IEEE 1584 Committee Fails to Modify Arc Flash Hazard Study Exemption

On Saturday 9/17, members* of the IEEE 1584 Working Group met in Toronto, ON to discuss the latest IEEE/NFPA Collaboration Testing report and to discuss changes to the IEEE 1584 Standard.  The meeting was attended by approximately fifty engineers and technicians from across the United States and Canada.

One of the most controversial items in the current Standard 1584® IEEE Guide for Performing Arc-Flash Hazard Calculations is the exemption for systems less than 240 volts and fed by transformers rated 125 kVA or less.  Section 4.2 page 6 states, “Equipment below 240 V need not be considered unless it involves at least one 125 kVA or larger low impedance transformer in its immediate power supply.” 

There are two problems with this statement.   The first is that IEEE 1584 Standard is for three phase systems only and it is not to be used for single phase systems.  A 125 kVA transformer is a standard single phase transformer size and not a standard three phase transformer (the closest standard three phase size is 112.5 kVA)

The second problem is the assumption that there is no serious arc flash hazard for these systems.  Last year several committee members performed experiments and found that 208 volt system fed by 112.5 kVA and 75 kVA still can create enough energy to ignite untreated cotton and polyester blends of clothing.  It depends upon, the amount of available fault current on the primary side and the transformer impedance.  If the parameters are within a certain range, the arc can be sustained and will not self extinguished as previously believed.  Obviously it appeared that our committee had set the cut off point for arc flash calculations too high.

Last spring, the IEEE/NFPA Collaboration Testing team did some testing of these smaller transformers and systems. They too confirmed that for 112.5 and 75 kVA transformers, the arcs sometimes will not self-extinguish and the arc flash energy levels exceeded 1.2 Cals/cm2 at a working distance of 18 inches.  Therefore, an arc flash hazard exists for these small distribution transformers.

During the Committee meeting in Toronto, we the committee members debated how to change the standard section and what language to use to lower this cut off point.  Mr. Jim Phillips proposed a change to the text to say the following.

Base upon the recent NFPA / IEEE test data it appears that up to 250 V and 5 kA, the incident energy does not exceed 4 cal/cm2.  (12 cycles duration)

This was later modified to state 208 Volts and the incident energy level does not exceed 8 cal/cm2. 

The voltage was changed to due to the fact the 1585 Standard is for three phase systems only.  Also, NFPA 70E has recently added a foot note to Section 130.5 Arc Flash Hazard Analysis (See complete text below) The footnote states:

Informational Note No. 4: For additional direction for performing maintenance on overcurrent protective devices, see Chapter 2, Safety-Related Maintenance Requirements. Informational Note No. 5: See IEEE 1584 for more information regarding arc flash hazards for three-phase systems rated less than 240 volts.

I recommended that we change the PPE level from 4 cals/cm2 to 8 cals/cm2 to align our Standard more closely with NFPA 70E - Informative Annex H Guidance on Selection of Protective Clothing and Other Personal Protective Equipment.  This annex recommends that a Simplified, Two-Category, Arc-Rated Clothing System be implemented for electrical workers.  The Standard recommends electricians wear 8 cal/cm2 clothing for everyday type work.  When additional protection is needed, then additional layers of arc rated clothing including a blast hood would be used. 

This passionate debate for these changes to the 1584 Standard went on for almost two hours.  Unfortunately, our committee did not reach a consensus.  The exemption remains unchanged.  It shows just how difficult it is to get fifty engineers and technicians to agree. 

A proposal was made that the 1584 Committee meet for one day before the 2012 Electrical Safety workshop.  This way, the committee members will have more time to discuss the proposed changes to the Standard.  Hopefully, this meeting will get scheduled and we can finally get the bar lowered and label these hazardous.

Changes to NPFA 70E Arc Flash Exemption

2009 NFPA 70E

130.3 Arc Flash Hazard Analysis.

An arc flash hazard analysis shall determine the Arc Flash Protection Boundary and the personal protective equipment that people within the Arc Flash Protection Boundary shall use. The arc flash hazard analysis shall be updated when a major modification or renovation takes place. It shall be reviewed periodically, not to exceed five years, to account for changes in the electrical distribution system that could affect the results of the arc flash hazard analysis.  The arc flash hazard analysis shall take into consideration the design of the overcurrent protective device and its opening time, including its condition of maintenance.

Exception No. 1: An arc flash hazard analysis shall not be required where all of the following conditions exist:

(1) The circuit is rated 240 volts or less.

(2) The circuit is supplied by one transformer.

(3) The transformer supplying the circuit is rated less than 125 kVA.

The Sections has now been changed to

130.5 Arc Flash Hazard Analysis.

An arc flash hazard analysis shall determine the arc flash boundary, the incident energy at the working distance, and the personal protective equipment that people within the arc flash boundary shall use.  The arc flash hazard analysis shall be updated when a major modification or renovation takes place. It shall be reviewed periodically, not to exceed 5 years, to account for changes in the electrical distribution system that could affect the results of the arc flash hazard analysis.

The arc flash hazard analysis shall take into consideration the design of the overcurrent protective device and its opening time, including its condition of maintenance.

Exception: The requirements of 130.7(C)(15) and 130.7(C)(16) shall be permitted to be used in lieu of determining the incident energy at the working distance.

Informational  Note No. 1: Improper or inadequate maintenance can result in increased opening time of the overcurrent protective device, thus increasing the incident energy.

Informational  Note No. 2: Both larger and smaller available short-circuit currents could result in higher available arc flash energies. If the available short-circuit current increases without a decrease in the opening time of the overcurrent protective device, the arc flash energy will increase. If the available short-circuit current decreases, resulting in a longer opening time for the overcurrent protective device, arc flash energies could also increase.

Informational Note No. 3: The occurrence of an arcing fault inside an enclosure produces a variety of physical phenomena very different from a bolted fault. For example, the arc energy resulting from an arc developed in the air will cause a sudden pressure increase and localized overheating. Equipment and design practices are available to minimize the energy levels and the number of at-risk procedures that require an employee to be exposed to high level energy sources. Proven designs such as arc-resistant switchgear, remote racking (insertion or removal), remote opening and closing of switching devices, high-resistance grounding of low-voltage and 5-kV (nominal) systems, current limitation, and specification of covered bus or covered conductors within equipment are techniques available to reduce the hazard of the system.

Informational Note No. 4: For additional direction for performing maintenance on overcurrent protective devices, see Chapter 2, Safety-Related Maintenance Requirements. Informational Note No. 5: See IEEE 1584 for more information regarding arc flash hazards for three-phase systems rated less than 240 volts.

* - Robert E. Fuhr, P.E. of Power Studies.com is a member of the IEEE 1584 committee.  Click here for more information about Mr. Fuhr’s experience