Electric Reliability


The reliability of the city of Rocky Mount’s electric system is evaluated using the following indices based on the number of sustained customer interruptions (i.e. those lasting longer than one minute). The city of Rocky Mount results for 2015 are as follows:

Value of Index Goal/Target 
SAIDI (Minues/Year) 50.50 Less than 60 
CAIDI (Minutes/Year) 49.02 Less than 60
ASAI (% based on year)
99.9904 Greater than 99.9885% 
MAIFI (Interruptions per year) 3.18 Less than 5 
SAIFI (Interruptions per year)
1.03 Less than 1.00 
Explanation of Indices
  • System Average Interruption Duration Index (SAIDI): SAIDI represents the total outage time in minutes that every city of Rocky Mount customer experienced in 2015.

  • Customer Average Interruption Duration Index (CAIDI): CAIDI represents the average time in minutes for the city of Rocky Mount to restore power.

  • Average Service Availability Index (ASAI): ASAI represents the percentage of hours that service was available to customers during the year based on the total number of hours demanded.

  • Momentary Average Interruption Frequency Index (MAIFI): MAIFI measures the average number of momentary interruptions that a customer experiences during a given time period.

  • System Average Interruption Frequency Index (SAIFI): SAIFI is the average number of interruptions that a customer would experience annually.


Below is a comparison between Rocky Mount, NC Public Power and Rocky Mount’s surrounding utility providers. In the case of all indices, a lower number indicates better reliability.

Utility  Total # of
(in minutes)
(# of interruptions) 
(in minutes) 
Dominion 121,248 134.00 1.24 108.06
Duke Energy Progress (DEP) 1,312,953 141.00 1.41 100.00
Edgecombe-Martin County EMC (2014 data) 11,441 62.50 0.85 73.53 
NC Public Power * 470,497 41.15 0.68 69.90
Rocky Mount 27,167 50.50 1.03 49.02

* Public power is municipally-owned and operated electric service. More than 70 communities in North Carolina serve more than 400,000 residential, commercial and industrial customers. These communities are collectively known as NC Public Power. For the purpose of the indices, averages of all the utilities were used.