Electricity has become an essential of modern life, both at home and on
the job. Some employees work with electricity directly, as is the case
with engineers, electricians, or people who do wiring, such as overhead
lines, cable harnesses, or circuit assemblies. Others, such as office
workers and salespeople, work with it indirectly. As a source of power,
electricity is accepted without much thought to the hazards encountered.
Perhaps because it has become such a familiar part of our surroundings,
it often is not treated with the respect it deserves.
OSHA's electrical standards address the government's concern that
electricity has long been recognized as a serious workplace hazard,
exposing employees to such dangers as electric shock, electrocution,
fires and explosions. The objective of the standards is to minimize such
potential hazards by specifying design
characteristics of safety in use of electrical equipment and systems.
OSHA's electrical standards were carefully developed to cover only those
parts of any electrical system that an employee would normally use or
contact. The exposed and/or operating elements of an electrical
installation - lighting equipment, motors, machines, appliances,
switches, controls, enclosures, etc. - must be so constructed and
installed as to minimize electrical dangers to people in any workplace.
The OSHA electrical standards were based on the National Fire Protection
Association's standard NFPA 70E, Electrical Safety
Requirements for Employee Workplaces, and the NFPA 70 Committee
derived Part I of their document from the 1978 edition of the National
Electrical Code (NEC). The standards extracted from the NEC were
those considered to most directly apply to employee safety and least
likely to change with each new edition of the NEC. OSHA's electrical
standards are performance oriented; therefore they contain few direct
references to the NEC. However, the NEC contains specific information as
to how the required performance can be obtained.
This discussion does not cover OSHA's Electrical Safety-Related Work
Practices Standard, which contains requirements for working on or near
energized and de-energized electrical equipment, the use of personal
protective equipment, and the safe use of electrical equipment.
This discussion covers requirements in OSHA's Design Safety Standards
for Electrical Systems that are frequently overlooked and may present
serious hazards. The reader is encouraged to consult the complete text
of OSHA's electrical standards for all of OSHA's requirements.
EXAMINATION, INSTALLATION AND USE OF EQUIPMENT
Examination
Electrical equipment shall be free from recognized hazards that are
likely to cause death or serious physical harm to employees.(1) Safety
of equipment shall be determined using the following considerations:
Suitability for installation and use in conformity with the
provisions of this subpart. Suitability of equipment for an
identified purpose may be evidenced by listing or labeling for that
identified purpose.
Mechanical strength and durability, including, for parts
designed to enclose and protect other equipment, the adequacy of the
protection thus provided.
Electrical insulation.
Heating effects under conditions of use.
Arcing effects.
Classification by type, size, voltage, current capacity, and
specific use.
Other factors which contribute to the practical safeguarding of
employees using or likely to come in contact with the equipment.
___________
FOOTNOTE(1) Note that this requirement is, in effect, and electrical
"general duty clause" similar to Section 5(a)(1) of the OSH
Act: "each employer shall furnish . . . a place of employment which
is free from recognized hazards that are causing or are likely to cause
death or serious harm to his employees."
Installation and Use
Listed or labeled equipment shall be used or installed in accordance
with any instructions included in the listing or labeling.
IDENTIFICATION OF DISCONNECTING MEANS AND CIRCUITS
Each disconnecting means required by this subpart for motors and
appliances shall be legibly marked to indicate its purpose, unless
located and arranged so the purpose is evident. Each service, feeder,
and branch circuit, at its disconnecting means or overcurrent device,
shall be legibly marked to indicate its purpose, unless located and
arranged so the purpose is evident. These markings shall be of
sufficient durability to withstand the environment involved.
A disconnecting means is a switch that is used to disconnect the
conductors of a circuit from the source of electric current. Disconnect
switches are important because they enable a circuit to be opened,
stopping the flow of electricity, and thus can effectively protect
workers and equipment.
Each disconnect switch or overcurrent device required for a service,
feeder, or branch circuit must be clearly labeled to indicate the
circuit's function, and the label or marking should be located at the
point where the circuit originates. For example, on a panel that
controls several motors or on a motor control center, each disconnect
must be clearly marked to indicate the motor to which each circuit is
connected. In the figure below, the Number 2 circuit breaker in the
panel box supplies current only to disconnect Number 2, which in turn
controls the current to motor Number 2. This current to motor Number 2
can be shut off by the Number 2 circuit breaker or the Number 2
disconnect.
If the purpose of the circuit is obvious, no identification of the
disconnect is required.
All labels and markings must be durable enough to withstand weather,
chemicals, heat, corrosion, or any other environment to which they may
be exposed.
Each Disconnect and Circuit Requires
Identification
WORKING SPACE ABOUT ELECTRIC EQUIPMENT
Note that this particular section is concerned with the safety of a person
qualified to work on the equipment (presumably an electrician).
Obviously, the hazard must be treated in a different way if the person
will remove guards and enclosures and actually work on the live parts.
Sufficient access and working space shall be provided and maintained
about all electric equipment to permit ready and safe operation and
maintenance of such equipment.
Clear Spaces
Working space required by this subpart may not be used for storage. When
normally enclosed live parts are exposed for inspection or servicing,
the working space, if in a passageway or general open space, shall be
suitably guarded.
GUARDING OF LIVE PARTS
It should be noted that the purpose of this requirement is to protect any
person who may be in the vicinity of electrical equipment against
accidental contact. These people are presumably not electricians working
on the equipment, and are not qualified or trained to be in close
proximity to live parts.
Except as required or permitted elsewhere in this subpart, live parts of
electric equipment operating at 50 volts or more shall be guarded
against accidental contact by approved cabinets or other forms of
approved enclosures, or by any of the following means:
By location in a room, vault, or similar enclosure that is
accessible only to qualified persons.
By suitable permanent, substantial partitions or screens so
arranged that only qualified persons will have access to the space
within reach of the live parts. Any openings in such partitions or
screens shall be so sized and located that persons are not likely to
come into accidental contact with the live parts or to bring
conducting objects into contact with them. It is good practice to
use covers, screens or partitions which can only be removed by use
of tools, so that unqualified persons are less likely to violate
them.
By location on a suitable balcony, gallery, or platform.
By elevation of 8 feet or more above the floor or other working
surface. Note that, although equipment elevated at least 8 feet is
considered to be guarded, this may not be adequate if material being
handled is likely to make contact with live parts.
In locations where electric equipment would be
exposed to physical damage, enclosures or guards shall be so arranged
and of such strength as to prevent such damage.
Entrances to rooms and other guarded locations containing exposed live
parts shall be marked with conspicuous warning signs forbidding
unqualified persons to enter.
You should be constantly aware of hazards in your workplace. New work or
changes may create a new hazard, or poor maintenance may allow
reappearance of old ones.
IDENTIFICATION OF CONDUCTORS
A conductor used as a grounded conductor shall be identifiable and
distinguishable from all other conductors. A conductor used as an
equipment grounding conductor shall be identifiable and distinguishable
from all other conductors.
The grounded conductor is an energized circuit conductor that is
connected to earth through the system ground. It is commonly referred to
as the neutral. The equipment grounding
conductor is not an energized conductor under normal conditions. The
equipment grounding conductor acts as a safeguard against insulation
failure or faults in the other circuit conductors. The equipment
grounding conductor is energized only if
there is a leak or fault in the normal current path, and it directs this
current back to the source. Directing the fault current back to the
source enables protective devices, such as circuit breakers or fuses, to
operate thus preventing fires and reducing the hazard of electrical
shocks.
The grounded and equipment grounding conductors of an electrical circuit
must be marked or color coded in a way that allows employees to identify
them and tell them apart from each other and from the other conductors
in the circuit.
The figure below illustrates a distribution panelboard. One means by
which each conductor's use is identified and made distinguishable from
the other circuit conductors is the use of color coding. Acceptable
color coding includes the method required by the National
Electrical Code, Section 210-5. The Code states: "The
grounded conductor of a branch circuit shall be identified by a
continuous white or natural gray color." Also, "The equipment
grounding conductor of a branch circuit shall be identified by a
continuous green color or a continuous green color with one or more
yellow stripes unless it is bare." Bare copper or aluminum wire is
permitted for use as a grounding conductor.
POLARITY OF CONNECTIONS
No grounded conductor may be attached to any terminal or lead so as to
reverse designated polarity.
A grounding terminal or grounding-type device on a receptacle, cord
connector, or attachment plug may not be used for purposes other than
grounding.
The above two subparagraphs dealing with polarity of connections and use
of grounding terminals and devices address one potentially dangerous
aspect of alternating current: many pieces of equipment will operate
properly even though the supply wires are not connected in the order
designated by design or the manufacturer. Improper connection of these
conductors is most prevalent on the smaller branch circuit typically
associated with standard 120 volt receptacle outlets, lighting fixtures
and cord- and plug-connected equipment.
When plugs, receptacles, and connectors are used in an electrical branch
circuit, correct polarity between the ungrounded (hot) conductor, the
grounded (neutral) conductor, and the grounding conductor must be
maintained.
Reversed polarity is a condition when the
identified circuit conductor (the grounded conductor or neutral) is
incorrectly connected to the ungrounded or "hot" terminal of a
plug, receptacle, or other type of connector.
The figure below shows the correct wiring for the common 120-volt outlet
with a portable hand tool attached.
Suppose now that the black (ungrounded) and white (grounded) conductors
are reversed as shown in the figure below. This is the traditional reversed
polarity. Although a shock hazard may not exist, there are other
mechanical hazards that can occur.
For example, if an internal fault should occur in the wiring as shown in
the figure below, the equipment would not stop when the switch is
released or would start as soon as a person plugs the supply cord into
the improperly wired outlet. This could result in serious injury.
The figure below shows the white (grounded) and green (grounding)
conductors reversed. Although it is not fitting, considering OSHA or
code terminology, to call this reversed polarity,
a hazard can still exist. In this case, due to the wiring error, the
white wire is being used to provide equipment grounding. Under certain
conditions, this could be dangerous.
The figure below shows an extremely
dangerous situation. In this example, the black (ungrounded) and green
(grounding) conductors have been reversed. The metal case of the
equipment is at 120 volts with reference to the surroundings. As soon as
a person picks up the equipment and touches a conductive surface in
their surrounding, they will receive a serious, or even deadly, shock.
Although the equipment will not work with this wiring error, it would
not be unusual for a person to pick up the equipment before realizing
this. The person may even attempt to troubleshoot the problem before
unplugging the power cord.
Correct polarity is achieved when the grounded conductor is connected to
the corresponding grounded terminal and the ungrounded conductor is
connected to the corresponding ungrounded terminal. The reverse of the
designated polarity is prohibited. The figure below illustrates a duplex
receptacle correctly wired. Terminals are designated and identified to
avoid confusion. An easy way to remember the correct polarity is
"white to light" - the white (grounded) wire should be
connected to the light or nickel-colored terminal; "black to
brass" - the black or multi-colored (ungrounded) wire should be
connected to the brass terminal; and "green to green" - the
green or bare (grounding) wire should be connected to the green
hexagonal head terminal screw.
GROUNDING
This section contains grounding requirements for systems, circuits, and
equipment. Grounding electrical circuits and electrical equipment is
required to protect employees against electrical shock, safeguard
against fire, and protect against damage to electrical equipment. There
are two kinds of grounding: (1) electrical circuit or system grounding,
and (2) electrical equipment grounding. Electrical system grounding is
accomplished when one conductor of the circuit is intentionally
connected to earth. This is done to protect the circuit should lightning
strike or other high voltage contact occur. Grounding a system also
stabilizes the voltage in the system so "expected voltage
levels" are not exceeded under normal conditions. The second kind
of ground is equipment grounding. This is accomplished when all metal
frames of equipment and enclosures containing electrical equipment or
conductors are grounded by means of a permanent and continuous
connection or bond. The equipment grounding conductor provides a path
for dangerous fault current to return to the system ground at the supply
source of the circuit should an insulation failure take place. If
installed properly, the equipment grounding conductor is the current
path that enables protective devices, such as circuit breakers and
fuses, to operate when a fault occurs. The figure below illustrates both
types of grounding.
GROUNDING PATH
The path to ground from circuits, equipment, and enclosures shall be
permanent and continuous.
This requirement was extracted from NEC 250-51, Effective
Grounding Path, which is more complete and fundamental to the
understanding of electrical safety. It states that the path to ground:
"shall be permanent and continuous." (If the path is
installed in such a way that damage, corrosion, loosening, etc. may
impair the continuity during the life of the installation, then
shock and burn hazards will develop.)
"shall have capacity to conduct safely any fault current
likely to be imposed on it." (Fault currents may be many times
normal currents, and such high currents may melt or burn metal at
points of poor conductivity. These high temperatures may be a hazard
in themselves, and they may destroy the continuity of the
ground-fault path.)
"shall have sufficiently low impedance to limit the voltage
to ground and to facilitate the operation of the circuit protective
devices in the circuit." (If the ground-fault path has a high
impedance, there will be hazardous voltages whenever fault currents
attempt to flow. Also, if the impedance is high, the fault current
will be limited to some value so low that the fuse or circuit
breaker will not operate promptly, if at all.)
It is important to remember the following
regarding safe grounding paths:
The fault current in A-C circuits will be limited by the sum of
resistance and reactance, and the only
low-reactance path is that which closely follows the circuit
conductors.
If a metallic raceway system is used, make sure that the
metallic system is continuous and permanent.
In cases where a metallic raceway system is not used, provide a
green or bare equipment-grounding conductor close to the supply
conductors to assure that all enclosures are bonded together and to
the source.
GROUNDING OF EQUIPMENT
CONNECTED BY CORD AND PLUG
Under any of the conditions described below, exposed
non-current-carrying metal parts of cord- and plug-connected equipment
which may become energized shall be grounded.
a. If in a hazardous (classified) location.
b. If operated at over 150 volts to ground, except for guarded motors
and metal frames of electrically heated appliances if the appliance
frames are permanently and effectively insulated from ground.
c. If the equipment is of the following types:
Refrigerators, freezers, and air conditioners;
Clothes-washing, clothes-drying and dishwashing machines, sump
pumps, and electrical aquarium equipment;
Hand-held motor-operated tools;
Motor-operated appliances of the following types: hedge
clippers, lawn mowers, snow blowers, and wet scrubbers;
Cord- and plug-connected appliances used in damp or wet
locations or by employees standing on the ground or on metal
floors or working inside of metal tanks or boilers;
Portable and mobile X-ray and associated equipment;
Tools likely to be used in wet and conductive locations; and
Portable hand lamps.
Under the conditions described above, exposed
non-current-carrying metal parts of cord- and plug-connected equipment
must be grounded. Grounding metal parts is not required where the
equipment is supplied through an isolating transformer with an
ungrounded secondary of not over 50 volts or if portable tools are
protected by an approved system of double insulation. To ground cord-
and plug-connected equipment, a third wire is commonly provided in the
cord set and a third prong in the plug. The third wire serves as an
equipment grounding conductor which is connected to the metal housing of
a portable tool and a metal grounding bus inside the service entrance
equipment. The service entrance equipment is located at the entrance
point of the electric supply for a building or plant and contains, or
serves other panelboards which contain, branch circuit protective
devices such as fuses and circuit breakers. The third wire provides a
path for fault current should an insulation failure occur. In this
manner, dangerous fault current will be directed back to the source, the
service entrance, and will enable circuit breakers or fuses to operate,
thus opening the circuit and stopping the current flow.
The figure below illustrates the potential shock hazard that exists when
no third wire, grounding conductor, is used. If a fault occurs, most of
the current will follow the path of least resistance. If the worker
provides a path to ground as shown, some portion of the current will
flow away from the grounded white conductor (neutral) and return to
ground through the worker. The severity of the shock received will
depend on the amount of current that flows through the worker.
The figure below illustrates the advantage of a properly connected
grounded conductor. It should be noted that properly bonded conduit and
associated metal enclosures can also serve as a grounding conductor.
Tools likely to be used in wet and conductive locations need not be
grounded if supplied through an isolating transformer with an ungrounded
secondary of not over 50 volts. Listed or labeled portable tools and
appliances protected by an approved system of double insulation, or its
equivalent, need not be grounded. If such a system is employed, the
equipment shall be distinctively marked to indicate that the tool or
appliance utilizes an approved system of double insulation.
GROUND-FAULT CIRCUIT-INTERRUPTERS
Introduction
In
most cases, insulation and grounding
are used to prevent injury from electrical wiring systems or equipment.
However, there are instances when these recognized methods do not
provide the degree of protection required. To help appreciate this,
let's consider a few examples of where ground fault circuit interrupters
would provide additional protection.
Many portable hand tools, such as electric drills, are now
manufactured with non-metallic cases. If approved, we refer to such
tools as double insulated. Although this
design method assists in reducing the risk from grounding
deficiencies, a shock hazard can still exist. In many cases, persons
must use such electrical equipment where there is considerable
moisture or wetness. Although the person is insulated
from the electrical wiring and components, there is still the
possibility that water can enter the tool housing. Ordinary water is
a conductor of electricity. Therefore, if the water contacts
energized parts, a path will be provided from inside the housing to
the outside, bypassing the double insulation.
When a person holding a hand tool under these conditions touches
another conductive surface in their work environment, an electric
shock will result.
Double-insulated equipment or equipment with non-metallic
housings, that does not require grounding under the National
Electrical Code, is frequently used around sinks or in situations
where the equipment could be dropped into water. Frequently, the
initial human response is to grab for the equipment. If a person's
hand is placed in the water and another portion of their body is in
contact with a conductive surface, a serious or deadly electric
shock can occur.
In construction work and regular factory maintenance work, it is
frequently necessary to use extension cord sets with portable
equipment. These cords are regularly exposed to physical damage.
Although safe work procedures require adequate protection, it is not
possible to prevent all damage. Frequently, the damage is only to
the insulation, exposing energized conductors. It is not unusual for
a person to handle the cord often with the possibility of contacting
the exposed wires while holding a metal case tool or while in
contact with other conductive surfaces.
The amount of current which flows under such conditions will be
enough to cause serious human response. This can result in falls or
other physical injury and in many cases death.
Since neither insulation
(double insulation) nor grounding can
provide protection under these conditions, it is necessary to use other
protective measures. One acceptable method is a ground fault circuit
interrupter, commonly referred to as a GFCI.
How Ground-Fault Circuit-Interrupters Work
A ground-fault circuit-interrupter is not an
overcurrent device like a fuse or circuit breaker. GFCI's are designed
to sense an imbalance in current flow over the normal path.
The GFCI contains a special sensor that monitors the strength of the
magnetic field around each wire in the circuit when current is flowing.
The magnetic field around a wire is directly proportional to the amount
of current flow, thus the circuitry can accurately translate the
magnetic information into current flow.
If the current flowing in the black (ungrounded)
wire is within 5 (plus or minus 1) milliamperes (mA) of the
current flowing in the white (grounded) wire
at any given instant, the circuitry considers the situation normal. All
the current is flowing in the normal path. If, however, the current flow
in the two wires differs by more than 5 mA, the GFCI will quickly open
the circuit. This is illustrated in the figure below.
Note that the GFCI will open the circuit if 5 mA or more of current
returns to the service entrance by any path other than the intended
white (grounded) conductor. If the equipment grounding conductor is
properly installed and maintained, this will happen as
soon as the faulty tool is plugged in. If by chance this
grounding conductor is not intact and of low-impedance, the GFCI may not
trip out until a person provides a path. In
this case, the person will receive a shock, but the GFCI should trip out
so quickly that the shock will not be harmful.
Types of Ground-Fault Circuit-Interrupters
There are several types of GFCI's available, with some variations to
each type. Although all types will provide ground-fault protection, the
specific application may dictate one type over another.
Circuit-Breaker Type
The circuit-breaker type includes the functions of a standard
circuit breaker with the additional functions of a GFCI. It is
installed in a panelboard and can protect an entire branch circuit
with multiple outlets. It is a direct replacement for a standard
circuit breaker of the same rating.
Receptacle Type
The receptacle style GFCI incorporates within one device one or more
receptacle outlets, protected by the GFCI. Such devices are becoming
very popular because of their low cost. Most are of the duplex
receptacle configuration and can provide GFCI protection for
additional non-GFCI type receptacles connected "down
stream" from the GFCI unit.
Permanently Mounted Type
The permanently mounted types are mounted in an enclosure and
designed to be permanently wired to the supply. Frequently they are
used around large commercial swimming pools or similar wet
locations.
Portable Type
Several styles of portable GFCI's are available. The portable types
are designed to be easily transported from one location to another.
They usually contain one or more integral receptacle outlets
protected by the GFCI module. Some models are designed to plug into
existing non-GFCI protected outlets, or in some cases, are connected
with a cord and plug arrangement. The portable type also incorporate
a no-voltage release device which will disconnect power to the
outlets if any supply conductor is open. Units approved for use
outdoors will be in enclosures suitable for the environment. If
exposed to rain, they must be listed as rainproof.
Cord Connected Type
The power supply cord type GFCI consists of an attachment plug which
incorporates the GFCI module. It provides protection for the cord
and any equipment attached to the cord. The attachment plug has a
non-standard appearance and is equipped with test and reset buttons.
Like the portable type, it incorporates a no-voltage release device
which will disconnect power to the load if any supply conductor is
open.
Classes of Ground-Fault
Circuit-Interrupters
Ground-Fault Circuit-Interrupters are divided into two classes: Class A
and Class B. The Class A device is designed to trip when current flow,
in other than the normal path, is 6 milliamperes or greater. The
specification is 5 milliamperes ± 1 milliampere. The Class B device
will trip when current flow, in other than the normal path, is 20
milliamperes or greater. Class B devices are approved for use on
underwater swimming pool lighting installed prior to the adoption of the
1965 National Electrical Code.
Testing Ground-Fault Circuit-Interrupters
Due to the complexity of a GFCI, it is necessary to test the device on a
regular basis. For permanently wired devices, a monthly test is
recommended. Portable type GFCI's should be tested each time before use.
GFCI's have a built-in test circuit which imposes an artificial ground
fault on the load circuit to assure that the ground-fault protection is
still functioning. Test and reset buttons are provided for testing.
CABINETS, BOXES, AND FITTINGS
Conductors Entering Boxes, Cabinets, or Fittings
Since conductors can be damaged if they rub against the sharp edges of
cabinets, boxes, or fittings, they must be protected from damage where
they enter. To protect the conductors, some type of clamp or rubber
grommet must be used. The device used must close the hole through which
the conductor passes as well as provide protection from abrasion. If the
conductor is in a conduit and the conduit fits tightly in the opening,
additional sealing is not required.
The knockouts in cabinets, boxes, and fittings should be removed only if
conductors are to be run through them. However, if a knockout is missing
or if there is another hole in the box, the hole or opening must be
closed.
Covers and Canopies
All pull boxes, junction boxes, and fittings shall be provided with
covers approved for the purpose. If metal covers are used, they shall be
grounded. In completed installations, each outlet box shall have a
cover, faceplate, or fixture canopy. Covers of outlet boxes having holes
through which flexible cord pendants pass shall be provided with
bushings designed for the purpose or shall have smooth, well-rounded
surfaces on which the cords may bear.
FLEXIBLE CORDS AND CABLES
This standard for safe use of flexible cords is one of the most
frequently violated electrical standards, particularly in smaller
plants. There is a definite need and place for cords, but there is also
a temptation to misuse them because they seem to offer a quick and easy
way to carry electricity to where it is needed. The basic problem is
that flexible cords in general are more vulnerable than the fixed wiring
of the building. Therefore, cords should not be used if one of the
recognized wiring methods could be used instead.
Use of Flexible Cords and Cables
Flexible cords and cables shall be approved and suitable for conditions
of use and location. The standard lists specific situations in which
flexible cords may be used. Flexible cords and cables shall be used only
for:
a. Pendants (a lampholder or cord-connector body suspended by a
length of cord properly secured and terminated directly above the
suspended device);
b. Wiring of fixtures;
c. Connection of portable lamps or appliances;
d. Elevator cables;
e. Wiring of cranes and hoists (where flexibility is necessary);
f. Connection of stationary equipment to facilitate their frequent
interchange (equipment which is not normally moved from place to
place, but might be on occasion);
g. Prevention of the transmission of noise or vibration. (In some
cases vibration might fatigue fixed wiring and result in a situation
more hazardous than flexible cord.)
h. Appliances where the fastening means and mechanical connections are
designed to permit removal for maintenance and repair (e.g. water
coolers, exhaust fans);
i. Data processing cables approved as a part of the data processing
system.
Note that all of the above situations involve
conditions where flexibility is necessary. Unless specifically permitted
by one of these situations, flexible cords and cables may not be used:
a. As a substitute for the fixed wiring of the structure;
b. Where run through holes in walls, ceilings, or floors;
c. Where run through doorways, windows, or similar openings;
d. Where attached to building surfaces; or
e. Where concealed behind building walls, ceilings, or floors.
There is usually not much question about use
of the short length of cord which is furnished as part of an approved
appliance or tool; there is usually no question about an extension cord
used temporarily to permit use of the appliance or tool in its intended
manner at some distance from a fixed outlet; but there are questions
when the usage is not obviously temporary, and when the cord is extended
to some distant outlet in order to avoid providing a fixed outlet where
needed.
Flexible cord used in violation of this standard is likely to be damaged
by activities in the area; by door or window edges; by staples or
fastenings; by abrasion from adjacent materials; or simply by aging. If
the conductors become partially exposed over a period of time, there
will be danger of shocks, burns, or fire.
Identification, Splices and Terminations
Flexible cords shall be used only in continuous lengths without splice
or tap. Hard service flexible cords, No. 12 or larger, may be repaired
if spliced so that the splice retains the insulation, outer sheath
properties, and usage characteristics of the cord being spliced.
Flexible cords shall be connected to devices and fittings so that strain
relief is provided which will prevent pull from being directly
transmitted to joints or terminal screws.
In
most cases, insulation and grounding
are used to prevent injury from electrical wiring systems or equipment.
However, there are instances when these recognized methods do not
provide the degree of protection required. To help appreciate this,
let's consider a few examples of where ground fault circuit interrupters
would provide additional protection.
