1. Official Federal Data Sources
- U.S. EIA Form 861 Annual Electric Power Industry Report (2024): We parse every electric utility's official IEEE 1366 / standard reliability filing (
Reliability_2024.xlsx) and residential revenue/sales filing (Sales_Ult_Cust_2024.xlsx&Short_Form_2024.xlsx) across 3,113 U.S. utilities (3,655 utility-state operating records). - DOE / OpenEI U.S. Utility Rate & ZIP Code Lookup Tables: Maps 32,125 U.S. ZIP codes directly to their Investor-Owned, Cooperative, and Municipal electric utilities. For the remaining 1,517 rural/PO-box Census ZCTAs not listed in OpenEI, we match the nearest in-state mapped ZIP code using U.S. Census Bureau Gazetteer coordinates and clearly label the data source on the page.
- U.S. Census Bureau Gazetteer Coordinates: Provides geographic center coordinates and population for all 33,791 ZIP Code Tabulation Areas (ZCTAs) and 10,255 cities and towns.
2. Understanding SAIDI, SAIFI & CAIDI
| IEEE 1366 Metric | Full Engineering Name | What It Means for Your Home |
|---|---|---|
| SAIDI | System Average Interruption Duration Index | Total minutes (or hours) of power outage the average customer experiences over a full year. EIA reports this both With Major Event Days (including severe storms) and Without Major Event Days (everyday grid issues). |
| SAIFI | System Average Interruption Frequency Index | How many separate blackouts the average customer experiences per year (for example, 1.4x / yr). |
| CAIDI | Customer Average Interruption Duration Index | Average restoration time per outage (SAIDI ÷ SAIFI)—how long you are typically in the dark once the power goes out. |
3. How Grid Reliability Grades (A to F) Are Assigned
We compare each utility's total annual outage duration (SAIDI With Major Event Days) against the U.S. national distribution (where the median state SAIDI is 280 minutes / 4.7 hours per year and the customer-weighted national average including major hurricane/storm states is 611 minutes / 10.2 hours per year):
| Annual Outage Time (SAIDI With Storms) | Reliability Grade | Recommended Home Backup Tier |
|---|---|---|
| Up to 120 min/yr (≤ 2.0 hrs/yr) | Grade A — Low Outage Risk | 1,000Wh–1,500Wh LiFePO4 Portable Power Station for fridge, Wi-Fi & electronics. |
| 121 – 240 min/yr (2.0 – 4.0 hrs/yr) | Grade B — Moderate Outage Risk | 1,500Wh–2,000Wh LiFePO4 Power Station (plus furnace transfer switch in northern states). |
| 241 – 420 min/yr (4.0 – 7.0 hrs/yr) | Grade C — Elevated Storm Risk | 3,500W–7,500W Dual-Fuel Generator or 2kWh–3.6kWh Expandable Home Battery + Sump Backup. |
| 421 – 720 min/yr (7.0 – 12.0 hrs/yr) | Grade D — High Outage Risk | 7,500W–9,500W Dual-Fuel Portable Generator + 30A Manual Transfer Switch. |
| Over 720 min/yr (> 12.0 hrs/yr) | Grade F — Severe Outage Risk | 9,500W–12,500W Dual-Fuel Generator (30A/50A Transfer Switch) or Whole-Home Standby Generator. |
4. How the Interactive Backup Wattage Sizer Works
To prevent overload trips when electric motors kick on, our calculator computes:
- Total Continuous Running Watts: The sum of the steady-state running wattage of every appliance you check.
- Peak Starting Surge Watts: Your total continuous running watts plus the largest single motor starting surge increment (
Surge Watts - Running Watts) among your selected appliances (since motors rarely start at the exact same millisecond). - Recommended Minimum Generator / Inverter Rating: Applies a 20% NEC continuous-load safety headroom so your generator or battery inverter isn't redlining at 100% capacity.