The NEC helps the industry understand the safety implications of performance testing

New requirements in NEC Sections 240.67 and 240.87 impact overcurrent protection devices (OCPDs) 1,200 amps and higher or those that can adjust to 1,200 amps and higher. These updates mandate performance testing at the time of installation. Ground-fault protection of equipment (GFPE) at service equipment is an example of an NEC requirement that mandates performance testing to ensure safety technologies are functioning correctly when installed.

With changes including performance testing per manufacturer instructions and recommended test procedures, the electrical industry will soon see significant improvements in power system design and arc flash protection performance. 

  Overview of changes

New text in NEC Sections 240.67 and 240.87 identifies that, when technologies are installed to reduce incident energy, technicians must conduct performance testing at the time of installation. In addition, changes make clear to installers, designers, inspectors and equipment owners that requirements regarding larger OCPDs must respond to lower arcing currents that can occur in equipment.

The arc reduction requirements that began as part of the NEC 2011 code review took a significant step forward in NEC 2020, with changes found in three key areas:

  1. Installation documentation
  2. Safety methodologies
  3. Testing procedures

1) Installation documentation

Documentation requirements changed slightly. A new requirement now mandates proof that installations have arc reduction technologies operating based upon arcing fault current. As always, documentation must be made available to those authorized to design, install, operate or inspect an installation as to the location of all OCPDs impacted. It's critical to understand when these requirements apply and to realize that organizations can always exceed minimum Code requirements by approaching every design with an eye on arc flash hazards.

2) Safety methodologies

When required

Installers, designers and authorities having jurisdiction must understand the entry point of requiring arc reduction technologies as part of 240.67 and 240.87. Circuit breaker requirements of 240.87 establish an arc reduction technology entry point based on circuit breaker ratings and the ability to adjust to 1,200 amps and higher. Fuse applications in Section 240.67 advise that arc reduction technologies are required on applications when a fuse is rated 1,200 amps and above, and only when arcing currents have a clearing time greater than 0.07 seconds. Whether fuse or circuit breaker, an arcing current evaluation must be conducted, documented and made available.

Arcing current

First introduced in 2017, "arcing current" is a term the NEC has yet to define. An informational note was added to NEC 2017, referencing IEEE 1584–2002, IEEE Guide for Performing Arc Flash Hazard Calculations, as a method of providing guidance when determining arcing current.

IEEE 1584-2018 defines arcing current as, "A fault current flowing through an electrical arc plasma." Arcing current is less than the available fault current (short-circuit current) at any point in the power distribution system due to the impedances of plasma and other materials present during an arc flash event. The additional impedance reduces current flow. This value of current will be critical in determining whether or not 240.67 and 240.87 requirements have been met, and in the case of fuses, whether or not an arc reduction technology is required.

Method to reduce clearing time

When an incident energy reduction technology is required, designers and installers may elect to use one of the following means to operate at less than the available arcing current to reduce the clearing time of larger OCPDs:

  • Zone selective interlocking (240.87)
  • Differential relaying (240.67 & 240.87)
  • Energy-reducing maintenance switching with a local status indicator (240.67 & 240.87)
  • Energy-reducing active arc flash mitigation system (240.67 & 240.87)
  • An instantaneous trip setting (temporary adjustment of the instantaneous trip setting to achieve arc energy reduction is not permitted) (240.87)
  • An instantaneous override (240.87)
  • Current-limiting electronically actuated fuses (240.67)

An approved equivalent means is a caveat for the requirements as arc energy reduction technologies continuously improve. The code making panel did not want to limit possibilities for future technologies.

The NEC clarified two issues during the 2020 code review. First, for circuit breakers with an adjustable instantaneous pickup, a "roll-down and back up again" instantaneous trip is not permitted to meet requirements. Field modification of setpoints via dials on the face of circuit breakers is not a good idea for many reasons reviewed and discussed by the code panel. Secondly, these changes help ensure that specified technologies respond to arcing currents provide the protection desired.

3) Testing procedures

Arc energy reduction systems must now be performance tested when installed. Because some of these technologies are complex, requirements mandate that testing be performed only by qualified individuals who follow manufacturer instructions. Qualified individuals must understand that it's possible to damage equipment during tests (e.g., injecting high currents through a fuse can open the fuse, which must then be replaced.) The qualified individual must also understand that some arc reduction technologies do not respond to current alone, demanding a mixture of tools and methods necessary to ensure proper installation.

Qualified individuals must provide a written test record and make that record available to the authority having jurisdiction. The record should be provided to the facility within which it is installed, with files available for future reference.

The rationale for change

Energy reduction requirements evolved with debate and due process of language improvements. While language was first introduced in 2011, it's my opinion that a focus on performance testing wasn't possible until today—code panel members and others in the industry needed time to reach a language consensus. Some argue more should be done, but I believe the overall intent is heading in the right direction.

During the 2020 code review, the code panel and others determined the NEC had to assure technologies are installed and that they are installed correctly at the time of installation, as is done with GFPE. The NEC requires GFPE testing (for equipment protection) when installed, yet did not require performance testing on installed worker-safety technologies.

The code making panel governing GFPE requirements for devices 1,000 amps and above (found in Sections 210, 215, 230 and 240) is the same code panel responsible for Sections 240.67 and 240.87. In some sense, 240.67 and 240.87 requirements are merely a continuation of what began with the GFPE requirements of NEC Section 230.95. Those requirements entered the NEC in 1971, but it wasn't until NEC 1978 that performance requirements at the time of installation were put in place. Section 240.87 followed a similar track. It entered the NEC in 2011; after three code review cycles, the NEC finally began discussing performance testing requirements at the time of installation.

Performance testing

Performance testing is a line item one can't afford to miss when bidding a project. The equipment and performance testing process of GFPE and arc reduction technologies can add significant cost if forgotten. It's essential to address their requirements upfront to maximize project efficiencies.

Here are some things to consider when developing a plan to meet NEC 2020 performance testing requirements:

Combined testing
Combine new performance testing requirements with those of GFPE (230.95 for OCPDs 1,000 amps and above). Projects must have on-site equipment to perform GFPE testing. This equipment can also be used to conduct additional testing for arc reduction.

Solution capabilities

The zones of protection offered by each technology are important to understand; test results may not make sense otherwise. Make sure you follow manufacturer instructions to test solutions correctly.

Current usage

Arcing currents are a function of available short-circuit current and can be quite high. However, technicians do not need to inject high currents to prove that transformers are installed properly and electronic trip units operate correctly. Verifying the entire system with a mix of low primary current injection testing and secondary current injection testing is the safest and most efficient method for success.

Unique conditions

Technologies like arc quenching equipment and active arc flash mitigation systems require more than primary current injection testing to ensure functionality. Light sources and manufacturer testing fixtures may be required.

What might the future hold?

The success of safety to a three-legged stool; one leg is no more important than the others. Today, three critical documents work in unison: the NEC (NFPA 70) provides installation requirements; NFPA 70E provides requirements for safe work practices; NFPA 70B reminds us of the critical role maintenance plays over time. Today the NEC mandates arc reduction technologies and requires assurances that these technologies work at the time of installation. 70E instructs all to leverage these technologies when justified energized work is performed, and 70B dictates periodic testing of these technologies throughout the life of the installation.

As equipment ages, and as devices are removed from and added to power systems, arcing currents change. Designers must remember to update single-line diagrams and systems analysis studies and make sure the technologies effectively provide arc energy reduction well after installation. In short, proper maintenance is vital.

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Arc flash: are you prepared?

Arc flash safety and NFPA 70E, OSHA's OSH Act -  is your facility in compliance?

Have you taken the proper steps to help protect your facility and its employees against the dangers of arc flash? Find out now. Simply answer a brief set of questions with Eaton's Reset Safety tool, and they will send you a customized preparedness profile to help you identify ways to reset safety in your facility. 

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CEDIA Releases Power Quality White Paper

Paper helps break down topics of electrical noise and power anomalies

The Custom Electronic Design & Installation Association (CEDIA) recently released The Quality of Power, a white paper that explores conditions and causes of electrical problems, and the solutions to deliver a better quality of power.

"There is no denying that technology is more a part of our daily lives than it has ever been before. The digital native generation does not know a world without the internet. With this demand for access to technology comes another sometimes overlooked need – the need for power that is free from transients, interruptions and noise," says Walt Zerbe, senior director of technology and standards. "CEDIA's new white paper explores why it is important to have quality power and how integrators can deliver better quality power to their clients."

The white paper helps break down the complex topics of electrical noise and power anomalies and what can be done to mitigate their effects.

CEDIA members can download a complimentary copy of The Quality of Power through the CEDIA Resource Catalogue. It is available to non-members for $99. 

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Creating safer conditions for electrical workers and protecting equipment through safety by design

Electrical workers and facility owners rely on technical professionals to take prudent and economical steps towards increasing worker safety and protecting facility equipment. "Safety by design" describes, what I believe to be, a comprehensive approach to incorporating practical and feasible electrical distribution system design solutions. The three pillars of success for electrical safety include:

  1. Eliminating hazards by establishing electrically safe working conditions.
  2. Implementing designs that reduce the likelihood of a hazardous occurrence.
  3. Reducing the potential severity of injuries should an accident occur when justified energized work is required.

When our industry is focused on these three pillars, the result is safer conditions for electrical workers and better protected equipment.

Safety by design – A three-part approach

Every electrical product and system must be designed with worker and equipment safety in mind. The following section explores in more detail the safety by design approach and its three components.

Part 1 - Eliminate the hazard

Hazard elimination is the act of establishing an electrically safe working condition. The NFPA 70E (National Fire Protection Association) committee helped provide clarity around this topic by adding an informational note to the definition of an electrically safe work condition which reads as follows:

"An electrically safe work condition is not a procedure, it is a state wherein all hazardous electrical conductors or circuit parts to which a worker might be exposed are maintained in a de-energized state for the purpose of temporarily eliminating electrical hazards for the period of time for which the state is maintained."

Establishing an electrically safe working condition is critical. While de-energizing equipment is an important goal, a worker will always have to dress in appropriate personal protection equipment (PPE) and use a test instrument to verify absence of voltage. Lock-out/tag-out procedures have to be followed which can range from simple to complex. In fact, there can be situations (e.g., verifying absence of voltage) when there isn't PPE with a rating high enough to protect the worker. For those situations, I believe we must incorporate system designs and solutions that minimize the likelihood of an occurrence and the severity of injury should an accident occur.

Part 2 - Designing for a reduction in the likelihood of occurrence

The following examples illustrate the many layers of safety that can be employed to reduce the likelihood of arc flash, arc blast and/or shock:

  • ELECTRICAL ONE-LINE DIAGRAMS: An important part of a facility's electrical infrastructure life begins even before ground is broken. This document is developed and used by engineers, suppliers, inspectors, workers and designers. Workers could be put at risk if one-line diagrams are not maintained and power system capabilities reviewed and updated as they change over time.
  • BARRIERS: Adding a local disconnect next to a panelboard or industrial control panel (ICP) that is accessed frequently for service provides electrical workers with clear visible indicators that the panel or ICP has been de-energized when the circuit breaker or switch is in the off position. When required absence of voltage testing is performed, the likelihood of an incident has been reduced.
  • DISCONNECTS: By placing a circuit breaker or fuse and switch in its own enclosure next to equipment, electrical workers have a readily accessible disconnect to remove voltage and establish an electrically safe working condition.
  • VISIBILITY: Equipping a panelboard with a window that allows workers to visibly see the blades being disconnected aids in worker verification reducing the likelihood of an incident.
  • INDICATORS: The presence of voltage indicators employed on equipment provides electrical workers a visible indication of which side of the disconnect is energized and which isn't.
  • KNOWLEDGE: Information on the condition and maintenance of equipment can provide electrical workers details that are critical to safety when performing justified energized work. Knowledge of the equipment itself is critical to recognizing hazards.
  • WORKING SPACE: Sometimes safety doesn't come in the form of a product, it can simply be in the fact that a design provides adequate working space for the electrical worker to safely perform functions.

Part 3 - Designing for a reduction in the severity of injuries

When justified energized work must occur, minimizing the danger associated with electrical hazards to the point at which injuries may be minor can be designed into the system. To that end, there are a variety of ways in which the electrical industry is making efforts to reduce the severity of injuries to workers should an accident occur.

  1. DECREASED CLEARING TIME: By placing a circuit breaker with arc reduction maintenance switch technology or a fuse and switch in its own enclosure next to an upstream of electrical equipment likely to be a part of justified energized work, provides reduced clearing times for arcing currents reducing the level of incident energy exposure. The achieved incident energy reduction downstream can be significant such that minimal PPE is required which could also decrease the likelihood of an event occurring.
  2. GFCI shock protection: GFCIs are specifically designed to protect people against electric shock from an electrical system, and to monitor the imbalance of current between the ungrounded (hot) and grounded (neutral) conductor of a given circuit.
  3. IEEE 1584 and arc flash calculations: New updates to the 2018 Guide for Performing Arc Flash Calculations offer significant changes that impact the way arc flash hazards in electrical systems are analyzed. More precise calculations help reduce the risk to employees and contractors.
  4. Arc reduction technologies: Arcing faults that occur within equipment need to be cleared as quickly as possible. Arc flash reduction technology reduces clearing times of arcing fault currents should a problem occur when working on energized electrical equipment. Arc Quenching equipment can extinguish an arc flash in approximately 4 milliseconds. Eaton's Arc Quenching Magnum DS low-voltage switchgear is a great example of such equipment. 

A trio of documents critical to safety

All of us in the electrical industry look to three key documents from the National Fire Protection Association (NFPA) that strategically work together to help increase safety for electrical workers by providing guidance and recommendations:

  • NFPA 70 The National Electrical Code (NEC) provides installation requirements
  • NFPA 70E-2021 covers the topic of electrical safety in the workplace
  • NFPA 70B covers electrical equipment maintenance

In particular, NFPA 70E includes requirements for safe work practices to protect personnel by reducing exposure to major electrical hazards, including shock, electrocution, arc flash and arc blast. These requirements rely on the fact that an electrical system was installed in accordance with the NEC and that maintenance has been performed leveraging reference materials found in NFPA 70B.

Recent changes to 70E highlight how important it is to design safety into systems and provide more detailed guidance for electrical workers. For example, the document addresses when the estimated incident energy exposure is greater than the arc rating of commercially available arc-rated PPE. We now have guidance for the purpose of absence of voltage testing. The following examples of risk reduction methods could be used to reduce the likelihood of occurrence of an arc flash, thus reducing the severity of exposure:

  • Use of non-contact proximity test instrument(s) or measurement of voltage on the secondary side of a low voltage transformer (VT) mounted in the equipment before use of a contact test instrument, to test for the absence of voltage below 1,000 volts
  • If equipment design allows, observe visible gaps between the equipment conductors and circuit parts and the electrical source(s) of supply
  • Increase the working distance
  • Consider system design options to reduce the incident energy level
In addition, the latest version of 70E recognizes the newly updated IEEE 1584, a resource that the industry will continue to explore and apply to new power system analysis studies. Protecting electrical workers means never settling

The effort to protect electrical workers and electrical equipment comes back to the three pillars of safety by design:

  • Eliminate the hazard
  • Reduce the likelihood of an occurrence
  • Reduce the severity of injuries

The goal has to be establishing an electrically safe working condition. For situations where justified energized work is required, designs must emphasize reducing the chances of something harmful occurring and reducing the severity of injuries should an accident occur.

When it comes to shock hazards, while the current flow cannot be reduced ways can be provided to avoid inadvertent contact. This means choosing specialized equipment that provides more fingersafe solutions and options for barriers that help prevent the worker from coming in contact with energized parts. In some ways, the work can judged based upon the complexity of PPE required for a task.

When designing electrical systems and the devices that go into those systems, a critical goal needs to be simplifying and safeguarding designs, so when systems need service or repair, electrical workers are safe in minimal PPE that consists of little more than their daily wear. Ultimately, electrical workers and our industry as a whole benefit most from a "never settle" approach to safety. Purchasing PPE at a higher Calorie capability than your solution demands doesn't spell success. We need to ask ourselves if we can do better. We don't have to settle for double digit calorie events anymore. We can do better. If we always strive for solutions that drive energy into the dirt, workers will eventually be safe in any situation. 

"We must incorporate system designs and solutions that minimize the likelihood of an occurrence and the severity of injury should an accident occur."

Thomas Domitrovich, vice president, technical sales Eaton Corp.

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The Unknown Danger of UPS Batteries

How removing the input transformer has affected the servicing of UPS batteries

Uninterruptible power supply (UPS) systems have come a long way since the original designs of the 20th century. Many of these improvements make systems more reliable, faster to repair, and safer for service personnel. Manufacturers have worked hard to reduce the weight, size, and cost of the systems, giving end-users additional space for IT equipment. One way they have accomplished this is by removing the input and output isolation transformers. The advantages and disadvantages have been discussed in numerous articles and whitepapers. This article specifically examines how removing the input transformer has affected the battery plants and the ability to safely service them.

The ABCs of a UPS
Reviewing the basic building blocks of a UPS system can help us understand how removing the input transformer would affect the operation of UPS system and the battery system.

The original double-conversion type UPS system (Fig. 1) was made up of the following:
• Input transformer
• Rectifier
• Inverter
• Output transformer
• Static switch
• Batteries

 Fig. 1. This diagram shows the basic building blocks of an original double-conversion type UPS.

The first component is the input transformer, which performs several functions, including: isolating the UPS system from the electric utility system, allowing for a 12-pulse rectifier, and reducing input current distortion. Of course, it can also be used to change the input voltage from one level to another. For example, a 480V source could be stepped down to 208V.
The next major component in this type of system is the rectifier. The primary function of the rectifier is to convert incoming AC power to DC power, which can then be used to support the input to the inverter and charge the batteries.
Continuing across Fig. 1 is the inverter, which converts DC voltage to AC voltage and supplies power to the output isolated transformer. The output transformer supplies conditioned power to the critical load.
A static switch, shown above the rectifier and inverter, is used to transfer the critical load from the inverter to the bypass line if there is a failure of the UPS system or if maintenance is required.
The last component in this type of system is the batteries. If input power is lost — typically because of an electric utility outage — then the batteries provide power to the inverter.

Risky removal
One advantage of the input transformer is that it isolates the batteries from the ground reference. The input transformer on these systems prevents a voltage potential between the DC bus, including the batteries and ground. If a short were to occur between the two, there would be no return path for current, and it could not flow (Fig. 2). If a battery did short to ground, then most systems have a circuit that would alarm. The system would often continue to operate until it could be shut down and the danger eliminated.

Fig. 2. The input transformer on a double-conversion type UPS system prevents a voltage potential between the DC bus, including the batteries and ground. If a short were to occur between the two, there would be no return path for current, and it could not flow.

With removal of the input transformer, the DC bus is no longer isolated from ground. There is both AC and DC potential between the batteries and ground, which includes the racks and cabinets. Because of this potential, if any conductive material (including humans) is connected, then current could flow through the item. This could lead to damaged tools, batteries, and racks or worse — injury or death of personnel (Fig. 3).

Fig. 3. With removal of the input transformer, the DC bus is no longer isolated from ground, which ultimately could lead to damaged tools, batteries, and racks or worse — injury or death of personnel.

Maintenance considerations
It's common practice on the original double-conversion type UPS systems to perform as much battery maintenance as possible while the UPS system is online supporting load. This allows for the critical load to stay protected during battery maintenance.
Vented batteries often have four preventive maintenances (PM) visits completed per year, while the UPS system has two. The two additional battery maintenance visits can be completed with very little risk to the critical load, allowing for the work to be completed during normal working hours.
Valve regulated lead acid (VRLA) batteries typically have two PM visits per year in conjunction with the UPS system. The battery maintenance is completed while the UPS system is online. Or, if it isn't a major UPS system inspection requiring a transfer to bypass, the batteries do not have to be taken offline at all.
Over the last 10 years, a few manufacturers have started supplying VRLA batteries inside a container often referred to as a "battery can" or "battery module" (Fig. 4).

Fig. 4. Some manufacturers have started supplying VRLA batteries inside a container often called a "battery can" or "battery module."

Modular battery systems have the same electrical dangers as open racks or battery cabinets. However, because the batteries are enclosed in a sealed box, there is no chance they can come into contact with personnel or ground. This gives a built-in safety feature during maintenance, because all the battery connections are enclosed and can't come into contact with tools or personnel.
Although modular batteries require periodic maintenance, it's not as invasive as traditional VRLA or vented batteries. Instead of using specialized test equipment to test each jar's voltage, internal resistance and specific gravity, if applicable, the UPS system runs a battery test at preprogrammed dates. If a problem is found, an alarm is generated, and appropriate personnel notified. This essentially eliminates risk to service personnel because there is no contact with the batteries while the system is online.

Battery most likely to succeed?

Over the last several years and for the foreseeable future, the use of lithium-ion (Li-ion) batteries to support UPS systems continues to increase. Again, the electrical danger of removing the input transformer would be the same as lead-acid batteries. However, much like the modular battery systems, the danger is reduced by the type of installation and the maintenance that is required. Personnel would not be exposed to the DC bus, and this reduces risk.
An example of the dangers involved can be seen in a recent event that occurred when a modern UPS system without an input transformer had an annual PM performed on its batteries. During the PM procedure, bolt re-torque activities were being completed. There was not enough clearance for an insulated torque wrench so the technician used his uninsulated torque wrench. After completing about half the plant, the technician's wrench made contact with a battery-retaining bracket while still in contact with the terminal bolt. This caused a bolted fault between the DC bus and ground, resulting in damage to the battery post, the battery rack, and the torque wrench (Fig. 5). Thankfully, the worker suffered no injuries.

Fig. 5. While performing an annual PM on its batteries, a technician's wrench made contact with a battery-retaining bracket while still in contact with the terminal bolt. This caused a bolted fault between the DC bus and ground.

Risk reduction
Using Li-ion or modular batteries would have prevented this incident from happening. However, not all installations are Li-ion or modular. What can be done to reduce the risk to personnel on these systems?
First and foremost, educate everyone who will be working with or around UPS systems of the dangers involved. In addition, use insulated tools and provide barriers where possible to prevent anyone from coming into contact with uninsulated battery terminals.
Whenever possible, all maintenance should be completed with the batteries disconnected from the UPS charging circuit. This will prevent a return path for current if contact is made between any battery connection and ground.
As with any service work in the electrical field, it's important to understand any and all dangers before working on or near equipment. Wherever possible, reduce or remove the danger before work is started. This not only protects the equipment but, more importantly, it also protects you.

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