EGC AS A RETURN PATH TO PREVENT ELECTROCUTION IN SOLIDLY GROUNDED SYSTEM

[bobby ocampo]

1. What happens if the OCPD malfunctions on a single line to ground fault in a solidly grounded system with EGC?
2.Will the person touching the metal panel be electrocuted?

 

[tom baker]

This is a very basic question, to make sure I am understanding please provide an illustration

 

[bobby ocampo]

This is a very basic question, to make sure I am understanding please provide an illustration

I hope discussions such as this will not be censored. I will prepare illustration

 

[bobby ocampo]

i have to do this step by step to prove my point to question the teachings that EGC for equipment grounding conductor is ONLY to operate the OCPD. I want to be proven wrong and IEEE 80. We can all learn and seek for the truth. Please be patient. Thanks in advance to all participants
First exhibit illustration is on SOLIDLY GROUNDED CORNER GROUNDED DELTA.

Without an EGC will the person touching the metal panel be electrocuted or experience a shock even without EGC?
Why or why not will the person touching the metal panel be electrocuted?
If the system is ungrounded will the person touching the metal panel be electrocuted?
Next illustration will have an EGC After this discussion.

 

[petersonra]

The EGC allows for fault current to flow in large enough quantities that it will trip the overcurrent protection device for the circuit. Once that happens there is no voltage on the EGC and no current on the EGC because the circuit is open. This does not work in circuits that are ungrounded because there's no path back to the source through the equipment grounding conductor.

 

[bobby ocampo]

The EGC allows for fault current to flow in large enough quantities that it will trip the overcurrent protection device for the circuit. Once that happens there is no voltage on the EGC and no current on the EGC because the circuit is open. This does not work in circuits that are ungrounded because there's no path back to the source through the equipment grounding conductor.

Please check my post with illustration above. Please be patient as I want to explain this step by step. I want to be proven wrong based on IEEE 80. We do this in preventing electrocution in substations. Thanks for your patience. Hope there will be no censorship.

I will try to answer your question point by point after my first illustration. Thanks for your comment.

 

[petersonra]

Please check my post with illustration above. Please be patient as I want to explain this step by step. I want to be proven wrong based on IEEE 80. We do this in preventing electrocution in substations. Thanks for your patience. Hope there will be no censorship.

I will try to answer your question point by point after my first illustration. Thanks for your comment.

I don't know what you mean by censorship. Just asking questions about the national electrical code or electricity in general is not going to result in any issues.

In the case of your sketch, it appears that you are showing a ground fault from the corner grounded conductor to the panel. The thing is that conductor is already connected to ground so the voltage between that conductor and ground is very low.

IEEE 80 is a specification for substation grounding and really doesn't have all that much to do with the national electrical code which is what we deal with mostly here.

 

[bobby ocampo]

I don't know what you mean by censorship. Just asking questions about the national electrical code or electricity in general is not going to result in any issues.

I have been censored in my other post. Its not you.

In the case of your sketch, it appears that you are showing a ground fault from the corner grounded conductor to the panel.

Yes you are correct. Thanks. My follow up question is what if the DELTA IS UNGROUNDED, Will the person touching the metal panel be electrocuted assuming the line to line voltage is 240 volts? 480 volts? Without EGC.

The thing is that conductor is already connected to ground so the voltage between that conductor and ground is very low.

How low will the voltage be to ground in your experience will it be specially if the panel is close to the transformer?

IEEE 80 is a specification for substation grounding and really doesn't have all that much to do with the national electrical code which is what we deal with mostly here.

I wil show the principles later to prove my point or I will be proven wrong. Physics of electricity is the same regardless of the voltage. Thanks for your comment. Let's continue to challenge the status quo.

 

[petersonra]

I am not sure I wish to challenge the so-called status quo. It's the status quo because it is long proven.

If the system is ungrounded Delta and one of the three lines comes in contact with the enclosure, this will be observed by the ground detect system in such a circuit. Presumably someone will fix it.

The voltage between the grounded conductor and Earth will be very close to zero. The actual voltage will be whatever the voltage drop is caused by the current flow in the grounded conductor. So it won't be zero necessarily, but very close.

There would be very little difference in safety between an intentional grounding of one of the phases, and an unintentional one. The voltage on the cabinet would end up being the same in both cases.

Perhaps it would be best if you tell us what it is you are trying to accomplish.

 

[bobby ocampo]

I am not sure I wish to challenge the so-called status quo. It's the status quo because it is long proven.

Not necessarily proven based on the available evidence that no one is questioning.

If the system is ungrounded Delta and one of the three lines comes in contact with the enclosure, this will be observed by the ground detect system in such a circuit. Presumably someone will fix it.

The question is will the person touching the metal panel be electrocuted if the system is UNGROUNDED?

The voltage between the grounded conductor and Earth will be very close to zero.

1. Thanks. Is the approaching to zero volts because of the connection to earth of one of the current carrying conductor to ground?
2. In this specific illustration of corner solidly grounded delta the potential was reduced to zero because it is connected to earth or some conducting body in replacement of the earth? Did connection to earth help to prevent electrocution because the current carrying conductor is now equal to the earth at zero volts?
3. Does it mean that connection to earth will reduce the voltage potential to zero and therefore prevent electrocution?

The actual voltage will be whatever the voltage drop is caused by the current flow in the grounded conductor. So it won't be zero necessarily, but very close.

Thanks. If the distance from the transformer is very close, will it very close to zero?
Is it clear that connecting to earth of a potential will reduce its voltage to zero? Connecting to earth will reduce the potential thereby touch potential is reduced to less than 50 volts as required in IEEE 80 to prevent electrocution?

There would be very little difference in safety between an intentional grounding of one of the phases, and an unintentional one. The voltage on the cabinet would end up being the same in both cases.

Perhaps it would be best if you tell us what it is you are trying to accomplish.

Now. Based on this illustration only. Connection to earth clearly reduces the touch potential if in this illustration line 1 is connected to earth. Let's call the top most current carrying conductor as line 1.
Can we now conclude that for this illustration earthing or connecting to earth reduces touch potential to a low value that will prevent electrocution?

 

[petersonra]

Can we now conclude that for this illustration earthing or connecting to earth reduces touch potential to a low value that will prevent electrocution?

I am not sure what point you are trying to make. In the illustration shown the voltage from the grounded conductor to ground is low. That is more of a fact than a conclusion.

 

[ptonsparky]

As drawn, you have no load at the panel other than the person. No voltage difference, no shock.
Add a load and the VD on line 1 comes into play.

 

[bobby ocampo]

I am not sure what point you are trying to make. In the illustration shown the voltage from the grounded conductor to ground is low. That is more of a fact than a conclusion.

So lets repeat. FOR THIS ILLUSTRATION, Connecting to earth one of the current carrying conductor will bring the potential to zero or approaching zero voltage. Therefore electrocution is minimize provided that the voltage drop is not to large. Is this safe to say now again for this illustration?
Any other questions or contentions to prove this conclusion wrong?

 

[bobby ocampo]

As drawn, you have no load at the panel other than the person. No voltage difference, no shock.
Add a load and the VD on line 1 comes into play.

Thanks for your comment. Regardless if there is a load or not the voltage to ground of the grounded current carrying conductor touching the panel will be approaching zero. The assumption is the metal panel is near the transformer so less voltage drop.

 

[ptonsparky]

What you have drawn is virtually every residential service in the US, other than distance. Are they safe? Doesn't matter that it is Corner ground.

Thanks for your comment. Regardless if there is a load or not the voltage to ground of the grounded current carrying conductor touching the panel will be approaching zero. The assumption is the metal panel is near the transformer so less voltage drop.

I think you answered it.

 

[paulengr]

1. What happens if the OCPD malfunctions on a single line to ground fault in a solidly grounded system with EGC?
2.Will the person touching the metal panel be electrocuted?

Not enough detail but…

Typically when an OCPD fails you have to consider zone 2 or backup protection. So for example in a typical residential panel normally the branch circuit breaker operates. If it doesn’t then the main will. However how fast this happens depends on the current. Say available short circuit current is 2 kA. Most residential breakers are UL curve C so they trip at 6-10x the marked current within about 1-2 cycles. So the 15-20 A breaker easily trips. But on a 400 A main it won’t trip instantaneously. We have to look at the thermal trip curve. We are at 2000 /400 A = 5x so we should trip in 3 seconds.

http://www.kentindustries.com/faz_trip_curve.gif

If it was a little higher, even 2.5 kA would trip “instantaneously”.

If it is only say 1 kA then we are at 2.5x and it can take a long time, about 20 seconds to trip. By then depending on the fault, it might melt/burn itself out. That’s the problem with high resistance faults.

In the mean time we have contact with a grounded (bonded) surface. Typically equipment grounds have lower impedance than the neutral. But say the hot, neutral, and ground are all similar. In my example with 2 kA on a 120 V circuit we know the impedance is 0.06 ohms assuming little voltage drop. As per this web site:

Wire Resistance Calculator - Cirris Inc

www.cirris.com

House wiring using 14 gauge is about a quarter ohm per 100 feet. Even if the bonding is near zero we would still be no more than about 20 feet from the distribution panel. If we are15 feet away we get 0.025 x 1.5 = 0.0375 ohms drop. We get the same drop in the neutral so to achieve 0.06 ohms with a parallel fault path the impedance must be0.01 ohms (parallel resistors). So we have two resistors in series. So the resistance on the neutral/ground circuit is 0.06 -p.0375 = 0.0226 ohms so by using the ratio the voltage at the fault is 120 x (0.0226 / 0.06) = 45 V.

As far as “electrocuted” you can be shocked at any voltage. You may not feel it but current flow is there. So technically yes.

Human resistance is about 1,000 ohms worst case through the epidermis so it does not affect the fault but does result in 45 / 1000 = 45 mA of current. This is not fatal but it will hurt and a victim can’t let go. Most safety standards set an upper limit in safe voltage at 50 VAC.

This is on a good, maintained system. On a poor system the fault current goes down so trip time increases. Voltage drop is not nearly as good so trip times are much longer and the shock hazard greatly increases.my example though is pretty “typical” for residential cases.

 

[jim dungar]

i have to do this step by step to prove my point to question the teachings that EGC for equipment grounding conductor is ONLY to operate the OCPD. I want to be proven wrong and IEEE 80. We can all learn and seek for the truth. Please be patient.

At low voltages, those below 600V, the earth is considered a poor conductor and therefore incapable of conducting enough current to reliably operate an OCPD as small as 15A.
IEEE80 applies to grounding in substations, where voltages exceed 2400V, and the earth is considered a conductor capable of conducting current.

An equipment bonding conductor's primary purpose is to bond conductive sources together in order to reduce touch potential between surfaces.
Electrocution can occur at extremely low voltages, typically over 48V, dependent upon several factors including the health of the individual.

 

[bobby ocampo]

What you have drawn is virtually every residential service in the US, other than distance. Are they safe? Doesn't matter that it is Corner ground.

I think you answered it.

Corner grounded is normally in industrial and commercial applications. In residential, supplied transformer by the utility is normally one leg with center tap delta transformer. Small residential is normally single phase 2 wire or single phase 3 wire. Thanks for your answer.

I hope that this topic will not be censored

 

[jim dungar]

As a side note, there was no censorship of the previous posts on this topic.
Yes, previous threads have been closed, but their contents are still available for viewing.
We ask all participants to follow the rules of this forum.

 

[bobby ocampo]

Not enough detail but…

Typically when an OCPD fails you have to consider zone 2 or backup protection. So for example in a typical residential panel normally the branch circuit breaker operates. If it doesn’t then the main will. However how fast this happens depends on the current. Say available short circuit current is 2 kA. Most residential breakers are UL curve C so they trip at 6-10x the marked current within about 1-2 cycles. So the 15-20 A breaker easily trips. But on a 400 A main it won’t trip instantaneously. We have to look at the thermal trip curve. We are at 2000 /400 A = 5x so we should trip in 3 seconds.

http://www.kentindustries.com/faz_trip_curve.gif

If it was a little higher, even 2.5 kA would trip “instantaneously”.

If it is only say 1 kA then we are at 2.5x and it can take a long time, about 20 seconds to trip. By then depending on the fault, it might melt/burn itself out. That’s the problem with high resistance faults.

In the mean time we have contact with a grounded (bonded) surface. Typically equipment grounds have lower impedance than the neutral. But say the hot, neutral, and ground are all similar. In my example with 2 kA on a 120 V circuit we know the impedance is 0.06 ohms assuming little voltage drop. As per this web site:

Wire Resistance Calculator - Cirris Inc

www.cirris.com

House wiring using 14 gauge is about a quarter ohm per 100 feet. Even if the bonding is near zero we would still be no more than about 20 feet from the distribution panel. If we are15 feet away we get 0.025 x 1.5 = 0.0375 ohms drop. We get the same drop in the neutral so to achieve 0.06 ohms with a parallel fault path the impedance must be0.01 ohms (parallel resistors). So we have two resistors in series. So the resistance on the neutral/ground circuit is 0.06 -p.0375 = 0.0226 ohms so by using the ratio the voltage at the fault is 120 x (0.0226 / 0.06) = 45 V.

As far as “electrocuted” you can be shocked at any voltage. You may not feel it but current flow is there. So technically yes.

Human resistance is about 1,000 ohms worst case through the epidermis so it does not affect the fault but does result in 45 / 1000 = 45 mA of current. This is not fatal but it will hurt and a victim can’t let go. Most safety standards set an upper limit in safe voltage at 50 VAC.

This is on a good, maintained system. On a poor system the fault current goes down so trip time increases. Voltage drop is not nearly as good so trip times are much longer and the shock hazard greatly increases.my example though is pretty “typical” for residential cases.

Please back read and see the first illustration exhibit that we are discussing. I will answer your question in different illustration later. I prefer to discuss it one situation at a time to prove my point on EGC and CONNECTION TO EARTH.
Thanks for your comment.
Please check the exhibit illustration above so I don't have to repeat it again.