Conductors entering cabinets/boxes/fittings protected from abrasion
Standard: 1910.
Use of flexible cords and cables
*
*
*
*
*
*Average number of Federal OSHA citations issued
between 2000 and 2003
DEFINITION
A physical agency caused by the motion of electrons, protons, and other charged particles, manifesting itself as an attraction, repulsion, magnetic, luminous, and heating effects, etc.
ELEMENTS & ATOMS
Every known substance – solid, liquid or gas is composed of elements
An atom is the smallest particle of an element that retains all the properties of that element
Each element has it’s own kind of atom
ATOMS
Inner part composed of protons & neutrons
Outer part composed of electrons
Protons = positive charge
Neutrons = no charge
Electrons = negative charge
ATOMS
Each element has a definite number of electrons ----and the same number of protons
They are oppositely charged and therefore attract each other. This tends to hold the electrons in orbit around the atom.
ELECTRICALLY BALANCED ATOM
FREE ELECTRONS
Some atoms are easily moved out of orbit
The ability to move or flow is the basis of current electricity
If channeled in a given direction, a flow of electrons occurs --- when flowed through a conductor it is dynamic electricity
VOLTAGE – unit of measurement of electromotive force (EMF)
CURRENT - Continuous movement of electrons past a given point. (measured in amperes)
RESISTANCE – Opposition to movement of electrons. Makes it possible to generate heat, control current flow, & supply correct voltage to devices
OHM’S LAW
George Simon Ohm
Formulated a mathematical relationship between:
Current
Voltage
Resistance
Resistance = Impedance
Resistance = DC
Impedance = AC
Interchangeable – Most Branch circuits
DIRECT CURRENT
Always flows in one direction
Used to charge batteries, run some motors, operate magnetic lifting devices and welding equipment.
ALTERNATING CURRRENT
More common in electrical work
Changes rapidly in both direction and value
Power companies produce power cheaper with alternating current
ELECTRICAL HAZARDS
SHOCK. Electric shock occurs when the human body becomes part of the path through which current flows.
The direct result can be electrocution.
The indirect result can be injury resulting from a fall or movement into machinery because of a shock
ELECTRICAL HAZARDS
BURNS. Burns can result when a person touches electrical wiring or equipment that is energized.
ARC-BLAST. Arc-blasts occur from high- amperage currents arcing through the air. This can be caused by accidental contact with energized components or equipment failure.
Arc Flash and Arc Blasts
Arc Flash:
80%-Burns due to ignition of clothing
Temperature-35,000 F
Fatal Burns-10 ft.
2000 people hospitalized with burns
Molten metal
Arc Blast:
Pressure Wave
Heat
Molten metal
Destruction of structures and life
Arc Blast
Cause
Short Circuit caused by working on energized equipment
Dropped Tool
Occurs in milliseconds
Temp: 30,000 degrees
Air expands very violently
15 tons of pressure
ELECTRICAL HAZARDS
ARC-BLAST. The three primary hazards associated with an arc-blast are:
Thermal radiation.
Pressure Wave.
Projectiles.
ELECTRICAL HAZARDS
EXPLOSIONS. Explosions occur when electricity provides a source of ignition for an explosive mixture in the atmosphere.
ELECTRICAL HAZARDS
FIRES. Electricity is one of the most common causes of fires both in the home and in the workplace. Defective or misused electrical equipment is a major cause.
EFFECTS ON THE HUMAN BODY
Depends on:
Current and Voltage
Resistance
Path through body
Duration of shock
Effects of AC Electricity
More than 3 mA- Painful shock- cause indirect accident
More than 10 mA- Muscle contraction – “No Let Go” danger
More than 30 mA- Lung paralysis, usually temporary
Effects of AC Electricity
More than 50 mA- Ventricular fibrillation, usually fatal
Each service, feeder, and branch circuit, at its overcurrent device, legibly and durably marked to indicate its purpose
Switches and circuit breakers must be clearly labeled to indicate its circuit’s function
Circuit breaker for motors
1,2,3, and 4
1910.303(g) Working Space
(1) Sufficient access and working space around all electrical equipment, provided & maintained to provide ready and safe operation and maintenance
(ii) Not used for storage
(ii) If located in aisle or general open area, working space shall be suitably guarded
1910.303(g)(1)(v) Illumination
Illumination provided for all working spaces about service equipment, switchboards, panel-boards, and motor control centers installed indoors.
1910.303(g)(1)(vi) Headroom
The minimum headroom of working spaces about service equipment, switchboards, panel-boards, or motor control centers shall be 6 feet 3 inches
6'3"
1910.303(g) Guarding of live parts
(2)(i) Live parts of electric equipment operating at 50 volts or more guarded against accidental contact by approved cabinets
Guarding live parts – 1910.303
(g)(2)(i) or other forms of approved enclosures, or by any of the following means:
(A) By location in a room, vault, accessible only to qualified persons
(B) By permanent, substantial partitions or screens
(C) By location on a suitable balcony or platform as to exclude unqualified persons
(D) By elevation of 8 feet or more above the floor or other working surface
1910. 303(g) Guarding live parts
(2)(iii) Entrances to rooms and other guarded locations containing exposed live parts shall be marked with conspicuous warning signs forbidding unqualified persons to enter
1910.303(h)(3)(ii) Illumination
Adequate illumination for all working spaces about electric equipment
The lighting outlets arranged that persons changing lamps or making repairs on the lighting system will not be endangered by live parts or other equipment
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
Identification of Conductors
Grounded conductor and equipment grounding conductors marked or color coated
So that employees can i.d. and tell apart
Grounded conductor is an energized circuit (conductor that is connected to earth through the system ground) Commonly referred to as the neutral
Grounding Conductors
Equipment grounding conductor acts as a safeguard against insulation failure or faults in the other circuit conductors
Not an energized conductor under normal conditions.
Energized if a leak or fault in the normal current path
Directs current back to the source
Enabling fuses or circuit breakers to operate
Identification of Conductors
Grounded conductor i.d. and distinguished from other conductors w/ white or gray
Equipment grounding conductor i.d. and distinguished w/ green, green w/ yellow stripes, or bare
1910.304(a) Use and identification of grounded and grounding conductors
(2) No grounded conductor may be attached to any terminal or lead so as to reverse polarity
(3) A grounding terminal on a receptacle, cord connector, or plug may not be used for purposes other than grounding
Summary of
Intent of
1910.304
Polarity of connections
Improper connection of these conductors (‘hot and neutral’) is most prevalent on smaller branch circuits:
Standard 120 volt receptacle outlets
Cord-and plug-connected equipment
Reversed Polarity
Reversed polarity is a condition when the grounded conductor (neutral) is incorrectly connected to the ungrounded (hot) terminal of a plug, receptacle, or other type of conductor
General. Means shall be provided to disconnect all conductors in a building or other structure from the service-entrance conductors.
The disconnecting means shall plainly indicate whether it is in the open or closed position and shall be installed at a readily accessible location nearest the point of entrance of the service-entrance conductors.
1910. 304 (d)(2) Services over 600 volts, nominal
Danger
(i) Guarded to make them accessible only to qualified persons
(ii) Signs warning of high voltage shall be posted where other than qualified employees might come in contact with live parts
1910. 304 (e)(1)(vi) Circuit breakers
1000kV
Danger
Circuit breakers shall clearly indicate whether they are in the open (off) or closed (on) position
1910. 304 (f) Grounding
(4) The path to ground from circuits, equipment, and enclosures shall be permanent and continuous
Grounding
There are two kinds of grounding:
1. Electrical circuit or system grounding
2. Electrical equipment grounding
Electrical System Grounding
One conductor of the circuit is intentionally grounded to earth
Protects circuit from lightning, or other high voltage contact
Equipment Grounding
All metal frames & enclosures of equipment are grounded by a permanent connection or bond
The equipment grounding conductor provides a path for dangerous fault current to return to the system ground at the supply source should a fault occur
Grounding Equipment Connected by Cord and Plug
Exposed non-current carrying metal parts of cord and plug connected equipment which may become energized shall be grounded
If in a hazardous location
If operated at over 150 volts
Note that properly bonded conduit and associated
metal enclosures can also serve as a grounding
conductor.
Ground fault circuit interrupters (GFCI’s)
A GFCI 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
Ground fault circuit interrupters (GFCI’s)
GFCI contains a special sensor that monitors the strength of the magnetic field around each wire in the circuit when current is flowing
The field is proportional to the amount of current flow
T
Ground fault circuit interrupters (GFCI’s)
If the current flowing in the black (ungrounded) wire is within 5 milliampers of the current flowing in the white (grounded) all the current will flow in the normal path
If the current flow differs by more than 5mA +/- 1mA, the GFCI will quickly open the circuit
Testing GFCI’s
GFCI’s are complex mechanisms, they must be tested on a regular basis
Installation must be correct according to the listing & labeling requirements or the GFCI will not protect as designed
Cabinets, cutouts boxes, fittings, and panelboards shall be weatherproof
Switches, circuit breakers, and switchboards shall be in weather proof enclosures
1910.305 (g)(1) Use of Flexible Cords & Cables
Flexible cords and shall be approved and suitable for conditions of use and location*
* The OSHA electric standard (1910.305) lists specific situations in which flexible cords may be used
1910.305 (g)(1)(iii) Prohibited uses of flexible cords
Except for the previously listed exemptions, flexible cords may not be used for:
(A) As a substitute for fixed wiring of the structure;
(B) Where run through holes in walls, ceilings, or floors;
(C) Where run through doorways, windows, etc..
Judgment of application
There are usually citations when the usage is obviously not temporary; and,
When the cord is extended to some distant outlet in order to avoid providing a fixed outlet where needed
Identification, Splices and Terminations
Flexible cords shall only be used in continuous lengths, no taps or splices
Damaged cord
improperly repaired
Identification, Splices and Terminations
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
1910.305 (g)(2)(ii)
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.
Note: The National Electric Code allows
splice in 14 gauge or greater wire
Safety-Related
Work Practices
1910.331-335
1910.331 Scope
Covers:
Qualified persons (those who have training in avoiding the electrical hazards
Unqualified persons (those with little or no such training)
Working on or near the following:
Premises wiring
Wiring for connection to supply
Other wiring
1910.332 Training
Scope:
The training requirements contained in this section apply to employees who face a risk of electric shock that is not reduced to a safe level by the electrical installation requirements of 1910.303 through 1910.308
Employees shall be trained in and familiar with the safety-related work practices required by 1910.331 through 1910.335 that pertain to their respective job assignments
Footnote to Table S-4
(1) Workers in these groups do not need to be trained if their work or the work of those they supervise does not bring them or their employees close enough to exposed parts of electric circuits operating at 50 volts or more to ground for a hazard to exist.
1910.332 Training
(b)(3) Qualified persons: (i.e. those permitted to work on or near exposed energized parts) shall, at a minimum, be trained in and familiar with the following:
(i) The skills and techniques necessary to distinguish exposed live parts from other parts of electric equipment
(ii) The skills and techniques necessary to determine the nominal voltage of exposed live parts
(iii) The clearance distances specified in 1910.333(c)
1910.333 (a)(1) Deenergized parts
Live parts to which an employee may be exposed shall be deenergized before the employee works on or near them:
Unless the employer can demonstrate that deenergizing introduces additional or increased hazards or is infeasible
Live parts that operate at less than 50 volts to ground need not be deenergized if there will be no increased exposure to electrical burns or to explosion due to electric arcs
1910.333(b) Working on or near exposed deenergized parts
(1) Conductors and parts of electric equipment that have been deenergized but have not been locked out or tagged in accordance with paragraph (b) of this section shall be treated as energized parts
1910.333(c)(4) Illumination
Employees may not enter spaces containing exposed energized parts, unless illumination is provided that enables the employees to perform the work safely
1910.333(c)(4) Illumination
Employees may not reach blindly into areas which may contain energized parts.
1910.333(c)(7) Portable ladders
Portable ladders shall have nonconductive siderails if they are used where the employee or the ladder could contact exposed energized parts
1910.333(c)(8) Conductive apparel
Conductive articles of jewelry and clothing (such a watch bands, bracelets, rings, key chains, necklaces, etc...) may not be worn if they might contact exposed energized parts
Portable equipment shall be handled in a manner which will not cause damage
Flexible electric cords connected to equipment may not be used for raising or lowering the equipment
Flexible cords may not be fastened with staples or otherwise hung in such a fashion as could damage the outer jacket or insulation
1910.334 (a)(2)(i) Use of equipment
Portable cord and plug connected equipment and flexible cord sets (extension cords) visually inspected before use for external defects (such as loose parts, or damage to outer jacket or insulation) and for evidence of possible internal damage (pinched or crushed outer jacket)
Extension cords which remain connected once they are put in place and are not exposed to damage need not be visually inspected until they are relocated
1910.334 Use of equipment
A flexible cord used with grounding type equipment shall contain an equipment grounding conductor
Attachment plugs and receptacles may not be connected or altered in a manner which would prevent proper continuity of the equipment grounding conductor at the point where plugs are attached to receptacles
1910.334 (c)(1) Use
Only qualified persons may perform testing work on electric circuits or equipment
1910.334 Use of equipment
(c)(2)"Visual inspection." Test instruments and equipment and all associated test leads, cables, power cords, probes, and connectors shall be visually inspected for external defects and damage before the equipment is used.
If there is a defect or evidence of damage that might expose an employee to injury, the defective or damaged item shall be removed from service, and no employee may use it until repairs and tests necessary to render the equipment safe have been made.
1910.335 Safeguards for personnel protection
(a)(1)Employees working in areas where there are potential electrical hazards shall be provided with, and shall use, electrical protective equipment that is appropriate for the specific parts of the body to be protected and for the work to be performed
1910.335 Safeguards for personnel protection
(a)(1)(ii)Protective equipment shall be maintained in a safe, reliable condition and shall be periodically inspected or tested, as required by 1910.137 *
*1910.137 Electrical protective equipment
1910.335 Safeguards for personnel protection
(a)(2)(i)When working near exposed energized conductors or circuit parts, each employee shall use insulated tools or handling equipment if the tools or handling equipment might make contact with such conductors or parts
1910.335 Safeguards for personnel protection
(b)The following alerting techniques shall be used to warn and protect employees from hazards which could cause injury due to electric shock, burns, or failure of electric equipment parts:
Safety signs and tags
Barricades
Attendants
1910.335 Safeguards for personnel protection
(b)(1)Safety signs, safety symbols, or accident prevention tags shall be used where necessary to warn employees about electrical hazards which may endanger them, as required by 1910.145
1910.335 Safeguards for personnel protection
(b)(2)Barricades shall be used in conjunction with safety signs where it is necessary to prevent or limit employee access to work areas exposing employees to uninsulated energized conductors or circuit parts
1910.335 Safeguards for personnel protection
If signs and barricades do not provide sufficient warning and protection from electrical hazards, an attendant shall be stationed to warn and protect employees
