Glossary of Terms

Load (Electric)

The amount of electric power delivered or required at any specific point or points on a system. The requirement originates at the energy-consuming equipment of the consumers.

Local Utility Delivery Charges

Delivery charges cover the use of the delivery company's poles and wires, costs associated with reading the meter, public programs, transition charges, taxes and other costs of doing business experienced by the delivery company. These charges are typically passed through on the single bill option. These charges are consistent for customers regardless of their supply source (ComEd or a retail marketer).


As electricity moves through the network of poles and wires, energy is lost. The amount of electricity measured at the meter is less than originally produced at the generation facility. To account for this variance with any product that does not include losses, supply costs are multiplied by transmission and distribution loss factors to determine this cost component.

Current PJM Transmission Losses

Transmission Losses (assessed by PJM) are line losses incurred while transporting electricity from the generating station to the distribution system. Current transmission losses are 1.6% of metered volumes.

Current ComEd Distribution Losses

Distribution losses are line losses incurred while moving electricity along the distribution system to the customer's electric meter. Distribution Loss Factors are in ComEd's Rate RCDS tariff and range from 2.8% to 7.5% depending upon customer class. After 2006, these same distribution loss factors will be defined in ComEd’s Rate RDS and proposed percentages range from 5.07% to 7.71% depending on customer class.

Changes in Transmission & Distribution Losses

Any changes in Transmission or Distribution Losses due to tariff or rate changes through approved PJM/ComEd rate cases.

Market-Based Pricing

Electric service prices determined in an open market system of supply and demand under which the price is set solely by agreement as to what a buyer will pay and a seller will accept. Such prices could recover less or more than full costs, depending upon what the buyer and seller see as their relevant opportunities and risks.

Market Clearing Price

The price at which supply equals demand for the Day Ahead and/or Hour Ahead Markets.

Maximum Demand

The greatest of all demands of the load that has occurred within a specified period of time.

Megawatt (MW)

One million watts.

Megawatthour (MWh)

One million watthours.


One million cubic feet.

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