EST 51 Electrical Safety

Eye Protection - Goggles

Goggles fit snuggly to the face and provide better protection against spilled liquids than glasses. Can be worn over standard prescription glasses. May be tinted for low-voltage arc protection

Excessive heating is the most common cause of electrical fires. Some of the causes are:

Looping a conductor several times can result in overheating, Excessive heating can also result from excessive thermal insulation, Over voltage conditions can overheat a conductor, The most common cause of overheating, however, is poor electrical connections

insulators

Materials with very high resistance, or opposition to current

Which NEC regulation covers grounding and bonding?

NEC section 250 as well as IEEE 142 and 1100

NIOSH

National Institute for Occupational Safety

Putting Out a Fire

Never use a Class A extinguisher on an energized electrical fire, Multi-use fire extinguishers are becoming more common, Know where fire extinguishers are located at your job site and know how to use them.

reaction to the human body by current between 10 mA & 20 mA

Painful shock, loss of muscular control. individual cannot let go, but may be thrown away from the circuit if extensor muscles are stimulated.

Hand Protection

Rubber gloves are worn to protect against electrical shock. Rubber gloves must be checked for holes or leaks before each use Class 00 Maximum AC Voltage 500v Class 0 Maximum AC Voltage 1000v Class 1 Maximum AC Voltage 7500v Class 2 Maximum AC Voltage 17,000v Class 3 Maximum AC Voltage 26,500v Class 4 Maximum AC Voltage 36,000v

List the three current pathways that a shock current can take through the body. Which is the most dangerous?

Touch potential (hand to hand through the heart) Step potential(foot to foot through the lower body) Touch step potential(right hand to right foot, or left hand to left foot through the body). Most dangerous is

Current pathways through the body

Touch potential (hand to hand through the heart) is the most dangerous Step potential (foot to foot through the lower body) Touch step potential( right hand to right foot, or left hand to left foot through the body)

Putting Out a Fire (Cooking Oils an Fats)

Wet Chemical

ground fault circuit interrupter

a device that senses an imbalance in current between the hot conductor and the neutral conductor

arc flash

a sudden, explosive arc of electrical energy, most residential 120/240 volt circuits do not have enough energy to cause an arc flash, in high voltage circuits, an arc flash can vaporize metal and project a plasma arc. Medium - high voltage circuits (600 volts and higher) are much more susceptible to arc flashes.

What items need to be bonded in any structure?

all metallic conductive materials

Current is measured in

amps or milliamps

what causes a high- resistance connection?

an electrical connection that is not secure

Freezes

an electrical shock that causes muscles to contract and a person cannot let go of the circuit

What is freezing?

an electrical shock that causes muscles to contract where a person cannot let go of the circuit

Electrical fires are ignited by

arcing, short circuits, excessive heating of conductors or devices

What is the most common shock-related injury?

burns

List three reasons why materials need to be bonded.

cannot receive an electrical shock if you touch two different metal objects, effective grounding, prevents acing or sparking, assures any over current protection

Home electrical outlets

carry up to 15 amperes (15,000mA) of current

If resistance is higher ?

current will be lower

Water and/or sweat will make the body's resistance to electrical shock

decrease

What is the most common shock related injury

electrical burns

Shock- related injuries

electrical burns, falls, internal bleeding, nerve and muscle damage, kidney failure

reaction to the human body by current at 1 mA

faint tingle

what is the most common electrical source of residential fires?

fixed wiring

Electrical Fire Hazards

fixed wiring, electrical cords and plugs, lighting fixtures, switches/ receptacles, lamps and bulbs, circuit breakers/fuses, meters/meter boxes, transformers

reaction to the human body by current below 1 mA

generally not perceptible

Ground

ground refers to the earth

What is the difference between grounding and bonding?

grounding is the act of connecting to the ground so it has zero electrical potential where bonding is joining two electrical conductors together.

why is an electrical arc more likely to start an industrial fire than a residential fire?

industrial have higher voltages

Grounding

intentionally connecting the electrical system or equipment to earth ground

What is an arc flash?

is a sudden explosive arc of electrical energy

Ground fault

is an unintended connection of an energized conductor to the ground

Earth Ground

is the electrical zero reference point

difference between no perceived effect to possible death is

little more than 1/10 of an ampere (100mA)

List three causes of conductors and components over-heating

looping a conductor upon itself, excessive thermal insulation, and over-voltage conditions, most common is poor electrical connections

Explain the best procedure for making sure that a circuit is truly de-energized?

meter a circuit that you know is powered to make sure your meter is working. Then meter the deenergized circuit to make sure there is no power. Then meter the powered circuit to make sure the meter is still working.

ground fault occurs

neutral conductor will have less current then the hot conductor, if the difference is greater than 5 mA, the device quickly de-energizes the circuit

you should work with how many hands although it is not always possible

one hand

Milliampere (mA) is

one thousandth (1/1000) of an ampere, so 1000 milliamperes equals 1 ampere

Resistance

opposition to the flow of current

Bonding

permanently joining conductive, non-current carrying material (like pipes, conduits, and enclosures) so they have the same potential

reaction to the human body by current between 5 mA & 10mA

slight shock felt; not painful, but disturbing. May have trouble releasing the circuit

Current

the flow of electrical charge through a conductor

Voltage

the force or pressure that causes electrical current

Creep

the further loosening of connecting materials due to heating

What is the purpose of the lockout/tag out practice?

to make sure that a circuit is truly deenergized and that it stays that way until work is completed

List and describe the five classifications of fires

1. common combustibles like wood, paper, or cloth 2.flammable liquids, like oil, gasoline, paints, tar 3.Live electrical equipment 4.Combustible metals 5.Cooking oils and fats

A GFCI opens a circuit if there is a current imbalance between the hot and neutral lines. What is the amount of current imbalance that causes the GFCI to open the circuit?

5mA

Hazardous Locations

Most jobsites have moving equipment that can strike or crush you. Toxic chemicals or explosive gases can be present. Confined spaces that have restricted access and are not designed for normal occupancy present additional hazards

Lockout/tagout

a common method of making sure that a circuit is de-energized and that it stays that way until work is completed

what is a glowing connection?

a point where a connection reaches a very high temperatures that can easily ignite any nearby combustible material.

Personal Protective Equipment (PPE)

clothing and equipment used to protect a worker from injury on the jobsite, Proper PPE requirements are outlined in NFPA 70E®: Standard for Electrical Safety in the Workplace, and Relevant parts of OSHA's Title 29

If voltage is higher?

current will be higher

reaction to the human body by current between 20 mA & 100mA

extremely painful Breathing is difficult

When a circuit is locked out, who keeps the key?

the person working on the circuit

If you are wet or standing in water, any electrical shock you receive will be more severe than if you were dry

true

What do you do if someone is Frozen as a reaction to an electrical shock

turn off the power to the circuit, if you cant use something with a high resistance to push or pry the person from the circuit, a piece of wood or pvc pipe will work well

The body's resistance to electrical shock is

very high

Glowing connection

very high temperatures that can easily ignite any nearby combustible material

Putting Out a Fire (wood, paper, or cloth)

water, chemical foam, dry chemical

How can you tell if a shock is serious?

you can't, get medical help immediately

What is the lowest current level that may cause death if you get a shock?

100mA

At what current range does freezing occur?

10mA to 20mA

What i is the current rating for most of the electrical outlets in a residential building?

15A

Working at Heights

A harness and lanyard is one type of fall protection worn when you can fall 6 feet or more

high-resistance connection

A high-resistance connection heats up when current is present. If an electrical connection is not secure, it can result in a high resistance connection, The connection will reach a point where it becomes a GLOWING CONNECTION that can easily ignite any nearby combustible material

Current in measured in

Amperes (amps)

Common-sense Rules for Working Safely

Avoid Working Alone Learn First Aid Do Not Rush - "No job is so important that we cannot take the time to do it safely." Use the Right Tools Know What You're Doing - If you don't, ask for help Stay Sober Stay Alert - Just as you practice defensive driving on the road, be aware of other workers around you

Putting Out a Fire (Live electrical equipment)

CO2, dry chemical

Putting Out a Fire (Flammable liquids, oil, gasoline, paints, tar)

Carbon dioxide (CO2), dry chemical, aqueous forming foam(AFFF)

reaction to the human body by current between 100 mA & 800mA

Cardiac and /or respiratory arrest. Likely fatal!

Head Protection

Class C - Low impact protection. Not designed for protection from contact with electrical conductors. Class G - Some impact protection. Offers protection from contact with "low- voltage" conductors Class E - Impact protection Designed to reduce the danger of exposure to highvoltage conductors

Which type of fire extinguisher should never be used on an electrical fire?

Class-A , you should use a Class - C

Checking that a circuit de-energized

Connect your meter to a circuit that you know is powered and take a reading, This verifies that your meter is working properly, Use your meter to test the locked and tagged circuit to ensure the circuit truly is powered down, Retest your meter on the powered circuit to confirm that the meter is still working properly

Eye Protection - Safety glasses

Constructed of impact-resistant lenses with side-shields. They may be tinted to protect against low-voltage arcs. They may have prescription lenses.

Eye Protection - Face Shield

Covers the entire face Offers the best protection against flying objects Can be worn over standard prescription glasses. May be tinted for arc protection.

Putting Out a Fire (Combustible Metals)

Dry Powder

Hearing Protection

Earplugs & earmuffs are types of hearing protection

Protective Clothing

Electricians should wear natural-fiber clothing. Synthetic fibers like rayon, polyester and nylon should not be worn. Jewelry should not be worn. Fire-retardant clothing and non-conductive boots may be required on some jobs