Testing and applying IEEE 1584’s new arc flash requirements

Guest contributor: Kevin J. Lippert, manager, codes & standards, Eaton

An arc flash analysis quantifies incident energy to better protect against an arc flash hazard. The latest updates to the Institute of Electrical and Electronics Engineers (IEEE) Std 1584TM 2018 Guide for Performing Arc Flash Calculations have made significant strides toward furthering electrical safety. The Guide, a widely accepted method for performing arc flash hazard calculations, is now backed by nearly 2000 additional tests — more than any other method — to provide the information necessary to complete an arc flash risk assessment.

Of course, arc flash analysis is never an exact science and, the use of IEEE 1584 is not mandatory. But I strongly recommend electrical engineers embrace the new version of IEEE 1584, as its formulas and mathematical models are based on a multitude of varied field conditions and the most up-to-date science.

New requirements lead to new questions

Consultants and electrical engineers have been using IEEE 1584 to calculate incident energy since the Guide’s inception in 2002. Many engineers have a comfort level with the 2002 version of the Guide and are very accustomed to its calculation methodologies, so they may have reservations about the 2018 version. Further, some professionals are beginning to raise questions as they apply the 2018 version in real-world scenarios.

Let’s take the new addition of electrode configuration as an example. Engineers have begun applying this aspect of the Guide on new projects, as data and equipment details are more likely available to meet the parameter needs of equations. However, these professionals question whether they have the same level of clarity for older systems and existing projects. In these cases, electrode configurations and box dimensions may be unclear or very difficult to ascertain, making the implementation of the 2018 version questionable for existing systems. Some engineers have indicated they would revert to the 2002 version in such instances.

Situations vary, so toggling between the 2002 and 2018 calculations may sometimes seem logical, but in practice, doing so creates confusion. At Eaton, we think it is important to eliminate that confusion.

Clarifying requirements through independent studies

Our mission is to help professionals adopt the 2018 Guide and increase confidence in their data and calculation results. Today, my engineering colleagues at Eaton use updated IEEE 1584 equations to model electrical systems and perform sample calculations to define the differences between the 2002 and 2018 versions.
Our mission is to help consultants and electrical engineers understand and adopt the 2018 Guide and increase confidence in their data and calculation results.

With each new power distribution system model, we gain a better understanding of the increases and decreases of incident energy value applications calculated from the 2002 version and recommend how to apply the updated Guide moving forward.
Our preliminary findings suggest:

  • Three additional electrode configurations — vertical electrodes (metal box with an insulating barrier (VCBB)), horizontal electrodes (metal box (HCB)) and horizontal electrodes (open air (HOA)) — represent perhaps the most significant changes to the Guide. Generally, the horizontal electrode configurations result in higher calculated incident energy than the vertical configurations.
  • The Guide now accounts for engineered electrical assemblies and tests to North American ANSI/IEEE Standards and those in other world regions thanks to higher calculated arcing current values in the 2018 version. We also see an increase in incident energy values. We believe one of the reasons this occurs is because the 2018 update offers more selection options for phase conductor spacing.
  • Additional options for enclosure size are now available, allowing for more accurate modeling based on actual equipment conditions. In most cases, larger enclosures result in slightly lower incident energies as plasma arc events partially dissipate in voluminous enclosures.

How to account for real-world applications

While preliminary, I expect our findings to impact many field applications. Topping the list is additional training that may be required to perform surveys, collect data and complete accurate calculations due to the sheer number of alternatives and variables to consider. In my opinion, consultants and electrical engineers should prepare for significant procedural changes:

  • Higher arcing currents calculated using the 2018 Guide could be offset by faster clearing times of the overcurrent protective device (OCPD). Higher currents mean a better chance that protective devices will operate in the instantaneous region and result in faster clearing times. This may offer lower calculated incident energies than the 2002 version, which has a lower arcing current but a longer clearing time.
  • Engineers should pay close attention to time-current characteristic (TCC) curves and work to understand relationships between arcing currents and clearing times based on protective device selection and the many settings available.
  • The 2018 Guide is not definitive in suggesting a 240V low-end threshold for system analysis, stating only that sustainable arcs are less likely but possible in systems with available short circuit currents of 2000A or less. The former Guide defined a low-end for analysis stating that equipment below 240V not be considered unless it involves at least one 125kVA transformer or larger.
  • There is a gap in the methodology used to establish bus configurations for equipment. Clarity and direction should be provided in an application-style guide to help manufacturers and power system engineers understand configurations that apply to diverse electrical components and assemblies.

Implement IEEE 1584 across all systems

I believe consultants and electrical engineers should embrace and begin using the 2018 edition of IEEE 1584 moving forward. As with any new change in engineering practice, I expect an adjustment period during which professionals will acclimate to the Guide’s new calculations. Further, while IEEE 1584 is not a mandatory requirement, I believe more users will accept how the updated Guide enhances safety across all electrical systems, both existing and new:

Existing equipment

If you’ve changed your OCPD, its settings, or are approaching the five-year update threshold mandated by National Fire Protection Association (NFPA) 70E Section 130.5(G), calculating incident energy based on IEEE 1584 makes great sense because its models are based on the most current data available.

New equipment

Higher incident energy calculations should cause users to look for alternative methods of reducing arc flash risk. We’ve determined that some IEEE 1584 calculated incident energies are higher. As a result, engineering controls such as arc reduction maintenance switches and arc quenching technologies will mitigate the risk of increased arc flash energies. Design engineers should take it upon themselves to understand the options of engineering controls to reduce or eliminate the risk of arc flash events.


CMA/Flodyne/Hydradyne is an authorized  Eaton Electrical distributor in Illinois, Wisconsin, Iowa and Northern Indiana.

In addition to distribution, we design and fabricate complete engineered systems, including hydraulic power units, electrical control panels, pneumatic panels & aluminum framing. Our advanced components and system solutions are found in a wide variety of industrial applications such as wind energy, solar energy, process control and more.

The pros and cons of soft starters vs. VFDs by application

Guest contributor: Eaton

Motors often require large amounts of energy when quickly accelerating to full speed. Soft starters and variable frequency drives can both be used to reduce inrush currents and limit torque— protecting your valuable equipment and extending the life of your motor by reducing motor heating caused by frequent starts and stops. Choosing between a soft starter and a variable frequency drive often depends on the application, system requirements, and cost (both for initial startup and over the life cycle of the system).

Soft starters

A soft starter is a solid-state device that protects AC electric motors from damage caused by sudden influxes of power by limiting the large initial inrush of current associated with motor startup. They provide a gentle ramp up to full speed and are used only at startup (and stop, if equipped). Ramping up the initial voltage to the motor produces this gradual start. Soft starters are also known as reduced voltage soft starters (RVSS).


Soft starters are used in applications where:

• Speed and torque control are required only during startup (and stop if equipped with soft stop)
• Reducing large startup inrush currents associated with a large motor is required
• The mechanical system requires a gentle start to relieve torque spikes and tension associated with normal startup (for example, conveyors, belt-driven systems, gears, and so on)
• Pumps are used to eliminate pressure surges caused in piping systems when fluid changes direction rapidly

How does a soft starter work?

Electrical soft starters temporarily reduce voltage or current input by reducing torque. Some soft starters may use solid-state devices to help control the flow of the current. They can control one to three phases, with three-phase control usually producing better results.


Most soft starters use a series of thyristors or silicon controlled rectifiers (SCRs) to reduce the voltage. In the normal OFF state, the SCRs restrict current, but in the normal ON state, the SCRs allow current. The SCRs are engaged during ramp up, and bypass contactors are pulled in after maximum speed is achieved. This helps to significantly reduce motor heating.

Benefits of choosing a soft starter

Soft starters are often the more economical choice for applications that require speed and torque control only during motor startup. Additionally, they are often the ideal solution for applications where space is a concern, as they usually take up less space than variable frequency drives.

Variable frequency drives

A variable frequency drive (VFD) is a motor control device that protects and controls the speed of an AC induction motor. A VFD can control the speed of the motor during the start and stop cycle, as well as throughout the run cycle. VFDs are also referred to as adjustable frequency drives (AFDs).


VFDs are used in applications where:

• Complete speed control is required
• Energy savings is a goal
• Custom control is needed

How do VFDs work?

VFDs convert input power to adjustable frequency and voltage source for controlling speed of AC induction motors. The frequency of the power applied to an AC motor determines the motor speed, based on the following equation:

N = 120 x f x p

N = speed (rpm)
f = frequency (Hz)
p = number of motor poles

For example, a four-pole motor is operating at 60 Hz. These values can be inserted into the formula to calculate the speed:

N = 120 x 60 x 4

N = 1800 (rpm)


AC supply: Comes from the facility power network (typically 480V, 60 Hz AC)
Rectifier: Converts network AC power to DC power
Filter and DC bus: Work together to smooth the rectified DC power and to provide clean, low ripple DC power to the inverter
Inverter: Uses DC power from the DC bus and filter to invert an output that resembles sine wave AC power using a pulse width modulation (PWM) technique
•  Pulse width modulation: Switches the inverter semiconductors in varying widths and times that, when averaged, create a sine waveform


Benefits of using a VFD

• Energy savings
• Reduces peak energy demand
• Reduces power when not required
• Fully adjustable speed (pumps, conveyors, and fans)
• Controlled starting, stopping, and acceleration
• Dynamic torque control
• Provides smooth motion for applications such as elevators and escalators
• Maintains speed of equipment, making drives ideal for manufacturing equipment and industrial equipment such as mixers, grinders, and crushers
• Versatility
• Self-diagnostics and communications
• Advanced overload protection
• PLC-like functionality and software programming
• Digital inputs/outputs (DI/DO)
• Analog inputs/outputs (AI/AO)
• Relay outputs

Energy savings

VFDs offer the greatest energy savings for fans and pumps. The adjustable flow method changes the flow curve and drastically reduces power requirements. Centrifugal equipment (fans, pumps, and compressors) follow a general set of speed affinity laws. The affinity laws define the relationship between speed and a set of variables:

• Flow
• Pressure
• Power

Based on the affinity laws, flow changes linearly with speed while pressure is proportional to the square of speed. The power required is proportional to the cube of the speed. The latter is most important, because if the motor speed drops, the power drops by the cube.


In this example, the motor is operated at 80 percent of the rated speed. This value can be inserted into the affinity laws formula to calculate the power at this new speed:


Therefore, the power required to operate the fan at 80 percent speed is half the rated power.ia04003002e-9

Selecting the correct equipment for your needs

Choosing a soft starter or a variable frequency drive often depends on your application. Soft starters are smaller and less expensive when compared with VFDs in larger horsepower applications. Larger VFDs take up more space and are usually more expensive than soft starters.

That being said, while a VFD is often more expensive up front, it can provide energy savings of up to 50 percent, thereby producing more cost savings over the life of the equipment.

Speed control is another advantage of a VFD, because it offers consistent acceleration time throughout the entire operating cycle of the motor, not just during startup. VFDs can also provide more robust functionality than soft starters offer, including digital diagnostic information.

It is important to note that a VFD can initially cost two to three times more than a soft starter. Therefore, if constant acceleration and torque control is not necessary, and your application requires current limiting only during startup, a soft starter may be a better solution from a cost standpoint.


CMA/Flodyne/Hydradyne is an authorized  Eaton Electrical distributor in Illinois, Wisconsin, Iowa and Northern Indiana.

In addition to distribution, we design and fabricate complete engineered systems, including hydraulic power units, electrical control panels, pneumatic panels & aluminum framing. Our advanced components and system solutions are found in a wide variety of industrial applications such as wind energy, solar energy, process control and more.