NORTHEAST UTILITIES SYSTEM Exhibit 21 SUBSIDIARIES OF THE REGISTRANT Northeast Utilities The Connecticut Light and Power Company (100%) - CL&P Capital, L.P. (3%) - Research Park, Inc. (100%) - The City and Suburban Electric and Gas Company (100%) - Electric Power Incorporated (100%) - The Connecticut Transmission Corporation (100%) - The Nutmeg Power Company (100%) - The Connecticut Steam Company (100%) - Connecticut Yankee Atomic Power Company (34.5%) - Yankee Atomic Electric Company (24.5%) - Maine Yankee Atomic Power Company (12%) - Vermont Yankee Nuclear Power Corporation (9.5%) Public Service Company of New Hampshire (100%) - Properties, Inc. (100%) - New Hampshire Electric Company (100%) - Connecticut Yankee Atomic Power Company (5%) - Yankee Atomic Electric Company (7%) - Maine Yankee Atomic Power Company (5%) - Vermont Yankee Nuclear Power Corporation (4%) North Atlantic Energy Corporation (100%) North Atlantic Energy Service Corporation (100%) Western Massachusetts Electric Company (100%) - Connecticut Yankee Atomic Power Company (9.5%) - Yankee Atomic Electric Company (7%) - Maine Yankee Atomic Power Company (3%) - Vermont Yankee Nuclear Power Corporation (2.5%) Holyoke Water Power Company (100%) - Holyoke Power and Electric Company (100%) Charter Oak Energy, Inc. (100%) - Charter Oak (Paris) Inc. (100%) - COE Development Corporation (100%) - COE (UK) Corp. (79.9%) - COE (Gencoe) Corp. (49%) - COE (UK) Corp. (20.1%) - COE Argentina I Corp. (100%) - COE Argentina II Corp. (100%) - COE Tejona Corporation (100%) - COE Ave Fenix Corporation (100%) Northeast Nuclear Energy Company (100%) Northeast Utilities Service Company (100%) The Quinnehtuk Company (100%) The Rocky River Realty Company (100%) Mode 1 Communications, Inc. (100%) NUSCO Energy Partners, Inc. (100%) HEC Inc. (100%) - HEC International Corporation (100%) - HEC Energy Consulting Canada, Inc. (100%) - Southwest HEC Energy Services L.L.C. (100%)