National Grid
Secondary Area Networks and Secondary Spot Networks

While National Grid serves the vast majority of its customers from radial primary overhead distribution systems, DG installations on distribution secondary network systems require study to ensure the DG does not degrade the reliability, power quality, safety, or operation of the network system. Therefore, customers in the downtown districts of Brockton, Lynn or Worcester should contact National Gridís Distributed Generation Services (DGS) department ( to determine if the proposed location is served by a distribution secondary network system.

Customers can also click here to view maps of National Gridís Secondary Networks.

This should be done while the project is still in the planning stage, and certainly before purchasing equipment or beginning installation. If it is determined that the proposed location is served by a secondary network, National Gridís DGS will review the Customerís plans and discuss options with the Customer.

More about Secondary Networks

Unlike radial distribution systems that deliver power to each customer in a single path from source to load, underground secondary area network systems deliver power to each customer through a complex and integrated system of multiple transformers and underground cables that are connected and operate in parallel.

The connection of customer DG on networks is an emerging topic, which poses some issues for National Grid to maintain adequate voltage and worker safety and has the potential to cause the power flow on network feeders to shift (reverse) causing network protectors within the network grid to trip open. Therefore, to ensure network safety and reliability, additional information will be required for National Gridís analysis:

  • Customerís existing* or proposed electric demand profile showing minimum load during peak generation time,
  • Customerís expected generation profile shown for a 24-hour period and typical 7-day duration, and
  • Customerís complete electric service single-line diagram showing the configuration of the proposed generation and other metered tenants, if any, up to the service point supplied by National Gridís secondary network EPS.

  • * In addition, National Grid may need to install recording equipment at all meters to determine the total demand of the network service when obtaining the service connectionís electric demand profile.

For more technical information on parallel generator installations, please refer to the Companyís ESB 756 and its Appendix C on the Companyís web site at: /non_html/shared_constr_esb756.pdf.