Ihab Saad – Subpart K Electricity
AI: Summary ©
The speakers discuss potential hazards associated with electrical work, including injuries and fatal deaths, and the potential consequences of a shock. They suggest protection measures, including using insulated hardware and devices with strain relief, and avoiding electrical overheating. The importance of proper safety and GFCI protection is emphasized, as well as the need for proper equipment grounding and inspection for safety. The speakers also discuss the importance of proper safety and GFCI protection for electrical equipment and access to electrical rooms.
AI: Summary ©
Welcome to another safety class. And today we're going to talk
about subpart K, which is electrical work. Remember that one
of the four
areas of focus for OSHA right now, which are the focus for includes
electrocution, which is the result of misuse of electrical appliances
or electrical current. So today we're going to learn about what
are the dangers and the hazards associated with electricity, and
how to protect against these different hazards.
Some of the most frequent citations related to electrical
work include branch circuits, ground fault protection, assured
equipment, grounding conductor program, lack of that grounding
path, ground fault, circuit interrupters, GFCIs, guarding
life, parts and equipment, installation and use. These are
some of the most frequently cited violations related to electricity.
What are the ranges of electricity? Basically five people
die every week out of electrocution.
It causes the deaths, death of 12% of the younger workforce.
Basically, most of those who die, or a large amount of those who
die, are young people in the construction industry who do not
have enough experience to the exposure and protection from
electrical current. In addition to the risk of electro fusion, we
also have another risk related to electricity, which is the risk of
fire. So
fire may result from electrical
misuse.
So today we're going to talk about six different types of electrical
hazards, three of them are direct and three are indirect. The direct
ones include shock, which is an electrical shock that might not
kill electrocution, which is death due to electrical shock, and the
third one is burns due to electrical shock as well. The
indirect ones, if someone gets shocked while working on a
platform, they might fall. So number fall. Number four is false.
Number five is fires. Again, if not paid attention to that
electrical current, may ignite something which might cause fire.
And if that thing that's going to be ignited is explosive, then it
might cause, in addition to fire, an explosion as well. So
basically, six types of electrical hazards, three direct and three
indirect.
When does an electrical shock happen? It happens when the
current flows through the body. An electrical shock is received when
electrical current passes through the body, and when you are in the
loop, when the person that's being shocked is in the loop. So you
will get an electrical shock if a part of your body completes the
electrical circuit by touching a live wire or an electrical ground,
or touching a live wire and another wire at a different
voltage. So as long as there's a different difference in the
voltage between the two wires, this is going to cause an
electrical shock, because the difference is going to go through
the body of that person holding the two wires.
So it shows here, for example, this is the source of electricity,
and then you're standing on another on another metal, for
example, which is
conducts electricity. So the circuit is closed through your
body, and that's where the shock happens. The severity of the shock
depends on the path of the current through the body, the amount of
current or the intensity of the current flowing through the body,
and that's going to be measured in amperes or amps, and the duration
of the shocking current through the body. Of course, the longer
the exposure, the more severe the injury is going to be.
Low voltage does not mean low hazard. And that's a
misconception, because people think, oh, it's low voltage. So
there's no risk there. There is still a risk. Because again, when
we see the amount that can cause a shock or even electrocution,
you're gonna find that it's not that big. Anyway,
currents above 10 milliamperes, we mentioned that the current
intensity is going to be measured in amps or amperes. A milliampere
is one over 1000 of an ampere so currents above 10 milliamperes can
paralyze or freeze muscles, and that would be a relatively light
shock. Currents more than 75 milliamperes can cause a rapid,
ineffective heartbeat, and that will occur in a few minutes,
unless a defibrillator is used. So this is almost killing 75
milliamperes. 75 milliamperes is not much current. A small power
drill uses 30.
Times as much you can imagine, just the power drill uses 70
times, 30 times the amount that can lead to killing a person.
So 1 million ampere, as it shows here at the bottom, is one over
1000 of an ampere.
Remember these numbers, by the way, the 10, the 75
now to give you an idea about, when would you feel the shock? 3
million amperes. We were talking about 10, and we're talking about
75 3 million pairs would cause a painful shock.
And if that person, as we said before, is standing on a platform,
that jolt might make them fall. So adding another injury, which is
regard to result from Fall, 10 million pairs plus are going to
cause muscle contraction. So you won't be able to let go, if you're
holding that's why you won't be able to let go. 30 million pairs
are going to cause lung paralysis, which is usually reversible and
temporary.
50 milliampere might cause ventricular fibrillation, which
might cause heart arrest.
10 milliamperes to four amperes certain fatal ventricular
fibrillation, which is not gonna be reversible through a
defibrillator, and over 4 million pairs. In addition to that, that's
going to be severe burns and heart paralysis. So as you can see, it's
really dangerous if you don't know what you're dealing with.
The burns are the most common,
and they are related to shocks, and they come from touching wires,
touching electrical wiring or equipment that is improperly used
or maintained the hands, usually, which is the the part of the body
that touches this equipment or this wire is going to be getting
it. And it may be very severe injury, depending, again, on the
intensity of the current, the exposure, the time of exposure,
the length of the time, and so on and so forth. So it needs
immediate attention to try at least to minimize the long term
effects of that bird.
Fault, as we just mentioned, is an indirect injury. Electric shock
can cause indirect injuries. It can cause death if the fall is
from a high level and there's no fault protection system, so
workers in elevated locations who experience a shock may fall,
resulting in serious injury or death, especially that if the
person is in a case of shock, they won't be able to reduce the impact
of their fall by using their hands or something like that. They might
lose lose consciousness, and that might lead to death.
Fire as the second indirect hazard, most commonly caused by
current flowing through high resistance due to faulty wiring,
igniting insulation and or other material. You something that you
might remember from your physics classes, energy can change its
form, which means we have the electrical current, which is
electrical energy, and if there's very high resistance, as in a
heater, for example, what happens is that this electrical energy is
converted into thermal energy, or heat. So in this case, if the
current keeps flowing through high resistance is going to cause that
high resisting material to heat up, and that might cause a fire.
Heat created from high currents flowing through a wire. This is
analogous to two objects being rubbed together very fast. Heat is
generated through that friction at full speed. The skin of a jet, for
example, is around 600 degrees Fahrenheit. That shows you just
the effect of friction, even flowing through air,
the heat of friction to maintain continuity of flow, as the
diameter of a pipe decreases, the velocity of the fluid must
increase and the heat of friction increases as well. So think about
it this way, the electrical wire or conductor. Think about it as a
pipe where there's a fluid flowing through it. If you narrow the
cross section of the pipe, what's going to happen? The speed is
going to increase. So I think that that's the Bernoulli effect, or
something like that. So likewise with wires, when a wire decreases
in cross sectional area due to damage, current must increase
through that portion of the wire, and heat increases possibility to
the point that surrounding materials are set off on fire if
there's a pinch in the wire, for example, due to a sharp edge or a
corner or being squeezed by a door jam or something like that.
That what's going to happen is reduction in the cross section of
the wire, and the intensity of the heat is going to increase. The
heat is going to increase, which might melt the insulation shield
and start to fight
the third indirect hazard is explosions, which can be caused
when electricity provides the ignition source, or arc jumping
through an air or fuel mixture in the atmosphere. So in fact, the
arcing effect can happen without direct connection, without
directly touching. So it can happen through the air. The air
itself, in this case, is going to act as the conductor.
So the six hazardous electrical conditions are going to be
exposed. We talked about six hazards, but six conditions here,
which is something totally different. What might cause that
electrical overcharge that might lead to a shock or to
electrocution or to arcing. So we have exposed electrical parts that
are not properly insulated proximity to power lines, the arc
effect that we talked about inadequate wiring, which in this
case, you have too much current flowing through a very narrow
wire, which is going to lead to, again, overheating. It's similar
to reducing the cross section of the conductor. Defective cords,
poor or no grounding, so the excess charge cannot be discharged
to the ground and overloaded circuits, again, if the circuit
carries a flow of a certain intensity exceeding the design
capacity of that circuit.
Look at this picture, for example. Here. This is something taken from
a construction site, and you can see here exposed electrical parts.
Here are the six hazards that we talked about, and this is the
first one. The box cover was removed and the wiring was
exposed. So first of all, we have several issues here.
Even the connection between different wires is not done
properly, so that can lead definitely to electro fusion, or
to at least shocks.
So if you have a junction box, you should use either covers or guards
or barriers. So you have to guard the live parts, the parts that
receive current of electric equipment operating at 50 volts or
more against accidental contact. Obviously here, the connections
are not done properly, and there's no proper insulation.
So to protect the control number one, isolate electrical parts.
We're going to use either cabinets or boxes or fittings. The
conductors going into them must be protected, and unused openings
must be closed. Of course, here we have an unused opening that's not
properly closed. They try to close it with something like duct tape,
and that's not a proper closure for such an opening. So this is
not properly done. Here we have the wires getting into that
junction box, and again, it's closed using
duct tape. That's not the proper closure.
I think this picture speaks for itself. You have a junction box,
it does not have a cover. You have openings that are not properly
closed. So here at least two violations in this picture, and
again, the connections here are not done in any professional way,
by the way.
The second hazard is going to be the power lines do not get near
power lines, whether on dry conditions or even on wet, on wet
or dry conditions, you should not get too close to a power line if
it is still activated. If you're gone, if someone's going to work
on power lines, they must be deactivated.
Watch for cranes ladders. What can get you close to the power line?
Cranes, ladders, scaffolds, backhoes, scissor lifts and raised
dump truck beds. The problem with cranes is that the person might
not touch the wires, but part of the crane, which is metal, is
going to touch that wire, so it's going to close the circuit, and
the person might get electrocuted. Same thing with the ladder, if the
ladder touches, and if it's something like an aluminum ladder,
for example, touches the wire, and again, that's gonna cause the
closing the circuit, which is gonna electrocute the person
standing on that ladder. Same thing for the scaffold. Now for
the ladders we're gonna see later, that you should not use any metal
ladders close to electricity. There are.
To protect conductors entering boxes, etc, from abrasion,
especially if you're going to have a sharp edge
in the box, make sure that you have a smooth protection to
prevent the abrasion and the cutting of the insulation or the
pinching of the cross section of the wire
close unused openings in junction boxes, as we have seen in the
picture, which was not done, not done properly. But now we know
that you must have these plugs that are exactly the size of the
opening and that would close it properly if
you're going to be working outdoors or in wet locations, you
must have weatherproof enclosures that are going to be waterproof.
Basically,
protect hardware from water. Water and electricity are a very bad
combination, so we're going to try to protect any hardware, or any
equipment, electrical equipment that we're working with from
contact with water. So we're going to make that protection through
cabinets, boxes, switches, circuit breakers, etc.
Here we have, for example, a cord that's going through a door
opening, and if that door closes, what's going to happen is going to
squeeze that cord, pinch it and cause it basically to to break the
insulation, which is going to be a hazard, as we just discussed. So
the cause causes of damage include aging, which is natural wear and
tear, if that cord has been used for a long time, edges of doors
and windows, staples for fastening, if you're going to
attach it to a wall abrasion from adjacent materials, whether it's a
junction box that has a sharp edge and impact from activity in the
area, if something drops on that cord, it might cause that tear
into the insulation couple.
So insulate live wires, check before use. Use three wire type
cords only that are going to have a grounding wire, hard cord, hard
duty cords only use only course mark for hard or extra hard usage,
as we have seen in the print on the wire itself, and provide
strain relief. Strain relief, if you have
here, for example,
this connection has strain relief. This widened part here is called a
strain relief. So again, if you pull from here, it's not going to
cause any damage to the wire. Use only cords connection devices and
fittings equipped with strain relief, and you're going to see it
through again the widening at the neck or the edge of that wire.
Don't pull on course if you want to disconnect it from the power
supply, don't just pull the cord, but
remove it properly by pulling from the plug itself. Remove course by
pulling on the plugs, not the cords, and use only hard service
rated cores, cores not marked for hard or extra hard use should not
be used or which have been modified must be taken out of
service immediately because they cause a source of hazard.
Again, we have, we have some repetition here. If you're gonna
use extension cords, they have to be three wire type, hard duty or
extra hard duty. Protect them from damage.
Again, from any of the reasons that we have mentioned on the
previous slides, no pinch points. Make sure that there's no
narrowing in the cross section of that wire, no nails, staples, etc.
So if you're going to suspend them or you're going to attach them to
a wall, use something other than a nail or a staple through the wire
itself.
Use plugs with ground pins. The three pins, one of them is going
to be the ground pin, so path to the ground must be continuous. Use
only plugs with ground pins, no missing ground pin. Sometimes
people would just break that ground pin because they can't find
a
grounded socket. That would be a big risk that you're taking this
position. No reversing polarity, no grounded conductor shall be at.
Can be attached to any terminal, reversing its designated polarity,
and it must have general disconnect, which is something
like a main breaker must be, must have a disconnect that allows all
conductors to be disconnected from service entrance, so a master
circuit breaker that can disconnect the whole area
repairs to extension cords. If there has been a tear or a
some damage to an extension cord, you can.
Repair only.
Extension cords made of
made out of 12 gage or larger
of that type, of course. So if it's less than 12 gage, you should
not try to repair it. Repairs must maintain the insulation. So the
splices by connecting, for example, or lengthening must
maintain outer sheath insulation properties, so no electrical tape.
The electrical tape by itself is not going to be enough insulation
and strain relief must be provided that's going to extend the service
life of such a cord.
Hazard number five, we talked about grounding. Grounding is a
low resistant, resist for for grounding
a low resistance path from a tool to the earth to disperse unwanted
current. As you know, the Earth has an infinite resistance. So any
excess current, if it's sent to the ground, the ground is going to
be able to absorb it without any problems. When a short occurs,
energy flows through the ground and not through you. The short
circuit, basically, is
a discontinuity in the amount or intensity of the current flow. So
you have a high intensity and an area of low intensity. If that
happens, there's going to cause the shock or the electrocution. So
there's no continuity. If you have grounding, the ground is going to
absorb that difference. If you do not have grounding, then the
person who is in contact with such a wire will have to absorb that
difference, and it can be fatal.
This picture, for example, shows an improper connection. Of course,
there is no strange relief. For example, the wire is not properly
connected, so tools plugged into improperly grounded circuits may
become energized.
A broken wire plug on an extension cord are going to cause electrical
shock or electrocution.
So grounding is a very common OSHA violation here. What's wrong with
this picture? It's missing the third
element here, which is the ground
part. It has strain relief, which is good, but again, the
grounding wire has been removed or broken
ground. Your equipment, power supply systems, electrical
circuits and equipment have to be grounded and inspect frequently to
make sure that the path to the ground is continuous. Inspect
before each use to make sure that the equipment is in a proper
working condition, and don't remove the ground prongs. Again,
the problem here in this picture that the ground is that the ground
prong has been removed. Never do that.
The last one is overloading circuits. The Hazards result from
too many devices plugged in to one circuit, causing heated wires and
possibly a fire if you do not have a proper circuit breaker, which
can alert you in case of overloading. If you have the
proper circuit breaker, it's going to trip first and disable that
circuit so everyone's going to be safe. If you do not have that
circuit breaker, then the current is going to keep flowing, which is
going to cause that heating and may lead to fires
using damage tools without the proper insulation may cause the
overheating and no, in case you don't have any overcurrent
protection, that can cause the overloading of circuits. So if you
don't have any fuses, circuit breakers or GFCIs, as we're going
to see in the few next few slides. So here, for example, it doesn't
appear that we have any of the above.
The Hazards are going to result from melting the wire insulation,
because, again, there's too much heat flowing through the current
due to the resistance which is going to melt the insulation.
This situation can cause arching and a fire in the area where the
overload exists, even inside a wall that's very dangerous.
The electrical circuit protective devices, predominantly the circuit
breakers. They automatically open the circuit. If unsafe current is
detected, they shut off the electricity. So, for example, the
fuse is gonna melt. The fuse is a thin wire of a certain material
that's easy to melt if heated too much. You have these at home. You
have these in your car. For example, one of the very common
mistakes each one of these.
Is rated for a certain current intensity. If you replace a
defective fuse with one that has a higher current intensity, that's
very dangerous, because, again, it's going to allow for more
current to flow, causing the hazard to occur.
The circuit breakers are going to trip. The circuits breakers are
reversible, so if it trips, you can reconnect it again, and the
GFCIs are going to isolate the load.
These are all protections to your circuits.
The GFCIs protect you from shock. You can see the GFCIs in your
bathroom, for example, you're going to find this. This is a
ground fault circuit interrupter, which is the GFCI, and it has a
reset button. So again, when it feels there's a drop in the
current or an a discontinuity in the intensity of the current, is
going to trip and stop that circuit immediately. So it detects
current drop between the black and white wires. The GFCI is cost
electricity off in 1/40 of a second if a ground fault is
detected. So if it detects that there's a difference in the
intensity and the ground cannot take that is going to cut off the
current in 1/40 of a second. Very quick use GFCIs on all 120 volt
single phase, 15 and 20 MP receptacles, or have an *
equipment grounding conductor program. Now this is a portable
GFCI. Here it connects to the socket, and here it connects to
the device, and it has a movable GFCI here for temporary use. This
one is permanent. It's going to be located in the wall.
Again. GFCIs are designed to cut off a flow of electricity if a
current leakage is detected in electrical circuit, and designed
to trip at four to six milliamps, relatively low current, which is
still at the painful shock left, but at least it's less than the
lethal
for temporary power, GFCIs or assured equipment grounding
conductor program are required for all temporary power during
construction, like the yellow one that we just saw, GFCIs are
required on temporary 120 50 volts, 15 to 20 ampere outlets,
and GFCIs not are not required on permanent power unless the tool is
used with an extension cord. In this case, you're going to need a
GFCI. That's
just a repetition of what we just said.
Never snip off the ground prong on a plug that will negate the safety
feature of a GFCI, because, again, the GFCI is going to measure the
current going to the ground, so if the ground prong is not there,
that renders it useless.
Here's an example on how they work. Joe's outside with his power
drill, and it's raining again, as we mentioned before, electricity
and water, very bad combination. Joe standing on the ground, and
since his drill is wet, there's the path from the hot wire inside
the drill through Joe to the ground. If electricity flows from
hot to ground through Joe, it would kill him, because he was
he's going to absorb that difference in electricity. The
GFCI senses the current flowing through Joe? Because not all of
the current is flowing from hot to neutral as expected. Some of it is
flowing through Joe to ground. There's the current leak, and as
soon as the GFCI senses that, it trips the circuit again between
1/30 and 1/40 of a second and cuts off electricity, Joe is going to
be safe.
GFCIs are going to be required on generators, all portable
generators of five kilowatt or greater kilo, means 1000
GFCI protection can be built in or added as a pigtail. The pigtail
was the yellow one that we saw on the previous slide.
A short equipment grounding Program, or aegp, is a specific
written procedure adopted by the employer. If you cannot use the
GFCI, then you must have an aegp. All core sets, receptacles and any
equipment connected by cord shall be inspected before each day use.
That's part of the assured equipment grounding program.
And this is a written program that must be kept on site. The OSHA
inspector is going to inquire about it, and he's going to check
it.
And it has to be implemented by a competent person in electricity.
It covers equipment connected by plug and cord, all cords, plugs
and receptacles that are not part of the building or the structure,
the temporary ones and any power tool. Before first use, your Ghana
test, and you're gonna test at least every three months. And
after service, if any repair or maintenance has been done, and
after possible damage, if it has been hit, for example, by
something, and you replace it or repaired it, then you're gonna
inspect it and test it again. Test records must be kept again. This
is going to be part of the inspection done by the OSHA
inspector.
The electrical equipment must be inspected before installation and
to make sure that it's suitable for the intended use, use per the
manufacturer's instructions, which are going to be listed within the
manual, labeled on the equipment itself and certified equipment to
be used for manufacturers. Instructions. Label all the
breakers. All circuit breakers must be labeled with the capacity
that they can carry.
Now access to 50 plus volts must be controlled either by restricted
areas or by a physical location. Restricted area means it's going
to be accessible only by qualified or authorized persons. So
basically, you're going to have a locker or a room or an enclosure
or partition or something like that, and only allowed personnel
are going to be able to access it or by physical location, by
elevating it eight feet or above, above the floor of working
surface, so no one is gonna bump into it by accident.
Electrical equipment as well must be protected enclosures or guards
must be used where electrical equipment is exposed to physical
damage. Electrical rooms must be marked. The entrances to
electrical rooms containing exposed light parts must be marked
with warning signs for bidding entrance by unqualified personnel.
If you're going to do some splicing of the conductors must
use splicing devices designed for that purpose, like wire nuts, or
by brazing, welding or soldering to make sure that they there's a
good connection between the two wires being sliced.
Manufacturers information must be legible. If there's going to be a
stamp on the wire or something like that, designating its
capacity, this must remain easily legible on that wire, so
electrical equipment must not be used unless the manufacturers name
trademark and other markets giving voltage, current, voltage, etc,
are legible again as a means of protection,
if you're going to have a an electrical equipment enclosure for
600 volts or less,
these working spaces cannot be used for storage. They're going to
be primarily only for electrical equipment. So they're not used for
storage. They're not used for partial occupancy. They must have
access and elbow room, allowing for people who are going to make
any maintenance or repair or connections to work inside
sufficient access and working space must be provided and
maintained around all electrical equipment and workspace clearances
are going to be according to table k1 in your code Book, three square
feet in front of the electrical equipment in the direction of
access to the live parts. That's the minimum that must be
available.
You must lock out and tag out controls on equipment during
service and repair with clear identification that this equipment
is defective and it needs maintenance or repair to prevent
energizing circuits. Circuits or equipment that are de energized
must be locked and tagged to prevent unauthorized reenergizing
at any point.
So here, for example, we have a lockout, basically you turned it
off and you have a lock that is going to disable you from
reactivating it, unless you have the key to that lock. So apply
locks to power source after de energizing tag, deactivated
controls tag de energized equipment and circuits at all
points when they can be energized, just to make sure that no one
energizes them by mistake, and the tags must identify the equipment
or the circus the circuits being worked on.
This, for example, is a single lock that locks only one circuit
or the access to one circuit. And this is a multi lock,
where you can have six locks attached to that.
Here we have the enclosure clearly marked as high voltage with the
danger sign. So use barriers or guards like this, for example, pre
pre planned work and post warning and use protective measures,
including protective equipment and keep work areas clear, of course,
debris or trip hazards, so that no one can trip inside that room.
Here, obviously we have a cord that's totally defective because
the insulation is worn out and the wire is exposed. So don't use worn
or frayed cords. Don't fasten with staples, as we just mentioned,
don't hang from nails. Don't suspend objects with them.
Plan your work with others. Here we have lockout tagout. So here we
have the lock and the tag on a circuit breaker. Plan Your to lock
out and tag out equipment, remove jewelry that can get the
hung on on these wires or
cause tears in these wires. Avoid wet conditions and avoid overhead
power lines.
Use proper hardware. This is the GFCI, as we mentioned. Use and
test them. The switches, check them, the insulation, check it to
make sure that there's no tear. Extension plugs use three prong
types. Make sure that the ground prong is there. Extension course
use only when necessary, and assure in proper condition and
right type for job, whether it's hard use or heavy or extra hard
use and heavy duty or extra heavy duty and the connectors use the
correct ones.
Train the employees to use safe practices, including de energizing
before starting to work. Use only course, tools, etc, that are in
good condition, lock out and take out procedures. You have to train
them on that. And you have to train them on using the proper
personal protective equipment.
So as a summary, these hazards are inadequate wiring, leading to
overheating or overloading of the circuit, exposed electrical part,
leading to electrocution or shock by touch, bad insulation on
wiring. Ungrounded tools and electrical systems, overloaded
circuits, damaged power tools and equipment, wrong personal
protective equipment and tools, overhead power lines working too
close to overhead power lines and wet conditions make all hazards
worse. The protective measures are going to be proper grounding,
using GFCIs, using fuses and circuit breakers, guarding life.
Parts lock out and deg out on the equipment that needs maintenance,
or the circuits that need maintenance, proper use of
flexible cords, again, do not pull from the cord itself, but from the
plug. Close electric panels, if they're going to include
electrical equipment and trained personnel for the knowledge of the
hazards and how to deal with these hazards to minimize their
occurrence.
Some quick questions, at what amperage will a GFCI trip? Do you
remember the number four to six milliamperes.
What is the proper way to repair an extension cord? Repair only.
The only ones that can be repaired are 12 gage or larger. Repair must
maintain insulation properties and shrink sleeve can be used to for
that connection. And you can. You have to make sure that the
properties of the wire or of the conductor are clearly printed and
are legible on that extension cord.
What should we do to protect unauthorized employees from
entering electrical rooms with live parts? We mentioned two air
two measures, one of them is the physical, and the other one is
making the mark in the room with the warning signs for bidding
interest by unqualified and unauthorized persons. What types
of electrical cords are acceptable for use in construction? Usually
three wire type,
hard or extra hard duty, heavy or extra heavy duty. These are the
only course that are extension cores that are properly used in
construction sites.
That's basically our presentation on electrical hazards sub chapter
K, I hope you have learned a few things to keep you safe when
working with electricity. See you in another lecture you.