Arc flash and electrical hazard signs: what has to be on the label

What does the National Electrical Code require?

NEC 110.16(A) requires a general warning on switchboards, switchgear, enclosed panelboards, industrial control panels, meter socket enclosures and motor control centers in other than dwelling units that are likely to require examination, adjustment, servicing or maintenance while energized. The label warns qualified persons of potential arc flash and shock hazards; it does not carry the calculated numbers. NEC 110.16(B) goes further for service and feeder equipment rated 1,000 amps or more: the label must show the nominal system voltage, the available fault current, the clearing time of the upstream overcurrent device, and the date the label was applied. The NEC is the installation code the electrical inspector enforces; NFPA 70E is the work-practice standard the employer follows.

What does OSHA require?

• Entrances to rooms and other guarded locations containing exposed live parts must be marked with conspicuous warning signs forbidding unqualified persons to enter.
• Entrances to buildings, rooms or enclosures with exposed live parts or conductors over 600 volts must be kept locked unless under observation by a qualified person, and must have permanent, conspicuous warning signs reading substantially DANGER, HIGH VOLTAGE, KEEP OUT.
• Indoor installations over 600 volts that are accessible to other than qualified persons: metal-enclosed switchgear, unit substations, transformers, pull boxes and connection boxes must be marked with appropriate caution signs.
• Safety signs, safety symbols or accident prevention tags must be used where necessary to warn employees about electrical hazards that may endanger them, as required by 1910.145. That means Danger for an immediate threat of death or serious injury, Caution for a lesser hazard, and tags with a signal word and major message such as High Voltage.
• Barricades must be used with safety signs where needed to prevent or limit access to work areas with uninsulated energized conductors or circuit parts; conductive barricades may not be used where they could create a contact hazard. If signs and barricades are not enough, an attendant is stationed.
• Each disconnecting means for a service, feeder, branch circuit, motor or appliance must be legibly marked to indicate its purpose, with marking durable enough for the environment. Equipment must carry the manufacturer’s name and ratings.

How do you read the label to choose PPE?

Find the PPE statement. If it gives incident energy, the arc rating of everything worn over the chest and face must be at or above that number: 6.2 cal/cm² at 18 inches calls for clothing with an arc rating of at least 6.2, and the face protection the same. If it gives a PPE category, the category table sets the minimum arc rating: category 1 is 4 cal/cm², category 2 is 8, category 3 is 25, category 4 is 40, each with its listed face, head, hand and foot protection. Then find the arc flash boundary: everyone inside that distance while the equipment is being worked on energized wears the PPE, not just the person at the panel. The label gives the exposure; the garment label gives the rating; the rating must meet or exceed the exposure.

What does a label have to be printed on?

Neither standard names a material. The NEC requires its markings to be of sufficient durability to withstand the environment, and OSHA says the same of equipment markings. In practice an arc flash label lives on a painted steel door in a plant for 5 years, so the label stock is a vinyl or polyester with an aggressive adhesive, printed by thermal transfer so the numbers do not fade or smear. Label printers built for this take a template with the standard fields and print one label per piece of equipment from the study data; a facility printer does arc flash labels, pipe markers and safety signs on the same machine. Hand-written labels are allowed by the standards but rarely survive the review interval.