Environmental, Health and Safety Services

Electrical Safety Definitions

Approved:  Acceptable to the authority having jurisdiction, which can include an approval process that includes listed and labeled equipment.

ATPV:  Arc-thermal performance value refers to the arc rating of flame resistant clothing, expressed in calories per square centimeter (cal/cm2).

Bare-hand work:  A technique of performing work on live parts, after the employee has been raised to the potential of the live part.  The expertise necessary to perform this type of work can be acquired only by specialized training.

Disconnecting means:  A device, or group of devices or other means by which the conductors of a circuit can be disconnected from their source of supply.  Ex.  circuit breakers, fuses, for appliances, space-heating equipment, motors and controllers, and air-conditioning and refrigerating equipment.

Electrically safe work condition:  A state in which the conductor or circuit part to be worked on or near has been disconnected from energized parts, locked/tagged in accordance with established standards, tested to ensure the absence of voltage, and grounded if determined necessary.

Enclosure:  The case or housing of apparatus, or the fence or walls surrounding an installation to prevent personnel from accidentally contacting energized parts, or to protect he equipment from physical damage.

Energized:  Electrically connected to or having a source of voltage.

Exposed:  The circuit is in such a position that, in case of failure of supports or insulation, contact with another circuit may result.

Exposed (to live parts):  Capable of being inadvertently touched or approached nearer than a safe distance by a person.  It is applied to parts that are not suitably guarded, isolated, or insulated.

Exposed (wiring):  On or attached to the surface or behind panels designed to allow access.

FR (flame-resistant) clothing:  The property of a material whereby combustion is prevented, terminated, or inhibited following the application of a flaming or non-flaming source of ignition, with or without subsequent removal of the ignition source.  FR clothing will have an ATPV expressed in cal/cm2, which can be related to the hazard/risk category.  Examples include: flame-retardant treated cotton, meta-aramid, para-aramid, and poly-benzimidazole fibers.

Ground fault:  An unintentional, electrically conducting connection between an ungrounded conductor of an electrical circuit and the normally non-current-carrying conductors, metallic enclosures, metallic raceways, metallic equipment, or earth.

Hazard/risk category:  a rating 0 through 4 indicating the seriousness of the electrical exposure, with 4 being the most serious.  Hazard/risk analysis considers both shock and arc flash hazards.  Table 130.7(C)(9)(A) is used to relate work tasks to a hazard/risk category rating.

Incident energy:  The amount of energy impressed on a surface, a certain distance from the source, generated during an electrical arc event.  One of the units used to measure incident energy is calories per centimeter squared (cal/cm2).

Insulated:  Separated from other conducting surfaces by a dielectric (including air space) offering a high resistance to the passage of current.

Insulated (tools):  The tool manufacturer has assigned a voltage rating to the insulating material.

Isolated (as applied to location):  Not readily accessible to persons unless special means for access are used.

Labeled: Equipment or materials to which has been attached a label, symbol, or other identifying mark of an organization that is acceptable to the authority having jurisdiction and concerned with product evaluation, that maintains periodic inspection of production of labeled equipment or materials, and by whose labeling the manufacturer indicates compliance with appropriate standards or performance in a specified manner.  For example: UL (Underwriter’s Laboratories) or CSA (Canadian Safety Association).

Listed:  Equipment, materials, or services included in a list published by an organization that is acceptable to the authority having jurisdiction and concerned with the evaluation of products or services, that maintains periodic inspection of production of listed equipment or materials or periodic evaluation or services, and whose listing states that the equipment, material, or services either meets appropriate designated standards or has been tested and found suitable for a specified purpose.

Live parts:  Energized conductive components.

Meltable clothing:  Clothing made from flammable synthetic materials that melt at temperatures below 600ºF, such as acetate, nylon, polyester, polypropylene, and spandex, either alone or in blends.  Not permitted to be used when exposed to live electrical hazards.

Mode 1 :  All (research) operations are conducted in a positively de-energized (i.e. "cold") state.

Mode 2 :  All (research) manipulative operations of uninsulated parts are conducted with the equipment in a positively de-energized state. When measurements and observation of equipment functions are necessary, the equipment is energized (i.e. "cold to hot") and some, or all, protective barriers are removed and interlocks bypassed.

Mode 3 :  All (research) manipulative operations are conducted with the equipment fully energized and some or all normal protective barriers removed (i.e. "hot").

Natural fiber clothing:  Clothing made from non-melting flammable materials, such as cotton, wool, rayon, or silk.  This type of clothing is permitted for hazard/risk categories 0 and 1 provided the flash hazard analysis is 2.0 cal/cm2 or less, and that the fabric will not ignite and continue to burn under the arc exposure hazard conditions to which it will be exposed.  Note that these fabrics could ignite and continue to burn on the body, resulting in serious burn injuries; however, clothing that does not melt may be used for low level arc flash exposures.

Qualified person:  A person trained and knowledgeable of the construction and operation of equipment or a specific work method and be trained to recognize and avoid the electrical hazards that might be present with respect to that equipment or work method.

Unqualified person:  A person who might be exposed to electrical hazards and must be trained to understand how the exposure could occur and how to avoid injury.  Examples include: office workers, janitors, equipment operators, apprentices, or workers from crafts other than electrical.

Ventricular Fibrillation (V-fib): An abnormal heart rhythm that commonly occurs during heart attacks. The ventricles of the heart are quivering instead of beating rhythmically.

Voltage-rated:  The maximum use voltages for rubber insulated equipment, as indicated below:

Class of Equipment

Maximum Use Voltage
a-c – rms











Working space :  access and working area around electric equipment to permit ready and safe operation and maintenance. See Table 3.