Electrical Safety in Residential Construction LEP

1
Electrical Safety in Residential Construction
LEP

• OSHA Onsite Consultation Program

2
Course Objective

• Review the major hazards of working with
  electricity on a residential construction site
• Discuss methods of protection from electrical
  hazards
• Discuss proper examination and use of cords and
  power tools
• Develop an understanding of grounding
• Describe the function of a ground fault circuit
  interrupter (GFCI)
• Discuss safety-related work practices

3
Electrical Hazards

• Inadequate wiring or insulation
• Improper grounding
• Overloads
• Accidental contact with overhead and buried power
  lines

4
Injury

• There are four main types of electrical injuries
• Electrocution (death due to electrical shock)
• Electrical shock
• Burns
• Falls

5
Fatalities In Construction 1998 to 2001
6
Overhead Powerline Hazards

• Most people dont realize that overhead
  powerlines are usually not insulated
• Powerline workers need special training and
  personal protective equipment (PPE) to work
  safely
• Do not use metal ladders instead, use
  fiberglass ladders
• Beware of powerlines when you work with ladders
  and scaffolding

7
Electrical Terminology

• Current the movement of electrical charge
• Resistance opposition to current flow
• Voltage a measure of electrical force
• Conductors substances, such as metals, that
  have little resistance to electricity
• Insulators substances, such as wood, rubber,
  glass, that have high resistance to electricity
• Grounding a conductive connection to the earth
  which acts as a protective measure

8
Electrical Shock

• Received when current passes through the body
• Severity of the shock depends on
• Path of current through the body
• Amount of current flowing through the body
• Length of time the body is in the circuit
• LOW VOLTAGE DOES NOT MEAN LOW HAZARD

9
How is an electrical shock received?

• When two wires have different potential
  differences (voltages), current will flow if they
  are connected together
• In most household wiring, the black wires are at
  110 volts relative to ground
• The white wires are at zero volts because they
  are connected to ground
• If you come into contact with an energized (live)
  black wire, and you are also in contact with the
  white grounded wire, current will pass through
  your body and YOU WILL RECEIVE A SHOCK

10
Dangers of Electrical Shock

• Currents greater than 75 mA can cause
  ventricular fibrillation (rapid, ineffective
  heartbeat)
• Will cause death in a few minutes unless a
  defibrillator is used
• 75 mA is not much current a small power drill
  uses 30 times as much

Defibrillator in use
mA milliampere 1/1,000 of an ampere
11
Effects of Electric Current on the Human Body
12
Effects of Electric Current on the Human Body
13
Electrical Burns

• Most common shock-related, nonfatal injury
• Occurs when you touch electrical wiring or
  equipment that is improperly used or maintained
• Typically occurs on the hands
• Very serious injury that needs immediate
  attention

14
Effects of Electric Current on the Human Body
15
Effects of Electric Current on the Human Body
16
Falls

• Electric shock can also cause indirect or
  secondary injuries
• Workers in elevated locations who experience a
  shock can fall, resulting in serious injury or
  death

17
Inadequate Wiring Hazards

• A hazard exists when a conductor is too small to
  safely carry the current
• Example using a portable tool with an extension
  cord that has a wire too small for the tool
• The tool will draw more current than the cord can
  handle, causing overheating and a possible fire
  without tripping the circuit breaker
• The circuit breaker could be the right size for
  the circuit but not for the smaller-wire
  extension cord

Wire gauge measures wires ranging in size from
number 36 to 0 American wire gauge (AWG)
18
Grounding Path

• The path to ground from circuits, equipment, and
  enclosures must be permanent and continuous
• Violation shown here is an extension cord with a
  missing grounding prong

19
Electrical Protective Devices

• These devices shut off electricity flow in the
  event of an overload or ground-fault in the
  circuit
• Include fuses, circuit breakers, and ground-fault
  circuit-interrupters (GFCIs)
• Fuses and circuit breakers are overcurrent
  devices
• When there is too much current
• Fuses melt
• Circuit breakers trip open

20
Ground-Fault Circuit Interrupter

• This device protects you from dangerous shock
• The GFCI detects a difference in current between
  the black and white circuit wires
• (This could happen when electrical equipment is
  not working correctly, causing current leakage
  known as a ground fault.)
• If a ground fault is detected, the GFCI can shut
  off electricity flow in as little as 1/40 of a
  second, protecting you from a dangerous shock

21
Grounding Hazards

• Some of the most frequently violated OSHA
  standards
• Metal parts of an electrical wiring system that
  we touch (switch plates, ceiling light fixtures,
  conduit, etc.) should be at zero volts relative
  to ground
• Housings of motors, appliances or tools that are
  plugged into improperly grounded circuits may
  become energized
• If you come into contact with an improperly
  grounded electrical device, YOU WILL BE SHOCKED

22
Protection From Electrical Hazard

• Listed or labeled equipment shall be used or
  installed in accordance with any instructions
  included in the listing or labeling.

23
Listed or Labeled Equipment

• Homemade extension cords employing metal outlet
  boxes (example shown below) are NOT acceptable

24
Listed or Labeled Equipment
25
Listed or Labeled Equipment
26
Relocatable Power TapsUL 1363

• Intended only for indoor use as a temporary
  extension of a grounding alternating-current
  branch circuit for general use.
• Not intended for use at construction sites

27
Transient Voltage Surge Suppressors UL 1449
28
Selecting Flexible Cords

• Examples of these types of flexible cords include
  hard service cord (types S, ST, SO, STO) and
  junior hard service cord (types SJ, SJO, SJT,
  SJTO).

29
Flexible Cords In Construction

• Extension cord sets used with portable electric
  tools and appliances shall be of three-wire type
  and shall be designed for hard or extra-hard
  usage.
• Flexible cords used with temporary and portable
  lights shall be designed for hard or extra-hard
  usage.

30
Hard-service or extra-hard-serviceflexible cord
markings

• S - Hard Service Flexible Cord
• SJ - Junior Hard Service Flexible Cord
• E - Thermoplastic elastomer insulation
• T - Thermoplastic insulation
• O - Jacket is oil resistant
• OO Jacket and Conductors are oil resistant
• W-A rating, suitable for outdoor use.

31
(No Transcript)
32
Use of Flexible Cords

• More vulnerable than fixed wiring
• Do not use if one of the recognized wiring
  methods can be used instead
• Flexible cords can be damaged by
• Aging
• Door or window edges
• Staples or fastenings
• Abrasion from adjacent materials
• Activities in the area
• Improper use of flexible cords can cause shocks,
  burns or fire

33
Permissible Uses of Flexible CordsExamples
Stationary equipment-to facilitate interchange
Pendant, or Fixture Wiring
Portable lamps, tools or appliances
34
Prohibited Uses of Flexible CordsExamples
Run through walls, ceilings, floors, doors, or
windows
Concealed behind or attached to building surfaces
Substitute for fixed wiring
35
Cord or Tool Insulation Damage

• You are more likely to receive a shock if the
  tool is not grounded or double-insulated.

36
Hand-Held Electric Tools

• Hand-held electric tools pose a potential danger
  because they make continuous good contact with
  the hand
• To protect you from shock, burns, and
  electrocution, tools must
• Have a three-wire cord with ground and be plugged
  into a grounded receptacle, or
• Be double insulated, or
• Be powered by a low-voltage isolation transformer

37
Power Tools

• Never carry a tool by the cord.
• Never yank the cord to disconnect it from the
  receptacle.
• Keep cords away from heat, oil, and sharp edges
  (including the cutting surface of a power saw or
  drill).
• Disconnect tools when not in use, before
  servicing, and when changing accessories such as
  blades, bits, etc.
• Avoid accidental starting. Do not hold fingers on
  the switch button while carrying a plugged-in
  tool.
• Use gloves and appropriate safety footwear when
  using electric tools.

38
Power Tools

• Store electric tools in a dry place when not in
  use.
• Do not use electric tools in damp or wet
  locations unless they are approved for that
  purpose.
• Keep work areas well lighted when operating
  electric tools.
• Ensure that cords from electric tools do not
  present a tripping hazard.
• Remove all damaged portable electric tools from
  use and tag them "Do Not Use."
• Use Double-Insulated Tools.

39
Temporary Wiring NM Cable

• Section .405(a)(2)(ii)(B) permits Romex-style
  electrical cable (nonmetallic-sheathed cable-type
  NM) to be used as temporary wiring.
• Temporary wiring of nonmetallic-sheathed cable
  shall be secured by staples, cable ties, straps
  or similar fittings designed and installed so as
  not to damage the cable.
• Cable shall be secured in place at intervals not
  exceeding 4½ feet and within 12 inches from every
  cabinet, box or fitting.

40
Temporary Wiring NM Cable

• No branch-circuit conductors shall be laid on the
  floor.
• This cable is permitted to be run up the outside
  of walls as temporary wiring for both exposed and
  concealed work in normally dry locations.
• Also, it is permitted to install the cable in air
  voids in masonry block or tile walls where such
  walls are not exposed or subject to excessive
  moisture or dampness. Also note
  1926.405(a)(2) requires that, temporary wiring
  shall be removed immediately upon completion of
  construction or the purpose for which the wiring
  was installed.

41
Temporary Power Pole

• Look up underneath the panel for missing
  knock-out plugs.
• Cover all holes for missing breakers.
• Ensure that the cover is on the panel and that it
  is closed.
• Install a GFCI in the panel.

42
Temporary Power Source

• The generator is a temporary power source so the
  builder has used a cord protected by a ground
  fault circuit interrupter (GFCI) to protect
  workers against electrocution
• If the extension cord was plugged into an outlet
  in the house, it would still need a GFCI because
  the extension cord provides temporary power.

43
Temporary Lighting

• All lamps for general illumination shall be
  protected from accidental contact or breakage.
  Metal-case sockets shall be grounded.
• Temporary lights shall not be suspended by their
  electric cords unless cords and lights are
  designed for this means of suspension.
• Flexible cords used with temporary and portable
  lights shall be designed for hard or extra-hard
  usage

44
Overload Hazards

• If too many devices are plugged into a circuit,
  the current will heat the wires to a very high
  temperature, which may cause a fire
• If the wire insulation melts, arcing may occur
  and cause a fire in the area where the overload
  exists, even inside a wall

45
Temporary Lighting
46
(No Transcript)
47
Some Examples of OSHA Electrical Requirements . .
. .
48
(No Transcript)
49
(No Transcript)
50
(No Transcript)
51
Guarding of Live Parts

• Must guard live parts of electric equipment
  operating at 50 volts or more against accidental
  contact by
• Approved cabinets/enclosures, or
• Location or permanent partitions making them
  accessible only to qualified persons, or
• Elevation of 8 ft. or more above the floor or
  working surface
• Mark entrances to guarded locations with
  conspicuous warning signs

52
Guarding of Live Parts

• Must enclose or guard electric equipment in
  locations where it would be exposed to physical
  damage
• Violation shown here is physical damage to
  conduit

53
Cabinets, Boxes, and Fittings

• Junction boxes, pull boxes and fittings must have
  approved covers
• Unused openings in cabinets, boxes and fittings
  must be closed (no missing knockouts)
• Photo shows violations of these two requirements

54
Clues that Electrical Hazards Exist

• 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

55
Training

• Train employees working with electric equipment
  in safe work practices, including
• Deenergizing electric equipment before inspecting
  or making repairs
• Using electric tools that are in good repair
• Using good judgment when working near energized
  lines
• Using appropriate protective equipment

56
Summary

• Hazards
• Inadequate wiring
• Exposed electrical parts
• Wires with bad insulation
• Ungrounded electrical systems and tools
• Overloaded circuits
• Damaged power tools and equipment
• Using the wrong PPE and tools
• Overhead powerlines
• All hazards are made worse in wet conditions

• Protective Measures
• Proper grounding
• Using GFCIs
• Using fuses and circuit breakers
• Guarding live parts
• Proper use of flexible cords
• Training

57
The End

• Every reasonable effort has been made to prepare
  this document using the most current, correct,
  and clearly expressed information possible.
  However, inadvertent errors may occur. The Ohio
  OSHA On-Site Consultation Program disclaims any
  responsibility for typographical errors and the
  accuracy of the information contained in this
  document. The information and data included in
  this document have been compiled by the Ohio OSHA
  On-Site Consultation staff from a variety of
  sources that are subject to change without
  notice. The Ohio OSHA On-Site Consultation
  Program makes no warranties or representations
  whatsoever regarding the quality, content,
  completeness, suitability, adequacy, sequence,
  accuracy, or timeliness of such information and
  data.

58
(No Transcript)
59
OSHA minimum clearance distances from overhead
power lines

•  Less than 300 volts 2 feet
• 300 volts to 50,000 volts 10 feet
• More than 50,000 volts 10 feet 4 inches for
  every 10,000 volts over 50,000 volts

60
Introduction

• An average of one worker is electrocuted on the
  job every day
• Electrocutions are the fourth leading cause of
  death among construction workers in the United
  States. An average of 140 construction workers
  are killed each year by contact with electricity
  (based on government data from 1992 to 1997).