A good client summoned me to investigate an accident that occurred when a maintenance electrician was replacing a 30-ampere (A), bolt-in circuit breaker. An electrical arc developed while the electrician was changing out the circuit breaker. My client wanted to know which code or standard applied to this type of installation and if the electrician violated them during the replacement procedure.
Application of NFPA 70
My visual inspection of the equipment revealed that some aspects of the equipment complied with the National Electrical Code (NEC), NFPA 70. For example, the provisions outlined in NEC Section 110.26(A)(1) through (A)(3) dictated the minimum equipment working space; the installation had complied with this requirement. After carefully reviewing Article 408, I determined that the installation complied with parts III and IV, as well as 408.55, pertaining to wire-bending space, which was very important in replacing the bolt-in circuit breaker. Also, the electrical arc flash hazard warning label was posted on the panelboard as required by Section 110.16.
Since my inspection revealed signs of overheating problems, I concluded that Section 310.15(A)(3) (1) through (4) were never applied to the design of the circuits from the panel to the loads they served. It was also evident that the number of current-carrying conductors in raceways (adjustment factors) was never considered, nor was the routing of raceways through high ambient temperatures (correction factors). Such conditions require the ampacity of conductors to be derated to comply with sections 310.15(B)(3)(a) and 310.15(B)(2).
Application of NFPA 70B
Annex A to Subpart S of OSHA 1910 references NFPA 70 and NFPA 70E. Section 200.1, Informational Note, refers the user of NFPA 70E to NFPA 70B to obtain maintenance requirements pertaining to serving and repairing electrical equipment and for the safe operational condition of related components. The electrician said that he never evaluated the condition of the wiring and components in the panel-board or the condition of the wire connected to the circuit breaker. However, he noticed that, roughly two circuit breakers above the one he was replacing, the wire connected to the circuit breaker had an overheating problem. I asked the electrician if he had evaluated the insulation on the wiring connected to all the circuit breakers in the panelboard to verify whether there were heating problems as outlined in Chapter 17 of NFPA 70B.
Circuit breaker loading
The conductor with melted insulation had not been checked for compliance with the 80 percent breaker-loading requirement as required by Section 17.2.
Inspection and cleaning
According to electrical personnel, the connections of the wiring to the circuit breakers had not been checked for heating problems in accordance with Section 17.9. Also, the electrical personnel had not conducted yearly infrared inspections to detect hot spots as recommended by Section 11.17.5.
Circuit breaker operation
Section 17.7 recommends that molded-case circuit breakers be at least manually operated as outlined in sections 17.8 through 17.10. With a good preventive maintenance program, circuit breakers are usually reliable and dependable devices, but such a program was not in place at the time of my inspection.
Application of NFPA 70E
The facility adopted NFPA 70E and used the Table H.2 to Annex H. The facility used “Everyday Work Clothing” with an arc rating of 8 cal/cm2. Calculations showed that the arc rating of 8 was sufficient for the job assigned to the maintenance electrician. However, the electrician removed his rubber gloves and face shield. When the arc flash occurred, his hands and face were severely burned. The supervisor signed off on an “Energized Electrical Work Permit” by the provisions listed in Informational Note 1 to Section 130.2(A). However, the supervisor was unaware of the electrician’s decision to remove some of his personal protective equipment (PPE). This decision created the burn hazard. The sad thing is this electrician had been trained how to work safely but didn’t follow this training.
There was a lot of blame to go around in this accident. The circuit breaker and circuit wiring installed never factored into the design the appropriate derating of ampacities for adjustment or correction factors. The facility failed to exercise the proper circuit breaker operation and perform yearly infrared inspections, among other things. They did not have a maintenance program. The electrician failed to follow company safety policies. Due to the conduct of all involved, this preventable accident occurred.
STALLCUP is the CEO of Grayboy Inc., which develops and authors publications for the electrical industry and specializes in classroom training on the National Electrical Code and other standards, including those from OSHA. Contact him at 817.581.2206.