Glossary of Terms
Notification that electric reserves are lower than normal and steps are being taken by utility personnel to maintain the integrity of the on-line generation and transmission facilities.
When possible, the public would be alerted that load shedding or rolling blackouts are imminent.
Advisories to be announced when conditions are such that further steps to manage capacity could affect the public.
An almost instantaneous cutting of power to customers because demand for electricity has outstripped supply.
Public appeals when an immediate reduction in power usage is necessary to avert overload of the electrical system. Public appeals are made when other efforts (e.g. emergency purchases, voluntary curtailment, contracted curtailment and voltage reduction) have been unsuccessful in bringing supply and demand back into balance.
If, after other steps to manage capacity have been taken and the demand for electricity continues to exceed generating capacity, the electric utility can reduce voltage by five percent. This reduction essentially stretches out the available supply of electricity to all customers. It is rarely noticed by customers but may affect sensitive electronic equipment.
Public appeal to customers to conserve electricity in anticipation of heavy electrical demand and unhealthy air quality conditions, usually due to humid weather.
Temporary interruption of electrical service. ISO New England would implement rolling blackouts only if and when New England's electrical system is unable to meet heavy peak demands because of an extreme deficiency in the power supply. By temporarily disconnecting electrical circuits on a rotating basis, a majority of customers have power, inconvenience is minimized and a more serious widespread problem is averted. Each rotation is of a specific duration, usually no longer than a few hours, but it could take longer in some locations due to the manual nature of the operation.