Neutral Connection in a System Grounding

[don_resqcapt19]

... Importance of connecting to earth is to reduce the potential of the energized metal piece to ground potential for safety in a solidly grounded system.

Please show me how that works. The connection to earth does not change the voltage on the faulted part. Does the voltage on an ungrounded conductor go away when you connect it to a load?

 

[bobby ocampo]

Please show me how that works. The connection to earth does not change the voltage on the faulted part. Does the voltage on an ungrounded conductor go away when you connect it to a load?

The line to line voltage of an UNGROUNDED CONDUCTOR will not go away but the voltage of one line accidentally conneted to ground will have a value equat to almost zero measuring from the line to ground if the EGC is connected to earth. This is the reason why there is a continuity of service in an Ungrounded and HRG system. The operation will continue despite a single line to ground fault and shutdown can be scheduled unlike a solidly grounded system. Sorry I don't know how to post an illustration in the forum. Illustration can be seen in Industrial Power Systems Handbook by Beeman on what happens with HRG and UNGROUNDED SYSTEM during a single line to ground fault.

 

[bobby ocampo]

You really have learned nothing from reading this thread, have you?

Can you explain how you will reduce the potential of an accidentally energized metal enclosure in an UNGROUNDED system and HRG SYSTEM?

Single line-to-ground fault in this two type so system is very low and acceptable to have continuity of service. In this type of system EGC is required but not to operate the OCPD on a single line to ground fault.

How do you reduce that accidentaly energized metal enlosure if the fault in a solidly grounded system is only an arcing ground fault that the current is low enough not to operate the OCPD but can energized the metal enclosure?

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[jim dungar]

Can you explain how you will reduce the potential of an accidentally energized metal enclosure in an UNGROUNDED system and HRG SYSTEM?

I know I am not going to rely on dirt only for <600V systems.
I think of research stations on glaciers or on a sand dune in the Sahara, much less those on ships.

 

[tryinghard]

?However in an Ungrounded system where there is no neutral conductor the bonded EGC is connected to the metal case of the transformer then connected to earth through a grounding rod.

Neutral if connected to earth is solidly grounded. If neutral is not connected to earth then the system is considered ungrounded?

There is no neutral involved with an ungrounded system and if there is in must be grounded as per NEC which makes it a grounded system. If a neutral is not bonded at its source or the first disconnect it is a violation and extremely dangerous! There is no such thing as a safe grounded system that does not bond the neutral and in this light there is no such thing as an ungrounded system that includes a neutral!

The transformer must be connected to earth through an electrode as described in 250.52 one of the over seven electrodes listed is the metal frame of the building.

 

[tryinghard]

?the voltage of one line accidentally conneted to ground will have a value equat to almost zero measuring from the line to ground if the EGC is connected to earth.

How much potential will exist at 3?, & 5?, & 10?, & 25? from your electrode?

 

[tryinghard]

Can you explain how you will reduce the potential of an accidentally energized metal enclosure in an UNGROUNDED system and HRG SYSTEM?

BY INSTALLING 250.21! We like to be code compliant its safe!

How do you reduce that accidentaly energized metal enlosure if the fault in a solidly grounded system is only an arcing ground fault that the current is low enough not to operate the OCPD but can energized the metal enclosure?

BY INSTALLING 250.2 AN EFFECTIVE-GROUND-FAULT PATH!


I have a question for you:
If your 20A circuit included an effective ground fault path it will probably have .5 ohms or less, how much current can be on your circuit if you have a short with 120V? What will your OCP do with this short?

 

[don_resqcapt19]

The line to line voltage of an UNGROUNDED CONDUCTOR will not go away but the voltage of one line accidentally conneted to ground will have a value equat to almost zero measuring from the line to ground if the EGC is connected to earth. This is the reason why there is a continuity of service in an Ungrounded and HRG system. The operation will continue despite a single line to ground fault and shutdown can be scheduled unlike a solidly grounded system. Sorry I don't know how to post an illustration in the forum. Illustration can be seen in Industrial Power Systems Handbook by Beeman on what happens with HRG and UNGROUNDED SYSTEM during a single line to ground fault.

All of my posts are based on the much more common solidly grounded system. Please tell me how this works for a solidly grounded system.

 

[bobby ocampo]

All of my posts are based on the much more common solidly grounded system. Please tell me how this works for a solidly grounded system.

There is a fault called ARCING GROUND FAULT. Most of the fault are actually not direct connected to ground in a solidly grounded system. This type of fault is when the insulation begins to deterioriate and fault is not yet as high as a direct single line to ground fault.

For this reason, the code requires a ground fault protection for OCPD of 1000 amps and more for system voltages of more than 150 volts to ground with a maximum setting of only 1200 amps. The current in this situation may not trip the circuit breaker without ground fault protection. If this ARCING GROUND FAULT happens inside the metal piece, it will increase the potential of the metal piece and if the EGC is not connected to the ground there is a big hazard of electric shock. If the metal piece is energized by the arcing ground fault and fault current is low enough not to trip the OCPD despite of the single line to ground fault then the only protection is the connection of the bonded EGC to earth.

This shows the importance of connecting to earth of the bonded EGC similar to the purpose of the connection of the bonded EGC in UNGROUNDED and HRG SYSTEM.

 

[bobby ocampo]

There is no neutral involved with an ungrounded system and if there is in must be grounded as per NEC which makes it a grounded system. If a neutral is not bonded at its source or the first disconnect it is a violation and extremely dangerous! There is no such thing as a safe grounded system that does not bond the neutral and in this light there is no such thing as an ungrounded system that includes a neutral!

The transformer must be connected to earth through an electrode as described in 250.52 one of the over seven electrodes listed is the metal frame of the building.

Are you saying that ungrounded system is a violation of the code? Are you saying also that High Resistance Grounding is also a violation of the code? When is it removed from the NEC?

 

[bobby ocampo]

I know I am not going to rely on dirt only for <600V systems.
I think of research stations on glaciers or on a sand dune in the Sahara, much less those on ships.

Sorry Sir, Don't understand your comment please clarify.

 

[tryinghard]

Are you saying that ungrounded system is a violation of the code? Are you saying also that High Resistance Grounding is also a violation of the code? When is it removed from the NEC?

I am saying there is NO neutral involved in an ungrounded system, an ungrounded system only includes the phase conductors.

 

[jim dungar]

...If this ARCING GROUND FAULT happens inside the metal piece, it will increase the potential of the metal piece and if the EGC is not connected to the ground there is a big hazard of electric shock.

To reduce the hazard of electrical shock the metal piece must be bonded to the electrical system, not to dirt. Actually it needs to be bonded to what ever you are using as your reference plane. A research station on top of a glacier, on a sand dune or aboard a ship has no connection to dirt, but their "ground-fault" protective devices continue to operate correctly.

The majority of Ground Fault devices actually look for an unbalance of current on the normal conductive paths, they don't care what actually causes the unbalance. I think we would have a lot less confusion over how and why these devices operate if we had followed the Europeans and called them Residual Current Devices instead of using the word ground in their description.

 

[don_resqcapt19]

There is a fault called ARCING GROUND FAULT. Most of the fault are actually not direct connected to ground in a solidly grounded system. This type of fault is when the insulation begins to deterioriate and fault is not yet as high as a direct single line to ground fault.

For this reason, the code requires a ground fault protection for OCPD of 1000 amps and more for system voltages of more than 150 volts to ground with a maximum setting of only 1200 amps. The current in this situation may not trip the circuit breaker without ground fault protection. If this ARCING GROUND FAULT happens inside the metal piece, it will increase the potential of the metal piece and if the EGC is not connected to the ground there is a big hazard of electric shock. If the metal piece is energized by the arcing ground fault and fault current is low enough not to trip the OCPD despite of the single line to ground fault then the only protection is the connection of the bonded EGC to earth.

This shows the importance of connecting to earth of the bonded EGC similar to the purpose of the connection of the bonded EGC in UNGROUNDED and HRG SYSTEM.

It doesn't matter what kind of fault that you have, the connection to earth does not remove the voltage from the faulted part on a solidly grounded system, unless you are standing on top of the grounding electrode and even in that case the voltage is still there, you are just touching two things that are at the same potential. As soon as you get away from the grounding electrode you will have a potential. And yes a ground mat can remove the potential in the area of the mat, but that is not a installation method that can bu used in normal building installations, and even where you can use one there is still a step potential at the edge of the grounding mat. The only way to remove the voltage from faulted equipment that is supplied from a solidly grounded system is to open the supply circuit. The conenction to earth does very little to improve the safety of a faulted solidly grounded system.

 

[LarryFine]

The grounded conductor is actually a double-edged sword. There are advantages and disadvantages to grounding.

Solidly grounding a conductor actually increases the risk of shock, yet it's necessary for the operation of GFCI devices.

 

[jim dungar]

Solidly grounding a conductor actually increases the risk of shock, yet it's necessary for the operation of GFCI devices.

I know no GFCI device that requires a ground.

GFCIs (as well as the overwhelming majority of larger GF devices) work solely on: what goes out must come back in, no more and no less (than their set point). They do not care where any missing current may be going, nor where any excess current comes from.

 

[LarryFine]

I know no GFCI device that requires a ground.

GFCIs (as well as the overwhelming majority of larger GF devices) work solely on: what goes out must come back in, no more and no less (than their set point). They do not care where any missing current may be going, nor where any excess current comes from.

I know the GFCI devices themselves require no EGC. That's not what I'm saying. The system must be grounded, though.

If the supply system is not grounded, there's no pathway for current outside of the intended circuit conductors; no shock.

 

[jim dungar]

If the supply system is not grounded, there's no pathway for current outside of the intended circuit conductors; no shock.

If the current is taking any unintended path it is a fault. Lets say that you have a 3-wire system with a conductor touching a metallic raceway.
If the system is bonded to the raceway, but not to ground. Any fault to the raceway will be sensed as an unintended current flow, ground (dirt) is not necessary. If the 3-wire system is not bonded then there is no fault;the first connection to the raceway simply creates a bonding path.

 

[bobby ocampo]

It doesn't matter what kind of fault that you have, the connection to earth does not remove the voltage from the faulted part on a solidly grounded system, unless you are standing on top of the grounding electrode and even in that case the voltage is still there, you are just touching two things that are at the same potential. As soon as you get away from the grounding electrode you will have a potential.

The issue is in reducing the energized metal piece to grund potential to reduce electric hazard. If connecting to earth can reduce the energized metal piece in an UNGROUNDED SYSTEM AND HRG SYSTEM to prevent electric shock hazard then why can't it not reduce electric shock hazard in a SOLIDLY GROUNDED SYSTEM in an ARCING GROUND FAULT where the fault current is still very low that the OCPD can not yet sense the fault despite the bonded EGC but the metal piece is already energized?

And yes a ground mat can remove the potential in the area of the mat, but that is not a installation method that can bu used in normal building installations, and even where you can use one there is still a step potential at the edge of the grounding mat.

The step potential is based on the voltage drop in the system due to the fault current flowing. In an arcing ground fault the fault current is very small therefore the step potential is still very small but the energized enlclosure will be an electric shock hazard because it has potential to ground if the bonded EGC is not connected to the reference plane which is the earth.

Same is true with UNGROUNDED SYSTEM AND HRG SYSTEM. If the accidentally energized metal piece is not grounded during a single line-to-ground fault then personnel touching the metal piece will receive an electric shock if the metal piece is not connected to the reference plane which is the ground.

In these two systems, just like in an ARCING ground fault, fault current is very low. and OCPD may not sense the fault and not operate despite the bonded EGC connected to the neutral. However the metal piece is already accidentaly energized and if this is not connected to the reference ground plane which is the earth what do you think will happen to the personnel touching the energized metal piece? Step potential at this very low level fault is therefore very low too.

The only way to remove the voltage from faulted equipment that is supplied from a solidly grounded system is to open the supply circuit. The conenction to earth does very little to improve the safety of a faulted solidly grounded system.

The idea is to reduce electric shock by reducing energized metal part to ground potetial. In an ungrounded system, line-to-line voltage is still present to allow continuity of service even if one of the current carrying conductor touches a metal piece. The energized metal piece if not connected to the ground will have a hazardous potential from the ground if not connected to the reference plane which is the earth or dirt as most are calling it. The best way to reduce electric shock in a very LOW FAULT CURRENT is to connect the metal piece to the ground. Or install a ground fault protection in a solidly grounded system. Line-to-line voltage is still present but voltage potential of the energized metal piece to ground is now at ground potential.

 

[bobby ocampo]

To reduce the hazard of electrical shock the metal piece must be bonded to the electrical system, not to dirt. Actually it needs to be bonded to what ever you are using as your reference plane. A research station on top of a glacier, on a sand dune or aboard a ship has no connection to dirt, but their "ground-fault" protective devices continue to operate correctly.

Is it important sir to connect the EGC to the reference plane for safety on hazards of electric shock?


Most ships that I have been to are UNGROUNDED SYSTEM.