Don’t Open Energized Controllers
We’ve probably all heard or used the old adage, “What you don’t know won’t hurt you,” when referring to things that one would better off not knowing, but there are some things that not knowing can indeed hurt you. One such thing that tends to be an unknown to most water-based fire protection system inspectors is the arc flash hazard associated with electric fire pump controllers. The occurrence of an arc flash involves the rapid release of energy through an arcing fault between a phase bus bar and another phase bus bar, neutral, or a ground. Initiation of such an event can be caused by contamination tracking over insulated surfaces, dust, dropping tools, accidental touching, condensation, material failure, corrosion, or faulty installation, among other means. An arc fault causes an ionization of the air and resultant formation of highly conductive plasma through which a sustained arc is established and maintained until such time that the current is interrupted. As the temperature of the arc increases, the resistance of the plasma path decreases causing an increasing current flow and resultant increase in temperature, quickly elevating the severity of the event. The temperature of the arc flash can reach as high as 35,000°F. These temperatures can cause severe burns to human skin, the ignition of nearby combustibles, and even liquefy or vaporize metal parts in the vicinity of the event, including copper, aluminum, and steel. The resultant rapid volumetric expansion of material (conservatively estimated as up to 40,000 to 1 – vaporing copper expands 67,000 times its volume) in transitioning from a solid to a vapor creates an explosive pressure with sufficient concussive force to cause physical damage to equipment and severe injury to personnel within the area. The blast pressure can exceed 2,000 lb/ft2 with a pressure wave velocity exceeding 700 mph. Damaging sound waves (as high as 140-160 dB) and flash injuries can occur resulting in loss of hearing and vision. These injuries can be very severe including death of the exposed individual.
This hazard is recognized by the provisions of NFPA 25, Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems, (2017 edition), sections 4.9.6 and 126.96.36.199 which indicate that legally required precautions must be taken when testing or maintaining electric controllers for motor-driven fire pumps. The provisions of NFPA 25, sections A.188.8.131.52 and A.4.9.6 further provide a reference for the user to NFPA 70E®, Standard for Electrical Safety in the Workplace®, (2015 edition) for additional safety guidance. NFPA 25, section A.4.9.6 also provides warning of the unusual hazard associated with electric fire pump installations installed in accordance with NFPA 20, Standard for the Installation of Stationary Pumps for Fire Protection, which discourages the installation of a disconnect in the power supply connection. Additionally, in the United States the provisions of OSHA’s selection and use of work practice standard 29 CFR 1910.333(c) provides that individuals working on exposed live parts must be qualified and must be familiar with the proper use of special precautionary techniques, personal protective equipment (PPE), insulating and shielding materials, and insulated tools. Furthermore, the provisions of the General Duty Clause of 29 U.S.C. §654(a)(1) provide an overarching requirement that employers shall furnish to each of his/her employees a place of employment, which is free from recognized hazards that cause, or are likely to cause, death or serious physical harm to the employee. This provides a baseline statement that marks the utmost importance of safety in the conduct of work and sets a basis of such in requiring that safety be paramount in the conduct of any work application. However, knowledge of the true level of hazard associated with arc flash for electric fire pump installations is not generally understood by those individuals tasked with completing such work or by their employers.
In order to truly understand the hazard, the provisions of NFPA 70E (2015 edition), section 130.5 require that an arc flash risk assessment be performed to determine if an arc flash hazard exists. Where an arc flash hazard is found to exist, the risk assessment shall also determine the appropriate safety-related work practices required, the arc flash boundary distances (location at which the incident energy equals 1.2 cal/cm2), and the required PPE necessary for work conducted within such boundary distances. The results of this assessment must be documented as provided by NFPA 70E, section 130.5(3)(A) and the electrical equipment itself must include labeling that specifically indicates:
1) the nominal system voltage,
2) the arc flash boundary, and
3) at least one of the following:
- a) the available incident energy and corresponding working distance or the arc flash PPE category needed for work on the equipment (but not both),
- b) the minimum arc rating of clothing, or
- c) site-specific level of PPE as provided by NFPA 70E, section 130.5(3)(D).
The owner of the electrical equipment is responsible for the documentation, installation, and maintenance of this field-marked labeling. Experience has shown this labeling to be virtually nonexistent in the field and even if it were in place would an inspector understand the hazard associated with a designation showing some number of cal/cm2 or would it simply be dismissed as meaningless to the inspector? Where an inspector is faced with conducting work inside an energized unlabeled electric fire pump controller without proper documentation they have no means to determine what specific level of PPE is necessary for the safe completion of such work and as such should not engage in the activity.
The determination of the required arc flash PPE can be established by conducting an incident energy analysis to determine the incident energy exposure level at the anticipated working distance of the employee’s face and chest area from the prospective arc flash source for the specific task being performed, as provided in annex D of NFPA 70E or it can be established using the PPE Category Method as included in NFPA 70E, table 130.7(C)(15)(A)(b) for alternating current systems where the specific provisions of the table apply to the conditions being considered. Again, a typical fire pump installation is considered a motor control center (MCC) with a voltage rating of 600V or less. For this type of equipment, table 130.7(C)(15)(b) includes two separate line entries. The first entry allows for a maximum available short circuit current of 65kA with a maximum fault clearing time of 0.03 seconds (2 cycles) and requires Category 2 PPE arc-flash protection. The second entry allows for a maximum available short circuit current of 42kA and the maximum fault clearing time of 0.33 seconds (20 cycles) and requires Category 4 PPE arc-flash protection. An anticipated working distance of 18 inches is indicated in both cases. It is important to understand that these are just examples of the calculated arc flash incident energy and associated designation of required PPE under those specific conditions indicated. Under any other conditions beyond these specific limits for short circuit current and clearing time indicated in table 130.7(C)(15)(A)(b), the exact conditions must be assessed individually to establish the specific incident energy for which the PPE must then be selected from NFPA 70E, table 130.7(C)(16). A select number of recognized methods are provided in annex D of NFPA 70. It is also important to note that the incident energy covered by the provisions of NFPA 70E, table 130.7(C)(16) for Category 4 PPE is a minimum of 40 cal/cm2. Beyond that limit, selection of appropriate PPE must be made based on the actual incident energy protection afforded by the PPE and not the Category of PPE. Some manufacturers have PPE designated for incident energy levels significantly higher than 40 cal/cm2. The protection afforded by the use of the designated PPE may not prevent all arc flash burn injuries but rather is intended to reduce potential burn injury and increase survivability. Additionally, arc rated PPE is not intended to address the resultant explosive physical impact trauma beyond the thermal effects of the arc flash whereas arc blast PPE (including hard hat, hearing protection, safety glasses, etc.) can include a degree of protection from physical impact. As the incident energy rises above 40 cal/cm2, the concussive impact potential can exceed that protectable by conventional means. The fact is many electric fire pump installations are designed to have incident energy level well in excess of 40 cal/cm2 and have no means for disconnect for power and no overcurrent protection.
For fire pump installations, the provisions of NFPA 20, chapter 9 and National Electric Code (NEC), Article 695 permit the installation of a single disconnecting means between the source of power and the fire pump controller/transfer switch under the following conditions:
- The disconnecting means must be identified as being suitable as service entrance equipment
- The disconnecting means must be lockable in both the closed and open position
- The disconnecting means must be located remote from other building and other fire pump disconnecting means
- The disconnecting means must be marked “Fire Pump Disconnecting Means”
- A placard must be installed adjacent to the controller indicating the location of the disconnecting means and location of any keys needed to unlock such
- The disconnecting means must be supervised in the closed position by:
- 1) central station, proprietary station or remote station signaling device;
- 2) local signaling service that sounds an audible alarm at a constantly attended location;
- 3) locking of the disconnecting means in the open position; or
- 4) sealing of the disconnecting means in the open position where located within a fenced enclosure or building under control of the owner with weekly inspections.
While a single disconnecting means is permitted under the above conditions, the installation of a disconnecting means is not required under the provisions of either NFPA 20 or the NEC. As a result, it is rare to find the installation of such within the power feed to the fire pump controller due to the increased cost of installing such devices. This typical lack of disconnecting means limits the ability to de-energize the fire pump controller, requiring that work be completed on an energized controller.
For fire pump installations, the provisions of NFPA 20, chapters 9 and 10 and NEC, Article 695 provide that the only overcurrent protection required for squirrel cage or wound-rotor induction motors shall be within the fire pump controller and shall have a time delay of between 8 and 20 seconds at locked rotor current, and 3 minutes at 300 percent of the motor full-load current. Other means of overcurrent protection, while not recommended by NFPA 20 and the NEC, would have to be rated higher than that specified above to limit the opportunity for tripping of other overcurrent protection prior to that located within the controller. If installed, the overcurrent protection device must be sized in accordance with either of the following:
- Sized to carry the locked rotor current of the fire pump plus the full-load current of all other connected loads for an indefinite period of time
- The overcurrent protection device must not be field adjustable and must not open:
- Within 2 minutes at 600 percent of the full-load current,
- With a restart transient of 24 times the full-load current, or
- Within 10 minutes at 300 percent of full-load current
This is intended to ensure continuity of power to the fire pump under certain adverse overload conditions to keep the fire pump operational regardless of risk to the conductors. As a result, it is rare to find the installation of such within the power feed to the fire pump controller due to the increased cost of installing such devices. The only other overcurrent protection typical for a fire pump installation would be the primary fuse found in the transformer supplying power to the installation. Both the rating and associated operating time delay [typically beyond that indicated in NFPA 70E, table 130.7(C)(15)(A)(b)] associated with these devices cause an increase in the exposure to an electric arc flash incident energy beyond that normally anticipated for typical motor control centers. As a result, each installation condition must be individually assessed to determine the incident energy associated with the specifics of that installation. The determination of the appropriate PPE must then be selected based on such a determination.
The calculation of the incident energy in accordance with NFPA 70E, annex D requires a thorough knowledge and understanding of the operating conditions at hand as well as the principals and limitations of the various calculation methods presented.
The provisions of NFPA 70E, annex D include four suggested methods for determination of incident energy, each with associated limitations as summarized on NFPA 70E, table D.1.
The utilization of any of these methods requires a thorough understanding of the methods and limitations thereof for proper determination of incident energy associated with a specific installation and should only be undertaken by qualified individuals. This analysis is not within the typical purview of a water-based fire protection system inspector.
A number of activities are included in NFPA 25 that require the inspector to access the interior of the fire pump controller while the panel may be energized. Where the controller is not provided with a separate disconnect, the controller would generally remain continuously energized unless power is pulled at the supplying transformer.
NFPA 25, section 184.108.40.206(2)(a) requires that electric motor voltage and current levels be recorded on all lines at each of the required flow conditions during the annual performance test of the fire pump. This would normally include churn, rated and 150 percent flows. With variable speed controllers, additional flow point readings would be needed. Additionally, NFPA 25, section 220.127.116.11(3) requires that the electric motor voltage and current levels be taken with the pump operating at peak operating load after transfer of power to the alternate power source for installations that include an automatic transfer switch.
For older fire pump controllers, inspection personnel must conduct work inside the energized fire pump controller. With the advent of a requirement in NFPA 20 to include voltage and current meters from the exterior of fire pump controllers, inspection personnel would no longer be required to open the fire pump controller to take the necessary readings. This was initially included in the 1999 edition of NFPA 20 as follows: “Means shall be provided on the exterior of the controller to read all line currents and all line voltages.” The committee substantiation included with the modification is as follows, “This is to eliminate a recognizable hazard, i.e., high available fault current. A fire pump controller enclosure serves to contain such a fault and is tested to verify its integrity.” The current language in the 2016 edition of NFPA 20 has been tweaked slightly over the years to include accuracy criteria for the installed meters and reads as follows, “10.3.4.3 Means shall be provided on the exterior of the controller to read all line currents and all line voltages with an accuracy within +/-5 percent of motor nameplate voltage and current.”
Interestingly, the provisions of NFPA 25, table A.18.104.22.168 provides that the installed voltmeters and ammeters on the face of the controller be inspected for accuracy (5 percent) annually. If checked in place, this would require that inspection personnel must conduct work inside the energized fire pump controller to complete the task of verifying accuracy of the installed voltmeter and ammeter. It should also be noted that the inclusion of this task as an inspection activity would not appear to be correct but should likely have been included as a test activity. Alternatively, the voltmeter and ammeter could be removed and bench tested and then reinstalled; however, this work would also likely require work inside the energized fire pump controller. Inclusion of this provision within NFPA 25 appears to be contrary to the original intent of the change made to NFPA 20 in 1999 to minimize the exposure to personnel to the hazards associated with work inside of an energized fire pump controller.
The provisions of NFPA 25, table A.22.214.171.124 also includes additional provisions for the following activities that need to be completed which would likely also involve internal access to the fire pump controller. NFPA 25 contains as many as 14 specific tasks that need to be completed that will likely involve internal access to the fire pump controller.
NFPA 25, section 126.96.36.199(2) requires that during the weekly/monthly churn tests on controllers that include electronic pressure sensors, that the inspector record the current pressure and the highest and lowest on the controller event log. This work may involve inspection personnel making internal access to an energized fire pump controller.
NFPA 25, table 188.8.131.52 and section 184.108.40.206 provide that the fire pump alarm signals be tested annually. For an electric fire pump this would include pump running, loss of power, and phase reversal. For the first two items, such testing can be completed directly by operating the fire pump and by disengaging power on the controller; however, testing for phase reversal would be tested by simulating an alarm condition rather than an actual reversal of the electrical phase. This simulation can be accomplished by jumpering across the terminals within the fire pump controller, or by jumpering across the terminals at the monitor module installed outside the controller (where so equipped). Some controllers may include a test button inside the controller that simulates the same condition as jumpering the terminals. In any event, testing of this monitored condition may involve inspection personnel making internal access to an energized fire pump controller. NFPA 25, section 220.127.116.11.1 further recognizes the hazard of conducting such work on an energized fire pump controller with a reinforcing mandate that such only be done by qualified personnel using appropriate PPE.
As a result of the hazards associated with arc flash with electric fire pump controllers, a TIA was submitted to and approved by the NFPA 25 Technical Committee to address this issue. See NFPA 25, TIA-2 online at nfpa.org/assets/files/AboutTheCodes/25/TIA_25_17_2.pdf. As a result the inspector is no longer required to routinely conduct periodic work within an energized electric fire pump controller, thereby diminishing the resultant exposure to the arc flash hazard and protecting the inspector from the hazard they didn’t even know existed.
IMPORTANT NOTICE: This article and its content are not a Formal Interpretation issued pursuant to NFPA Regulations. Any opinion expressed is the personal opinion of the author and presenter and does not necessarily present the official position of the NFPA and its Technical Committee.
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AUTHOR’S NOTE: Tracey Bellamy, PE, CFPS, is chief engineering officer for Telgian Corporation, Atlanta, Georgia. He is active in NFPA and represents the company on a number of technical committees including NFPA 13, 30B, and 101. Bellamy is a graduate of the University of South Carolina with undergraduate and master’s degree in civil engineering. He is a registered fire protection and civil engineer.