Chapter 30 powerpoints Flashcards
Commercial buildings require high levels of power for:
Lighting
Motors
Heating elements
Other loads
Different size _______________ are used depending on the amount of power required and the type of loads.
power distribution systems
Relatively low voltage levels:
Used for small commercial applications by the local utility.
Like gas stations, restaurants.
208 V to 240 V
Medium voltage levels:
- Used for mid-sized commercial applications.
- Like small office buildings.
460 V to 480 V
Used for large commercial applications
Like colleges, small businesses, hotels
Voltages must be delivered and distributed to different transformer banks throughout a building
High levels: 1000 V and up
an assemblage of equipment installed for switching, changing, or regulating the voltage of electricity. Where high voltage is reduced.
Substation
The exact voltage level used to operate different loads in commercial applications depends on:
The loads
The given application
The NEC
NEC limits the voltage level to 120 V between conductors that supply:
Lighting fixtures, cords, and plugs that connect loads up to 1440 VA (volt-amperes)
Motors up to ¼ HP in dwelling units and guest rooms of:
Hotels
Motels
Similar rooms of occupancies
Commercial power needs include the same needs as residential _______________.
(1Φ) and industrial (3Φ) systems
Commercial customers use low-voltage _______ and ______.
3Φ and 1Φ power
Power companies use _________ to deliver power to customers through different distribution systems.
transformers
Primarily use________ connected in different combinations to deliver the correct power.
1Φ transformers
The distribution system used varies based on the _________.
application
Common commercial distribution systems include:
120/240 V, 1Φ, 3-wire
120/208 V, 3Φ, 4-wire
120/240 V, 3Φ , 4-wire
277/480 V, 3Φ, 4-wire
All ________________ read a voltage between the conductor and a ground point (grounded conduit, green ground wire, et c.)
ungrounded (hot) conductors
The voltage on the ___________ of a transformer begins to drop if the transformer is overloaded. The higher the overload, the greater the voltage drop
secondary side
This is the primary serviced used to supply most residential buildings.
Distribution Systems: 120/240 V, 1Φ, 3-Wire Service
In commercial wiring, small appliance usage includes more than typical _____________.
residential small appliance usage
Three-phase circuits include three individual __________________.
ungrounded (hot) powerlines
- Is used to supply customers that require:
- A large amount of 120 V, 1Φ power
- Low-voltage 3Φ power
- Includes three ungrounded (hot) lines and one grounded (neutral) line.
- Each hot line has 120 V to ground when connected to the neutral line
Distribution Systems: 120/208 V, 3Φ, 4-Wire Service
Is used to supply customers that require large amounts of:
3 Φ power with some 120 V
240 V, 1 Φ power
Distribution Systems: 120/240 V, 3 Φ, 4-Wire Service
Is the same as the 120/208 V, 3Φ, 4-wire service except the voltage levels are higher. Includes three ungrounded (hot) lines and one grounded (neutral) line.
277/480 V, 3Φ , 4-Wire Service
Voltage Variation Effects on AC Motors are?
All motors are designed to operate at the given voltage. A motor operates if the voltage varies below or above the rated voltage. Is a change in the motor’s performance.
