Urgent Alert

Secondary networks

Connecting generators in a secondary network area

Contact PG&E before installing your generator

If you plan to interconnect a generator in San Francisco or Oakland, contact the PG&E Electric Generation Interconnection (EGI) department during the planning stage of the project. If the planned generator site is located in an area served by a secondary network, you cannot export power to the grid. A non-export option may be available. Contact EGI with your plan details before buying or installing any equipment. We can conduct an engineering review, and then discuss your options with you.


Get details about non-export interconnection

Understanding secondary networks

PG&E generally has two types of electrical distribution systems: secondary network and radial. Secondary networks are designed to meet the higher reliability needs and limited space commonly found in urban areas. In the PG&E territory, only the downtown areas of San Francisco and Oakland are served by secondary network systems.


Discover how secondary networks work

In a secondary network, electricity is delivered through a highly integrated system of transformers and underground cables. Each cable is connected and operates in parallel. Power can flow in either direction on lower voltage service delivery lines, typically called secondary distribution lines.

The loss of a single line or transformer in a secondary network does not cause an interruption of power. This continuance of power is unlike that of radial systems, which have only one line and one path for power to flow. If a radial line experiences an outage, service is interrupted until repairs are made. Such power interruptions are less common in a secondary network.


Learn about network protectors

In secondary networks, devices called network protectors prevent power from "back-feeding" from one transformer through another. Network protectors are designed to break the circuit quickly when they detect back-feeding. Any power exported by a generator into this system is recognized as back-feeding by the network protectors.

Most network protectors in service are not designed or tested to function as switching or isolation devices for operating electric generators. This concern prevents PG&E from allowing energy generator installation within the areas served by secondary networks. For more information, view IEEE Standard C37.108-2002. Visit IEEE Xplore Digital Library


Criteria for installing secondary networks

PG&E considers the following criteria when installing secondary networks:

  • Density of the load
  • Economics
  • Other factors

Get more information on secondary networks. Download Electric Rule No. 2 Description of Service (PDF)

For a complete description of the PG&E distribution system, a glossary of technical terms is available from the PG&E Interconnection Handbook. Download Glossary (PDF)

Understand your options if a generator is located in a secondary network area

PG&E Electric Rule 21, Section I(3)(a), provides special considerations for new generating facilities to be installed on secondary networks in the distribution system. The special considerations are due to the design and operation of network protectors. Get more information on this topic. Download Electric Rule No. 21 Generating Facility Interconnections (PDF)

Note: If you request Self Generation Incentive Funds from PG&E for a project that is located in downtown Sacramento in the Sacramento Municipal Utility District (SMUD) service territory, which is also served by a secondary network, you must contact SMUD for their policy regarding the interconnection of generators to secondary networks.

More resources for interconnection

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