What Is Saifi Saidi Caidi?

This post may contain affiliate links. If you click one, I may earn a commission at no cost to you. As an Amazon Associate, I earn from qualifying purchases.

Key Takeaways:

  • SAIDI, SAIFI, and CAIDI are metrics used to measure electric power utility reliability.
  • SAIDI refers to System Average Interruption Duration Index, or the average outage duration per customer.
  • SAIFI stands for System Average Interruption Frequency Index, measuring the average interruptions per customer.
  • CAIDI is the Customer Average Interruption Duration Index, or the average restoration time.
  • These metrics provide insight into a utility’s service reliability and response performance.
  • Tracking SAIDI, SAIFI, and CAIDI helps utilities benchmark and improve their operations.


Power outages can range from a minor inconvenience to a major disruption for homes and businesses. For electric utilities, service reliability is a key priority and performance indicator. Understanding metrics like SAIDI, SAIFI, and CAIDI provides useful insights into a utility’s ability to deliver uninterrupted power to its customers. This comprehensive, 2,000+ word guide will analyze these industry standards for assessing electric service dependability.

Specifically, readers will learn the precise definitions of SAIDI, SAIFI, and CAIDI along with how these metrics are calculated and utilized. Relevant examples and statistics will demonstrate the real-world implications of these reliability indices. Most importantly, this article will explain how tracking these metrics over time enables utilities to benchmark performance and target improvements for optimizing service quality. With expanding electrification, dependable electric service is more crucial than ever for supporting our modern economy and way of life.

By thoroughly evaluating these vital reliability metrics, this content will empower readers to better understand the performance of their electric utilities. Let’s dive in to unpack SAIDI, SAIFI, CAIDI, and how power providers leverage these indices to deliver resilient and robust electric service.

A Background on Power Reliability Metrics

The modern economy relies on consistent and uninterrupted electric service. Utility companies are focused on limiting disruptions and restoring power quickly when outages occur. To benchmark and improve their performance, utilities track key reliability metrics like SAIDI, SAIFI, and CAIDI. But what exactly do these indices mean?

SAIDI, SAIFI, and CAIDI are standardized metrics that provide utilities with quantitative insights into the dependability of their electric service. Specifically, these acronyms stand for:

  • SAIDI: System Average Interruption Duration Index
  • SAIFI: System Average Interruption Frequency Index
  • CAIDI: Customer Average Interruption Duration Index

While the terminology sounds highly technical, the underlying concepts are relatively straightforward. In simple terms:

  • SAIDI measures the total duration of interruptions per customer.
  • SAIFI indicates how often service disruptions occur.
  • CAIDI assesses the average time needed to restore power after an outage.

Utility engineers calculate these indices using operational data on outage causes, frequency, duration, and number of impacted customers. The metrics provide an objective view of service reliability over time and across different distribution circuits or regions.

Next, let’s explore the specifics of how SAIDI, SAIFI, and CAIDI are defined and derived.

SAIDI – Tracking Total Customer Interruption Duration

SAIDI stands for System Average Interruption Duration Index. This index measures the total duration of interruptions for the average customer over a period of time, typically one year. SAIDI represents the cumulative amount of time power is out for the service territory across all customers served.

Specifically, SAIDI is calculated as:

SAIDI = Total Customer Interruption Duration / Total Number of Customers Served

The units for SAIDI are reported in minutes or hours of interruption per customer for the year. A higher SAIDI value indicates more extended or frequent disruptions, while a lower value signals better service reliability.

For example, a SAIDI of 60 minutes means the average customer experienced a total of one hour of cumulative interruptions over the last year. This could represent several smaller outages or one extended event. By comparing SAIDI year-over-year, utilities can gauge improvements or degradations in outage duration.

According to the Energy Information Administration, the average U.S. SAIDI value for 2018 was around 200 minutes per customer. However, performance varies significantly across different power providers. Monitoring SAIDI helps utilities benchmark against other providers and internal targets. Minimizing outage duration is a priority to limit disruption and costs for customers.

SAIFI – Measuring Interruption Frequency

While SAIDI focuses on total outage duration, SAIFI specifically measures the frequency of service interruptions. SAIFI stands for System Average Interruption Frequency Index.

Mathematically, SAIFI is defined as:

SAIFI = Total Number of Customer Interruptions / Total Number of Customers Served

The output represents the average number of sustained interruptions per customer over the analysis period, typically annually. A lower SAIFI indicates less frequent disruptions, while a higher value points to more outages impacting customers.

For example, if a utility has 100,000 customers and experienced 50,000 total customer interruptions last year, the SAIFI would be 0.5 interruptions per customer. This means the average customer experienced one outage every two years. As with SAIDI, power providers track SAIFI over time to assess reliability trends and compare against benchmarks.

According to the American Public Power Association, U.S. public and private utilities average around 1.1 interruptions per customer annually. However, top performing utilities achieve SAIFI levels of 0.5 or less. Strategies like grid automation and proactive maintenance help minimize outage frequency. Monitoring SAIFI motivates organizations to continually improve in this area.

CAIDI – Evaluating Restoration Times

The final metric, CAIDI, provides insight into how quickly a utility can restore service after an outage occurs. CAIDI stands for Customer Average Interruption Duration Index.

This index is calculated by dividing SAIDI by SAIFI:


In other words, CAIDI considers the total duration of interruptions and the total number of outage events to determine the average time it takes service to resume after any given disruption. CAIDI is often viewed as representing the utility’s reliability or responsiveness in resolving outage situations.

Using the examples above with a SAIDI of 60 minutes and SAIFI of 0.5, the CAIDI would be 60/0.5 = 120 minutes. Thus, the average restoration time is 120 minutes per customer interruption. Utilities aim to minimize CAIDI by deploying infrastructure and staffing that allows for rapid power restoration.

Trends in CAIDI demonstrate whether a provider’s outage response capabilities are improving or declining over the long term. According to the American Public Power Association, top performing utilities achieve CAIDI levels of around 60-90 minutes.

Real-World Impacts and Usage of SAIDI, SAIFI, CAIDI

While SAIDI, SAIFI, and CAIDI are quantitative metrics, they have tangible impacts on utilities and customers. These indices influence everything from costs and customer satisfaction to staffing and infrastructure planning.

On the customer side, extended or frequent disruptions can lead to inconvenience, lost productivity, and business impacts. For example, a 2020 Lawrence Berkeley National Laboratory study estimated the annual cost of U.S. power interruptions at $100 billion. SAIDI, SAIFI, and CAIDI metrics directly relate to this customer value proposition.

For utilities, poor reliability scores hurt customer perceptions but also have internal implications. Maintaining staff, equipment, and processes to minimize SAIDI and SAIFI requires investment. At the same time, elevated CAIDI can indicate inadequate field workforce, maintenance regimes, or outage management systems.

Regulators like public utility commissions often track and set performance targets for SAIDI and SAIFI. Missing these goals can jeopardize rate increases or profitability for the utility.

Across the industry, SAIDI, SAIFI, and CAIDI benchmarks allow utilities to compare their reliability against peers. Performance on these metrics also helps utilities qualify for awards like PA Consulting’s Grid Reliability award or the Reliable Public Power Provider designation.

Internally, utilities analyze SAIDI, SAIFI, and CAIDI trends to reveal strengths, weaknesses, and opportunities. Areas with deteriorating reliability can be targeted for capital improvements like grid hardening and automation. Utilities may also augment field staffing, maintenance schedules, equipment, or vegetation management to directly address SAIDI, SAIFI, and CAIDI performance.

Methodology for Tracking Service Reliability

To accurately calculate SAIDI, SAIFI, CAIDI, utilities follow standardized procedures for outage data collection and analysis. Establishing rigorous tracking methods ensures metrics are consistent and comparable across time periods and providers.

Industry groups like the Institute of Electrical and Electronics Engineers (IEEE) and Edison Electric Institute (EEI) publish guidance on reliability index methodology. Key elements include:

  • Data sources: Outage management systems, customer calls, field reports, SCADA, and other utility operational data.
  • Qualifying interruptions: Sustained disruptions exceeding a minimum duration threshold, like 5 minutes.
  • Customer impact: Number of metered accounts affected, using outage management system data.
  • Major event exclusion: Catastrophic event days are excluded to focus indices on typical performance.
  • Reporting interval: Daily system totals are aggregated to annual values. Some utilities report monthly or quarterly SAIDI, SAIFI, CAIDI as well.

Following established guidelines ensures meaningful, accurate measurement of service reliability over the long term. Statistics can be segmented by geography, customer class, or other groupings to deliver additional insights. With rigorous tracking methods, SAIDI, SAIFI, and CAIDI serve as reliable barometers of utility performance.

Improving Service Reliability Using SAIDI, SAIFI, CAIDI Metrics

While measuring reliability indices is important, the ultimate goal is leveraging insights from SAIDI, SAIFI, and CAIDI to improve performance. Utilities employ various strategies, driven by their reliability metric trends, to enhance service quality for customers.

For example, utilities may target capital investments on the worst-performing circuits identified based on high SAIDI and SAIFI contributions. Priority upgrades could include:

  • Grid hardening and resiliency programs.
  • Protective equipment and automation enhancements.
  • Overhead to underground line conversions.
  • Improved vegetation management.

To reduce CAIDI and restoration times, utilities may focus on:

  • Fleet and field force readiness.
  • Logistics and inventories for equipment and materials.
  • Modern outage management systems and data integration.
  • Communications and coordination procedures.

Broader initiatives like predictive analytics, smart grid technologies, and utility workforce training may also be deployed to address reliability performance gaps highlighted by SAIDI, SAIFI, and CAIDI trends.

Top quartile utilities benchmark via industry resources like the IEEE and EEI to identify and adopt best practices. Within an organization, cross-functional teams evaluate reliability indices to pinpoint areas for continuous improvement.

With diligent tracking and targeted actions, SAIDI, SAIFI, and CAIDI metrics can drive a cycle of benchmarking, goal-setting, execution, and measurement to enhance the customer service experience.

Frequently Asked Questions

What impacts SAIDI and SAIFI metrics for utilities?

SAIDI and SAIFI are primarily influenced by the number of outages, duration of outages, and customers affected by outages over a period of time. Key drivers include weather, animals, vegetation, equipment failures, and external incidents. Utilities aim to minimize both the frequency and duration of service disruptions.

Why are major event days excluded from reliability index calculations?

Catastrophic events like severe storms are excluded from SAIDI, SAIFI, and CAIDI so the metrics reflect typical day-to-day service quality. Storm days skew results and are not representative of normal utility performance. Excluding major events provides a more accurate picture of reliability.

How quickly do utilities need to restore power to provide good CAIDI?

According to industry research, top quartile utilities restore power within 60-90 minutes on average after an outage occurs (CAIDI of 60-90 minutes). Achieving this level of performance requires investments in response infrastructure, personnel, and processes.

What are the impacts of poor reliability as measured by SAIDI, SAIFI, and CAIDI?

High SAIDI and SAIFI indicate frequent and long-duration outages, which translate to significant disruption and costs for customers. Elevated CAIDI suggests slower restorations, resulting in extended outage periods. Poor reliability damages customer satisfaction, leads to regulatory scrutiny, and requires greater utility investments.

How can smart grid technologies help improve SAIDI and SAIFI?

Smart grid automation and sensors can pinpoint outage locations faster and isolate disruptions to smaller customer groups. This helps utilities restore customers sooner and reduces outage impacts and durations. Smart grid equipment can also enable proactive maintenance and hardening.

Key Takeaways on SAIDI, SAIFI, CAIDI

  • SAIDI, SAIFI, and CAIDI offer objective and standardized metrics for evaluating electric service reliability.
  • Tracking outage duration, frequency, and restoration time over time provides insights into a utility’s strengths and weaknesses.
  • Utilities analyze SAIDI, SAIFI, and CAIDI trends to target investments and initiatives for driving reliability improvements.
  • Customers benefit through fewer interruptions, shorter outages, and reduced disruption to their homes and businesses.
  • With diligent benchmarking and monitoring, SAIDI, SAIFI, and CAIDI can be leveraged to continuously enhance power delivery dependability.


Reliable electricity is vital for supporting our quality of life and economy. SAIDI, SAIFI, and CAIDI offer utilities data-driven metrics to benchmark and optimize their service performance for customers.

This comprehensive guide explained how these indices measure outage duration, frequency, and restoration times. Examples demonstrated their real-world impacts. We also covered how utilities collect data and leverage insights from SAIDI, SAIFI, and CAIDI to target improvements through investments, maintenance, staffing, and innovative solutions.

While outage disruptions may never be fully eliminated, these key reliability indices help motivate utilities to constantly strengthen their infrastructure, operations, and customer service. By providing a quantitative view of reliability, SAIDI, SAIFI, and CAIDI empower utilities to continually advance the resiliency and dependability of electric service

About The Author

Scroll to Top