Overview and Learning Outcomes
Overview
Electricity is a potential safety hazard in every workplace. Despite an abundance of regulations and
rules about electrical safety, workers continue to be injured and killed when exposed to electricity.
In this module we will examine the basics of electricity with a focus on its measurable properties.
We will review typical regulations and codes that govern installation of electrical conductors, and
the design of electrically-powered equipment.
We will also examine the workplace rules that govern work on and near electrically-energized
equipment.
Learning Objectives
On successful completion of this module, you should be able to:
 Explain the measurable properties of electricity: voltage, current, and resistance.
 Discuss the types of injuries typically associated with contact with electricity.
 Name the regulations, standards, and codes that govern the installation and design of
electrical conductors and electrically-powered equipment.
 Locate and discuss the OHS regulations that govern work practices on and near energized
equipment.
 Manage an assured grounding program for portable electric tools/cords.
 Discuss the role of GFCI in electrical safety.
How Much Electricity?
There are a variety of ways in which the “amount” of electrical energy can be stated. The critical
measures that every OHS professional needs to understand are voltage, current, and resistance.
#definition
 Voltage is best considered as the electrical pressure in a circuit and is sometimes described
as the potential difference between a conductor and the ground.
 Current is the volume of electricity in the circuit.
 Resistance is the amount of blockage of electrical flow.
/definition
Voltage, current and resistance are related to each other, and this relationship is described by the
basic Ohm’s Law, which states: V = I x R
V = voltage (in volts)
I = current (in amps)
R = resistance (in ohms)
Knowing any two of the variables in the equation allows us to solve for the third.
A more useful variation of Ohm’s Law is: I = P/E
I = current (amps)
P = power required by the machine (watts)
E = voltage (volts)
Let’s apply this variation to a couple of typical situations in the home.
The majority of the wiring in homes in Canada operates at a voltage of 120 volts. Circuit breakers in
the home are designed to stop the flow of electricity when the current exceeds 10–30 amps (more
on this later). Some appliances are specifically designed to provide a lot of resistance to electrical
flow: If you have an electric stove or toaster then the elements on the stove and toaster are
designed to resist the flow of electricity. When the electrical flow is restricted by the element a
significant amount of electrical energy is converted into thermal energy which we use to cook.
You have installed a 60 watt incandescent bulb into a luminaire. The luminaire is serviced with a
typical 120 volt service. Knowing these two variables we can calculate the amount of amperage
(volume of electricity) that is flowing in the circuit when you turn the lamp on:
I = P/E
I = 60 watts/120 volts
I = 0.5 amps
You are using an electric hairdryer that requires 800 watts of power to heat and blow. Again, the
voltage in the house conductor is 120 volts:
I = 800 watts/120 volts
I = 6.7 amps
#reveal
A microwave oven requires 1650 watts of power to operate. Assuming a voltage in the conductor to
the outlet for the oven of 120 volts, what is the electrical current in the conductor when the oven is
turned on?
Which of the numbers given below is the correct answer? Click the Reveal button to check your
answer.
a) 7.27 amps
b) 13.8 amps
c) 19.8 volts
On reveal: 1650 watts/120 volts = 13.8 amps
/reveal
What Kind of Electricity?
Frequency and Type of Current
Depending on the electrical demands of the equipment the current provided to a machine may be
alternating current (AC) or direct current (DC). The electrical flow in an AC conductor reverses
direction on a regular basis. The flow in a DC conductor is always in the same direction.
In an AC conductor the number of times that the current flow changes direction per second is called
the frequency of the current. If you check an electrical appliance in your home you should see that
the AC frequency for those appliance was 60 hertz (or cycles per second). The frequency of the AC
current in your home is always 60 Hz.
High and Low Voltage
You will frequently hear talk in the workplace about high voltage lines or low voltage equipment. As
we have seen, voltage is a measure of the amount of electrical pressure in a circuit.
There is actually no true dividing line between low and high voltage, and it is certainly not true that
high voltage = high hazard and low voltage = low hazard. The distinction is established in local OHS
regulations.
#definition
WorkSafeBC defines low and high voltage as follows:


Low voltage means a potential difference (voltage) from 31 to 750 volts inclusive, between
conductors or between a conductor and ground
High voltage means a potential difference (voltage) of more than 750 volts between conductors or
between a conductor and ground
/definition
We will see later in the module that there are different workplace rules applied to work on and near
high voltage conductors and equipment versus low voltage.
Hazards from Electrical Contact
You may have heard the old saying, “It’s not the voltage that will kill you, it’s the amperage.”
This saying really is true. Contact with a higher voltage conductor in which very little current is
flowing presents a lower risk than contact with a lower voltage conductor in which a large amount
of current is flowing.
So how much electricity does it take to cause injury in the workplace? The major factors that
determine the type of and severity of electrical injuries are current, and the time the worker is
exposed to the current.
Depending on the current and the time the worker is exposed to the current (and also depending on
other factors such as the type of current, frequency of an AC current, and location on the body
where the electricity enters), several injuries may occur. Click on each one included below to learn
more about them.
#accordion
Electrical Shock Injuries
These injuries result when the body’s own electrical system is overloaded by electricity from the
external source. The following injuries are typical:
a)
b)
c)
Muscle damage due to prolonged and severe contraction.
Damage to tissues surrounding muscles due to excess muscle contraction (particularly of
concern if brain tissue is damaged).
Cardiac arrhythmia or arrest.
Burns
Because there is a resistance to the flow of electricity through the body some portion of the
electrical energy will be converted to thermal energy (just like the element on an electric stove).
These thermal burns may occur at the site where the electricity entered the body, where it exited
and at any point along the path in between.
Sometimes an electrical arc is created during contact with an energized source. In those cases arc or
flash burns may occur to the skin or eyes.
Indirect Injuries
If a person contacts an energized conductor there is a chance that the shock may cause them to fall
or may actually throw them some distance.
/accordion
Often the voltage of the conductor may significantly affect the nature of injuries suffered by the
worker. Consider the following:
Typically, low voltage conductors have comparatively lower currents. When a worker grabs hold of
a typical energized 120 volt AC conductor, they are now subject to a current that will cause the
muscles of the hand to contract. The 60 Hz frequency of the AC conductor means that the muscles
are being forced into contraction 60 times per second! The relatively low current means that the
force of the contraction will be strong, but not strong enough to force the hand off of the conductor.
Even if the person consciously tries to unclench their hand, their muscles are being told to contract
60 times per second and there is no way that our conscious control of muscle movement can
overcome that kind of stimulation. The person is literally unable to release from the conductor. In
these low voltage situations there is often significant injury because there is a combination of
enough current and a long contact time with the current.
Typically, higher voltage conductors have higher currents. When a worker contacts a higher voltage
conductor, the force of the first muscle contractions are often so great that the worker is knocked
free of and away from the conductor. In this case the injuries may be comparatively minor because,
although there was sufficient current to produce injury, the contact time with the conductor is much
reduced.
This is not to say, however, that contact with a high voltage conductor is “better” than with a low
voltage conductor. It simply explains the various types of electrically-related injuries seen in the
workplace. The “advantages” of contact with a high voltage conductor are pretty much negated if
the first huge shock causes the heart to stop and throws the worker off of a roof.
Click through the slides to see the difference that each range of electric power has on the human
body.
#interaction
Interaction: Elastic Image Slider
See file: Electricity Effects.pptx
Images uploaded into Teamwork
/interaction
Safe Work Around Electricity
Work around electricity is highly regulated by OHS regulators and others, and the regulations that
are in place tend to be prescriptive.
We need to make the following distinctions before we proceed:
1. Regulators distinguish between work that is done on energized equipment and work that is done
near energized equipment.
2. OHS regulators establish definitions of low and high voltage, and establish regulations for each
3. Work that can be done on energized equipment and that work must be done only when the
equipment is de-energized.
Designing and Installing Equipment for Electrical Safety
One of the most effective controls against electrical injuries is to ensure that equipment is first
designed for electrical safety and then installed with safety as the primary objective.
The general regulatory scheme for ensuring safe design and installation of electrical equipment in
each province/territory is a provincial/territorial electrical code and related regulations (usually
based on the Canadian Electrical Code, CSA C22.1, C22.2 and C22.3) that specifically govern:
a) The required design of electrical equipment (the Canadian Electrical Code Part II sets design
requirements for industrial products, for example, CSA 22.2 No. 105 Electrical Equipment for
Woodworking Machines)
b) Requirements for the installation of electrical conductors and equipment (the Canadian
Electrical Code Part I covers electrical installations)
c) Qualifications of workers that install and maintain electrical conductors and equipment (for
example, the BC Electrical Safety Regulation and the Alberta Safety Codes Act govern worker
qualifications).
Provincial/territorial OHS and other regulators in Canada have noted that there is often an
unnecessary overlap in the requirements for electrical worker safety between OHS regulations and
other related regulations. Some provinces have proposed a consolidation of these various rules and
regulations. For example, Alberta has proposed the Electrical and Communications Worker SafeWork Regulations.
OHS professionals should consult with their local OHS regulator to determine the most current
electrical safety regulatory scheme.
Local OHS regulations that relate to various aspects of electrical safety and which provide general
requirements to conform with design and installation codes and regulations. For example, Part 4.3
of the WorkSafeBC OHS Regulation :
#quote
(2) Unless otherwise specified by this Regulation, the installation, inspection, testing, repair and
maintenance of a tool, machine or piece of equipment must be carried out
(a) in accordance with the manufacturer's instructions and any standard the tool, machine or
piece of equipment is required to meet
/quote
It is be becoming typical for OHS regulators to recognize the qualifications for electric workers as
established in other legislation as the appropriate regulatory standard. For example, the WCB of BC
has repealed the section on electrical qualifications from the OHS Regulation (19.2) and has stated:
Repealed. [B.C. Reg. 312/2003, effective October 29, 2003.]
*Statutes or regulations covered by other jurisdictions apply to electrical qualifications.
Work on Energized High and Low Voltage Equipment
In this section, we will spend a lot of extra time looking at regulations and beginning to recognize
the highly prescriptive regulatory environment that surrounds work on and near energized
equipment.
Far too many deaths and injuries have occurred when unqualified workers have used unsafe work
practices on or near energized electrical systems — as a result, OHS regulators and others have set
out very prescriptive electrical regulations and enforce them rigidly.
The basic process for designing safe work on energized equipment is pretty straightforward for the
OHS professional:
1. Look for a way in which the work can be done with the equipment de-energized.
2. Look for ways in which the amount of energy to the system can be reduced, if it cannot be
eliminated.
3. Only permit appropriately qualified workers to work on energized equipment.
4. Work with appropriately qualified workers to design safe work procedures.
Each regulatory jurisdiction will have its own specific regulatory scheme to deal with the issue of
“qualified” workers. Typically, the regulator first recognizes a general group of workers that are
permitted to work on energized electrical equipment.
#definition
Electrical worker means a person who meets the requirements of the Electrical Safety Act for
installing, altering or maintaining electrical equipment (BC OHS Regulation 19.1)
Authorized worker in Sections 562-569 means a competent worker authorized by the employer
to install, change or repair electrical equipment (Alberta OHS Code Part 1)
Electrical worker in the case of work of electrical installation as defined in The Electrical
Inspection Act. 1993 that is regulated by that Act, means a person who is authorized pursuant to
The Electrical Licensing Act to perform that work and in the case of any work with electrical
equipment that is not regulated by The Electrical Inspection Act, 1993 means a person who is
qualified to perform that work (Saskatchewan OHS Regulations Part XXX)
Qualified electrical worker means the holder of a journeyman’s certificate in the electrician trade
pursuant to The Apprenticeship and Trade Certification Act and includes an apprentice in the
trade while under the supervision of a journeyman or the holder of a journeyman’s certificate in
the power lineman trade….. (Saskatchewan OHS Regulation Part XXX).
/definition
And following the definition the documents commonly add specific regulatory requirements for
various voltages and work processes:
Certified utility arborist means a person who has completed a course of instruction, has a
minimum of 1,200 hours of practical experience and is certified by an authority acceptable to the
Board; (BC OHS Regulation 19.1)
An employer or contractor may permit a competent worker who is not an electrical worker to
change bulbs or tubes, to insert or replace an approved fuse, to a maximum of 750 volts, that
controls circuits or equipment …….(Saskatchewan OHS Regulation Part XXX).
#key-point
The bottom line for the OHS professional considering work that must be done on energized
electrical systems is:
a) Clearly understand the regulatory scheme for your jurisdiction to ensure that your employer
is only authorizing “qualified” workers to do the work.
b) Confirm the qualifications of each of the workers that will be working on the system
c) Ensure that one or more “qualified” workers helps you to write the safe work procedures for
the work
d) Limit the risk by limiting the number of both qualified and unqualified workers that are
permitted in the work area.
/key-point
Work Near Energized High and Low Voltage Equipment
Risk Assessment
High voltage is most commonly encountered in the workplace in the form of power lines that deliver
high voltages that will ultimately be reduced (transformed) to lower voltage for direct use in the
workplace. Most “high voltage” deaths and injuries are the result of accidental contacts with high
voltage (and sometimes low voltage) power lines.
When workplace deaths and injuries occur as a result of contact with high voltage conductors, the
accident investigation almost always reveals:
a) The work being done had absolutely nothing to do with the conductor — the work just
happened to be going on in the vicinity of the conductor.
b) Contact is usually with conductors carrying voltages of 25,000 volts (25 kV) or less (the
common voltage in the power lines serving commercial and industrial customers) rather
than with
60–500 kV main power lines that come from the power source and are carried high on high
metal towers or posts).
c) The workers involved were aware that there was a high voltage line in their work area, but
did not take appropriate steps to reduce the risk of contact with the conductor.
d) Workers often assumed that high voltage lines were “insulated” to a degree that would
prevent injury in the event of contact.
e) Additional workers were injured in the course of attempting to rescue others injured by the
initial contact with the high voltage conductor.
Touch and Step Potential
Why do most birds that sit on overhead power lines not get fatally electrocuted even though the
line is carrying 5, 10, 20, or more kV of electricity and is minimally or not at all insulated? And for
that matter, how is it that linemen can work on energized very high voltage transmission lines (500
kV and higher) while seated in the passenger compartment of a helicopter hovering immediately
beside the line?
#image – align:right
File: tower-1824047_1920.jpg
Alt: Electrical tower
Caption: Electrical tower with high voltage cables
License: CC0 Public Domain, pixabay.com
/image
The reason is “potential difference.” Remember that voltage can
be defined as the potential difference between a conductor and
the ground. When we describe a high voltage power line as a 25
kV line we are saying that there is a difference of 25,000 volts
between the line and the ground adjacent to it (which in theory
should be at 0 volts). As long as the power line is safely designed and installed to ensure that none
of the voltage in the power line can make it to the ground there is no movement of electricity and
no current flow to the ground.
When a bird sits on an energized 25 kV power line there is essentially a zero potential difference
between its two legs because the bird is not contacting any path to the ground. There is voltage in
the line, but essentially no current flow through the bird’s body. The bird is insulated from contact
with the ground because glass or ceramic insulators keep the power line from directly contacting
the pole supporting the line.
But, if the bird was to extend its wings and have one of the wings contact the power pole it would
be fatally electrocuted. A path has now been established to the ground (power line  bird’s leg 
bird’s body  wing  power pole  ground) and because a potential difference of 25 kV exists
between the power line and the ground, a huge amount of current will now flow through the bird.
#key-point
In the OHS profession, this potential difference is called touch potential.
/key-point
A related phenomenon is step potential. Once electricity finds a path to ground (whether it be
through the bird’s wing and power pole or through the boom of a crane that has contacted a power
line), the ground in the immediate area becomes electrified. The voltage at the point of contact
with the ground would be the highest and would then decrease with distance away from that point
(the ripple effect). If one region near the point of contact in the electrified region has a voltage of,
say, 5 kV, and another further away has a voltage of 4 kV, there is a potential difference of 1000
volts between these two points and any person that places one foot in one area, and the other foot
in another would be electrocuted as current flowed through the two points of contact.
Safe Limits of Approach
A basic and necessary safety practice when work is being done near energized high voltage
conductors is the enforcement of the Limits of Approach.
Every OHS regulator includes limits of approach in their regulations. A typical limit of approach
regulation would be:
#quote
19.24 Minimum clearance
(1) The employer must ensure that at least the minimum applicable distance specified in Table 19-1
is maintained between exposed, energized high voltage electrical equipment and conductors
and any worker, work, tool, machine, equipment or material, unless otherwise permitted by this
Part.
(2) The employer must accurately determine the voltage of any energized electrical equipment or
conductor and the minimum distance from it required by subsection (1).
Table 19-1: General limits of approach
Voltage
Phase to phase
Minimum distance
Metres
Feet
Over 750 V to 75 kV
3
10
Over 75 kV to 250 kV
4.5
15
Over 250 kV to 550 kV
6
20
Source: WorkSafeBC. OSH Regulation
/quote
This is a very prescriptive and straightforward requirement: The regulator in each jurisdiction will
say you must stay a minimum of X meters away from a conductor with X voltage and no less!
The objective of safe limits of approach is to establish a large margin of safety between the work
that is being done and the energized electrical conductor. If during the course of work a situation
arises (e.g., crane boom swings too widely, metal pipe is lifted up too high, paint roller pole is swung
around too far) there should be plenty of room between the work and the conductor to ensure the
conductor is not contacted, and a touch potential established.
Which of the images below represent a touch potential and which one is a step potential? When you
have figured out, click Reveal to read our answer.
#image
File: touch-and-step-potential.jpg
Alt: Touch and Step potential
/image
#reveal
The image on the left is a depiction of a touch potential situation; the image on the right depicts a
step potential situation.
Touch: The potential difference between an energized source (at X volts) and the ground (at 0 volts)
that will cause current to flow when a path to ground is established.
Step: The potential difference that exists between the point of energy contact with the
ground/surface (at X volts) and points at a distance from that source (at < X volts) that will cause
current to flow through a person who bridges any two points with a potential difference.
/reveal
Work Inside the Limits of Approach
Sometimes the nature of the work to be done means it is not possible to maintain the safe limits of
approach. This will obviously increase the risk of electrical injuries, and so regulators again are highly
prescriptive in these situations:
19.25 Assurance in writing
(1) If the minimum distance in Table 19-1 cannot be maintained because of the circumstances of
work or the inadvertent movement of persons or equipment, an assurance in writing on a form
acceptable to the Board and signed by a representative of the owner of the power system, must
be obtained.
(2) The assurance must state that while the work is being done the electrical equipment and
conductors will be displaced or rerouted from the work area, if practicable.
(3) If compliance with subsection (2) is not practicable the assurance must state that the electrical
equipment will be isolated and grounded, but if isolation and grounding is not practicable the
assurance must state that the electrical equipment will be visually identified and guarded.
(4) The safeguards specified in the assurance must be in place before work commences and
effectively maintained while work is taking place.
(5) If guarding is used,
(a) neither equipment nor unqualified persons may touch the guarding, and
(b) a safety watcher must be designated, or range limiting or field detection devices acceptable
to the Board must be used.
(6) The assurance must be available for inspection at the workplace, as close as practicable to the
area of work, and must be known to all persons with access to the area.
19.26 Assurance not practicable
(1) If exposed high voltage electrical equipment and conductors cannot be isolated, rerouted or
guarded, work must not be done within the minimum distance in Table 19-1 until approval is
obtained from the Board and the following precautions are taken:
(a) the area within which equipment or materials are to be moved must be barricaded and
supervised to restrict entry only to those workers necessarily engaged in the work;
(b) a safety watcher must be designated;
(c) a positive means must be provided for the safety watcher to give a clear, understandable
stop signal to workers in the area, and the watcher must give the stop signal by no other
means.
(2) While equipment is in motion in an area in proximity to energized electrical equipment or
conductors, no person other than the equipment operator may touch any part of the equipment
or the material being moved by it.
(3) No person may move a load or any rigging line from its position of natural suspension if it is in
proximity to an energized electrical conductor or equipment.
19.27 Specially trained
(1) A worker who has taken a course of instruction approved by the Board may work up to the
adjusted limits of approach in Table 19-2 when all the following conditions apply:
(a) the high voltage electrical equipment is energized to a potential of not more than 75kV;
(b) the Board has determined that rerouting, de-energizing or guarding of the equipment is not
practicable for the type of work being performed;
(c) the work is not being done for the owner of the power system;
(d) the work is of a type that must be done regularly;
(e) the worker follows written safe work procedures acceptable to the Board.
(2) A qualified electrical worker may work closer than the limits specified in Table 19-2 provided the
worker is authorized by the owner of the power system and uses procedures acceptable to the
Board.
Table 19-2: Adjusted limits of approach
Minimum distance
Voltage
Phase to phase
Metres
Feet
Over 750 V to 20 kV
0.9
3
Over 20 kV to 30 kV
1.2
4
Over 30 kV to 75 kV
1.5
5
Part 9 of the WorkSafeBC Regulation (specifically Regulation 19.24.2) also when passing under
exposed electrical equipment allows for differing Minimum clearance distance and conductors.
This would apply to work involving the movement of equipment under exposed electrical
equipment or conductors but not performing work. An example would be moving an excavator
onto a site, under powerlines.
Work Near Low Voltage Energized Equipment
#image
File: electrician-1080554_1920.jpg
Alt: Electrician installing an electrical socket
Caption: Alt: Electrician installing an electrical socket
License: CC0 Public Domain, pixabay.com
/image
A startling number of deaths and injuries result from worker contact
with energized low voltage equipment. OHS researchers and
investigators have suggested the reasons for this may be:
a) The term low voltage implies low risk to untrained workers.
b) Many workers routinely do work on low voltage energized equipment in their own home
and come to believe the practice is low risk.
c) Many workers have seen qualified workers working on energized low voltage equipment
and believe that they are now aware of all of the potential hazards.
d) the design and installation regulations and standards that are in place in Canada for low
voltage equipment are so effective that any one person rarely hears about low voltagerelated accidents.
e) Many workers believe that low voltage systems are fully equipped with protective devices.
Regardless, the number of accidents related to low voltage contact continues to be high.
WorkSafeBC and BC Hydro recommend the following steps be taken in regard to working on
energized low voltage electrical equipment (this information is taken from the WorkSafeBC
publication Working Safely Around Electricity
#key-point
1. Think ahead to be able to assess all of the risks associated with the job.
2. Know the electrical system.
3. Limit the time that workers are working on exposed parts of the system.
4. Use approved insulating barriers to cover as many live parts as possible.
5. Use approved insulating barriers to cover grounded metalwork.
6. Where possible limit the potential current at the site of the work.
7. Use approved personal protective equipment where practical (e.g., approved rubber gloves
and safety footwear).
8. Have workers remove highly conductive personal items such as rings and wristwatches.
/key-point
Assuring the Safety of Low Voltage Portable Power Tools
Experience in the workplace has shown that electrocution by portable electrically-powered tools is a
real and significant hazard. Investigation often leads to the conclusion that problems in grounding
system that is in place in the tools and extension cords was a key factor in the injury.
An OHS professional in a workplace in which electrically powered tools are used must take the steps
to ensure that these tools do not become an electrocution hazard. Click on each of the following
steps to learn more about what they include.
#accordion
Only permit approved electrical tools and extension cords to be used on the job.
The tools themselves should be double-insulated. A double­insulated tool is
manufactured so that the electrical motor is electrically isolated from the case of the
tool. Double-insulated tools sold in Canada can be identified by looking at the label on
the tool: The words “double insulated” and/or the double­insulation symbol will
appear on the label.
Note that almost all OHS regulations say that double­insulated tools do not need to be grounded,
but it is pretty much standard practice to have a double-insulated tool attached to a properly
grounded extension cord and receptacle.
Use only heavy-duty extension cords that are CSA-approved for outdoor use.
Assure grounding is adequate in the extension cords and receptacles.
The grounding wire in a typical 120 volt extension cord and receptacle is designed to ensure that
“leaking” electricity moves safely to ground rather than through a worker. But the grounding
system needs to be checked regularly to ensure that it is functioning. If the insulation on hot (usually
black) or neutral (usually white) wire in the extension cord or to the receptacle becomes damaged
then a short circuit can occur that will negate the value of grounding. If the three wires are
incorrectly attached to a plug or receptacle there will be no grounding (incorrect polarity).
Grounding is assured by one of two methods:
a) Receptacles or cords end can be checked with a simple polarity tester. Receptacles are checked
simply by plugging in the tester and reading the light code that appears. Cords are tested by
plugging the cord into a previously checked receptacle and then applying the polarity tester to
the female end of the cord.
b) Extension cords can also be checked using a basic continuity tester or any multimeter with a
continuity function. The cord is checked by inserting one of the probes into one of the openings
in the female end and touching the other probe to the matching prong of the male end. Proper
wiring and grounding is seen when there is a continuous flow of current with minimal resistance
through the wire that connects the female and male ends. (Check with a qualified electrician to
learn how to do this).
Use a Ground Fault Circuit Interrupter especially in wet locations
A ground fault circuit interrupter (GFCI) is an electronic device that looks for evidence that electrical
current is “leaking” from a circuit. It measures current on both the hot and neutral wires. If current
leakage (ground fault) of 5 mA or more is detected, the GFCI
breaks the circuit to prevent any further flow of electricity.
GFCI’s are readily available from safety and electrical equipment
suppliers and may be applied at the receptacle (GFCI receptacle)
or in the electrical panel (GFCI-equipped circuit breaker), or more
commonly on many construction sites, as a portable device into
which the tool or extension cord is plugged.
A misconception that some workers may have is that the circuit breakers in the electrical panel
provide the same protection that a GFCI will provide. This is not correct. Breakers are designed to
trip when the amount of current being drawn by equipment on the circuit exceeds the ability of the
wire to carry that much current. Circuit breakers typically are designed to trip when the current
being forced through the wire is in the range of 10–30 amps. But as we have seen, even a trip at 10
amps is inadequate to protect against an electrocution hazard.
GFCI used in Canada are designed to trip when a “leakage” of 5 mA is detected in the circuit. In this
way, the circuit is broken well before a current level that is dangerous to workers is encountered.
Circuit breakers are designed to protect against fire from overheated wires. GFCI are designed to
protect against leakage of current that might lead to electrocution.
Based on what you have read, how would you explain the difference between a GFCI and a circuit
breaker?
Write down your explanation, then click Reveal to see our answer.
#reveal
GFCI is a life-safety device that breaks a circuit when a leakage of current is detected at a level
that is above the threshold of electrocution sensation, but below the level at which there is a
risk to health.
Circuit breaker is a fire-safety device that breaks a circuit when the current being drawn
through a circuit begins to exceed the capacity of the circuit and the circuit wires begin to
overheat.
/reveal
The image below is of a typical circuit breaker panel that is found in most homes. Can you identify
whether there are any GFCI breakers on this panel?
When you figured out, click Reveal to check your answer?
#image
File: Breaker_pannel01.jpg
/image
#reveal
#image
File: Breaker_pannel02.jpg
/reveal
Equipment Contact with Energized Conductors
In this section, we will look briefly at the safety recommendations to avoid equipment such as
telescopic booms or ladders accidentally contacting energized conductors, especially high-voltage
conductors (and what to do if they do).
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Watch this video for a great explanation of what to do when your equipment contacts highvoltage conductors: Electrical Safety: Crane Truck Contact
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This is a video that shows what happens when a crane boom contacts high-voltage
conductors: Boom Truck Crane Cooks After Power Line Connection
The Electrical Safety: Crane Truck Contact video instructs people to shuffle or hop but not step when
moving away from an energized area. Why is critical to move away only by shuffling or hopping?
Write your answer down then click Reveal to read our explanation.
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If a crane boom contacts an energized conductor, the boom, chassis and tires will provide a
path to ground for the electricity. The ground around the crane will become energized and
energy will be present at some distance from the point of contact with the ground (ripple
effect). A person who tries to run or walk away from the crane may well find themselves
creating a step potential. Shuffling or hopping maintains the feet in areas of essentially equal
voltage.
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We will look more closely at the issues of crane and boom contact with electrical conductors, and
contact with conductors during excavation elsewhere in Workplace Hazards and Controls 2.
Many power utility system owners have educational programs for both workers and the public. BC
Hydro Public Safety has put the finishing touches to a new online electrical awareness training
system for trades, in an effort to prevent workplace injuries.
The course is free, takes approximately 45 minutes to complete, and students are provided with a
BC Hydro certificate upon course completion. You will need to create an account and will be issued
as certificate of completion.
Here’s the link: http://bchydropublicsafety.udutu.ca/