What is the purpose of equipment grounding and bonding in this case for UNGROUNDED and HRG system? Does it mean that if there is NO equipment grounding for UNGROUNDED AND HRG SYSTEM, the personnel is still safe on electrocution if one of the ungrounded conductor touches the non-current metal part? Remember that equipment grounding will not be able to trip the OCPD on a single line to ground fault?

Now if a second phase happens to fault you still get immediate shutdown - so it is wise to take care of the first ground fault as soon as possible after it is indicated.

This is not my concern. My main concern in on the first line to ground fault and the safety of personnel on a single line to ground fault.

 

[Smart $]

I am more concerned on a single-line-to-ground fault in UNGROUNDED SYSTEM AND HRG. Why will it be safer in UNGROUNDED SYSTEM as compared with a SOLIDLY GROUNDED SYSTEM if non-current carrying metal parts are bonded? What makes bonding safer if the OCPD will not trip in an UNGROUNDED SYSTEM?

You're comparing the first fault on an ungrounded system to the first fault on a grounded system. The comparison should be the first fault of an ungrounded system to a normal-operating grounded system... because the first fault simply makes the ungrounded system grounded.

 

[bobby ocampo]

Faraday cage effect. Same way an open neutral may force reading of 230 volts to remotve earth but everything bonded in the structure will be closer to zero.

Is this the purpose of equipment grounding and bonding in an UNGROUNDED SYSTEM so that all bonded together will be closer to zero? Is this zero voltage?

 

[mbrooke]

Is this the purpose of equipment grounding and bonding in an UNGROUNDED SYSTEM so that all bonded together will be closer to zero? Is this zero voltage?

Yes, even in grounded systems. Bonding is what brings everything to zero or near zero potential.

 

[mbrooke]

You're comparing the first fault on an ungrounded system to the first fault on a grounded system. The comparison should be the first fault of an ungrounded system to a normal-operating grounded system... because the first fault simply makes the ungrounded system grounded.

True, but keep in mind that in an ungrounded system, a fault can still shock or even electrocute someone. An EGC prevents that from happening.

 

[kwired]

Is this the purpose of equipment grounding and bonding in an UNGROUNDED SYSTEM so that all bonded together will be closer to zero? Is this zero voltage?

That IMO is one function of the EGC whether the system is grounded or not. Equipment grounding is required regardless of whether you have a grounded or ungrounded system for all of the same reasons either case. Only difference between an ungrounded and grounded system is we intentionally connect one conductor of the grounded system to the grounding electrode and equipment grounding conductors and we do this at the service equipment or near the source of separately derived systems to help minimize objectionable current. Now if there is a ground fault on an ungrounded system away from service/source, we start to set up possibility of objectionable current flow, but this is intended to be a temporary condition and is supposed to be indicated by the required ground detection system. If you disregard the indication by the ground detection system you are setting yourself up for more potential hazards.

 

[Smart $]

True, but keep in mind that in an ungrounded system, a fault can still shock or even electrocute someone. An EGC prevents that from happening.

But an EGC is required even on an ungrounded system. Everything is essentially the same with the exceptions there is no MBJ/SBJ and there is a ground detector.

 

[bobby ocampo]

True, but keep in mind that in an ungrounded system, a fault can still shock or even electrocute someone. An EGC prevents that from happening.

How will EGC prevents electrocution from happening if in an UNGROUNDED system first line to ground will not trip the OCPD?

https://www.youtube.com/watch?v=mpgAVE4UwFw

See how it was explained at the 15minute mark.

 

[bobby ocampo]

That IMO is one function of the EGC whether the system is grounded or not. Equipment grounding is required regardless of whether you have a grounded or ungrounded system for all of the same reasons either case.

What are the reason and purpose for equipment grounding?

Only difference between an ungrounded and grounded system is we intentionally connect one conductor of the grounded system to the grounding electrode and equipment grounding conductors and we do this at the service equipment or near the source of separately derived systems to help minimize objectionable current.

Is ground fault considered objectionable current in the Code?

Now if there is a ground fault on an ungrounded system away from service/source, we start to set up possibility of objectionable current flow, but this is intended to be a temporary condition and is supposed to be indicated by the required ground detection system. If you disregard the indication by the ground detection system you are setting yourself up for more potential hazards.

My concern is the possible electrocution on a single line to ground fault in an UNGROUNDED SYSTEM or HIGH RESISTANCE GROUNDED SYSTEM. What can EGC do to prevent electrocution and HOW will it protect persons from electrocution without tripping the OCPD?

 

[kwired]

How will EGC prevents electrocution from happening if in an UNGROUNDED system first line to ground will not trip the OCPD?

https://www.youtube.com/watch?v=mpgAVE4UwFw

See how it was explained at the 15minute mark.

The examples in that video were for grounded systems. In an ungrounded system the first ground fault essentially makes the ungrounded system a grounded system, the system bonding jumper (or temporary equivalent may be better wording) is at the fault location. There is no objectionable current paths when the first fault occurs because there is no other path back to the source. Introduce more ground faults on the same phase conductor and you get similar situation you get with a grounded system with multiple bonds between grounded conductor and EGC - which allows for objectionable current flow on components not intended to be carrying current - which can lead to harmful touch voltages in/around equipment.

 

[kwired]

What are the reason and purpose for equipment grounding?



Is ground fault considered objectionable current in the Code?





My concern is the possible electrocution on a single line to ground fault in an UNGROUNDED SYSTEM or HIGH RESISTANCE GROUNDED SYSTEM. What can EGC do to prevent electrocution and HOW will it protect persons from electrocution without tripping the OCPD?

I've been patient, most of these questions I feel have been answered more then once between this and another current thread you are active in. A little understanding of electrical theory is needed to understand some of it. Outside of capacitively coupled voltages in an ungrounded system - there is no voltage between an ungrounded system and other objects not part of the system. We still bond conductive objects together to make an equipment grounding system as well as install a grounding electrode system to keep those other objects from developing voltages between them whether dealing with a grounded system or not. I will say it again, the first fault on an ungrounded system effectively makes the system a now grounded system with the ground point at the fault location. There is no other path back to the source so there is no stray current flowing in non current carrying components. The idea is the fault detection equipment will indicate there is a fault and it will be fixed ASAP. Disregarding that indication of a fault will introduce more hazards if more faults develop.

Ground fault current is not objectionable current. What is objectionable is high impedance in an equipment grounding conductor path, or intentionally using the equipment grounding conductor intentionally to carry normal operating current. The path is intended to have lowest possible impedance to ensure the fault current will be as high as possible - which results in faster operation of the overcurrent device.

 

[bobby ocampo]

The examples in that video were for grounded systems.

HIGH RESISTANCE GROUNDED is a grounded system based on IEEE 142. What is the purpose then of EGC for HRG? HRG allows NO TRIPS for single line to ground fault like UNGROUNDED SYSTEM.

In an ungrounded system the first ground fault essentially makes the ungrounded system a grounded system, the system bonding jumper (or temporary equivalent may be better wording) is at the fault location.

With the first ground fault, what will happen if there is NO EGC?

Wiht the first grounnd fault what will happenn if there is EGC?

There is no objectionable current paths when the first fault occurs because there is no other path back to the source. Introduce more ground faults on the same phase conductor and you get similar situation you get with a grounded system with multiple bonds between grounded conductor and EGC - which allows for objectionable current flow on components not intended to be carrying current - which can lead to harmful touch voltages in/around equipment.

Are ground fault considered objectionable currents??

What do you mean by introduce more ground fault on the same phase conductor

 

[kwired]

HIGH RESISTANCE GROUNDED is a grounded system based on IEEE 142. What is the purpose then of EGC for HRG? HRG allows NO TRIPS for single line to ground fault like UNGROUNDED SYSTEM.



With the first ground fault, what will happen if there is NO EGC?

Wiht the first grounnd fault what will happenn if there is EGC?




Are ground fault considered objectionable currents??

What do you mean by introduce more ground fault on the same phase conductor

HRG has all the voltage drop across the resistor intentionally inserted into the grounded conductor when there is a fault to "ground". Everything bonded to the EGC/GEC is still at ground potential. When a fault occurs the entire EGC/EGC is raised to the same voltage as the phase that is faulted to it. Say it is a 277/480 system with HRG, phase A faults to G. Voltage between A and G will be at or near zero. Voltage from G to the XO terminal of transformer will be dependent on what resistor is used for the HRG system. The user is not subjected to shock because everything is still at/near ground potential. (there can be exceptions, and they can be complicated by deteriorating conditions of components - but that can all happen in grounded systems as well).

Ungrounded systems really are not much different - they just have no reference to ground at all instead of the high impedance reference under normal operating conditions.

When I say introduce more ground faults on the same phase conductor I am talking about a situation where maybe machine A has a fault to ground on phase C. It will continue to run for an infinite time that way, the ground detection system will indicate there is a ground fault though. Should the operator(s) ignore the fault indicator - maybe for a few hours maybe for a few years - and a ground fault on phase B develops anywhere in the system we have a short circuit through the EGC, metal frame of equipment, etc. between phase B and C - it will immediately open overcurrent device(s) because of the high current that will result. But if we should have a second ground fault on phase C, maybe on the opposite end of the facility we now have multiple parallel paths through all EGC's, metal frames of equipment, building steel, etc. for the now "grounded C phase" current to flow - this is just as objectionable of current as bonding the neutral multiple times in a typical grounded system can produce.

 

[Smart $]

With the first ground fault, what will happen if there is NO EGC?

An EGC is required, essentially for all circuits... so quit asking. I realize it is a possibility, but it is not supposed to be. To have such a scenario is either by fault or by non-compliance... and that in itself would be considered the first ground fault.

 

[mbrooke]

How will EGC prevents electrocution from happening if in an UNGROUNDED system first line to ground will not trip the OCPD?

https://www.youtube.com/watch?v=mpgAVE4UwFw

See how it was explained at the 15minute mark.

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.