FAC-003-4 Revisited

FAC-003-4 Revisited


By Randall H. Miller, Director of Research and Development

In the summer of 1996, western North America experienced duel power outages, and in August of 2003, eastern North America had its turn. These catastrophic outages occurred during region-wide heatwaves, generating unusually high electrical demand across broad areas of the country, as well as instability in transmission grids. The outages were disasters. Commerce ceased, grocery stores lost produce and frozen goods in the heat, industry ground to a halt, traffic snarled as traffic lights no longer functioned, hospitals and first responders were undermined, and domestic life was left dysfunctional. People lost their lives. Now, over 16 and 23 years later, these blackouts that motivated development of the North American Electric Reliability Corporation’s (NERC) Transmission Vegetation Management Standard (FAC-003) are fading into memory.

At the time, many transmission lines across entire regions were operating at or near their rating. The combination of heavy loads of electricity and high ambient temperatures caused some transmission lines to be knocked out of service when they sagged into trees. Their electrical loads were instantaneously transferred to other lines already operating at capacity, and the additional electricity put them out of service. Their current shifted to other strained lines, causing them to shut down in turn. Soon the control centers across regions were overwhelmed by unmanageable runaway outages in a phenomenon known as cascading, leaving millions in the dark.

A confluence of factors contributed to the catastrophic outages. First is the nature of the electrical grid. Electricity is the only commodity that is produced, transported, delivered and consumed in the same instant. Our electric system is an engineering marvel, containing coordinating control centers that work to overcome daunting logistical challenges. In specific regions of North America, many transmission lines are intertied so the electricity that passes throughout one utility’s system is shared with other utilities. The resulting interconnect provides efficiencies; electrical demand is rarely simultaneously high across broad geographic regions. Power delivery can be directed instantaneously to areas of greatest demand, optimizing generating capacity and avoiding the need to unnecessarily build expensive power plants that are only used during periods of localized peak demand. Transmission lines that are part of each interconnect are those designated as part of the interconnection reliability operating limit (IROL) or the western interconnect as designated by the Western Electricity Coordinating Council (WECC). While the interconnectivity maximizes efficiency with existing resources, it potentially leaves the grid exposed to the type of cascading outages that occurred in 1996 and 2003 (Miller and Kempter 2008).

A second contributing factor to those outages was that the utility industry inadequately protected the bulk transmission system from vegetation during that period. Many rights-of-way were overgrown and outages on bulk transmission lines were not uncommon. It was only a matter of time before catastrophic outages occurred, which they inevitably did in 1996 and 2003.

FAC-003-4 Development

The aftermath of the 2003 eastern blackout was a desperate time in utility vegetation management (UVM). Three catastrophic outages initiated by trees in seven years exposed gaping deficiencies in UVM, and that had to be remedied quickly. Steve Cieslewicz and Bob Novembri, then of CN Utility Consulting, were commissioned by the Federal Energy Regulatory Commission (FERC) to investigate the 2003 incident (Cieslewicz and Novembri 2004). Cieslewicz and Novembri determined that the utilities’ vegetation management programs whose lines triggered the northeastern blackout occurred were consistent with standard practice of the era, and that standard practice was clearly inadequate.

Out of that, and other investigations, came FAC-003. The first Transmission System Vegetation Management Standard’s Drafting Team was convened in 2004 and the initial version (FAC-003-1) became mandatory in July 2007. The standard was revised, and FAC-003-2 became enforceable in July 2014. It has since undergone two revisions. One revision’s only change was to extend enforcement to generation owners who operated applicable transmission segments, and the current revision FAC-003-4, adjusted calculated mandatory clearance limits to comport with flash distances determined by research conducted by the Electric Power Research Institute (EPRI). The mandatory clearance limit is referred to as the minimum vegetation clearance distance (MVCD), which is the maximum flash-over distance between trees and power lines of various voltages as determined by EPRI. They are presented in FAC-003-4.

FAC-003-4 has seven requirements:

  • Requirement 1 and 2 are intended to prevent vegetation encroachment inside the MVCD of lines that are part of an IROL or Major WECC Transfer Path and all others energized at 200 kV and above, respectively.
  • Requirement 3 mandates documented maintenance specifications, strategies, procedures and processes to prevent flash-over. The documentation must consider engineered sag and sway of the conductor, as well as the interdependence of vegetation growth rates, treatment methods and the frequency of inspection.
  • Requirement 4 directs transmission and generation owners to have an imminent threat procedure whereby the applicable control center is notified of vegetation conditions that could cause an outage at any moment.
  • Requirement 5 compels transmission and generation owners to guarantee work that constrains, such as legal injunctions to not result in violations of the MVCD.
  • Requirement 6 orders annual inspection of applicable lines.
  • Requirement 7 ensures applicable transmission and generation owners complete the annual work plan needed to prevent violation of the MVCD.

These requirements fall into three categories:

  • Performance-based: Requirements 1 and 2
  • Competency-based: Requirement 3
  • Risk-based: Requirements 4-7

Requirement 1 and 2 are worded almost exactly the same. The difference is in applicability. Requirement 1 applies to lines that are either an element of an IROL or of a Major WECC Transfer Path. Requirement 2 applies to those that are rated at 200kV or more but are not part of an IROL or Major WECC Transfer Path. FAC-003-4 makes this distinction because cascading events are more likely due to outages affecting IROL or WECC transfer path lines than others. So, violations of Requirement 1 can be penalized more severely than those of Requirement 2.

Requirements 1 and 2 are violated if: a tree is observed within the MVCD, a tree originating from inside the right-of-way breached the MVCD when it fell, vegetation caused a sustained outage due to movement of applicable lines, and vegetation originating from inside the right-of-way or resulted from an intrusion into the MVCD attributable to growth or sag. NERC defines a sustained outage as the deenergized condition of a transmission line resulting from a fault or disturbance following an unsuccessful automatic reclosing sequence and/or unsuccessful manual reclosing procedure.

FAC-003 classifies sustained outages in four categories, with subclassification A for outages that occur on an IROL or Major WECC Transfer Path and B for lines 200kV and above that are not.

  • Category 1A – Sustained outages produced by vegetation growing into Requirement 1 lines or Requirement 1 lines sagging into vegetation.
  • Category 1B – Sustained outages produced by vegetation growing into Requirement 2 lines or Requirement 2 lines sagging into vegetation.
  • Category 2A – Sustained outages due to fall-ins from vegetation originating from inside the right-of-way on Requirement 1 lines.
  • Category 2B – Sustained outages resulting from fall-ins from vegetation originating from inside the right-of-way on Requirement 2 lines
  • Category 3 – Sustained outages produced by vegetation falling into applicable lines from vegetation originating from outside the right-of-way.
  • Category 4A – Sustained outages due to lines and trees originating from inside the right-of-way blowing together.
  • Category 4B – Sustained outages due to lines and trees originating from outside the right-of-way blowing together.

The North American blackouts of 1996 and 2003 occurred during the summer months due to Category 1 outages. They coincided with periods of unusually high demand from region-wide heat waves, and lines sagging into the transmission lines, which served as catalysts for cascading. Consequently, Category 1 outages are considered more serious than other types that are not dependent on heavy loads. Further, Category 1 outages are evidence of an inadequate vegetation management program and probably indicate that there are violations of more than just Requirement 1 and Requirement 2. As a result, they carry greater violation severity due to their potential to cause a transmission grid failure.

The definition of a violation of Requirements 1 and 2 including either a “real time” observance of a breach of the MVCD or the existence of a sustained outage due to a grow-in or sag-in gives utilities some cover. For example, if routine inspections identify a tree with a brown top directly under an applicable line but outside the MVCD, there is evidence that flash-over between the transmission line and tree might have occurred. However, if no otherwise unexplained sustained outage has been recorded at the site, it would not be a violation of Requirement 1 or 2 since the tree is outside the MVCD and no sustained outage has been identified. So, the situation is still in compliance with FAC-003-4, even though the tree may very well have breached the MVCD at some point. The utility would be wise to act to remove or prune the tree for greater clearance, but it would not be a violation of the standard.


FAC-003 violations are investigated by the Regional Entity in cooperation with NERC and FERC. Fines are determined with reference to: the Violation Severity Level of the infraction, the quality of the mitigation plan offered by the transmission or generation owner, whether the utility has had an FAC-003 violation in the past, whether a violation was self-reported, and other factors. Category 1 outages are considered serious by Regional Entities and utilities can be fined as much as much as one million dollars per violation per day for FAC-003 violations (Miller 2011). However, fines have generally been leveled in the low hundreds of thousands of dollar range. For example, in June 2019, a utility was fined $120,000 for a violation of Requirement 2 (NERC 2019b). In addition to a six-figure fine, the offending utility’s reputation is compromised as their penalty is widely publicized.

How Successful has FAC-003 Been?

The FAC-003 series of transmission vegetation management standards have been successful insofar as no vegetation-caused cascading outage has occurred since they were first adopted. However, outages and fines have been levied.

FAC-003 Category 1 Sustained outages 2007-2018.

From 2007 when FAC-003 was first enforced, through 2018, there have been 42 Category 1 sustained outages (Figure 1). In 2007 there were 16 outages, 11 in 2018, and three or fewer each year since. No outages were recorded in 2013, 2014 and 2016. In the past decade, the average of Category 1 outages in North America is only 1.5 per year.

By contrast, there have been an average of over 18 Category 3 outages a year since 2007 (Figure 2) (Novembri undated, NERC 2019). Category 3 outages peaked in 2018 when 31 were reported. However, 27 of these were associated with weather-related events and one was due to human error (NERC 2019). Many of off-right-of-way outages appear to be largely out of the control of vegetation managers; not only in 2018, but historically true as well.FAC-003 Category 3 Sustained outages 2007-2018.

Given that there are over 190,000 miles of applicable transmission lines reticulating the continental United States along with many millions of trees that could possibly interfere with the facilities, an average of 18 Category 3 and 1.5 Category 1 outages a year over the past decade is a solid industry record. Even three Category 1 outages a year for 2017 and 2018 is a significant accomplishment, particularly when compared to the 16 that were documented in 2007.

The improvement in Category 1 outages came as a result of a considerable amount of work. Transmission and generation owners have aggressively removed trees from the right-of-way since 2007, often over considerable public resistance (Miller 2011). In some respects, the utility industry can be justifiably proud of achieving near perfection in managing Category 1 outages in recent years. On the other hand, it reflects negatively on the industry to have waited until it caused multiple blackouts and subjected to enforcement action to keep trees from growing into critical lines. In that context, NERC and FERC are reasonable to continue to strictly enforce FAC-003-4, since even one Category 1 outage a year potentially puts an intertie at risk. We as an industry should strive to ensure that the accomplishment of zero such outages from 2011, 2013 and 2014 are the norm and not the exception.


Sixteen years have passed since the August 14, 2003 catastrophic that disabled eastern North America. FAC-003 was developed as a result and it has been successful in preventing cascading outages since its inception. Category 1 outages pose the greatest risk of initiating a cascading event. Since the adoption of the first version of FAC-003, Category 1 outages have been reduced from 16 a year to an average of only 1.5 a year. Utility vegetation managers can be proud of that accomplishment, yet NERC and FERC have no choice but to continue to enforce FAC-003 with the goal of flawless compliance.


This article was published in “Along the Lines,” a section of the Wright Service Corp. biannual newsletter, The Wright Perspective. Read the full newsletter here.

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