Equipment Grounding for Ungrounded System

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bobby ocampo said:
Earth is required in NEC. Earth is considered zero potential for safety. This can be proven on a single-line-to-ground fault in an Ungrouded system and HRG.
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Did you see Mike Holt's diagram above that completely disproves the idea that the connection to earth reduces shock hazard?
 
bobby ocampo said:
If EGC will not be properly sized may cause it to become a fuse and therefore be removed out untintentionaly.


It is dangeours and very hazardous to say that the earth connection is less important. Arcing Ground Faults are single line to ground faults in SOLIDLY GROUNDED SYSTEM that are smaller in magnitude the the bolted single-lline-to-ground fault. This ARCING GROUND FAULT is most of the time even less than the ampere trip rating of the OCPD. Even with the best BONDED EGC the OCPD will not operate because the ground fault is still too low. However due to this ARCING GROUND FAULT, the accidentally metal piece of equipment will now be energized and if the energized metal piece of equipment is not conneted to the EARTH will cause electric hazard.



In premises wiring of 480 volts, line-to-neutral voltage is more than 150 volts to ground. The code requires a ground fault protection for OCPD rated 1000amps or more for the protection against ARCING GROUND FAULT. Maximum setting of GROUND FAULT PROTECTION only up to 1200 amps. If the main cirucuit breaker in a premises wiring 3000Amps this means that ground fault due to ARCING will have current of less than 3000amps. If the main circuit breaker has not ground fault protection, it means that it will not trip on an ARCING GROUND FAULT. If the arcing ground fault energizes the metal part and it is not connected to earth then there is a danger of electric shock. It is important to note that ARCING GROUND FAULT is low enough NOT TO OPERATE the OCPD despite the bonded EGC.


Most of the people who are working near energized equipment or appliances are people who don't know better. Only small percentage of the population are Electrical Engineers and Electricians. These people who don't know better would have to be protected against the hazards in the use of electricity.
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Even if the OCPD is arc fault protection capable the algorithm requires several repetitive faults to occur until the I2t 'quantity' is large enough that heating is suspected. Each arcing fault energizes the case and exposes the user to electrocution If the EGC is not in place.
 
weressl said:
... Each arcing fault energizes the case and exposes the user to electrocution If the EGC is not in place.
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Even with the EGC in place there is still an elevated voltage on the faulted equipment. It is be of a much lower level with an arcing fault than with a bolted high current fault, but it will still be energized.
 
You guy's are talking about using earth as a fault path.


What is you opinions of 250.4(A)(5) and (B)(4)'s last sentence, "The earth shall not be considered as an effective [ground] fault-current path"?
 
all i can say is AMEN

all i can say is AMEN

but the discussion has been very educational re: grounding and bonding, for anyone who followed along. whether you like it or not, it seems that those who know, educate those who don't, even thru discourse. what a great place :cool:
 
don_resqcapt19 said:
Even with the EGC in place there is still an elevated voltage on the faulted equipment. It is be of a much lower level with an arcing fault than with a bolted high current fault, but it will still be energized.
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Can this be solved by connecting the metal piece to earth to reduce electric shock because of the energized metal piece due to the ARCING GROUND FAULT?

Isn't this similar to ungrounded system and HRG system?
 
coulter said:
Oh yeah. However, it's been made clear to me that's nothing I could ever suggest.

carl
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Please, do tell, when was this?

Roger
 
tryinghard said:
You guy's are talking about using earth as a fault path.


What is you opinions of 250.4(A)(5) and (B)(4)'s last sentence, "The earth shall not be considered as an effective [ground] fault-current path"?
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Earth is not use as a fault path to trip the OCPD. Connection to earth is used to reduce the potential of the energized metal piece to earth potential. This is also the purpose of connecting the neutral of the solidly grounded system so that potential of the current carrying conductor will be limited to line to ground fault.
 
tryinghard said:
touch.gif


!
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Based on the illustration, what will happen if another grounding rod is installed 3 feet and 5 feet respectively and is bonded to the ground rod installed near the post with zero potential?

Will this electric shock still happen?

In this illustration, what is the value of the fault current? What is the assumed resistance of the earth in this illustration?

To reduce step potential to ground or earth as in this illustration there are two solution. One is when fault current is low and another is when resistance is low because step potential is equal to I_fault current multiplied by resistance of the ground. If resistance to ground is reduced to a small amout because of installation of another grounding rod bonded to the first grounding rod, step potential will be reduced.
 
George Stolz said:
Bobby, how many ground rods are required in the installation pictured above?
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Depends on the measured resistance of the earth and prospective fault current. What do you think was the prospective fault current in the illustration? What do you think was the measured ground resistance in the illustration.

If the system grounding in the illustration was an ungrouded system, do you think this step potential will happen? Please answer.

If fault current is a low ARCING GROUND FAULT and its value is less than the ampere trip rating of the OCPD, do you think OCPD will still open even with a bonded EGC to the source? Please answer.

Based on Ohms law V_step potential = I_fault current times R _resistance of the earth.


Step potential will be low enough that illustration will not happen but the metal pole may still be energized and the person touching the pole will receive an electric shock equal to 120 volts if the pole is not conneted to ground.

Same principle applies to ungrounded and HRG system if one of the current carrying conductor touches the metal piece.
 
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