Choosing a NEC Compliant PV System Interconnection Point in an Existing Electrical Distribution System

When it comes to choosing an interconnection point for your PV system, it may be tempting to connect to the nearest electrical distribution equipment to save money on cable and conduit. However, it's essential to choose a NEC compliant interconnection point to ensure your system operates safely and effectively.

According to the National Electric Code (NEC), where distribution equipment or feeders are fed simultaneously by a primary source of electricity and one or more other power sources, the feeders or distribution equipment shall comply with the relevant section 705.12 (A) and 705.12(B). This means that any piece of equipment in the electrical distribution system that is being fed by both the primary source and the PV system must comply with the code.

Suppose you plan to connect a PV system to a distribution panel that is linked to a switchgear, which in turn is connected to the grid. In that case, you need to consider not only the distribution panel's compliance with 705.12 but also that of the switchgear. This is because the switchgear can be fed by both the PV system and the grid, and all the electrical components between the point of interconnection and the second power source must comply with the relevant NEC code.

When evaluating a PV interconnection point, it's recommended to start at the grid supply and move backward to a perspective point of interconnect to evaluate each piece of the multiple-fed equipment against code 705.12. This evaluation should include determining the location of the electrical panels, checking the condition of the electrical panels and breakers, examining the grounding and bonding system, and confirming the power source(s) to the electrical system.

The simplest way to connect a PV system to an existing electrical distribution system is to connect it to the service equipment (i.e., main switchgear, main switchboard, or main panel) rather than connecting to a secondary or tertiary panel. If you're going with the simple route, it's recommended to connect at the grid side of the main breaker. Alternatively, you can connect to the load side of the main breaker as long as you're connecting to the bus at the opposite end of the main breaker.

In conclusion, choosing a NEC compliant interconnection point for your PV system is critical for ensuring safe and effective operation. By evaluating the existing electrical distribution system, complying with NEC section 705.12, determining the interconnection point, installing the required equipment, and testing the system, you can be confident that your PV system is connected properly and meets code requirements. It's always advisable to work with a qualified electrical engineer to ensure the system is installed and connected safely.