This excerpt taken from the PCG 10-K filed Feb 18, 2005.
Day-Ahead Market Congestion Management
Prior to the start of the ISO Day-Ahead process, the ETC Facilitator will provide the ISO with an hourly reservation for ETC schedules utilizing Path 15. The ISO will determine the hourly amount of the Path 15 operating limit available for New Firm Uses3 for use in its Congestion Management Process4 by subtracting the ETC megawatt reservation amount from the operating limit for Path 15 for each hour. After the deadline for receiving Day-Ahead Preferred Schedules, the ISO performs its Congestion Management Process and determines the Usage Charges, if any, for each hour of congestion on Path 15. ETC Parties whose schedules over Path 15 are submitted to the ISO by the ETC Facilitator will not be assessed Usage Charges associated with their Path 15 schedules by the ETC Facilitator.