Working with electrical systems has inherent risks, and working with Renewal Energy (RE) systems is no exception. This article offers a look into the installer’s world of required electrical safety guidelines and procedures.
OSHA & NFPA 70E
The mission of the Occupational Safety and Health Administration (OSHA) is to assure safe and healthful working conditions by “setting and enforcing standards and by providing training, outreach, education, and assistance.” OSHA addresses installing, servicing, and working near or on electrical systems and equipment in Parts 1910 Subpart S and 1926 Subpart K, providing guidance on “what” to do. The National Fire Protection Association’s 70E, the Standard for Electrical Safety in the Workplace, is guidance on “how” to do it.
Formal development of 70E began in 1976 at the request of OSHA, with the first edition published in 1979. Its intent is to reduce exposure to the hazards of shock and arc-flash while working on electrical equipment. It is “tailored to fulfill OSHA’s responsibilities [and be] fully consistent with the NEC.” While not official OSHA doctrine, 70E is indirectly enforced through the General Duty Clause of the Occupational Safety and Health Act, and is listed as a reference for “information that can be helpful in understanding and complying.” Updated on a three-year cycle like NFPA 70 (the National Electrical Code), the current edition of 70E is 2015.
NFPA 70E has three chapters: Chapter 1 covers work practices and procedures; Chapter 2 addresses safety-related maintenance requirements; and Chapter 3 modifies the first two for special equipment (which includes batteries over 48 VDC nominal, but does not address PV systems). The Informative Annexes at the back of 70E provide guidelines, templates, examples, and additional information.
Section 105.3 of 70E states the “employer shall provide the safety-related work practices and shall train the employee, who shall then implement them,” and Section 110 provides guidance on electrical safety training programs. NFPA 70E, OSHA 10- and 30-hour construction, and specialized (scaffolding, fall protection, etc.) training is available and recommended—in fact, safety training is required for one to become a “qualified person” per NFPA 70 and 70E.
Electrically Safe Work Condition
Electrically safe means “disconnected from energized parts,” “locked/tagged,” and “tested to ensure the absence of voltage.” As long as there is no danger of arcs or burns, electrical equipment that operates at less than 50 volts is not required to be de-energized. The Informational Note to the definition of “Voltage, Nominal” in 70E states that actual operating voltage can vary, meaning that 48 VDC nominal battery banks (with voltage that swings above and below 50 V due to state of charge) do not have to be de-energized to be worked on.
PV modules and batteries present unique challenges, in that it can be difficult or impossible to truly “turn off” the power, but NEC-required disconnects provide the means to isolate equipment from all power sources. Remember to always use a clamp-on ammeter to verify a lack of current before operating non-load-break rated disconnects, such as module quick connectors and touch-safe fuse holders.
Using a lockout ensures disconnected power sources stay disconnected, and a tagout shows who is responsible for the lockouts. Section 120.2 in 70E provides detailed requirements and sample procedures (Informative Annex G). Always use the appropriate locks, tags, hasps, and breaker and switch locks. Electrical tape over a breaker handle is not a lock!
Section 110.4(A)(5) requires that when the circuit/system is 50 volts or more, “the operation of the test instrument shall be verified on a known voltage source before and after an absence of voltage test is performed.” Test your meter on an outlet, a AA battery, or other power supply to make sure you do not get a false negative when verifying a lack of voltage.
Only qualified persons are allowed to work on equipment that is not in an electrically safe work condition. Regardless of the work, 110.1(H) requires a “pre-work meeting” to discuss the hazards and procedures for the job—and be sure to document it, so that it can be demonstrated to OSHA that the meeting happened.
Shock Hazard
The “limited approach boundary” signifies the distance at which unqualified personnel—such as homeowners, other contractors, or members of your crew who have not yet received the necessary training—must be kept back from exposed, energized parts due to the risk of shock. This is generally 3.5 feet for AC systems with a line-to-line voltage of 50 to 750 V (which includes typical residential and many commercial service voltages), as well as DC systems of 100 to 1,000 V [Tables 130.4(D)(a) and (b)]. A limited-approach boundary is not specified for AC systems below 50 V or DC systems below 100 V.
The “restricted approach boundary” is the distance from an exposed, energized wire or circuit at which there is an increased likelihood of shock for “personnel working in close proximity.” The restricted approach boundary is 1 foot for AC systems of 151 to 750 VAC line-to-line, as well as for DC systems from 301 to 1,000 VDC. The boundary for 50 to 150 VAC and 100 to 300 VDC is “avoid contact.”
Section 130.7(D)(1) provides requirements for insulated tools, nonconductive ladders, and other tools and equipment that must be used when working within the restricted approach boundary. A formal “energized electrical work permit” (see Annex J of 70E) is generally not required for qualified persons in the restricted approach boundary, provided they follow 70E guidelines and industry-accepted safe practices, and use the correct safety gear.
Arc-Flash Risk
Workers can accidentally create electrical arcs when testing, commissioning, or working on or around energized electrical equipment. These arcs can release tremendous amounts of energy and be extremely dangerous. The arc-flash boundary is the distance at which a worker could be exposed to a level of incident energy of 1.2 calories per square centimeter (cal/ cm2)—the energy level associated with second-degree burns.
Information for determining the arc-flash boundary is provided in Annex D, and an incident energy analysis can be performed based on the distance of the worker’s face and chest from the circuit part being worked on. IEEE 1584 Guide for Performing Arc Flash Hazard Calculations also provides guidance for AC systems. If the task corresponds to one of the specific categories in 70E Tables 130.7(C)(15)(A)(b) or (B), then the boundary—and corresponding level of personal protective equipment (PPE)—from the table(s) can be used.
AC arc flashes are a significant risk in commercial and industrial applications, due to large fault currents available from the utility grid through the service transformers. An arc-flash hazard is much less likely to be present in residential grid-direct applications—usually the service transformer must be 125 kVA or larger. Additionally, residential-scale battery-based inverters are not capable of delivering enough current to present an arc-flash risk. Clearly defined guidance on how to assess these possible hazards is not provided in 70E or other sources.
For commercial applications (non-dwelling units), the AC output of a newly installed PV system must be considered when updating equipment labeling regarding the arc-flash hazard in accordance with 70E Section 130.5(D), and Sections 110.16 and 110.24 of the NEC.
Considerations for DC arc flashes were added to 70E in 2012, but the arc-flash hazard PPE categories in Table 130(C) (15)(B) do not address systems below 100 VDC. While two studies are referenced in Annex D, there is not a lot of data regarding arcs on batteries below 50 VDC nominal. While a short-circuited battery can melt a wrench, batteries present more of a thermal or acid-blast issue, and the actual arc-flash hazard may be minimal or non-existent.
For PV systems, 70E guidance, research, and testing, and industry standards are even less developed. Residential PV arrays connected to string inverters fall within the DC voltage parameters of the arc-flash hazard categories in Table 130.7(C)(15)(B), but at relatively low and inherently limited levels of DC short-circuit current—they are insignificant compared to 4,000 A which is the first equipment rating in the Table. Larger PV systems may operate at levels of current the table considers, but in many cases at 1,000 VDC—above the 600 VDC maximum the table addresses. In some cases, electrical engineers can provide an analysis, but this can be a prohibitive expense for residential or smaller commercial arrays. There is a clear need for codes and standards to better address potential DC arc-flash hazards to keep up with the rapidly growing PV and energy-storage markets.
Personal Protective Equipment (PPE)
Appropriate PPE is required within the arc-flash boundary or when there is a shock hazard. Several tables in Section 130.7(C) provide guidance on when, and what level of PPE is required. In general, if there is an arc-flash hazard, PPE is required for tasks including:
- Removal of or opening of covers, which exposes live parts
- Examining insulated cable with physical manipulation
- Working on energized components (including voltage testing)
In some cases, arc flash hazard PPE is required for tasks where it otherwise would not be, such as when equipment shows signs of poor installation or maintenance, or of impending failure. That makes sense—if it is old and/or sketchy, treat it with extra caution!
Table 130(C)(15)(B) lists the PPE category for working on energized equipment within the arc-flash boundary, but remember that PPE is the last line of defense against hazards, which must first be eliminated and/or controlled. “Hot” work should only be performed for purposes of commissioning, maintenance, troubleshooting, or inspection—or when the circuit is truly an integral part of a continuous process (which is unlikely for our field of work). OSHA 1910 Subpart I provides information on all types of PPE; additional guidance and requirements are in 70E Section 130.7 and Informative Annexes H and M.
Eye protection is always required, and it must be labeled with the ANSI Z87.1 standard.
Rubber insulating gloves with leather protectors are required for shock protection in the restricted approach boundary. Typical ratings include Class 00 (750 VDC or 500 VAC) and Class 0 (1,500 VDC or 1,000 VAC). Sleeves (if your arm and not just your hand will be in the restricted approach boundary), insulated blankets, mats and bare line covers, and higher-voltage rated gear are also available. Be sure to follow industry best practices and requirements for taking care of your gloves—inspect and air test before each day’s use. Get in-service gloves recertified every six months; gloves can be stored for up to 12 months before being placed into service.
For the lowest level of potential arc-flash risk, with incident energy of up to 1.2 cal/cm2, non-melting or untreated natural fiber pants and long-sleeve shirts are required, along with a hard hat (class G or E); safety glasses or goggles; and hearing protection. As needed, use heavy-duty leather gloves or (when there is a shock hazard) insulated gloves with leather protectors.
When there is an arc-flash hazard greater than 1.2 cal/cm2, arc-rated clothing must be worn—they will not continue to burn after the ignition source is removed and provide a thermal barrier during the extreme explosive, thermal event that is an electrical arc blast. When arc-rated clothing is required, underwear must also be non-meltable! Materials such as nylon, polyester, spandex shall not be worn next to the skin [130.7(C)(9)(c)], though there is an exception for an “incidental amount of elastic used on non-melting fabric underwear or socks.”
Arc-rated clothing and additional PPE requirements are defined in four categories. Category 1 and 2 cover the majority of work that would be performed on residential and commercial-scale systems. Category 3 and 4 apply to higher-power and higher-voltage systems and involve heavy suits and/or layering. Note that for all categories, if a jacket, rainwear, or hard-hat liner is worn to deal with the weather, it must be arc-rated to the appropriate level.
Category 1 (minimum arc rating of 4 cal/cm2) requires an arc-rated long-sleeve shirt, pants, and face shield or hood; hard hat; safety glasses; hearing protection (ear canal inserts); and leather gloves (the ones satisfying the insulated gloves requirement, not a second set). Leather footwear is optional. Category 1 covers the majority of residential systems (if there is an arc-flash risk), some commercial AC applications, and some DC systems:
- 240 VAC or below, maximum 25 kA short-circuit current
- 100 to < 250 VDC, short-circuit current < 4 Ka
- 250 to ≤ 600 VDC, short-circuit current < 1.5 kA
Category 2 adds a higher arc rating (minimum of 8 cal/cm2), mandates leather footwear, and adds a requirement for a balaclava for additional protection of the neck, head, and face. Category 2 covers many commercial and industrial systems, and additional DC systems:
- Numerous 277 and 480 VAC applications
- 100 to < 250 VDC, short-circuit current 4 to < 7 kA
- 250 to ≤ 600 VDC, short-circuit current 1.5 to < 3 kA
In some cases, it is easiest to dress for the worst—wearing arc-rated clothing with a minimum value of 8 cal/cm2 whenever on the job covers Category 1 and some of Category 2, which is the work most PV installers will be involved with (see Annex H Table H.2, and note that in some cases, depending on the hazard analysis, an arc-rating of greater than 8 cal/cm2 may be required—Category 2 essentially covers 8 to < 25, where Category 3 begins). However, this same strategy could also be overkill for residential-only work where Category 1 or less may be sufficient—and especially so for the many non-energized construction aspects of installing a PV system, such as mounting modules, pulling conductors in conduit, or hanging inverters—which is the case regardless of system size.