What is a 'direct connection' under the definition of 'separately derived system'?

[BretHeilig]

Hey all,

Been re-reading my solar codes lately, and I can't get my brain around NEC 2011 100.1's definition of 'Separately Derived System'. It reads:

"A premises wiring system whose power is derived from a source of electric energy or equipment other than a service. Such systems have no direct connection from circuit conductors of one system to circuit conductors of another system, other than connections through the earth, metal enclosures, metallic raceways, or equipment grounding conductors"

So what's a 'direct connection'? Does wiring through a solar backfeed breaker count as a direct connection to circuit wiring? If that's so, basically no PV array is an SDS unless it is fully grid-independent, which would seem not to be a useful distinction to even bother making. Is there another way to read this?

Thanks all,


Bret

 

[Smart $]

Hey all,

Been re-reading my solar codes lately, and I can't get my brain around NEC 2011 100.1's definition of 'Separately Derived System'. It reads:

"A premises wiring system whose power is derived from a source of electric energy or equipment other than a service. Such systems have no direct connection from circuit conductors of one system to circuit conductors of another system, other than connections through the earth, metal enclosures, metallic raceways, or equipment grounding conductors"

So what's a 'direct connection'? Does wiring through a solar backfeed breaker count as a direct connection to circuit wiring? If that's so, basically no PV array is an SDS unless it is fully grid-independent, which would seem not to be a useful distinction to even bother making. Is there another way to read this?

Thanks all,


Bret

Your reasoning is sound.

An example of a direct connection would be a backup generator that connects through an ATS/MTS which does not switch the neutral.

 

[jaggedben]

A grid tie only solar system is not an SDS, since the premises wiring is directly connected to the inverter and the inverter cannot function without the grid in any case.

A totally off grid system would be considered an SDS, and would have to follow 250.30 and other applicable articles.

A system that is grid-interactive with battery backup could theoretically be either, but none that I have worked on have been an SDS; I'm also not aware of any major off-grid products that switch the neutral when they go into backup mode. On a first consideration I don't think it would make much sense to design a battery-backup system in that way.

 

[Zee]

Isn't the term used to distinguish "direct connection" from a transformer and how it transmits electrical energy as opposed to a "direct connection" of wire and how it conducts electrical current.......

Their reference to ground is, in effect, separately derived.

Cheers Bret! I know you from another life! :roll: