Equipment Grounding for Ungrounded System

[weressl]

There is a large difference between the majority of electric work being done and substations.

At the voltages we usually deal with (under 277 volts or 120 volts to ground the connection to earth does virtually nothing.

Raise the voltage to 10, 20, 30 KV and that connection to earth becomes much more effective.

Also if I recall substations have entire grounding grids under them for step potential protection. With an entire grid under foot your essentially 'standing on the rod' as Don mentioned earlier.

Ok Bob, I am game. Try a little experiment.

1. Disconnect the EGC from any metallic enclosure.
2. Remove the grounding connection from the casing to the ground electrode.
3. Connect the hot leg to the casing.
4. Touch the casing.
5. How do you feel?
6. Now reconnect the grounding connection between the casing and the ground electrode.
7. Touch the casing.
8. How do you feel?

Report back. I recommend that before you touch the casing you use a voltmeter.......:grin:

 

[iwire]

Ok Bob, I am game. Try a little experiment.

1. Disconnect the EGC from any metallic enclosure.
2. Remove the grounding connection from the casing to the ground electrode.
3. Connect the hot leg to the casing.
4. Touch the casing.
5. How do you feel?
6. Now reconnect the grounding connection between the casing and the ground electrode.
7. Touch the casing.
8. How do you feel?

Report back. I recommend that before you touch the casing you use a voltmeter.......:grin:

Potentially dead either way.

Unless there are different levels of death I don't see how it makes much difference.

 

[weressl]

Potentially dead either way.

Unless there are different levels of death I don't see how it makes much difference.

Why don't you try it, instead of living on your mistaken beliefs that you understand how things work?

I don't want you to believe what I say, I want you to conduct an experiment and let us know what you find.

Or you just simply do not want to be bothered by facts you find, your mind is made up already?

 

[iwire]

Why don't you try it, instead of living on your mistaken beliefs that you understand how things work?

I don't want you to believe what I say, I want you to conduct an experiment and let us know what you find.

Or you just simply do not want to be bothered by facts you find, your mind is made up already?

Right back at you, have you tried that experiment or are you just stuck in your beliefs?

 

[weressl]

Right back at you, have you tried that experiment or are you just stuck in your beliefs?

It is unecessary for me to try it since I know what the results will be.:wink:

It is you who need to prove it that you would be dead in either case. I manintain that you are wrong in that.:smile:

BTW it is not a belief in my part, it is science and I am offering a demonstration of it for you.

 

[peter d]

BOTH should be important. Both bonded EGC and connection to earth. Both are important.

How is this all important connection to earth (dirt) going to be of any value on AC systems on airplanes and ships?

 

[iwire]

It is unecessary for me to try it since I know what the results will be.:wink:

Oh, well then by all means

 

[weressl]

How is this all important connection to earth (dirt) going to be of any value on AC systems on airplanes and ships?

The 'earth' in those cases will be the structure itself.

 

[coulter]

bobby 0 -

IEEE Std 142-1991

"2.1.2 Electric-Shock Exposure
Electric shock injuries result from contact with metallic components that are unintentionally energized [10].7 Effective equipment grounding practices can minimize these personal injuries.

A breakdown of insulation can cause accidental contact between an energized electrical conductor and the metal frame that encloses it. Such contact tends to energize the frame to the voltage level of the conductor. Avoiding shock-hazard voltage requires nullifying this tendency. The equipment-grounding system should do this by forming a low impedance path to ground."

The current version of ieee142 is 2007. It doesn't read the same as your 1991 version. Perhaps the IEEE has learned a few things in the last 16 years.

Suggest you read the current version of 142, 2.1.2, particularly b and c. For impedance grounded or ungrounded systems, the IEEE is far more concerned with an effective path for fault current than attaching the metal parts to a conductor that has a low impedance to earth.

Also suggest reading the current version of 142.1.3 Purposes of system grounding.

Thirty years ago I completely understood NEC 250.4. Then about 20 years ago some of us started wondering just how the NEC came up with the physics that explained the reasoning behind 250.4. - there does not appear to be any. Oh yeah, lightning strilkes are easier to mitigate if the non-current metal parts have a connection to ground - but a 1000ohms is as good as the NEC mandated 25ohms.

Finally, the IEEE and the NEC are coming around. The term "bonding" is being differentiated from "grounding". Most of the issues you have been discussing are dealt with through bonding - As has been said, grounding adds very little to the safety.

You like thought experiments - this one has already been brought up, (iwire) but I'll change it a little and see if it makes sense to you:

Put an insulated (dry wood is fine) pallet out in the middle of your yard. set a metal structure on it (a bread box will work). Attach a single wire to a standard house service, grounded, 120/240V, 1pole, 20A cb - other end to the bread box. Wet the soil around the pallet. Turn on the CB. Measure the voltage to ground by sticking one probe in the wet earth at least 3 feet from the box, and the other probe on the box.

Voltage to ground = ???

Turn off the CB. Drive a ground rod and connect to breadbox. For this experiment, let's say the ground rod measures 25ohms to earth. Turn On the CB. Measure the current going to the bread box. Measure the voltage to ground. Make sure the earth probe is at least 3' from the ground rod.
Current = ???
Vbg = ???

What do you think will happen if you stand three feet from the ground rod and reach out an touch it?

Grounding the system did nothing to make it safe from a fault to the non-current carrying parts.

A direct fault to ground did not even draw enough current to trip a 20A Cb.

Square D's parent has some interesting papers on the subject. I think they are on Mikes Holt's site somewhere. Perhaps one of the posters know where they are. I think we Americans could learn a lot for the Norwegians (arrggg - Americans are not the best ? Wash my mouth out with soap)

carl

 

[peter d]

The 'earth' in those cases will be the structure itself.

Yes, but that is bonding, not earthing. Neither a ship nor airplane will have the connection to earth/dirt that Bobby Ocampo seems to be implying is so important.

 

[roger]

Yes, but that is bonding, not earthing.

And this is where the NEC should have accepted Don's proposals and used Equipment Bonding Conductor way back when for a better distinction for those that don't understand the difference between bonding and grounding/earthing

Neither a ship nor airplane will have the connection to earth/dirt that Bobby Ocampo seems to be implying is so important.

And Bennie would disagree with that statement since you could carry a bucket of dirt on either of those.:grin:

Roger

 

[peter d]

And Bennie would disagree with that statement since you could carry a bucket of dirt on either of those.:grin:

Roger

Of course I did have the "bucket of dirt" in mind when I made that post.

 

[roger]

Of course I did have the "bucket of dirt" in mind when I made that post.

I should have known that. :wink:

Roger

 

[bobby ocampo]

How is this all important connection to earth (dirt) going to be of any value on AC systems on airplanes and ships?

The case of the ship will serve us the earth and all bonded EGC will be connected to the structure of the ship or airplane.

 

[bobby ocampo]

bobby 0 -



The current version of ieee142 is 2007. It doesn't read the same as your 1991 version. Perhaps the IEEE has learned a few things in the last 16 years.

Suggest you read the current version of 142, 2.1.2, particularly b and c. For impedance grounded or ungrounded systems, the IEEE is far more concerned with an effective path for fault current than attaching the metal parts to a conductor that has a low impedance to earth.

You may have forgotten the first part sir. Please quote "a"

Also suggest reading the current version of 142.1.3 Purposes of system grounding.

I will appreciate if you can email a copy so I can answer you or please try to quote the complete provision of that specific artilce or section in 142.

Thirty years ago I completely understood NEC 250.4. Then about 20 years ago some of us started wondering just how the NEC came up with the physics that explained the reasoning behind 250.4. - there does not appear to be any. Oh yeah, lightning strilkes are easier to mitigate if the non-current metal parts have a connection to ground - but a 1000ohms is as good as the NEC mandated 25ohms.

Finally, the IEEE and the NEC are coming around. The term "bonding" is being differentiated from "grounding". Most of the issues you have been discussing are dealt with through bonding - As has been said, grounding adds very little to the safety.

You can experiment a Bonded EGC not connected to earth in an UNGROUNDED AND HRG SYSTEM. There will be a potential equal to the line to neutral voltage of the system. Or potential will be equal to line-to-line divided by 1.732. After the experiment tell us if connection to earth is not important.

 

[bobby ocampo]

Yes, but that is bonding, not earthing. Neither a ship nor airplane will have the connection to earth/dirt that Bobby Ocampo seems to be implying is so important.

Equipment bonding is interconnection of the different non-current carrying metal part and connecting it to the case will be the reference earth for the ships or airplane. It will be hazardous if the Bonded EGC will not be connected to the ships structure.

 

[bobby ocampo]

It is unecessary for me to try it since I know what the results will be.:wink:

It is you who need to prove it that you would be dead in either case. I manintain that you are wrong in that.:smile:

BTW it is not a belief in my part, it is science and I am offering a demonstration of it for you.

I will conduct an experiment on a solidly grounded system but at a reduced voltage of 21voltsY/12 volts. I have already verified importance of connection to ground of the BONDED EGC in UNGROUNDED AND HRG SYSTEM.

Based on science and vector equivalent of electrical system, importance of connection to earth is very important. T

 

[peter d]

Equipment bonding is interconnection of the different non-current carrying metal part and connecting it to the case will be the reference earth for the ships or airplane. It will be hazardous if the Bonded EGC will not be connected to the ships structure.

Thanks, I have the concepts of bonding and grounding under control.

In the case of a ship or an airplane, there is no "reference earth" because nothing is connected to the earth itself. Bonding the metal structure of those is simply bonding, not grounding. Yet you keep mixing the terms which makes your arguments very difficult to understand.

 

[peter d]

Based on science and vector equivalent of electrical system, importance of connection to earth is very important.

Let's get down to brass tacks here. Are you suggesting that the connection to EARTH (=Dirt) is important?

 

[peter d]

The case of the ship will serve us the earth and all bonded EGC will be connected to the structure of the ship or airplane.

How can something that has no physical connection to earth be considered something that will "serve us the earth?" Again, your use of terms is very confusing.

Yes, the EGCs in those systems are BONDED. They are in no way, shape or form earthed or have anything to do with the earth.