Summary of Indices

SAIFI

System average interruption frequency index (sustained interruptions). The system average interruption frequency index is designed to give information about the average frequency of sustained interruptions per customer. The definition is:

Total Number of Customer Interruptions / Total Number of Customers Served

SAIDI

System average interruption duration index. This index is commonly referred to as Customer Minutes of Interruption, and is designed to provide information about the average time the customers are interrupted. The definition is:

The Sum of Customer Outage minutes / Total Number of Customers Served

CAIDI

Customer average interruption duration index. CAIDI represents the average time required to restore
service to the average customer per sustained interruption. The definition is:

The Sum of Customer Interruption Durations / Total Number of Customer Interruptions.

CAIFI

Customer average interruption frequency index. This index gives the average frequency of sustained
interruptions for those customers who experienced a sustained interruption. The customer is counted
once regardless of the number of times interrupted.

Total Number of Customer Interruptions / Total Number of Customers Interrupted