continuous grounding conductor
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Ed MacLaren
Senior Member
Re: continuous grounding conductor
If by "continuous grounding conductor" you mean an equipment grounding conductor, the answer is yes.
In the sketch, the 208/120 volt system is a Separately Derived System (SDS).
Ed
[ April 07, 2003, 10:59 PM: Message edited by: Ed MacLaren ]
If by "continuous grounding conductor" you mean an equipment grounding conductor, the answer is yes.
In the sketch, the 208/120 volt system is a Separately Derived System (SDS).
Ed
[ April 07, 2003, 10:59 PM: Message edited by: Ed MacLaren ]
Ed MacLaren
Senior Member
Re: continuous grounding conductor
The padmount transformer in the sketch above supplies the 480 volt building service (System 2). My "interpretation" of the SDS definition is "a system that derives it's energy from a source other than the building or facility's service", so to me it is not.
However, the 480 volt system (service) is definitely "derived separately" from the 7200 volt distribution system. (System 1)
So if the 7200 volt system was the service to the facility, than System 2 would be an SDS.
Ed
[ April 10, 2003, 07:40 AM: Message edited by: Ed MacLaren ]
I suppose it depends on one's definition of what an SDS is.
The padmount transformer in the sketch above supplies the 480 volt building service (System 2). My "interpretation" of the SDS definition is "a system that derives it's energy from a source other than the building or facility's service", so to me it is not.
However, the 480 volt system (service) is definitely "derived separately" from the 7200 volt distribution system. (System 1)
So if the 7200 volt system was the service to the facility, than System 2 would be an SDS.
Ed
[ April 10, 2003, 07:40 AM: Message edited by: Ed MacLaren ]
Re: continuous grounding conductor
A service to a premises can only be supplied, or derived. This is an accepted engineering standard.
Are you saying the padmount is a supplied source, and the user end transformer is derived from a source?
[ April 10, 2003, 01:10 AM: Message edited by: bennie ]
A service to a premises can only be supplied, or derived. This is an accepted engineering standard.
Are you saying the padmount is a supplied source, and the user end transformer is derived from a source?
[ April 10, 2003, 01:10 AM: Message edited by: bennie ]
- Location
- Illinois
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- retired electrician
Re: continuous grounding conductor
Bennie,
The primary to both transformers are "supplied sources". The secondary side of both transformers are "derived sources". The 'derived source'(secondary side) of a transformer becomes the supply source for all the equipment served by that transformer, including any additional transformers.
Don
Bennie,
The primary to both transformers are "supplied sources". The secondary side of both transformers are "derived sources". The 'derived source'(secondary side) of a transformer becomes the supply source for all the equipment served by that transformer, including any additional transformers.
Don
- Location
- Illinois
- Occupation
- retired electrician
Re: continuous grounding conductor
Bennie,
Thats not from any source that I know of. It is just how I read the code.
Don
Bennie,
Thats not from any source that I know of. It is just how I read the code.
Don
- Location
- Illinois
- Occupation
- retired electrician
Re: continuous grounding conductor
Bennie,
The code requires that the grounding electrode for the transformer be as near as practicable to and preferably in the same area as the transformer. The service grounding electrode could be used for this. In any case no matter what electrode is used at the transformer it is bonded to the service grounding electrode.
Don
Bennie,
The code requires that the grounding electrode for the transformer be as near as practicable to and preferably in the same area as the transformer. The service grounding electrode could be used for this. In any case no matter what electrode is used at the transformer it is bonded to the service grounding electrode.
Don
Re: continuous grounding conductor
The way I read bennie's last post was questioned if the Xo of the SDS ( the right-hand transformer in Ed's diagram ) could be connected to the building ground.
Assuming he meant "effectively grounded structural metal member of the structure" as in 250.30(A)(4)(1), yes , that is the first choice per the 2002 NEC.
The actual connection to the Xo can only be done at the same point as the bonding Jumper of 250.30(A)(1) [ last sentence ] or as per 250.30(A)(2))(a) [ last sentence ].
Glenn
The way I read bennie's last post was questioned if the Xo of the SDS ( the right-hand transformer in Ed's diagram ) could be connected to the building ground.
Assuming he meant "effectively grounded structural metal member of the structure" as in 250.30(A)(4)(1), yes , that is the first choice per the 2002 NEC.
The actual connection to the Xo can only be done at the same point as the bonding Jumper of 250.30(A)(1) [ last sentence ] or as per 250.30(A)(2))(a) [ last sentence ].
Glenn
Re: continuous grounding conductor
Effectively grounded structural members are bonded only if there is a low impedance ground ring around the building. Each structural member must be welded to the ground ring.(Shorted)
There is not many buildings with effectively grounded structural members, bonded to make one electrode.
When the ground for a transformer ends at the building ground, why not go there direct?
Effectively grounded structural members are bonded only if there is a low impedance ground ring around the building. Each structural member must be welded to the ground ring.(Shorted)
There is not many buildings with effectively grounded structural members, bonded to make one electrode.
When the ground for a transformer ends at the building ground, why not go there direct?
Re: continuous grounding conductor
Someone please explain how a transformer, if part of listed service equipment, can be connected to the building ground electrode?
A transformer one foot away from the listed equipment must be connected to a structural member or water pipe.
This is nonsense, and only shows the popular understanding of a separately derived system, is hogwash.
Someone please explain how a transformer, if part of listed service equipment, can be connected to the building ground electrode?
A transformer one foot away from the listed equipment must be connected to a structural member or water pipe.
This is nonsense, and only shows the popular understanding of a separately derived system, is hogwash.
- Location
- Massachusetts
Re: continuous grounding conductor
)
However a lot of the buildings we do here have a grounding ring with the building columns cad welded to the ring.
In a building with a steel "skeleton" how are these members not bonded, they are either welded or bolted solidly together (one would hope
)However a lot of the buildings we do here have a grounding ring with the building columns cad welded to the ring.
Re: continuous grounding conductor
Bennie, do you have access to the 2002 handbook? If so look at exhibit 250.15. It shows the wooden frame building you are referring too. If you do not have a copy it is simple a common ground electrode cable that starts at the water pipe and rises through the structure in which each transformer is bonded via "H" tap.
Although the buildings I work with are steel frame or poured concrete structures, exhibit 250.15 is precisely how I have been treating transformers for years. It forms the single point ground and prevents common mode current sort of. I say "sort of" because unless you isolate the raceways and equipment from incidental contact from the building structures like concrete, framework, and rebar-it is not really single point anymore. No one goes to that kind of trouble except some specialized industries.
Before anybody blast me about going to building steel or pipe nearby I do, but the primary path is dedicated to the building electrode system.
Bennie, do you have access to the 2002 handbook? If so look at exhibit 250.15. It shows the wooden frame building you are referring too. If you do not have a copy it is simple a common ground electrode cable that starts at the water pipe and rises through the structure in which each transformer is bonded via "H" tap.
Although the buildings I work with are steel frame or poured concrete structures, exhibit 250.15 is precisely how I have been treating transformers for years. It forms the single point ground and prevents common mode current sort of. I say "sort of" because unless you isolate the raceways and equipment from incidental contact from the building structures like concrete, framework, and rebar-it is not really single point anymore. No one goes to that kind of trouble except some specialized industries.
Before anybody blast me about going to building steel or pipe nearby I do, but the primary path is dedicated to the building electrode system.
Re: continuous grounding conductor
Bob: Do you think the rusted, painted, monocoat covered, loose, steel makes a credible ground electrode, when splices are not permitted in a ground electrode conductor?
Would you think the steel makes a better electrode when the building electrode is the same distance or less.
The grounding requirements, for a separately derived system, were written when the premises wiring system did not have a ground electrode system.
This is why there is no reference to the building ground, it did not exist at the time.
Bob: Do you think the rusted, painted, monocoat covered, loose, steel makes a credible ground electrode, when splices are not permitted in a ground electrode conductor?
Would you think the steel makes a better electrode when the building electrode is the same distance or less.
The grounding requirements, for a separately derived system, were written when the premises wiring system did not have a ground electrode system.
This is why there is no reference to the building ground, it did not exist at the time.
Re: continuous grounding conductor
Dereck: You are correct, except for mentioning the equipment ground conductor from the building ground to the secondary of the transformer.
When current is on both the building ground, and the transformer ground, there will be common mode voltage between the neutral and ground. They both terminate at the water pipe, but originate at different locations.
Dereck: You are correct, except for mentioning the equipment ground conductor from the building ground to the secondary of the transformer.
When current is on both the building ground, and the transformer ground, there will be common mode voltage between the neutral and ground. They both terminate at the water pipe, but originate at different locations.
- Location
- Massachusetts
Re: continuous grounding conductor
Bennie, It is a system that seems to work just fine, after all along with building steel you also end up connected to the equipment grounding conductor.
I know you are going to say something about parallel paths and I will not pretend to understand all of the intricacies of this like "common mode current", but for the literally hundreds of thousands buildings done this way and the limited problems arising it seems like it works.
As I asked you before how would you like to see it done, forgetting about the NEC?
Bennie, It is a system that seems to work just fine, after all along with building steel you also end up connected to the equipment grounding conductor.
I know you are going to say something about parallel paths and I will not pretend to understand all of the intricacies of this like "common mode current", but for the literally hundreds of thousands buildings done this way and the limited problems arising it seems like it works.
As I asked you before how would you like to see it done, forgetting about the NEC?
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