Equipment Grounding for Ungrounded System

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bobby ocampo

bobby ocampo

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Is equipment grounding important for ungrounded system?

What is the purpose of equipment grounding for ungrounded system?
 
bobby ocampo said:
Is equipment grounding important for ungrounded system?
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Yes and it is required by the NEC.


What is the purpose of equipment grounding for ungrounded system?
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Because at some point there will be ground fault that makes the system behave just like a grounded system. The EGC run with ungrounded systems bonds all non-current carrying metal parts together so they remain at equal potential if a second ground fault happens on an opposing phase before the first ground fault is cleared.
 
Does the equipment grounding for ungrounded system used as a return path to the source so that the equipment protection device will operate?

Isn't it that there is continuity of service on a single-line-to-ground fault in an ungrounded system? Meaning the protective device will not operate on a single-line-to-ground fault and therefore equipment grounding is not used as a return path to the source to trip the protective device?

Is equipment grounding important for a second ground fault wherein the second ground fault is already a line-to-line fault and the protective device will operate regardless of the equipment grounding?

What then is the importance of the equipment grounding?
 
bobby ocampo said:
Does the equipment grounding for ungrounded system used as a return path to the source so that the equipment protection device will operate?
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Yes pretty much in the same way as a grounded system.

Isn't it that there is continuity of service on a single-line-to-ground fault in an ungrounded system? Meaning the protective device will not operate on a single-line-to-ground fault and therefore equipment grounding is not used as a return path to the source to trip the protective device?
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With an ungrounded system the first ground fault will not operate the protective device and the equipment continues to operate. Also the ungrounded delta system will now behave as a corner grounded delta system.


Now if that first ground fault is not repaired the next ground fault if it is from a different phase then the first ground fault it will trip the breaker as this will be a line to line fault.

What then is the importance of the equipment grounding?
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First off the EGC provide personal protection because even an ungrounded system can provide a lethal shock due to capacitance coupling with grounded raceways etc.

Second, Imagine you have two machines located side by side both supplied from the same ungrounded delta source, neither machine is connected to an EGC.

Now lets say you have a phase A ground fault in machine one connecting the machines enclosure to phase A, the breaker will not trip and no one repairs that fault.

Now in the second machine you get a phase B ground fault, the breaker will not trip now either as that machine is not grounded and if a person touches both machines at the same time they will receive a line to line voltage shock.
 
bobby ocampo said:
...Is equipment grounding important for a second ground fault wherein the second ground fault is already a line-to-line fault and the protective device will operate regardless of the equipment grounding? ...
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Without equipment grounding the second ground fault may not result in a line to line fault. If there is no solid bonding between the two points of fault the fault current will travel on any path it can and will result in shock and fire hazards.
 
cadpoint said:
This thread went real deep real fast!

How's one to know that a fault is sitting there in the first place, thats not cleared ?
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Generally there would be ground fault indicating lights or alarm to notify maintenance personal to start looking for the ground fault.
 
A smart bus, I've never touched.
They exist and that's usually a client call, but I just haven't seen one.

I can only hope that everyone understands what there looking at, that their personal safety is paramount, and work it accordingly.
 
iwire said:
Yes pretty much in the same way as a grounded system.

With an ungrounded system the first ground fault will not operate the protective device and the equipment continues to operate. Also the ungrounded delta system will now behave as a corner grounded delta system.
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What is the purpose of equipment grounding on the first line-to-ground fault? What will happen to the person touching the metal enclosure assuming the single-line-to ground fault happened inside the metal enclosure if there is no equipment grounding? Will he be electrocuted?

Why is it that if there is an equipment grounding/bonding, the person touching the metal enlosure on the first line-to-ground fault will not be electrocuted?

Is the purpose of equipment grounding for ungrounded system a return path for the protective device to trip on the FIRST line-to-ground fault? Remember that the code allows continuity of service in the FIRST line-to-ground fault.

Or its purpose is to reduce the potential to ground of the enlosure so that no one will be electrocuted on the FIRST single-line-to-ground fault?

iwire said:
First off the EGC provide personal protection because even an ungrounded system can provide a lethal shock due to capacitance coupling with grounded raceways etc.
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What is the technical explanation why will the EGC provide personal protection if during the FIRST line-to-ground fault the EGC will not function as a return path to the source for the protective device to operate? and due to the capacitance coupling there is a danger of a lethal shock without an EGC?

Does it mean that Equipment Grounding Conductor is not always a return path to operate the protective devices specially on the FIRST line-to-ground fault?
 
The short answer is that an ungrounded system with one phase to ground fault will operate the same as an intentionally grounded system.
 
infinity said:
The short answer is that an ungrounded system with one phase to ground fault will operate the same as an intentionally grounded system.
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Please explain as an UNGROUNDED and HIGH RESISTANCE GROUNDED system operate differently from a SOLIDLY GROUNDED SYSTEM. This is a totaly different topic.
 
bobby ocampo said:
Please explain as an UNGROUNDED and HIGH RESISTANCE GROUNDED system operate differently from a SOLIDLY GROUNDED SYSTEM. This is a totaly different topic.
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It's right here. Iwire already answered it.

With an ungrounded system the first ground fault will not operate the protective device and the equipment continues to operate. Also the ungrounded delta system will now behave as a corner grounded delta system.


Now if that first ground fault is not repaired the next ground fault if it is from a different phase then the first ground fault it will trip the breaker as this will be a line to line fault.
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With a solidly grounded system, a single fault, whether it is line-to-line or line-to-ground, will operate the OCPD.
 
bobby ocampo said:
Please explain as an UNGROUNDED and HIGH RESISTANCE GROUNDED system operate differently from a SOLIDLY GROUNDED SYSTEM. This is a totaly different topic.
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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.
 
bobby ocampo said:
What is the purpose of equipment grounding on the first line-to-ground fault? What will happen to the person touching the metal enclosure assuming the single-line-to ground fault happened inside the metal enclosure if there is no equipment grounding? Will he be electrocuted?

Why is it that if there is an equipment grounding/bonding, the person touching the metal enlosure on the first line-to-ground fault will not be electrocuted?

Is the purpose of equipment grounding for ungrounded system a return path for the protective device to trip on the FIRST line-to-ground fault? Remember that the code allows continuity of service in the FIRST line-to-ground fault.

Or its purpose is to reduce the potential to ground of the enlosure so that no one will be electrocuted on the FIRST single-line-to-ground fault?



What is the technical explanation why will the EGC provide personal protection if during the FIRST line-to-ground fault the EGC will not function as a return path to the source for the protective device to operate? and due to the capacitance coupling there is a danger of a lethal shock without an EGC?

Does it mean that Equipment Grounding Conductor is not always a return path to operate the protective devices specially on the FIRST line-to-ground fault?
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For all practical purposes the EGC does very little on a single fault. In most cases with a single fault on an ungrounded system there is no difference in the safety of the system with or without EGCs. There is a huge difference when the second fault occurs so the code requires ungrounded systems to have EGCs and a grounding electrode system.
As far as your last question, the EGC is never a fault return path to open the OCPD on a single fault with an ungrounded system. There will never be enough current in this case to operate an OCPD. The fault current with a single fault will be very low, often less than an amp.
 
cadpoint said:
I'm going to go way out on the limb and say today in modern usuage and serviceing that U will never see an undgrounded service!
Maybe 2 to 3% of all the work you'll ever see in your life time.
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We have big glass plant customers and petrochemical customers that are still undgrounded to this point.
cadpoint said:
As earlier said, a grounded service, is a path to release the potentional difference, don't hug(touch) the can to touch a breaker! If your not part of the complete path to release this energy than no, one won't be a electrocuted, but you could well be shocked, from touching metal of an ungrounded service, but that frankly is if your on the wire circuits and not touching a breaker per say(breakers are electrically null per design) ... it'd be an equalization shock of the difference of your mass (body) to a closed looped because your not suppling a release path but you are creating an electrical imbalance due to ones own body mass, also not a good situation in any case!

Don't create a complete path where your in that path!

One hand on breaker, One arm behind back ...

Two arms touching is across the Heart, a deadly situation ...
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Sorry sir, please clarify what you mean. Let's focus our discussion on the purpose of equipment grounding conductor for UNGROUNDED SYSTEM or High resistance grounded system.
 
bobby ocampo said:
Sorry sir, please clarify what you mean. Let's focus our discussion on the purpose of equipment grounding conductor for UNGROUNDED SYSTEM or High resistance grounded system.
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Are you reading any of the responses here? That question has already been answered several times.
 
don_resqcapt19 said:
For all practical purposes the EGC does very little on a single fault. In most cases with a single fault on an ungrounded system there is no difference in the safety of the system with or without EGCs.
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There is a big difference because of the system capacitance. If the metal enclosure is accidentally energized due to a single line to ground fault, person accidentally touching the metal enlosure will be electrocuted if the metal enclosure is not grounded. You can measure a potential from enclosure to ground if there is no equipment grounding.

don_resqcapt19 said:
There is a huge difference when the second fault occurs so the code requires ungrounded systems to have EGCs and a grounding electrode system.
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Even the first ground fault, there is a danger of electrocution even if there is no return path for the current to the source.

don_resqcapt19 said:
As far as your last question, the EGC is never a fault return path to open the OCPD on a single fault with an ungrounded system. There will never be enough current in this case to operate an OCPD. The fault current with a single fault will be very low, often less than an amp.
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Does it mean that EGC is not always used as a return path to the source to open the OCPD? This means that EGC for ungrounded system is to reduce the voltage potential of the energized metal enclosure to ground potential similar to the purpose on the protection for static electicity?
 
Maybe this would help to understand the purpose of EGC for ungrounded system.


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Some loads are also using ungrounded system as compare to solidly grounded system for SAFETY. Not all loads must be disconnected for ground fault because it may more danger when a load is immediately cut-off.

I believe the code identify some applications that is not applicable for solidly grounded system.
 
Based on the first illustration. It shows that the EGC is not a return path to the source. EGC is used to reduce potential of the enclosure to ground. Therefore for safety it is important that equipment grounding conductor is connected to ground to reduce potential difference but not as a return path to operate the protective device in case of a single line to ground fault on an UNGROUNDED SYSTEM.
 
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