How vulnerable is your electrical system?

A discussion about vulnerabilities to electrical systems includes risks to facilities and recommendations for improved safety

By Richard A. Vedvik, PE September 30, 2020


Learning Objectives

  • Understand the codes and standards — and their updates — that guide electrical system design.
  • Learn about power system study needs and concerns.
  • Understand how age and environment affect electrical system risks.

The previous editions of NFPA codes allowed for electrical systems in commercial buildings to have vulnerabilities that modern versions of code have recognized. The 2020 edition of NFPA 70: National Electrical Code further enhances the protections of previous code cycle evolutions, including arc flash labels, selective coordination requirements, fire resistive construction and environmental conditions.

Facilities should be tracking the condition of the various electrical systems components during condition assessments. These assessments should factor in the importance of each component, which is determined through a risk assessment. If staff, occupants, patients or visitors could be injured or killed with the failure of that system, then the importance placed on reliability is high. Electrical systems and conditions that might need corrective action are:

  • Generator testing methods that do not simulate an outage.
  • Paralleling gear located within the generator room.
  • Lack of selective coordination or lack of a coordination study.
  • Unknown or incorrectly labeled arc flash conditions.
  • Lack of fire ratings on critical cables.
  • Circuit breakers that predate the 1970s.

Generator testing methods

Generators are usually tested using a switch on the face of an automatic transfer switch, as noted in NFPA 110: Standard for Emergency and Standby Power Systems Chapter 8.4.3. This switch provides voltage on the start conductors that tells the generators to start.

The 2017 edition of the NEC added a requirement for monitoring of start conductor integrity in 700.10(D)(3). Once the emergency source is accepted by the transfer switch, the transfer is made after programmed delays. While this electrical system test procedure verifies the integrity of the start conductors and verifies transfer switch operation, the actual performance and delays that occur with an actual utility outage are not verified. It may be several years between outages with projects occurring during that timeframe.

NFPA 110 8.4.3 also allows for ATS testing by opening the circuit breaker that feeds the normal side of the ATS, With this method, the ATS will see a loss of the normal source and send a start signal to the standby emergency power supply. Unfortunately, it is inconvenient to generate a utility outage for ATS that serve computers or patient care areas. It may even be hazardous to simulate a utility outage for critical processes or equipment without proper shutdown procedures. As a result, the emergency or life safety branch is usually the least disruptive ATS to test with.

When using this branch for testing, the facility will be alerted to alarms that will occur and staff should ensure the stairwells and elevators are clear so occupants aren’t left in the dark during the generator start transition. This process will reveal the actual behavior of the system in an outage. Delays identified in NFPA 110 8.4.5 can then be evaluated to ensure a proper start and transfer within the duration required in NFPA 110 Chapter 4.

For a Type 10 applications, this is within 10 seconds. Transfer delays can be programmed into the ATS logic and those delays cannot be properly evaluated using the test switch. Other delays in the ATS programming may inhibit transfer and it is important to develop a testing procedure that evaluates any and all programming logic.

Mimicking an outage for the generator room is another important step to confirm that the programming is correct. NFPA 110 Chapter 8.3.5 identifies the list of inspections that are required, which includes verifying system operation.

An example of electrical system system operation is programming in the paralleling gear that may inhibit the generator breaker closure if the battery charger sees a loss of normal power. Such a condition will only present itself during a utility outage within the generator room. The facility can perform weekly testing using the test switches and can also have a procedure for monthly or bimonthly outage testing using the methods described above.

Additionally, whenever projects or procedures change or effect ATS programming or wiring, outage testing should be performed. It’s suggested that an actual utility outage should be performed every 5 to 10 years, especially if the facility hasn’t had an outage. While it is certainly inconvenient to perform this testing for facilities that are occupied constantly, such as a hospital, it would be better to perform the outage in controlled conditions.

Electrical system locations

The locations of electrical equipment are typically unconditioned, which reduces longevity and increases risk. Environmental factors include the temperature range, humidity range and the dirt and dust accumulation within the space. Electrical rooms without heating, ventilation and air conditioning or with direct venting to the outdoors tend to suffer the largest fluctuations in temperature and humidity while also having high dirt accumulation. Equipment life spans in these locations are expected to be shortened with higher risks of failure.

While it is not common to consider conduit as a pathway for air transfer, the lack of seals in most electrical raceway systems allows for air transfer between rooms. When distribution equipment is located in rooms that are subject to high temperature and humidity, condensation can occur in distribution equipment where raceways serve air conditioned spaces.

These conditions are worsened in generator rooms due to the need for exterior cooling and combustion air and the lack of seals associated with intake and discharge operated louvers. Installations in climates with extreme cold should include supplemental heating, with the understanding that once the generators are running, the heating system will be ineffective.

Paralleling gear located in these rooms will suffer the highest risk of failure due to environmental conditions. Paralleling gear is also one of the most critical components in an electrical room. While NFPA 110 allows for emergency power supply system gear to be located in the EPS room, it may not be a good decision for long-term reliability. Facilities with this arrangement should have a policy for cleaning and investigation of electrical distribution equipment on schedule based on the environment.

Another area of consideration is the chance of flooding by either natural or man-made causes. The 2020 edition of the NEC addressed this in 700.12(A) and (B), which mimicked previous versions of NFPA 110 Chapter 7 or NFPA 99: Health Care Facilities Code section Locating critical electrical equipment in a basement was a common practice that leaves the equipment at risk of flooding from sprinkler systems, pipe breakage or other natural disasters. When equipment replacements are needed or desired, care should be taken to provide a new, compliant location when necessary and avoiding the trap of repeating prior approaches for convenience.

Age of the electrical system

Based on observations of electrical distribution systems across the country and participation is failure analysis studies, the reliability of electrical system components comes into question as components reach 40 years old. Even with the best environments, the materials used several decades ago present a series of challenges.

Circuit breakers can physically fail internally or the handles can break off. Broken handles occur when the plastics become brittle or the circuit breakers become difficult to close. Circuit breakers can fail in the on position, creating a fire or safety hazard. Circuit breakers can also fail in the off position, resulting in an extended outage that can present a risk to occupants. As equipment ages to the point where replacement parts become difficult to find, the risk of an extended outage increases (see Figure 2).

Selective coordination and updates

The short circuit current study should also include selective coordination and circuit breaker setting recommendations. This is a required step to verify the proper settings to minimize the risk of a cascading outage. When a facility has already had a study, it should be updated each time system changes are made.

To keep up with changes, the facility needs to have access to the software and files used to create the original study. If the facility lacks the staff or access, then a relationship with a local firm is recommended to assist with maintaining the program or the facility can require that engineering teams performing system changes should include program updates in their scope. Circuit breaker settings should be compared to recommendations from previous studies and adjusted when required.

Selective coordination of emergency power systems is required by NEC 700.32 for emergency branch systems, 701.32 for legally required branch systems, 517.31(G) for health care essential electrical systems, 708.54 for critical operation systems and 645.27 for information technology systems. The 2020 edition of the NEC includes new informational graphics that more clearly define what is required to be selectively coordinated on both the emergency side and the normal side of the associated ATS (see Figure 3). Simply put, the entire normal branch is not required to be coordinated. The overcurrent protective device on the load side of the ATS shall coordinate with both normal and emergency side OPCDs.

When making system changes, designers should pay close attention to the effects that those changes may have on existing systems. For example, if a project is putting a large addition on an existing building, the engineer needs to determine if the existing service can support the addition. In many cases, a large addition may require an increase in the building service. It is common to create the new service in the addition and back-feed the existing facility to minimize downtime and replace aging service entrance equipment.

Designers need to carefully evaluate the impact that this change will have on system ratings, short circuit current, arc flash values and selective coordination. If the available fault current increase from a larger service entrance transformer results in many existing panel ratings being exceeded, a corrective action should be part of the plans.

If a facility with aging equipment doesn’t have an accurate or recent study, this effort should become a priority. These studies require an electrician open up every panel to verify ratings and actual wire sizes.

Wire lengths and overall system wiring configuration is another important step to verify for report accuracy. The available short circuit current can change over time as buildings electrical systems are revised and transformer equipment is replaced. If a transformer is replaced with a more energy-efficient model, the new transformer may have a lower internal impedance, which increases the available short circuit current. As a result, the panels and equipment served by the replacement transformer may have become inadequately rated, further increasing the risk of a catastrophic failure or extended outage. Both the circuit breaker ratings and the panel ratings should be evaluated as part of a short circuit current study.

Arc flash labels in electrical system

As electrical systems are modified, so are the available arc flash values. While new projects need to evaluate the risk that the design will have on the equipment added in the project, any impacts to the existing equipment should be evaluated. If the facility has arc flash labels already, any project affecting the values should include updates to the software and labels.

If a facility lacks an accurate study, it will be difficult for engineers to verify that their design is not causing a hazardous condition. It’s also possible that previous studies may have made incorrect assumptions, resulting in labels that identify incorrect hazards (see Figure 4).

Engineers should identify this concern early in the project and discuss possible solutions with the facility. NEC 110.16(B) requires that service equipment be labeled with available fault current and clearing time of the overcurrent protective devices. The 2018 edition of NFPA 70E: Standard for Electrical Safety in the Workplace section 130.5 requires an arc flash risk assessment to identify the hazards present.

To determine the appropriate level of personal protective equipment that a worker must wear, an understanding of the available arc fault energy is necessary. It is commonly understood that actively working on live electrical cabling or gear requires appropriate PPE. What may be overlooked is that removing dead-front assemblies, opening the doors on transfer switches or removing panels for inspection or documentation also presents a hazard to personnel. Knowing the hazards present is the first step to taking appropriate action.

Arc energy reduction is a newer requirement in the NEC in Article 240.87 that limits the available arc fault energy downstream of circuit breakers with a frame size 1,200 amperes or larger. Even if the circuit breaker uses a lower amperage trip plug or setting, this requirement is based on what the OPCD can be set to. In the 2017 Edition of the NEC, Section 240.67 was added to echo this requirement for fuses as well.

One of the options allowed by NEC 240.87(B) is to add a switch to the face of the distribution equipment that adjusts the instantaneous time-current curve portion of the circuit breaker’s electronic trip unit. By making the system more sensitive the clearing time is reduced, thus reducing arc fault energy. Other options include zone-selective interlocking or differential relaying, which may be difficult to add to an existing electrical system.

Electrical system fire ratings

Various sections of code require fire ratings on cables that provide critical infrastructure. Fire ratings are also required where cables pass through evacuation zones for survivability with the intent being that a fire in adjacent buildings or areas should not compromise the building or area of interest. Because fire rating requirements have evolved over the decades, existing facilities may not have compliance with the latest codes. While there is no enforcement for retroactive applicability, the facility should evaluate where existing cable systems are venerable as part of their risk assessment process.

Generator start conductors are required to be two-hour fire rated or protected in such a way to achieve a two-hour fire rating and the start conductors should be routed separate from transfer switch control cables. Acceptable methods for achieving a two-hour rated system are defined in NEC 700.10(D)(1). If a facility lacks these two requirements, replacement of start conductors would be a valuable investment.

Emergency or essential electrical power conductors are required to be fire rated for occupancies listed in NEC 700.10(D) and NEC 517. The list includes assembly occupancies with an occupant load greater than 1,000 people, high-rise buildings (defined as an occupied floor that is 75 feet above a level of exit discharge per 2018 International Building Code Section 403), health care occupancies where occupants are not capable of self-preservation and educational occupancies with an occupant load greater than 300.

These conductors are usually longer, larger and routed though congested areas of the building resulting in expensive replacement or upgrade costs. Because of the cost and difficulty, it is not uncommon for facilities to avoid upgrades and rely on the lack of retroactive code enforcement. Some authorities having jurisdiction may look at other electrical system upgrades, such as replacement of generators or transfer switches as being a catalyst for bringing the entire system into modern applicable code compliance. System reliability should always be part of the discussions for both upgrade projects and acceptable risk.

Fire pump conductors are required to be fire rated per NEC Articles 695 and 700. Additionally, the location of the fire pump controller and transfer switch are required to be in a dedicated location separated by a two-hour fire barrier per 2018 IBC Section 913.

NFPA 20: Standard for the Installation of Stationary Pumps for Fire Protection includes requirements for a wide variety of pump types and configurations. The controller wires are also required to be part of a listed electrical circuit protective system per NEC 965.5(H). Feeders for the normal side are required to be sized for locked rotor current and should originate ahead of the main disconnect per NEC 695.4(B). Generator control wiring for fire pump service is also required to be fire rated per NEC 695.14.

If a facility lacks any of these arrangements, an upgrade should be considered. Evaluations of the fire pump and associated systems should be coordinated with applicable state and local fire marshals to determine appropriate steps and a plan of corrective action, if any.

Fire alarms and other low-voltage system conductors are another cabling system that has survivability requirements in NEC 760. This section lists appropriate cable types that are acceptable for each cable usage or rating. In addition, cabling that passes through rated walls requires equivalently rated fire stopping systems (see Figure 5).

Two circuit types are defined in NEC 760: nonpower limited fire alarm and power limited fire alarm. Notable requirements include a red-handled OCPD for branch circuits serving fire alarm equipment and the delineation between wiring methods defined in NEC 760.130. An evaluation of the current configuration of cabling is a prudent study for any facility older than 20 years. NEC 725.25 discusses removal of abandoned cable unless cables are appropriately labeled.

Fire alarm conductors are required to have survivability under NFPA 72: National Fire Alarm and Signaling Code Chapter 24, with Chapter 12 providing survivability definitions. For health care occupancies where self-preservation of occupants is not possible, the facility may have a partial evacuation or occupant relocation procedure.

For example, when evacuating patients in the intensive care unit is not desired, the facility will have a procedure for relocating those patients to another area. The fire ratings required in NFPA 101: Life Safety Code and IBC are intended to provide sufficient time to relocate occupants. Cable survivability is required for these occupancies.

As with other requirements for fire ratings, the intent of code is to allow for critical systems to continue for enough time as required to evacuate the facility and to operate despite a fire occurring in another part of the building. For example, a fire in the south wing of a building shouldn’t prevent the operation of the fire alarm system in the west wing.

While existing building systems may have been code-compliant when they were installed, the reason for code evolutions and updates is primarily to increase the safety of the systems to occupants and workers. As we look back at some of the previously tolerated practices, we can associate an unfortunate number of deaths that could have been prevented with modern code requirements. As a facility performs a risk assessment and determines the corrective actions required, an emphasis on safety and preservation of life should drive the order for which corrections are made.

Author Bio: Richard A. Vedvik is a senior electrical engineer and acoustics engineer at IMEG Corp. He is a member of the Consulting-Specifying Engineer editorial advisory board.