Electrical Standards*
Statistics
Electrocution: Among most frequent causes of occupational injury death in US
295 fatalities/year; 4309 lost time
1992-2002: 9% decrease
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Adequate/required PPE provided and worn?
Lockout/tagout procedures implemented and followed?
OSHA, NEC, NESC compliance?
(from NIOSH)
Electrical shock
Cannot see, smell, taste, or hear danger
Can recognize unsafe conditions
Conductors – substances with little resistance to electricity (such as metals)
Insulators – substances with high resistance to electricity (such as wood, rubber, glass, & bakelite)
*
Severity depends on:
Amount of current flowing through body
Length of time body is in circuit
Also: voltage, moisture, heart cycle, health
Low voltage is NOT low hazard!
*
Currents >75 mA* can cause ventricular fibrillation (rapid, ineffective heartbeat)
mA = milliampere = 1/1,000 of an ampere
Death within minutes unless a defibrillator is used
75 mA is not much current
(a small power drill uses 30 times as much)
*
1 mA: Perception level, slight tingling.
5 mA: Slight shock; not painful.
Can usually let go.
6-30 mA: Painful shock
*
50-150 mA: Extreme pain
Death possible
1 wire of energized circuit and ground
Metallic part in contact with energized wire and ground
*
Inadequate Wiring Hazards
What happens when a wire is too small to carry the current safely?
Overheating
Fuse acts as sacrificial
break first
Wire Gauge
1910 Subpart S = Electrical
1910 Subpart I = PPE
1910.137 Electrical Protective Devices
1926 Subpart K = Electrical
Protect against recognized hazards
Revised Subpart S based heavily on 2000 version
2004 version now published
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§ 302-308 and 399 updated: PM App. C
5 main groups of standards:
Design safety standards § 302-330
Safety-related work practices § 331-360
Reserved: maintenance, special equipment
Applicability of regulations
Conductors and equipment acceptable only if approved
Note: If installation is made in accordance with NEC or ANSI/NFPA it will be deemed in compliance.
See definitions
Suitability (check listing/labeling)
Insulation integrity
Circuit impedance…
Mechanical execution of work
Internal parts not contaminated
Mounting and cooling
Some electrical equipment normally produces arcs, sparks, flames, molten metal
Keep isolated from combustible material
*
Voltage, current, wattage, etc.
Durable markings in environment
Unless purpose is evident
Subtitles & Transitions
FOR EXAMPLE…
Space about electric equipment
Guarded when parts exposed
*
Guarding of live parts
Protection from damage
*
Enclosure / access control
Working space and guarding
Wiring Design and Protection
Grounded & equipment grounding conductors identifiable & distinguishable
Grounded = white or gray
Equipment grounding = green, or green with yellow strips, or bare
Polarity may not be reversed
Grounding devices not used for other purposes
*
(ungrounded) terminal
For >1 voltage system in a building
ID phase and system
*
Receptacles only on circuits matching voltage and current rating
Grounding contacts grounded
*
GFCI where required
*
*
For 2 outlets on branch circuit: Table S-4
*
50 A: receptacle branch-circuit rating
Cord connections: Outlet where flexible cords with plugs used
*
Clearance
12 feet – vehicular traffic
15 feet – truck traffic
*
Clearance from building openings
Not beneath or obstructing openings where materials may be moved
Above roofs: 8 ft above, 3 ft from edge
Pedestrians? Platform
Location of outdoor lamps
Under energized equipment unless
Clearance/other safeguards adequate
Services over 600 volts, nominal
Accessible only to qualified; warning signs
*
Protect conductors and equipment
Overcurrent devices readily accessible
To employees & building management
Located/shielded to avoid injury/burns
On/off position clearly indicated
*
AC 50V-1000V (unless exempt) under 4 conditions
Exemptions for AC 50V-1000V
Grounding connections
*
intentionally grounded to earth
Protects circuit from lightning
or other high voltage contact
*
Grounding
Metal frames / enclosures of equipment grounded by permanent connection or bond
Equipment grounding conductor provides path for dangerous fault current to return to ground
*
Shall have capacity to conduct safely any likely fault current.
Fault currents may be many times normal currents; can melt points of poor conductivity
High temperatures = hazard; can destroy ground-fault path
*
Nonelectrical equipment
Methods of grounding fixed equipment
*
GFCI overcurrent device like a fuse or circuit breaker
Designed to sense an imbalance in current flow over the normal path
Opens circuit if current in hot and grounded wires differ by 5mA 1mA
Must be installed correctly and tested
Wiring Methods, Components, and Equipment for General Use
1903.305
No wiring systems in ventilation ducts
*
Grounding receptacles
Disconnecting switches
Flexible cords protected from damage
Cables supported
Conductors entering boxes, cabinets, or fittings
Must be protected from abrasion
Openings must be closed, with or without wires running through
Covers and canopies
*
Gravity must not close switches
Warning if power may still be available while switch is closed
Faceplates where appropriate
Switchboards and panelboards
Switchboards with exposed live parts: in dry places accessible only to qualified persons
Panelboards: in enclosures with no live parts on front
Switches dead when open
Enclosures for wet locations
Insulated unless otherwise permitted
Approved type for use
Grounded
Ungrounded
In general much more easily damaged
Should not be used if recognized options can be used instead
Must be approved for conditions and location
Allowable purposes listed
May not be substituted for fixed wiring
May not be run through walls, ceilings, floors, doors, windows
May not be attached to buildings
May not be concealed in walls, ceilings, floors
May not be spliced, except hard service #14
Strain relief needed on connections
*
Obviously not temporary? No.
*
Receptacles, cord connectors, and attachment plugs (caps)
Appliances
Motors
Transformers
Capacitors
1903.306
Electric signs and outline lighting
Cranes and hoists
Classification based on flammable vapors, liquids, gases, combustible dusts or fibers
Each area considered individually
Documentation available for users, designers, installers, maintainers of electric equipment
*
Class II: combustible dust
Class III: easily ignitable fibers or flyings; not likely to be in suspension
*
Intrinsically safe
Approved and marked for class and properties of material present
Safe for hazardous (classified) location
NFPA 70 referenced
Equipment in Division 2 locations:
Division 1 approved equipment = OK
*
Zone = alternative to divisions for Class 1
Classified by chemical properties and likelihood of combustible atmosphere
Proper installation of conduit & equipment to avoid sparks in flammable/combustible atmosphere
Protection techniques for certain zones
*
Listing and marking:
(For same gas or vapor)
Marking requirements & exemption
*
Special Systems
Emergency power systems
Fire alarm systems
References for Further Information
*
Not a substitute for compliance with CFR
Appendices B and C removed
Safety-Related Work Practices
Qualified persons (who have training in avoiding the electrical hazards)
Unqualified persons (with little or no such training)
Working on or near:
Other wiring
Vehicles excluded
©2006 TEEX
1910.332 Training
Scope: employees with electric shock risk not reduced to safe level by installation requirements
Training content:
1910.331-335 and others necessary
*
comes close enough to exposed parts of electric circuits 50V
for hazard to exist
1910.333
Live parts deenergized before employee works on or near them:
Unless infeasible or causes greater hazard
<50V not deenergized if no increased exposure to burns or arcs
Examples in CFR
*
If not locked out or tagged out, treated as energized
Lockout/tagout rules followed in order
1910.147 provisions may also be OK
Written copy of procedures available
*
Lockout/tagout steps in section (2):
Deenergizing equipment
Verification of deenergized condition
Reenergizing equipment after work
Only qualified persons may work on energized electric circuit parts
For work near overhead lines:
Lines deenergized and grounded, or
Other protective measures provided
Working near overhead power lines
Unqualified person near energized lines
Person and longest conductive object not closer than 10 ft, + 4 in/10kV above 50kV
For elevated or ground work
Qualified person:
Table S-5: distance varies by voltage
Equipment: same distance as unqualified
*
Equipment: same distance as unqualified, with exceptions:
In transit, structure lowered: 4 ft +4 in/10kV
Insulating barriers, not part of vehicle
Aerial lift, insulated, with qualified person
Ground employees may not contact equipment without protection or distance
*
Illumination must allow safe work – may not reach blindly in
Confined space work requires protective insulation & secured doors
Conductive materials: prevent contact with energized parts
Portable ladders: nonconductive siderails
Conductive apparel not worn, or insulated
Housekeeping near live parts:
Interlocks may only be defeated temporarily by qualified person
Use of Equipment
Cords not used to raise/lower equipment
*
Extension cords
For external defects and evidence of internal damage
If not exposed to damage, only when relocated
Defect or damage: remove, do not use until repaired and tested
Plug and receptacle checked for compatibility
*
Conductive work locations (e.g. wet) require approved equipment and cords
Connecting plugs:
Protect hands from conductive path (water)
Locking connectors: properly secured
Never reenergize a blown fuse
Never reenergize a circuit breaker until it is safe (Overload or fault?)
Never modify overcurrent protection beyond § 304 requirements
*
Test instruments must be visually inspected
Must be rated for circuits & environment
Occasional use of flammable and ignitable materials: Do not use equipment that could ignite them
Safeguards for Personnel Protection
Personal protective equipment
Maintained, inspected, and tested
Insulating material protected
Nonconductive head protection
Eye or face protection for arcs, flashes, flying objects from explosions
Insulated tools or handling equipment
Shields, insulation for heating/arcing
Safety signs and tags
API RP 54
Section 10: Drilling and Well Servicing Rig Electrical Systems
API RP 14F for offshore wiring
API RP 500 and 505: area classification
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Tripped circuit breakers or blown fuses
Warm tools, wires, cords, connections, or junction boxes
GFCI that shuts off a circuit
Worn or frayed insulation around wire or connection
Subtitles & Transitions
FOR EXAMPLE…
Small Business Handbook section