Electrical Safety Myths and Facts 2

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1 Electrical Safety Myths and Facts 2 Copyright Material IEEE Paper No. ESW James R. White Senior Member IEEE Shermco Industries, Inc.2425 E. Pioneer Drive Irving, Texas jrwhite@shermco.com Abstract This paper reviews some of the more common electrical safety myths and misconceptions field electrical workers often have. Many of these misconceptions continue in spite of training and education. Some are handed down from worker to worker, similar to tribal knowledge. The real danger from these misconceptions is that they impede the truth and cause electrical workers to misjudge hazards and risks. Index Terms Myths, misconceptions, electrical safety, electrical shock, NFPA 70B, NFPA 70E, OSHA. I. INTRODUCTION This is the second paper concerning the electrical myths and misconceptions that electrical workers may have. Because of the hazardous nature of the job, these misconceptions can cause injury or even death to the worker who believes them, and possibly to those around him or her. This paper reviews some of the more common myths and misconceptions electrical workers may have concerning electricity and electrical safety. Readers are encouraged to use all or parts of the presentation as considered necessary to enlighten field workers and possibly prevent accidents that may be caused by them. II. HAZARD IS RISK AND RISK IS HAZARD When talking to people about hazards and risks, they seem to get the two confused. I often hear someone say, The hazard increased because the door was open or That s a way higher hazard because I am in a tight spot. What they are really talking about is the risk associated with a given task. The best explanation is to say the hazard is what the hazard is. In other words, the hazard does not change because of the task or other factors that may arise. If a piece of switchgear or MCC is energized, the hazard is the available short circuit current, the nominal voltage and the total clearing time of the OCPD (overcurrent protective device). Whatever task is being performed, that hazard does not change. The only way to eliminate the hazard is to shut the equipment off, which is the preferred approach. The task being performed will change the amount of risk involved with a task. The risk from reading a panelboard meter is far different than when racking a circuit breaker in or out of its cubicle. The risk can change due to environmental issues, aging equipment, lack of maintenance, etc., but the actual hazard is the same for a given piece of equipment. When using NFPA 70E (1) Table 130.7(C)(15)(a) there will be several Hazard/Risk Categories for a specified type of equipment. The hazard is provided in the heading for that equipment type. For example, for the equipment type Panelboards or other equipment rated >240 V and up to 600 V the hazard is given as a maximum of 25kA short circuit current available; maximum of 0.03 sec (2 cycle) fault clearing time at the voltages stated. The hazard is what the hazard is and does not change. The changes in HRC number (from HRC-0 to HRC-2) are task dependent and reflect what the 70E Technical Committee perceives as the risk that may be involved in that specific task. III. FR AND AR MEAN THE SAME THING Not really. In previous editions of NFPA 70E the term flame-resistant (FR) was used. In the 2004 edition the term arc rating was introduced. The 2000 through 2009 editions of NFPA 70E used FR exclusively to describe arc-rated clothing and PPE. In the 2012 edition of NFPA 70E wording was added to qualify what arc-rating was and to discontinue the use of flame resistant (FR). The preferred term is now arcrated (AR). In abbreviated terms, all arc-rated (AR) equipment is also flame resistant (FR), but not all FR is arc-rated. The best examples of this are the FR clothing used by fire fighters or steel and aluminum smelter workers. It is constructed of many of the same materials, but has not been specifically tested and certified for use to protect a worker from the electrical arc flash hazard. NFPA 70E Article 100, Definitions Informational Note No. 1 for arc rating states Informational Note No. 1: Arc-rated clothing or equipment indicates that it has been tested for exposure to an electric arc. Flame-Resistant (FR) clothing without an arc rating has not been tested for exposure to an electric arc. IV. VEHICLE TIRES ARE INSULATORS This one sort of makes sense. Tires are rubber and rubber is an insulator, right? Tires haven t been made solely of rubber since the 1950 s. Modern tires are made of synthetic rubber, carbon black (to provide color), with additives such as 1

2 silica, sulfur and zinc oxide, as well as anti-oxidants and antiozonants to prevent materials from breaking apart due to constant exposure to sunlight, heat, and ozone. Tires will be reinforced with layers (plies) of rayon, nylon or polyester and steel belts to provide strength and reduce the likelihood of puncture. The bead around the edge of the tire is reinforced with steel cable to provide a good seal against the rim. Some small amount of natural rubber is used by some manufacturers, but the rubber tire is a thing of the past. The steel belts and bead, along with the additives make tires fairly conductive to electricity. Numerous accounts have been publicized of trucks lifting their dump beds into overhead power lines, resulting in their tires blowing out or the driver exiting the vehicle, only to be electrocuted by the flow of current through the tires to ground, setting up voltage ground gradients. V. CURRENT-LIMITING FUSES ALWAYS LIMIT CURRENT Current-limiting fuses can be a great aid in reducing the arc flash hazard. They reduce the short circuit current with a characteristic known as let-through current and reduce the clearing time to less than ½ cycle. Figure 1 is the typical operating characteristic of a current-limiting fuse. Note the tremendous decrease in let-through current and the operating time. Even though the typical operating time is less than ½ cycle, most fuse manufacturers claim it will be less than ¼ cycle. One or the other would be a boon to electrical safety, but having both is akin to arc flash nirvana, right? engineers who are experienced in the finer points of electrical system characteristics. Without a full understanding of the quirks of electrical power systems, a facility safety director may believe his workers are protected, but instead they could be placed in grave danger by relying on faulty arc flash hazard warning labels. VI. ELECTRICITY TAKES THE PATH OF LEAST RESISTANCE I ve heard this one as long as I ve been in the trade. It s not that it s untrue; electricity does take the path of least resistance. It also takes any other path to ground that s available. The problem with truisms is that they have an element of truth, but may be misleading because you don t get all the information. As Figure 2 shows, if there are multiple paths to ground, some current will flow through them all. The path with the least resistance will have the most current flow; the path with the highest resistance will have the least current flow. If a piece of equipment has a loose ground lug or the equipment grounding conductor is partially broken or corroded, the intended ground may not present the lowest resistance. In this situation a person that touches the exterior of that piece of equipment may actually have a lower resistance than the intended grounding path and could be shocked or electrocuted. This is referred to as touch potential. 2A 5.33A 0.666A Figure 2 Multiple Paths to Earth Ground Figure 1 Typical Current-Limiting Fuse Characteristic Courtesy Cooper-Bussmann When properly applied, yes. The trick to current-limiting devices, whether they are fuses or circuit breakers, is that the short circuit current must be high enough to push the fuse (or circuit breaker) into its current-limiting region. If not, the fuse will respond as a dual-element fuse. One such situation that could cause the short circuit current to be less than anticipated would be a motor (or other device) fed from a long cable run. The impedance of the cable could reduce the short circuit current and the fuse would not respond with its current-limiting characteristic. This example is one of the reasons why arc flash studies must be conducted by Note in Figure 2 that R2, which has the lowest resistance also has the highest amount of current flow. A good, clean and tight ground or bonding connection is important to provide a safe work environment. VII. CIRCUIT BREAKER CONTACTS ARE DAMAGED DURING PRIMARY INJECTION TESTING On the surface, the logic is hard to deny. I m pumping sometimes tens of thousands of amps through a circuit breaker, causing it to trip. The situation is even worse when testing the Instantaneous function. The reality is that primary injection testing is the only method to fully test not only the programmer (OCPD), but also the power supply, interconnecting wiring and sensors. Secondary injection testing, although good for testing the programmer calibration, misses these critical items. Primary injection testing involves connecting a circuit breaker to a large high-current test set. These test sets are 2

3 portable in the sense that they have wheels. The largeroutput test sets weigh several hundred pounds. Figure 3 shows a typical primary injection test on a low-voltage power circuit breaker. the safety devices in automobiles. I had one student tell me I ve got lap belts, shoulder harnesses, crumple zones, air bags and side barriers in my doors. I can go as fast as I want to. I hope he was kidding. Since tens of thousands of people still die on the highways today, even after all the safety improvements in automobiles it is safe to say that statement is not true. The same false sense of security can raise its ugly head when discussing the arc-rated PPE and clothing available today. Once a worker puts it all on, he feels protected, safe. It s almost like wearing a suit of armor. Let the games begin! This attitude displays a lack of understanding about the issues involved with arc flash. Figure 3 High Current Primary Injection Test of a LVPCB By connecting to the test set through the circuit breaker s primary disconnects, large amounts of current can be driven through the circuit breaker, testing all elements of the OCPD. Because the voltage output from the test set is so low, the contacts are not materially damaged. Unlike interrupting a fault at 480 V, interrupting one at 7 to 12 V places much less stress on the device. Usually, polishing the contacts with a nonconductive abrasive pad is adequate to remove any marking that could take place. As far as hazards connected to using a primary injection test set, there can be considerable heating of the stabs and other current-carrying components, so sometimes wearing leather gloves is helpful. The voltage is so low that the shock hazard is almost non-existent and there is no arc flash hazard, again due to the very low voltage source. One last point is that when testing the Instantaneous function, the circuit breaker is only tested to the pickup of the Instantaneous function; not the interrupting rating. Instantaneous set points, even though they can be high, are still much lower than the interrupting rating, so the circuit breaker is not really being stressed. There is nothing wrong in doing a secondary injection test annually on the OCPD. Every three to five years, though, the full OCPD system needs to be tested and verified to ensure proper and safe operation. VIII. I M PROTECTED My Dad would often say There s no such thing as foolproof. As soon as you make it, along comes a better fool. Such is life. If there is a down-side to arc-rated PPE it s that people have a false sense of security. It can be compared to The first issue is that as good as IEEE 1584 (2) is, it is flawed. This was first pointed out by Dr. David Sweeting and Professor Stokes soon after it was first released. Further study has shown Dr. Sweeting s assertions to be correct. Users must understand that 1584 is at best an estimate, not a final conclusion. Secondly, incident energy is proportional to time. If the circuit breaker or other OCPD doesn t function in accordance with its manufacturer s specifications, the incident energy released during a fault could greatly exceed the estimated values. Lastly, working distance is critical, as incident energy will vary greatly depending on the distance to the arc source. Incident energy decreases by the inverse square of the distance, which is a good thing. As we move away from the arc source the incident energy drops rapidly. However, the opposite is also true. As we decrease the distance, the incident energy increases by the square of the distance. Just a few inches can make a considerable difference in the incident energy a worker would receive during an arc flash event. Body position is important to a worker s safety. This is illustrated by Informational Note No. 3 for the definition of arc rating (2012 NFPA 70E Article 100, Definitions ). Informational Note No. 3: ATPV is defined in ASTM F as the incident energy on a material or a multilayer system of materials that results in a 50 percent probability that sufficient heat transfer through the tested specimen is predicted to cause the onset of a second degree skin burn injury based on the Stoll curve, cal/cm 2. Even if all the circumstances are correct and the incident energy values are accurate, there is a 50% probability of a second-degree burn through the arc-rated clothing and PPE where bare skin is next to it. A difference of just 2 or 3 cal/cm 2 incident energy can increase that probability greatly. The up-side to this is that any injury that may be received will certainly be less than if no arc-rated clothing or PPE was worn, but certainly the ASTM F1509 definition provides clear indication that arc-rated does not mean injury-free. IX. THERE S NO ARC FLASH HAZARD IF THE DOOR IS 3

4 SHUT It s amazing how many workers actually believe this, even though NFPA 70E has clearly stated since 2009 that doors provide little or no protection from an arc flash. The following is from the 2012 edition of NFPA 70E: Informational Note No. 2: The collective experience of the task group is that, in most cases, closed doors do not provide enough protection to eliminate the need for PPE for instances where the state of the equipment is known to readily change (for example, doors open or closed, rack in or rack out). Table 130.7(C)(15)(a) [formerly 130.7(C)(9)] shows that when performing the task of inserting or removing (racking) circuit breakers from their cubicles, no reduction in HRC class is allowed for doors closed. Doors often have vents and other openings which allow the arc plasma and heat to pass through it. The latches on the typical 480 V equipment will pop open during an arcing event and the hinges could possibly separate. My experience has been that the hinge side holds better than the latch side, so I always stand to the hinge side. NFPA provides minimum safe work practice requirements, not necessarily best safe work practice requirements. When operating larger circuit breakers or other devices I prefer to wear arc-rated clothing with a rating of 8 to 12 cal/cm 2. In situations where I m unsure of its state of maintenance or condition, I will suit up in 65 cal/cm 2 arc-rated clothing and PPE. This is, of course only if the equipment cannot be deenergized. X. YOU CAN T OPERATE 480 V EQUIPMENT UNLESS WEARING ARC-RATED CLOTHING AND PPE Actually, NFPA 70E says the exact opposite. Under the definition for Arc Flash Hazard in NFPA 70E, Informational Note No. 1 states An arc flash hazard may exist when energized electrical conductors or circuit parts are exposed or when they are within equipment in a guarded or enclosed condition, provided a person is interacting with the equipment in such a manner that could cause an electric arc. This would lead one to believe that opening and closing a switch or circuit breaker would create an arc flash hazard. That is, until the rest of IN No. 1 is read, Under normal operating conditions, enclosed energized equipment that has been properly installed and maintained is not likely to pose an arc flash hazard. Interacting, in this context, is any task where the switch or device is installed or removed from an energized bus without the aid of arc extinguishers, such as bus bar, bus duct or a MCC bucket. Section 130.7(A) Informational Note No. 2 states It is the collective experience of the Technical Committee on Electrical Safety in the Workplace that normal operation of enclosed electrical equipment, operating at 600 volts or less, that has been properly installed and maintained by qualified persons is not likely to expose the employee to an electrical hazard. The operative words in this section are properly installed and maintained. The NFPA 70E Technical Committee grappled with this and agreed that this would not be an easy thing to do. Maintenance records and test results could be reviewed prior to the start of work, if they are available. If the equipment was maintained, those records should be available. The other method used by some service companies, such as NETA-member companies is to place calibration and test labels on their equipment. NFPA 70B (4) Recommended Practice for Electrical Equipment Maintenance 2013 edition added section Test or Calibration Decal System it states, General. After equipment testing, device testing, or calibration, a decal on equipment, in conjunction with test records, can communicate the condition of electrical equipment to maintenance and service personnel. This can be important for assessing the hazard identification and risk assessment for electrical safety procedures as well as the condition of electrical equipment. Such labels are shown in Figure 4. These labels are supposed to be color coded as red, yellow or white. Figure 4 Test or Calibration Decal System From NFPA 70B The red label indicates the equipment has a major defect and should not be placed into service. The yellow label indicates a minor issue that does not affect operation or safety and the white label indicates equipment that is fully serviceable. Since NFPA 70B is printed in black-and-white, the colors are described in the text, but not shown. Since NFPA 70E provides minimum requirements, it is also necessary to state that a worker should always follow his/her instincts and wear whatever PPE and clothing they believe is warranted. NFPA 70E does not prevent a worker from wearing such arc-rated clothing and PPE, but leaves it up to the worker to determine the need based on the equipment as it is found in service. XI. CIRCUIT BREAKERS WILL ALWAYS FUNCTION PROPERLY People tend to be optimistic about things, which is good. However, being over-optimistic is not so good. Why is it that a worker will walk up to a circuit breaker and operate it without ever giving a thought as to whether or not it will actually function correctly? Every day this scenario is repeated throughout the US over and over again. Most times nothing happens. Sometimes, especially if the circuit breaker has not received any maintenance in several years, bad things do happen. NFPA 70B recommends maintenance and testing of circuit breakers every three years, according to Table L.1 from Annex L, Maintenance Intervals. Figure 5 is from NFPA 70B, Annex L. The international Electrical Testing Association (NETA) has an ANSI standard for electrical equipment maintenance, ANSI/NETA MTS-2011 (5). Annex B of ANSI/NETA MTS-2011 offers a frequency of maintenance matrix that is based on 4

5 condition of the equipment and the reliability required. This method provides some flexibility based on these two factors and may be more appropriate for some facilities. Why is this level of maintenance required for circuit breakers? They are primarily mechanical devices. They are lubricated from the factory and adjusted. When in service, circuit breakers have current flowing through them lots of current. Whenever there is a large amount of current flow through a conductor, heat is created in the form of I 2 R (copper losses). The heat causes the factory-applied lubricants to dry out and they will flake off. Once that occurs, metal-to-metal wear begins. Adjustments can be affected by the wear, as well as the normal wear and tear or the circuit breaker can seize up and not work at all. I ve seen one circuit breaker partially open its contacts during a fault, which resulted in complete destruction of the circuit breaker. 43% had mechanical issues, mostly due to lack of lubrication and 11% failed to operate. Both of these surveys indicate that circuit breakers must be maintained and serviced on a regular basis or they will not function in accordance with their manufacturer s specifications. Depending on loading and environment, there is a three to five year interval that s required for maintenance and testing. XII. TURN IT OFF? I CAN DO THIS WITH MY EYES CLOSED There s an old saying in the electrical field There s old electricians and there s bold electricians, but there s no old, bold electricians. There s a lot of truth to that truism. However, it is also a fact that testosterone shrinks brain cells, or at least that s what my wife tells me. A quick look at YouTube and the point is difficult to argue with. A newspaper I was reading once had an article about a medical university that had just completed a multi-year study and had concluded that in men under the age of 25 the part of the brain that recognizes danger is underdeveloped. YouTube is filled with young men (and some not so young) risking life and limb to pull off some stunt and the results are usually not favorable. Even though this has humorous aspects to it, it also illustrates that younger men will take unwarranted risks, while (most) older men will not. Younger workers must be monitored more closely to ensure they do not become a victim of their egos. XIII. MEN AND WOMEN FACE THE SAME RISK FROM ELECTRICAL SHOCK Figure 5 Partial Table L.1 from NFPA 70B Annex L During the Technical Committee meetings for NFPA 70E, the question came up How do you know it is properly maintained? As discussed in the previous section, it s not easy, but the Test and Calibration Decal System would help if enough companies implemented it. Otherwise, a check of the maintenance records and test data is in order. The Reliability Subcommittee of the IEEE Industrial and Commercial Power Systems Committee, in IEEE Standard 493 (6) (the Gold Book) conducted a survey that included 1,469 failures of electrical equipment. In the survey, respondents were asked to describe their opinion of the maintenance quality in their plant. Inadequate maintenance was blamed for 16.4% of failures for all types of equipment. Table 5-2 in Std. 493 shows the facility s percentage of failures caused by inadequate maintenance vs. months since maintained. At 12 to 24 months the failure rate was 19%, when the circuit breakers had been in service more than 24 months the failure rate escalated to almost 78%! NETA (international Electrical Testing Association) surveyed their member companies about problems with circuit breakers (7). They received 340,000 responses. 22% of the circuit breakers had defects with their OCPD, while IEEE Standard 80 (8) Guide for Safety in AC Substation Grounding states that the average resistance for a 150 lb. man is 1,000Ω, while the average resistance for women is 750Ω. If both are exposed to a 120 V shock, the woman will have more current flow through her body, resulting in more injury. For 120-volt exposure: Men 120V = 120mA 1,000 Ω Women 120V = 160mA 750 Ω Figure 6, from Dr. Charles Dalziel s 1961 study (9) on the effects of electric shock contained the information in Figure 6. When looking at the heading labeled 60 Hz there are two columns; one for men and the other for women. Note that for every effect listed in this table, women suffered injury at a lower current value than men did. Women must be more conscious of the electrical shock hazard than men, as they are very likely to have more injury for the same exposure. This is not to say it is okay for men to make contact with any energized conductor or circuit part, only that women are at increased risk from the shock hazard. 5

6 Effects Direct Current Figure 6 From Deleterious Effects of Electric Shock, Dr. Charles Dalziel, 1961 XIV. CONCLUSIONS Information is one extremely important part of electrical safety. Misinformation can undue years of work and damage credibility to the point that nothing that is said further will correct the problem. Workers exposed to electrical hazards must have accurate information in order to make acceptable and safe decisions when working in the field. As with last year s paper, it is important to note that NFPA 70E requires an electrical system to be properly installed and maintained in order for the requirements of Chapter 1 to be met. If the maintenance requirements are not met in accordance with NFPA 70E Chapter 2, the requirements of Chapter 1 would very difficult to apply. NFPA 70B, as well as ANSI/NETA MTS-2011 can provide guidance for those needing information on maintenance requirements of electrical power systems and components. XVII. REFERENCES Current, ma Alternating Current 60 Hz 10 khz Men Women Men Women Men Women Slight sensation on hand Perception threshold Shock - not painful, muscular control not lost Shock - painful, muscular control not lost Shock - painful, let-go threshold Shock - painful and severe, muscular contractions, breathing difficult NFPA 70E, Standard for Electrical Safety in the Workplace, 2012 edition, Chapters 1 and 2 2. IEEE 1584, Guide for Performing Arc Flash Hazard Calculations 3. Stokes, A.D. and Sweeting, D.K. "Electric Arcing Burn Hazards", IEEE PCIC Conference Record, Paper PCIC , 9pp. 4. NFPA 70B, Recommended Practice for Electrical Equipment Maintenance, 2013 edition, Annex L 5. ANSI/NETA MTS-2011, Standard for Maintenance Testing Specifications for Electrical Power Distribution Equipment and Systems 6. IEEE Standard 493, IEEE Recommended Practice for Design of Reliable Industrial and Commercial Power Systems (Gold Book) 7. Widup, Ron and Heide, Kerry NETA Maintenance Testing Research on Electrical Power System Component Performance, Paper PCIC- 8. ANSI/IEEE, Guide for Safety in AC Substation Grounding, Std , pg Dalziel, Charles F., Deleterious Effects of Electric Shock, Meeting of Experts on Electrical Accidents and Related Matters, Geneva, October 1961 XVIII. VITA James White CESCP is the Training Director for Shermco Industries, Inc. located in Irving, Texas. He is a Senior member of the IEEE, the recipient of the 2011 IEEE/PCIC Electrical Safety Excellence Award, the 2008 IEEE Electrical Safety Workshop Chairman, Alternate international Electrical Testing Association (NETA) representative on NFPA 70E, Primary NETA representative on NFPA 70B, Primary NETA representative on NEC CMP-13 and is the NETA representative to ASTM F18. James is also a certified Level IV Senior Substation Technician with NETA, a Certified Electrical Safety Compliance Professional by NFPA, an inspector member of IAEI and serves on the NETA Safety and Training Committees. James is the author of Electrical Safety, A Practical Guide to OSHA and NFPA 70E and Significant Changes to NFPA 70E 2012 Edition both published by American Technical Publishers. 6