PJM Interconnection (PJM)

PJM is a regional transmission organization (RTO) that coordinates the movement of wholesale electricity in all or parts of Delaware, Illinois, Indiana, Kentucky, Maryland, Michigan, New Jersey, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, and the District of Columbia. PJM acts as an Independent System Operator (ISO), operates a competitive wholesale electricity market in its market area, and manages the high-voltage electricity grid to ensure reliability. PJM is also responsible for long-term regional transmission planning. 

PJM originally formed as a power pool in 1927 by three utilities for the purpose of sharing generation resources. Additional utilities joined the pool in 1956, 1965, and 1981. 

The history of PJM


PJM began its transition to an ISO in 1993 when the PJM Interconnection Association was formed to administer the power pool. In 1997, PJM became a fully independent organization. At that time, membership was opened to non-utilities, and an independent Board of Managers was elected.

On April 1, 1997, PJM opened its first bid-based energy market. Later that year, the Federal Energy Regulatory Commission (FERC) approved PJM as the nation’s first fully functioning ISO. PJM became the nation’s first fully functioning RTO in 2002. Since then PJM has continued to grow by integrating additional utility transmission systems into its operations. 


Map of PJM showing the various transmission zones
Source: PJM website