15. Electrical Safety - 20. Fire Protection and Prevention Flashcards
Electrons that do not flow in one direction in a circuit. Instead, the flow of electrons changes its direction, or polarity, constantly. The rate of changing polarity is called the frequency of ___. The major advantage of ___ over direct current is that voltage can be changed through the use of a transformer.
Alternating Current (AC)
Alternating Current (AC)
A specific measure of potential energy that is always relative between two points. The force pushing electrons to “flow” in a circuit.
Voltage (Volts)
Ampere (definition)
The number of electrons or charge passing a certain point in the circuit in one second
Ohm’s Law
A law that shows the fundamental relationship of electrical circuits, that is: the amount of electric current through a metal conductor in a circuit is directly proportional to the voltage impressed across it, for any given temperature. V = I * R, where V is the potential difference in volts, I is the current in amps, and R is the resistance in ohms.
Electrical Power
A function of both voltage and current, where power or P, is equal to current, I, multiplied by voltage, V.
P = I x V
P: watts
I: Amp
V: Volt
Formula of Total Resistance (Rt) in a series and parallel circuit? (R1, R2, R3)
Series:
Rt = R1 + R2 + R3
Parallel:
1/Rt = 1/R1 + 1/R2 + 1/R3
A high power discharge of electricity between two or more conductors. This discharge translates into heat, which can break down the wire’s insulation and possibly trigger an electrical fire.
Arc fault
A supersonic shockwave produced when the uncontrolled arc vaporizes the metal conductors.
Arc blast
This effect happens when an electric current passes through your body. This can burn both internal and external tissue and cause organ damage.
Electrical shock
An imbalance of electric charges within or on the surface of a material. The charge remains until it is able to move away by means of an electric current or electrical discharge.
Static electricity
The minimum distance from the energized item where unqualified personnel may safely stand. No untrained personnel may approach any closer to the energized item than this boundary. A qualified person must use the appropriate PPE and be trained to perform the required work to cross the limited approach boundary and enter the limited space.
Limited Approach Boundary
Arc Blast / Arc Fault / Arc Flash
When an arc fault occurs, there’s a massive electrical explosion. Both arc flash and arc blast are separate byproducts of that electrical explosion. The arc flash is the light and heat from the explosion, while the arc blast is a pressure wave that follows.
Current effect on human body:
- faint tingle
- slight shock felt
- painful shock, loss of muscular control
- extreme pain, respiratory arrest, possible death
- Rhythmic pumping of heart ceases, muscular contraction and nerve damage, likely death
- Severe burn, cardiac arrest, death probable
1 mA - faint tingle
5 mA- slight shock felt
6 - 25 mA - painful shock, loss of muscular control
50 mA- extreme pain, respiratory arrest, possible death
1,000 mA- Rhythmic pumping of heart ceases, muscular contraction and nerve damage, likely death
10,000 mA- Severe burn, cardiac arrest, death probable
Temperature of arc flash
Over 35,000 ºF
NFPA 70E
Standard for Electrical Safety in the Workplace,
Electrically safe work condition according to NFPA
- Identify power sources and label them
- Interrupting the load and disconnecting the power
- Visualize the open circuit
- LOTO
- Testing for Voltage
- Grounding
Causes of Electric Flash
Arc Flash Boundaries and definition
- Power source
- Restricted approach boundary (only qualified personnel with appropriate EPP)
- Limited approach boundary (only qualified personnel can ingress)
- Arc Flash boundary (where second degree burns could occur)
Arc flash causes
Contact with tools
Accidental touching
Condensation
Dust
Corrosion
Material failure
Faulty installation
The act of joining two electrical conductors together that are not supposed to be carrying current during normal operations to bring them to the same electrical potential.
Bonding
____; a fast acting circuit breaker designed to shut off electric power in the event of a ground-fault within as little as one fortieth of a second. It works by comparing the amount of current going to and returning from equipment along the circuit conductors.
Ground-Fault Circuit Interrupter (GFCI)
Installing one set of grounds at the work location between the conductors, the system neutral, if one exists, and the ground, which may be a tower or pole ground, to create a bonded work zone that will remain at a near identical state of electrical potential, hence the term “equipotential zone.”
Single point grounding
Types of GFCI
Circuit breaker GFCI
Receptacle GFCI
Portable GFCI
GFCI turn off the power when detects a difference of ____ mA. The time for the shut off is ____ seconds.
5 mA
1/40 second