110.15 High-Leg Marking
On a 4-wire, delta-connected system where the midpoint of one phase winding is
grounded, only the conductor or busbar having the higher phase voltage to
ground shall be durably and permanently marked by an outer finish that is orange
in color or by other effective means. Such identification shall be placed at each
point on the system where a connection is made if the grounded conductor is also
present.
The high leg is common on a 240/120-V 3-phase, 4-wire delta system. It is
typically designated as “B phase.” The high-leg marking, which is required to be
the color orange or other similar ]effective means, is intended to prevent
problems caused by the lack of standardization where metered and nonmetered
equipment are installed in the same installation. Electricians should always test
each phase relative to ground with suitable equipment to determine exactly
where the high leg is located in the system.
110.16 Arc-Flash Hazard Warning
Electrical equipment, such as switchboards, switchgear, panelboards, industrial
control panels, meter socket enclosures, and motor control centers, that are in
other than dwelling units, and are likely to require examination, adjustment,
servicing, or maintenance while energized, shall be field or factory marked to
warn qualified persons of potential electric arc flash hazards.
The marking shall meet the requirements in 110.21(B) and shall be located so as
to be clearly visible to qualified persons before examination, adjustment,
servicing, or maintenance of the equipment.
This section requires switchboards, panelboards, motor control centers, and other
equipment to be individually field or factory marked with proper warning labels to
raise the level of awareness of electrical arc-flash hazards and to decrease the
number of accidents that result when electricians do not wear the proper type of
protective clothing when working on “hot” (energized) equipment. Exhibit 110.8
is one example of an equipment warning sign as required by this section.
EXHIBIT 110.8 One example of an arc-flash warning sign. (Courtesy of the
International Association of Electrical Inspectors)
Exhibit 110.9 shows an electrical employee wearing personal protective
equipment (PPE) considered appropriate flash protection clothing for the flash
hazard involved. Suitable PPE appropriate to a particular hazard is described in
NFPA 70E®, Standard for Electrical Safety in the Workplace®.
EXHIBIT 110.9 An electrical worker clothed in personal protective equipment (PPE)
appropriate for the hazard involved. (Courtesy of KTR
Associates/ArcFlashPPE.com)
Accident reports confirm the fact that workers responsible for the installation or
maintenance of electrical equipment often do not turn off the power source
before working on the equipment. Working on electrical equipment that is
energized is a major safety concern in the electrical industry. This requirement
alerts electrical contractors, electricians, facility owners and managers, and other
interested parties to some of the hazards present when personnel are exposed to
energized electrical conductors or circuit parts, and emphasizes the importance of
turning off the power before working on electrical circuits. This section does not
apply to equipment in dwelling units. However, dwelling occupancies include
multifamily dwellings, which include multiple dwelling units and could have the
same electric service as a commercial office building. The intent is to provide
warnings to electricians working on these larger services.
Employers can be assured that they are providing a safe workplace for their
employees if safety-related work practices required by NFPA 70E have been
implemented and are being followed. (See also the commentary following the
definition of qualified person in Article 100.)
In addition to the standards referenced in the informational notes and their
individual bibliographies, additional information on electrical accidents can be
found in the 1997 report “Hazards of Working Electrical Equipment Hot,”
published by the National Electrical Manufacturers Association.
Informational Note No. 1: NFPA 70E-2012, Standard for Electrical Safety in the
Workplace, provides guidance, such as determining severity of potential
exposure, planning safe work practices, arc flash labeling, and selecting personal
protective equipment.
Informational Note No. 2: ANSI Z535.4-1998, Product Safety Signs and Labels,
provides guidelines for the design of safety signs and labels for application to
products.