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[bobby ocampo]

Grounding Vs. Bonding
The Big Picture​

• What is ?grounding?? What is ?bonding?? What?s the difference?

Grounding and bonding is probably the most discussed issue here, aside from 210.52?s design requirements.

The terms are defined in Article 100 and 250.2 of the NEC. Section 250.4 provides the performance requirements of Article 250. Grounding is a connection to earth, and bonding is the connection of items to each other.

Bonding is crucial inside a structure, because without it, if something goes wrong and an ungrounded conductor comes in contact with a piece of metal that someone can touch, that someone will receive a shock and potentially be electrocuted due to the uncleared fault. A quick and dirty definition for bonding is connecting electrical devices together in the attempt to trip a breaker, if an ungrounded conductor touches surface metal associated with the system.

This is true only SOLIDLY GROUNDED SYSTEM because of a very high current on a single line-to-ground fault but not on UNGROUNDED system and HIGH RESISTANCE GROUNDED SYSTEM. Single line-to-ground fault for UNGROUNDED SYSTEM and HIGH RESISTANCE GROUNDED SYSTEM is very small. A person will receive a shock if the piece of metal is not connected to earth but not because of an uncleared fault.

What does the earth have to do with this? Nothing.

Earth has something to do with safety to reduce the potential of the energized piece of metal to zero potential or ground potential. Justification can be seen in an UNGROUNDED SYSTEM or HIGH RESISTANCE GROUNDED SYSTEM.

Then why is it called an ?Equipment Grounding Conductor (EGC)? in the NEC if it?s primary purpose is to ?bond? things together? Simple answer: tradition. It?s always been called that, and the terms in the NEC have served to confuse people for a long time. Proposals have been made to change the term, and progress has been made, but the EGC continues to hold it?s misnomer.

I respectfully disagree sir. Vector diagram will show specially in a high resistance grounded system, that if an ungrounded conductor touches the ground its potential will be reduced to ground potential. This can be verified in an experiment both for UNGROUNDED SYSTEM and HRG system.

Electricity does not seek the path of least resistance to the earth. It seeks all available paths back to it?s source, in proportion to their resistance. The reason that a person gets shocked when touching an ungrounded conductor and the earth is because the neutral of the system is repeatedly connected to earth in a grounded electrical system. The earth becomes part of a return path to the transformer ? it?s part of one route back to the source; the earth is not the destination for the electricity.

Sir, Even if the neutral is not grounded to earth a person touching an ungrounded condutor will be electrocuted because of the system capacitance. Reference' Industrial Power systems handbook by Beeman.

Driving a ground rod to ?ground? any electrical equipment does not provide the low-resistance path required to trip breakers. Driving a ground rod, or using a Ufer, or a metal water pipe is not a substitute for an EGC. A ground rod with 25 ohms to earth will allow almost five amps to escape the system into the earth when directly energized from a 120V source. Five amps will never trip a 15A or 20A breaker, and in the meantime everything bonded to this ground rod will be energized to 120V.

The purpose of the ground rod is not to provide low resistance path but to make all equipment equipotential to the ground for safety. This can be proven by experiment on UNGROUNDED SYSTEM and HRG system.

 

[Dennis Alwon]

Bobby-- Again don't do this but if you take a piece of #12 and connect it to a ground rod directly without any GEC connected, then connect the #12 to a 20 amp breaker. What do you think will happen. It will not trip that breaker.

A good ground rod may help with lightning strikes not ground fault.

 

[don_resqcapt19]

The purpose of the ground rod is not to provide low resistance path but to make all equipment equipotential to the ground for safety. This can be proven by experiment on UNGROUNDED SYSTEM and HRG system.

While the grounding electrode system may very well provide an equipotential on those two types of systems it will not on a solidly grounded system. How ever those two system are not very common in comparison to solidly grounded systems. Many electricians will never see one of those systems in thier whole carreer. On a solidly grounded system that does not happen. There is a sharp voltage gradient around the ground rod. At 3' from the rod you will have about 75% of the system voltage. The only way to make it safe after the fault on a solidly grounded is to clear the fault. The EGC and the main bonding jump must be sized to carry enough current so that the OCPD opens quickly.

 

[bobby ocampo]

Bobby-- Again don't do this but if you take a piece of #12 and connect it to a ground rod directly without any GEC connected, then connect the #12 to a 20 amp breaker. What do you think will happen. It will not trip that breaker.

A good ground rod may help with lightning strikes not ground fault.

I respectfully disagree sir, ground rod are not only for lightning strikes. This serves as a reference ground potential such that if EGC is connected to this ground rod the accidentaly energized metal piece will be at ground potential. Otherwise the neutral of the transformer will not be connected to the ground anymore.

 

[bobby ocampo]

While the grounding electrode system may very well provide an equipotential on those two types of systems it will not on a solidly grounded system.

The code should specifically say that EGC that serves as a return path to trip the OCPD on a SINGLE line-to-ground fault is for SOLIDLY GROUNDED ONLY.

On other system accepted by the code UNGROUNDED SYSTEM AND IMPEDANCE GROUNDED SYSTEM, EGC serves as an equipotential connection of the equipment to the ground potential and not as a return path to the source on a single line-to-ground fault.

How ever those two system are not very common in comparison to solidly grounded systems.

More and more are using HRG now for continuity of service. It is important to know the importance of connecting the EGC to earth. The EGC connected to earth or ground will serve to reduce the accidentally energized metal piece to ground potential and not just a protection for lightning strikes.

Many electricians will never see one of those systems in thier whole carreer. On a solidly grounded system that does not happen. There is a sharp voltage gradient around the ground rod. At 3' from the rod you will have about 75% of the system voltage. The only way to make it safe after the fault on a solidly grounded is to clear the fault. The EGC and the main bonding jump must be sized to carry enough current so that the OCPD opens quickly.

HRG and LRG is starting to be popular because it has less hazard than a SOLIDLY GROUNDED SYSTEM IEEE 142-1991

 

[roger]

I respectfully disagree sir, ground rod are not only for lightning strikes.

At our voltages, lightning events and high voltage surges are indeed the primary reason for earthing a system.

Otherwise the neutral of the transformer will not be connected to the ground anymore.

And apply this reasoning to a raised wooden structure, who cares if there is a reference to earth and do you think it will change anything if it were?

Roger

 

[don_resqcapt19]

The code should specifically say that EGC that serves as a return path to trip the OCPD on a SINGLE line-to-ground fault is for SOLIDLY GROUNDED ONLY.

So submit a proposal for the 2011 code. The form is in the back of the code book and the proposals must be at the NFPA office prior to 5pm on Nov 7, 2008.

 

[don_resqcapt19]

HRG and LRG is starting to be popular because it has less hazard than a SOLIDLY GROUNDED SYSTEM IEEE 142-1991

That may be true for industrial type systems, but you can't use those systems if there are line to neutral loads and that is the type of system that most electricians work on. I stand by my statement that the vast majority of electricians have never seen a HRG or LRG system and never will.

 

[Dennis Alwon]

That may be true for industrial type systems, but you can't use those systems if there are line to neutral loads and that is the type of system that most electricians work on. I stand by my statement that the vast majority of electricians have never seen a HRG or LRG system and never will.

I am one of them-- never heard of HRG or LRG and I've been in business for over 30 years. I bet none of the local boys here ever heard of it either. I don't feel alone in my ignorance.

 

[bobby ocampo]

That may be true for industrial type systems, but you can't use those systems if there are line to neutral loads and that is the type of system that most electricians work on.

Code prohibits line-to-neutral loads for HRG and LRG. It is also used now in Data Centers and Hospitals for continuity of service and safety against arcing ground fault on solidly grounded system.

I stand by my statement that the vast majority of electricians have never seen a HRG or LRG system and never will.

I respectfully agree sir that to date that majority of electricians may have never seen an HRG and LRG system. However I respecfully disagree that they will never see one in the near future. More and more ungrounded system are being converted to HRG or LRG using a zigzag transformer. HRG is starting to be popular in low voltage system now.

 

[don_resqcapt19]

I respectfully agree sir that to date that majority of electricians may have never seen an HRG and LRG system. However I respecfully disagree that they will never see one in the near future. More and more ungrounded system are being converted to HRG or LRG using a zigzag transformer. HRG is starting to be popular in low voltage system now.

I don't see how given that the vast majority of electrical systems serve line to neutral loads and you can't use HRG or LRG on line to neutral loads. I don't see the use of line to neutral loads going away. Yes, I would agree that switching ungrounded systems to HRG or LRG would be a good idea.

 

[ryan_618]

The code should specifically say that EGC that serves as a return path to trip the OCPD on a SINGLE line-to-ground fault is for SOLIDLY GROUNDED ONLY.

It does in 250.4(A) and (B).

In all honesty though, should the NEC be the document that tells us these things, or should it be a textbook?