Mike Dolt Enterprises
Mike Dolt Enterprises
User: ggunn, Location: Austin, TX, USA
Asked on: Monday, March 14, 2011 at 12:33 pm EDT
Answered on: Tuesday, May 14, 2024 at 2:47 am EDT
Question: Is a grid tied PV system a separately derived system or not? One article in the NEC2008 says it is with no disclaimer. Another says that it "may be" provided it has no direct electrical connection to another source. What is a direct connection? Is a connection through a breaker considered direct? And then there's the language about having "no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system".The output of a grid tied PV system is by definition connected to the grid. The grounds are connected as well. Does that mean it cannot be considered to be separately derived?
Separately Derived System Definition
According to the National Electrical Code (NEC), a separately derived system is one that: Has no direct electrical connection to any other electrical source Has its own grounding electrode system that is electrically isolated from any other grounding electrode system Has overcurrent protection devices that are independent of the overcurrent protection devices protecting any other electrical source
Grid-Tied PV Systems
Are connected to the grid through an inverter Share the same grounding electrode system as the grid Are protected by overcurrent protection devices on the grid side of the inverter
Analysis
Based on the NEC definition, grid-tied PV systems do not meet the criteria of a separately derived system because: They have a direct electrical connection to the grid They share the same grounding electrode system as the grid
Use of the Term "May Be"
The article that states grid-tied PV systems "may be" considered separately derived likely refers to systems that have a direct electrical connection to the grid through a transformer. In this case, the transformer can provide electrical isolation and allow the PV system to be considered separately derived.
Direct Connection
A direct connection is any electrical connection that does not pass through an isolation device such as a transformer. A connection through a breaker is considered a direct connection.
Conclusion
Grid-tied PV systems that are connected to the grid through an inverter
are not separately derived systems according to the NEC. Flag for review