Is my house a separately derived system?
- Thread starter unsaint34
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- Location
- Massachusetts
Re: Is my house a separately derived system?
It might be but your house is fed by the utility, how that is done is not covered by the NEC and it's definitions.
It might be but your house is fed by the utility, how that is done is not covered by the NEC and it's definitions.
Re: Is my house a separately derived system?
How is NOT seperately derived?
Check the definitions in 100:
Separately Derived System.
A premises wiring system whose power is derived from a ... transformer, ... that has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.
Do windings count as "direct electrical connection"?
How is NOT seperately derived?
Check the definitions in 100:
Separately Derived System.
A premises wiring system whose power is derived from a ... transformer, ... that has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.
Do windings count as "direct electrical connection"?
- Location
- Massachusetts
Re: Is my house a separately derived system?
Celtic we can call it a separately derived system if we want.
To the NEC that utility owned transformer does not exist.
Let me ask this;
When grounding the service to this house do we follow 250.24 Grounding Service-Supplied Alternating-Current Systems or do we follow 250.30 Grounding Separately Derived Alternating-Current Systems?
[ March 30, 2005, 06:33 PM: Message edited by: iwire ]
Celtic we can call it a separately derived system if we want.
To the NEC that utility owned transformer does not exist.
Let me ask this;
When grounding the service to this house do we follow 250.24 Grounding Service-Supplied Alternating-Current Systems or do we follow 250.30 Grounding Separately Derived Alternating-Current Systems?
[ March 30, 2005, 06:33 PM: Message edited by: iwire ]
pierre
Senior Member
- Location
- Westchester County, New York
Re: Is my house a separately derived system?
Read the definition of SERVICE in Art 100, then read the definition of SEPARATELY DERIVED in Art 100.
Service mentions from the serving UTILITY, separately derived system does not.
Read the definition of SERVICE in Art 100, then read the definition of SEPARATELY DERIVED in Art 100.
Service mentions from the serving UTILITY, separately derived system does not.
Re: Is my house a separately derived system?
Please be open minded about why I still think my house might be a separately derived system. (I'm not trying to prove anyone wrong. I just wanted to learn accurately.)
THIS IS THE DEFINITION FROM ART 100:
A premises wiring system whose power is derived from a battery, from a solar photo system, or from a generator, TRANSFORMER, ... and that has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors orginating in another system.
THIS IS HOW I INTERPRETED IT.
That definition doesn't say anything about "utility." The tranformer that feeds my house is a isoltation transformer, which means that the secondary and the primary has absolutely NO electrical connection. Therefore the service drop, the serivice conductors, and my house system (the secondary side) has NO electrical connection, including a solidly connected grounded circuit conductor, to the primary side of the transformer. The conductors that are "electrically" connected to the primary side of the transformer are supply conductors orginating in another system.
Please be open minded about why I still think my house might be a separately derived system. (I'm not trying to prove anyone wrong. I just wanted to learn accurately.)
THIS IS THE DEFINITION FROM ART 100:
A premises wiring system whose power is derived from a battery, from a solar photo system, or from a generator, TRANSFORMER, ... and that has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors orginating in another system.
THIS IS HOW I INTERPRETED IT.
That definition doesn't say anything about "utility." The tranformer that feeds my house is a isoltation transformer, which means that the secondary and the primary has absolutely NO electrical connection. Therefore the service drop, the serivice conductors, and my house system (the secondary side) has NO electrical connection, including a solidly connected grounded circuit conductor, to the primary side of the transformer. The conductors that are "electrically" connected to the primary side of the transformer are supply conductors orginating in another system.
Re: Is my house a separately derived system?
Okay I just read the definition of "service." It sounds like Service includes all the conductors and equipment, including "transformers." Therefore even if the transformer is a isolation transformer, that is still considered a "service." Therefore my house is fed by "service."
I got it.
thanks guys.
Okay I just read the definition of "service." It sounds like Service includes all the conductors and equipment, including "transformers." Therefore even if the transformer is a isolation transformer, that is still considered a "service." Therefore my house is fed by "service."
I got it.
thanks guys.
- Location
- Massachusetts
Re: Is my house a separately derived system?
Here is how I see it.
In reality the transformer feeding service to your house fits the description of an SDS just as well as a customer owned 480-208Y/120 transformer.
However as I said before that utility owned transformer does not exist to the NEC. If we try to call your service an SDS we would end up using the wrong code sections for grounding.
As important as knowing the NEC definitions is knowing the scope of the NEC. What it covers and what it does not cover.
JMO, Bob
I try to keep an open mind and we are all here to learn.
Here is how I see it.
In reality the transformer feeding service to your house fits the description of an SDS just as well as a customer owned 480-208Y/120 transformer.
However as I said before that utility owned transformer does not exist to the NEC. If we try to call your service an SDS we would end up using the wrong code sections for grounding.
As important as knowing the NEC definitions is knowing the scope of the NEC. What it covers and what it does not cover.
Considering the NEC stops at the service point...
...in my opinion it is wrong to try to apply NEC definitions to equipment beyond the service point.
JMO, Bob
Re: Is my house a separately derived system?
I'm definitely open to being educated here.
carl
Just an observation: If it is truly isolated, it would be the first one I ever saw. Our utility guys could better speak to this than I, but, my understanding is all single phase, residential utility xfmrs are bonded from the primary neutral to the secondary neutral (high probability of oddball exceptions noted).
Note to iwire: There isn't much difference in the grounding between the two is there? Don't both use table 250.66?
I'm definitely open to being educated here.
carl
- Location
- Massachusetts
Re: Is my house a separately derived system?
Grounding a service following SDS grounding methods would (should ) result in a failure.
Most times grounding an SDS is as simple as connecting it to the nearest building steel and your done.
As we all know that is almost never enough for a service.
Carl your right the rules are similar but they are not the same.
Grounding a service following SDS grounding methods would (should
) result in a failure.Most times grounding an SDS is as simple as connecting it to the nearest building steel and your done.
As we all know that is almost never enough for a service.
- Location
- Illinois
- Occupation
- retired electrician
Re: Is my house a separately derived system?
coulter,
Don
coulter,
And so are our SDS's. Maybe not as directly but the primary grounded conductor is bonded to the secondary grounded conductor via the equipment grounding conductors and the main/system bonding jumpers.
Don
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