fc
Senior Member
- Location
- New Jersey
When you size the GEC for a separately derived ac system (Transformer) Do you size it to the Primary conductors or the secondary conductors?
Table 250.66
- Thread starter fc
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Re: Table 250.66
Primary conductors have to have a EGC based on the size of the OCPD or use the conduit, and does not have anything to do with the GEC. The GEC is based on the size of the secondary conductors. Read 250.30(2)(a)
[ May 21, 2003, 07:35 PM: Message edited by: dereckbc ]
Primary conductors have to have a EGC based on the size of the OCPD or use the conduit, and does not have anything to do with the GEC. The GEC is based on the size of the secondary conductors. Read 250.30(2)(a)
[ May 21, 2003, 07:35 PM: Message edited by: dereckbc ]
fc
Senior Member
- Location
- New Jersey
Re: Table 250.66
250.30 (2)A sized in accordance with 250.66 for the derived phase conductors. The derived phase conductors are the primary conductors?
250.30 (2)A sized in accordance with 250.66 for the derived phase conductors. The derived phase conductors are the primary conductors?
Re: Table 250.66
I know everyone is correct according to the present day understanding.
I still stick to my understanding, as taught in technical trade schools 50 years ago.
The transformer equipment ground, and earth ground, is the same conductor.
Will someone supply me the technical data for having a ground wire, on the neutral of a transformer, based on the size of the active conductors?
I can understand having a ground wire to the earth, on the premises wiring system.
There is no reference, in the code book, that a transformer is a separately derived system.
I challenge anyone to prove the grounding requirements for a separately derived system have anything to do with a transformer.
I know everyone is correct according to the present day understanding.
I still stick to my understanding, as taught in technical trade schools 50 years ago.
The transformer equipment ground, and earth ground, is the same conductor.
Will someone supply me the technical data for having a ground wire, on the neutral of a transformer, based on the size of the active conductors?
I can understand having a ground wire to the earth, on the premises wiring system.
There is no reference, in the code book, that a transformer is a separately derived system.
I challenge anyone to prove the grounding requirements for a separately derived system have anything to do with a transformer.
- Location
- Lockport, IL
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- Semi-Retired Electrical Engineer
Re: Table 250.66
Separately Derived System. A premises wiring system whose power is derived from a battery, from a solar photovoltaic system, or from a generator, transformer, or converter windings, and that has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.
A ?transformer? is not a ?separately derived system,? any more than a ?heat pump? is a ?HVAC System.? But a separate system can be derived from a transformer, and that transformer will be a component of the ?separately derived system.? This is from the Article 100 Definitions:
Separately Derived System. A premises wiring system whose power is derived from a battery, from a solar photovoltaic system, or from a generator, transformer, or converter windings, and that has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.
skd76
Member
- Location
- California
Re: Table 250.66
FC - You asked "The derived phase conductors are the primary conductors? "
No, the "derived" conductors would be the new voltage or the new system. You size the grounding electrode conductor by the new derived conductors. Most of the time that will be conductors attached to the secondary side of the xfmr.
FC - You asked "The derived phase conductors are the primary conductors? "
No, the "derived" conductors would be the new voltage or the new system. You size the grounding electrode conductor by the new derived conductors. Most of the time that will be conductors attached to the secondary side of the xfmr.
Re: Table 250.66
The derived system is the one not electrically connected to the supply source of another system.
Electrically connected means capable of carrying current. This does not state "must carry current".
The original definition was; Premises wiring with no external connections. Magnetic coupling is not considered electrical connection.
[ May 22, 2003, 06:36 PM: Message edited by: bennie ]
The derived system is the one not electrically connected to the supply source of another system.
Electrically connected means capable of carrying current. This does not state "must carry current".
The original definition was; Premises wiring with no external connections. Magnetic coupling is not considered electrical connection.
[ May 22, 2003, 06:36 PM: Message edited by: bennie ]
brian john
Senior Member
- Location
- Leesburg, VA
Re: Table 250.66
A transformer (depending on type) can and in most cases is a separately derived system. The secondary/load side/output has no wired connection to the primary/line side/input, other than through the grounding system. This hasn't changed in 50 years. The Grounding electrode Conductor (GEC) is based on the secondary phase conductors, whether the transformer is a step up or step down transformer. If the transformer is an autotransformer the transformer is not a separately derived system. There is a wired connection between the line and load whether it is a boost or buck autotransformer.
A transformer (depending on type) can and in most cases is a separately derived system. The secondary/load side/output has no wired connection to the primary/line side/input, other than through the grounding system. This hasn't changed in 50 years. The Grounding electrode Conductor (GEC) is based on the secondary phase conductors, whether the transformer is a step up or step down transformer. If the transformer is an autotransformer the transformer is not a separately derived system. There is a wired connection between the line and load whether it is a boost or buck autotransformer.
Re: Table 250.66
Except under fault conditions, which is the WHY of GEC's and EGC's the grounding conductors do not carry current, (current carrying Circuit Conductor of feeders and branch circuits).
Though the EGC's may not be so defined in the NEC, I do believe that is what is intended by the grounding requirements of 250.30.
Except under fault conditions, which is the WHY of GEC's and EGC's the grounding conductors do not carry current, (current carrying Circuit Conductor of feeders and branch circuits).
Though the EGC's may not be so defined in the NEC, I do believe that is what is intended by the grounding requirements of 250.30.
Re: Table 250.66
Without a GEC or EGC, what carries fault current in say a winding to winding fault? With this said I would think that all grounding would in effect connect all systems electrically (technically no SDS's) unless truly isolated.
I will leave this alone now.
Roger
[ May 22, 2003, 07:22 PM: Message edited by: roger ]
Without a GEC or EGC, what carries fault current in say a winding to winding fault? With this said I would think that all grounding would in effect connect all systems electrically (technically no SDS's) unless truly isolated.
I will leave this alone now.
Roger
[ May 22, 2003, 07:22 PM: Message edited by: roger ]
Re: Table 250.66
Separately derived system...A premises wiring system.
Show me where a transformer is a premises wiring system.
No, a transformer has not been considered a separately derived system for 50 years. There is no technical publication to substantiate this determination.
I recommend anyone who wants to prove me wrong, do so. The records are at the NEC archives describing the beginning and evolution of systems without external connections, later changed to separately derived systems.
Separately derived system...A premises wiring system.
Show me where a transformer is a premises wiring system.
No, a transformer has not been considered a separately derived system for 50 years. There is no technical publication to substantiate this determination.
I recommend anyone who wants to prove me wrong, do so. The records are at the NEC archives describing the beginning and evolution of systems without external connections, later changed to separately derived systems.
Re: Table 250.66
I know many are tired of my addressing this subject, so many times.
Thanks Roger, you are apparently the only one who has read the history and development of a separately derived system.
The reason I am obsessed with this issue is, I feel the grounding method for a separtely derived system only applies to the premises wiring, not to the source.
Power sources are all connected according to engineering standards, not by someones fabricated explanation of words they don't understand.
I know many are tired of my addressing this subject, so many times.
Thanks Roger, you are apparently the only one who has read the history and development of a separately derived system.
The reason I am obsessed with this issue is, I feel the grounding method for a separtely derived system only applies to the premises wiring, not to the source.
Power sources are all connected according to engineering standards, not by someones fabricated explanation of words they don't understand.
brian john
Senior Member
- Location
- Leesburg, VA
Re: Table 250.66
Roger:
In reality the earth is a grounding conductor. While soil is not the best current carrying conductor, it is required to be part of electrical systems. Therefore there are no separately derived systems
Roger:
In reality the earth is a grounding conductor. While soil is not the best current carrying conductor, it is required to be part of electrical systems. Therefore there are no separately derived systems
brian john
Senior Member
- Location
- Leesburg, VA
Re: Table 250.66
Bennie:
I'm new to this site so please humor me, and give me your explantion for your belief.
Bennie:
I'm new to this site so please humor me, and give me your explantion for your belief.
Re: Table 250.66
Brian,
Roger
Brian,
Your last sentence is not correct. This is the point of the argument. Simply stated, take a true isolated transformer, winding voltage to winding voltage,(magnetic coupling only) no grounding, and you have an SDS. All others, although maybe not auto transformers by definition, do have a common connection, more than magnetic coupling.
Roger
Re: Table 250.66
Roger is correct. A transformer that has the secondary star point connected to the supply source transformer star point, is not a separately derived system.
I am making these statements repeatedly, in hopes of getting the powers above to pay some attention to how corrupted the definition of a separately derived system has become.
The definition...A separately derived system is a premises wiring system.
Roger is correct. A transformer that has the secondary star point connected to the supply source transformer star point, is not a separately derived system.
I am making these statements repeatedly, in hopes of getting the powers above to pay some attention to how corrupted the definition of a separately derived system has become.
The definition...A separately derived system is a premises wiring system.
brian john
Senior Member
- Location
- Leesburg, VA
Re: Table 250.66
Roger:
And you support this as a viable system to use for standard distribution. Lastly there is capcitive grounding of the ungrounded transformer.
Roger:
And you support this as a viable system to use for standard distribution. Lastly there is capcitive grounding of the ungrounded transformer.
brian john
Senior Member
- Location
- Leesburg, VA
Re: Table 250.66
Bennie:
I am trying to have an understanding of why you feel this is a necessary discussion. Please if you could take the time to explain WHY oh WHY.
What's the significance.
Bennie:
I am trying to have an understanding of why you feel this is a necessary discussion. Please if you could take the time to explain WHY oh WHY.
What's the significance.
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