Blocks consist of equally sized (e.g. 100 MW) dispersed groups of distribution circuits which may be sequentially interrupted if generation operating reserves fall below 1-1/2%. The utilities would interrupt (blackout) a block for approximately 1 to 1-1/2 hrs then move on to the next block. The last block interrupted will be the last interrupted in future emergencies.
A Stage 2 emergency would precede a Stage 3 if time permits. Large users, in exchange for lower rates under Interruptible (non-firm) load programs, agree to curtail load when demanded by the utility. Such loads remain off if a Stage 3 follows; however, operation of the nonfirm tariff schedules is independent of the rotating outage process, which affects residential and other firm service tariff customers.
Essential customers, as determined by the Commission, and any other users on the same circuits, are exempt. Essential users include government and other agencies providing essential fire, police and prison services, hospitals, communication and broadcasting facilities, and others.
The utilities perform periodic internal reviews or customer surveys to confirm that essential customers continue to qualify. Customers may request inclusion on the list, if they feel entitled. If refused, they may file a formal complaint with the Commission.
Electrical outages can occur at any time without warning for several reasons such as accidents or natural causes or other events beyond utility control for which utilities cannot be held liable. As much notice as possible of Stage events is given, but for similar reasons a utility is not liable for customer damages when it must implement rotating outages.
ISO orders for curtailments may require only 10 minutes or less to implement. As circumstances (and time) permit, the utilities will notify large customers, having a demand of 300 kW or more, and other customers who can demonstrate major economic damage or clear and imminent danger to health or safety, by telephone and/or other means.
For all other customers, warning of imminent blackouts and other relevant information is given by mass media, and no individual notification is generally given.
Some utilities indicate the Rotating Block assignments on their customer bills or broadcasted on mass media the number of the next block to be blacked out, giving extra warning time. However, customers may be temporarily switched to other circuits for operational or maintenance reasons.
The utilities will notify customers on life support equipment and critical care customers, as time allows, of imminent rotating outages using automated or personal phone calls.