Electrical Flashcards
DC motor: characteristics
smooth acceleration to high speeds
found in elevators
Single-phase AC motor
3/4 horsepower or less
Three-phase induction motors
constant rpm unless heavily overloaded
power factor of 0.7-0.
very reliable
Universal motor
runs AC or DC current
speed varies based on load
found in mixers, hand drills and appliances
Watts/sq.ft.
Lighting
low: 2
avg: 3
high: 5
Watts/sq.ft.
Outlets
low: 1
avg: 2
high: 3
Watts/sq.ft
HVAC
low: 4
avg: 5.5
high: 7
Watts/sq.ft.
Misc.
low: 0.2
avg: 0.5
high: 0.7
FUSE
glass plug or fiber cartridge
if current exceeds flow rate, link will melt
glass fuses up to 30 amps
CIRCUIT BREAKER
automatically disconnect when current is excessive
can be reset
can be used as backup shutoff for working/examining
higher first cost than fuses; no replacement and low maintenance costs
GROUND FAULT (CIRCUIT) INTERRUPTER
detects continual current lost to ground even when power is shut off; breaks circuit
required in bathrooms, garages, outdoors, on construction sites and large/high voltage circuits
Grounding
redirects current to earth
insulated or bare wiring
fastened to steel cold water pipe - provides direct path to ground
components of a service drop
wires from main line
transformer
meter
disconnect switch
residential service
units
cost
100 amps min.
meters in kwh
8-18 cents per kwh
V=
I*R
