is a house a "separately derived system"?
- Thread starter rain252
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- Location
- Massachusetts
No as far as the NEC is concerned.
Think transformers, generators, batteries etc. those are, or can be, separately derived systems.
Think transformers, generators, batteries etc. those are, or can be, separately derived systems.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
I agree with Bob (haven't been doing that much, lately 
).
I do have a slightly different take on this than some Forum members. But I submit that the word "system," in the phrase "separately derived system," refers to the transformer secondary, and all downstream feeders, panels, branch circuits, and outlet devices. I further submit that the words, "separately derived" are referring to the point at which this particular "separately derived system" originates." In other words, it is "derived" by the transformer (or generator, or battery, or UPS, or other source), but it includes more than just the transformer. Therefore, I cringe when anyone asks if a transformer is an SDS. It is not. But a transformer can be the point at which the SDS is "derived."
Generally, a utility will not serve only one home with a pole-mounted transformer. The point at which power is delivered to the house is the meter. The home's electrical system starts at the meter, not at a transformer, and is therefore not an SDS.
). I do have a slightly different take on this than some Forum members. But I submit that the word "system," in the phrase "separately derived system," refers to the transformer secondary, and all downstream feeders, panels, branch circuits, and outlet devices. I further submit that the words, "separately derived" are referring to the point at which this particular "separately derived system" originates." In other words, it is "derived" by the transformer (or generator, or battery, or UPS, or other source), but it includes more than just the transformer. Therefore, I cringe when anyone asks if a transformer is an SDS. It is not. But a transformer can be the point at which the SDS is "derived."
Generally, a utility will not serve only one home with a pole-mounted transformer. The point at which power is delivered to the house is the meter. The home's electrical system starts at the meter, not at a transformer, and is therefore not an SDS.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Well, one could say that the electrical system supplying power to the house is. "SDS" seems to imply no DC connection between the system in question and the rest of the universe. Is there a "solidly-connected neutral?"rain252 said:
From the house's perspective, since the power is delivered from the outside world, it's not an SDS. If, on the other hand, a house were "off the grid" and self-sufficient as far as electricity isw concerned, then yes, it could be called an DS.
bphgravity
Senior Member
- Location
- Florida
The definition of SDS clearly states, "A premises wiring system whose power is derived from a source of electrical energy or equipment OTHER THAN A SERVICE." Service definition, "The conductors and equipment for delivering electrical energy from the SERVING UTILITY to the wiring system of the premises served.
That sums it up.
That sums it up.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
It also says:
" . . . and that has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system."
Having an inter-tied grounded conductor (neutral) renders a system that is otherwise "OTHER THAN A SERVICE" no longer an SDS, meaning that your definition is less that 100%.
I merely meant that a utility supply is a transformer, but now that I think about it, since the primary and secondary grounded conductors are inter-connected, it is clearly not an SDS.
Never mind.
" . . . and that has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system."
Having an inter-tied grounded conductor (neutral) renders a system that is otherwise "OTHER THAN A SERVICE" no longer an SDS, meaning that your definition is less that 100%.
I merely meant that a utility supply is a transformer, but now that I think about it, since the primary and secondary grounded conductors are inter-connected, it is clearly not an SDS.
Never mind.
- Location
- Bremerton, Washington
- Occupation
- Master Electrician
Actually a house is fed from a transformer and its really a SDS. But the rules for electrons change when we have a meter. I think this is what you are asking and the other answers gave you the code definition. If you draw it out it looks just like an SDS inside a building.
But knowing the definitions allows you to understand what rules to apply.
But knowing the definitions allows you to understand what rules to apply.
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