Unit 7: Electrical Fires and Building Electrical Systems Flashcards
(26 cards)
The requirement for ignition is that the heat
transfer from the electric source be ___________________
maintained long enough to bring the adjacent
fuel up to its ignition temperature, with air
present to allow combustion
“The physical phenomena arising from the behavior
of electrons and protons that is caused by the
attraction of particles with opposite charges and the
repulsion of particles with the same charge.”
Electricity
The flow of electrons due to a difference in
energy potential between two points on a
conductor.
Electricity
Terms
- Voltage (V) or electromotive force (E).
- Current (I) or amperes or amps (A).
- Power (P) or watts (W).
- Resistance (R).
- Inductance (L).
• All matter is made of atoms. • Protons + neutrons = nucleus. • Electrons form valance rings. • Number of electrons = number of protons. Outer ring has one to eight electrons. • One to two electrons in outer ring = unstable ring (conductor). • Examples: silver, copper, gold, aluminum.
Atomic Theory
• Four electrons in outer ring =
semiconductor.
• Resistance varies with temperature.
• Increased temperatures
lead to decreased resistance.
• Elements are silicon
and germanium.
• Used in transistors and diodes.Electrons
• Seven to eight electrons in the outer ring = stable ring (insulator). • Examples include various carbon molecules such as rubber, plastics and wood. • Movement of electrons from one atom to another is known as electricity. • Energy is required to initiate and continue this movement.
Electron structure
• Energy is transformed during this
movement to heat and magnetism.
• Heat and magnetism always accompany
electron flow in some amount.
..
What always accompanies electron flow?
Heat and magnetism
What is the Maximum “harmless” current.
5 Milliamps
Equipment
must be ___________________ before examination,
preventative maintenance or servicing is performed.
locked out and tagged out
“The physical phenomena arising from the behavior
of electrons and protons that is caused by the
attraction of particles with opposite charges and the
repulsion of particles with the same charge.”
Electricity
Voltage______ or electromotive force (E).
V
Current ______ or amperes or amps (A).
I
Power _______ or watts (W).
P
Has weight and takes up space.
Matter
When current flows, a _____________ is
generated.
A magnetic field
• Materials that allow current to flow freely with minimal resistance. • Copper and aluminum are two of the most recognized; both are used in electrical systems. • Gold and silver are also used, usually at point of contact.
Conductors
• They work the opposite of conductors; they oppose or stop the flow of current. • Some insulators are glass, porcelain, air and pure water. • However, a high enough voltage may defeat the insulator.
Insulators
• Electrical pressure that moves electrons through the conductor, known as electromotive force. • Shown in formulas as E.
Voltage
Current is also referred to as
Amperes
The rate at which electrons flow through a
conductor. Shown in formulas as_________ Measured in amperes (amps).
“I” (intensity)
• Opposition to current flow.
• Shown in formulas as “R.”
• Measured in ohms — Greek Omega Ω
.
Resistance
• Quantitative measurement of work done
consumed in an electrical circuit.
• Power is a larger issue over
a period of time.
Watts (W) or kilowatts (kW)
