Wonder if I could get an interpertation of rule 97 of the NESC. My application is single-point grounded wye 13.8V distribution. Past guidance from many EE's and NFPA board members has resulted in our grounding as follows: Lightning arrestors and equipment grounds to 4 ground rods located twenty feet from the secondary neutral ground (again, 4 ground rods). Since implementing this interpertation of rule 97 we haven't had the equipment damage (residential TV's/computers,etc.) and haven't had a problem with potential differences. Now I'm hearing from other EE's that it should all be bonded together and rule 97 ignored. Would appreciate any input.
NESC Rule 97
- Thread starter ruth
- Start date
- Status
charlie
Senior Member
- Location
- Indianapolis
Re: NESC Rule 97
Sorry, our system is 13.2 kV and is multi-grounded.
Sorry, our system is 13.2 kV and is multi-grounded.
Re: NESC Rule 97
I work for the US Army Corps of Engineers doing mostly military construction. The somewhat unusual distribution systems are located at Ft. Lewis and McChord AFB in WA state. I did high voltage line work for sixteen years. Hope someone out there can shed a little light on the subject or maybe provide a Point of Contact for clarification. We need standard designs for grounding and needless to say, would like to do it correctly.
I work for the US Army Corps of Engineers doing mostly military construction. The somewhat unusual distribution systems are located at Ft. Lewis and McChord AFB in WA state. I did high voltage line work for sixteen years. Hope someone out there can shed a little light on the subject or maybe provide a Point of Contact for clarification. We need standard designs for grounding and needless to say, would like to do it correctly.
Re: NESC Rule 97
Ruth: It has been over 20 years ago, but I was a research observer in the DOD Electromagnetic Compatibility Program at the South Pole Research Station. The team developed some of the present specs. I don't know if they will relate to your situation. Air Force MIL-I-16910, exibit RADC-2313.
You should have Mil specs to cover the grounding issue.
If you have the neutrals connected, at this transformer, it is a multi-ground system.
Are you saying the lightning arresters have a separate ground electrode from the neutral ground?
This is not unusual outdoors. It is not done or should not be done in a building.
Like I say,it has been over 20 years so anyone who wants, feel welcome to correct this.
Ruth: It has been over 20 years ago, but I was a research observer in the DOD Electromagnetic Compatibility Program at the South Pole Research Station. The team developed some of the present specs. I don't know if they will relate to your situation. Air Force MIL-I-16910, exibit RADC-2313.
You should have Mil specs to cover the grounding issue.
If you have the neutrals connected, at this transformer, it is a multi-ground system.
Are you saying the lightning arresters have a separate ground electrode from the neutral ground?
This is not unusual outdoors. It is not done or should not be done in a building.
Like I say,it has been over 20 years so anyone who wants, feel welcome to correct this.
Re: NESC Rule 97
Charlie: The spark gap neutral makes the transformer a separately derived system. There is no electrical connection to the primary source.
I couldn't pass up the opportunity to bring this up, even if no one but Roger believes me.
Have you noticed how intelligent he is?
Charlie: The spark gap neutral makes the transformer a separately derived system. There is no electrical connection to the primary source.
I couldn't pass up the opportunity to bring this up, even if no one but Roger believes me.
Have you noticed how intelligent he is?
Re: NESC Rule 97
Ruth
I would like to ask a few questions. When you say
"Single point grounding" what does that mean to you?
When you say 4 ground rods at 20 ft from the neutral ground do you mean 4 at the same location?
Is the secondary neutral ground seperate from the arrestor ground?
Regarding bonding does rule 97 suggest no bonding of grounds?
Ruth
I would like to ask a few questions. When you say
"Single point grounding" what does that mean to you?
When you say 4 ground rods at 20 ft from the neutral ground do you mean 4 at the same location?
Is the secondary neutral ground seperate from the arrestor ground?
Regarding bonding does rule 97 suggest no bonding of grounds?
Re: NESC Rule 97
Sorry for the tardiness in responding, I spend a lot of time in the field.
The distribution system is a single point grounded wye meaning the only place the primary neutral is grounded is at the station XFMR. There is NO system neutral. At a glance, most people would assume it's a Delta.
There are 4 ground rods around the transformer pad/vault forming a ground ring. The arrestor ground and case grounds are tied to that. The case/neutral bond strap is lifted and a 600V insulated neutral ground is then carried to a ground rod located 20' from the ground ring. Three additional rods are added at intervals of 10' (bare copper may be used to these rods. The only purpose of the four rods in series to to provide a better ground. And, hey, I didn't dream this up myself! Thanks for the input.
Sorry for the tardiness in responding, I spend a lot of time in the field.
The distribution system is a single point grounded wye meaning the only place the primary neutral is grounded is at the station XFMR. There is NO system neutral. At a glance, most people would assume it's a Delta.
There are 4 ground rods around the transformer pad/vault forming a ground ring. The arrestor ground and case grounds are tied to that. The case/neutral bond strap is lifted and a 600V insulated neutral ground is then carried to a ground rod located 20' from the ground ring. Three additional rods are added at intervals of 10' (bare copper may be used to these rods. The only purpose of the four rods in series to to provide a better ground. And, hey, I didn't dream this up myself! Thanks for the input.
Re: NESC Rule 97
Although the NESC does not call this a separately derived system, it meets the definition as spelled out in the NEC.
This connection does not provide a solid connection for a winding to winding fault containment, as the MGN system.
The derived neutral is not electrically connected to the supply conductors originating in another system.
Although the NESC does not call this a separately derived system, it meets the definition as spelled out in the NEC.
This connection does not provide a solid connection for a winding to winding fault containment, as the MGN system.
The derived neutral is not electrically connected to the supply conductors originating in another system.
Re: NESC Rule 97
Our end user is much as you'd expect in any medium sized city. Residential, commercial (shopping centers, etc.), large appartments (barracks) and a large amount of business-type occupancies. Again our current method of grounding was determined to be in compliance with Rule 97 of the NESC. I'm not so sure...should we be bonding it all together again? The problem we were having had nothing to do with RFI problems. Had to do with blowing things up. Our ground is mostly glacial till, which, as you know, means "forget a good ground." When we had lightning events or other massive faults we were finding the fault taking the neutral path into homes/offices. Doesn't do that anymore...but is it right?
Our end user is much as you'd expect in any medium sized city. Residential, commercial (shopping centers, etc.), large appartments (barracks) and a large amount of business-type occupancies. Again our current method of grounding was determined to be in compliance with Rule 97 of the NESC. I'm not so sure...should we be bonding it all together again? The problem we were having had nothing to do with RFI problems. Had to do with blowing things up. Our ground is mostly glacial till, which, as you know, means "forget a good ground." When we had lightning events or other massive faults we were finding the fault taking the neutral path into homes/offices. Doesn't do that anymore...but is it right?
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Re: NESC Rule 97
I gave a code update class at ft lewis last year. Most of the time there are article that don't apply, for example art 555 on marinas has limited application for most users, but at ft lewis they have a marina, they have modulars, signs, and so on. I was very impressed with the scope of their operation.
And as far as grounding, the glacerial till makes a very poor ground, we have the same soil conditions where I am.
My suggestion would be to use a ufer ground at all new locations.
I gave a code update class at ft lewis last year. Most of the time there are article that don't apply, for example art 555 on marinas has limited application for most users, but at ft lewis they have a marina, they have modulars, signs, and so on. I was very impressed with the scope of their operation.
And as far as grounding, the glacerial till makes a very poor ground, we have the same soil conditions where I am.
My suggestion would be to use a ufer ground at all new locations.
charlie
Senior Member
- Location
- Indianapolis
Re: NESC Rule 97
Ruth, I recommend you install a MGN and get rid of your single-point grounded wye 13.8V distribution. The reason behind the recommendation is that I know nothing about your system
Ruth, I recommend you install a MGN and get rid of your single-point grounded wye 13.8V distribution. The reason behind the recommendation is that I know nothing about your system
Re: NESC Rule 97
I was worried you were serious at first. Hundreds of miles of neutral and infrastructure changes would not be something we want our taxes spent on. Thank you so much for the Point of Contact! As I said before, we are currently grounding according to what we believe is the intent of the NESC. Differing opinions tend to make you doubt yourself, but also help you learn. I am anxious to hear Mr. Clapp's opinion. Thanks again!
I was worried you were serious at first. Hundreds of miles of neutral and infrastructure changes would not be something we want our taxes spent on. Thank you so much for the Point of Contact! As I said before, we are currently grounding according to what we believe is the intent of the NESC. Differing opinions tend to make you doubt yourself, but also help you learn. I am anxious to hear Mr. Clapp's opinion. Thanks again!
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