Unit 1: Pie Circle Formulas Flashcards
Learn to apply Ohm’s Law (E=IR), Power Law (P=EI), and their variations using the pie chart method to calculate voltage, current, resistance, and power in electrical circuits.
Fill in the blank:
Solar photovoltaic system dc circuits on or in one- and two-family dwellings shall be permitted to have a maximum voltage of no greater than ________.
1000 volts
What is the MINIMUM height allowed for a fence enclosing an outdoor installation of 2,400- volt electrical equipment?
7 feet
Where power for equipment is directly associated with the radio frequency distribution system is carried by the coaxial cable, and the power source is a power limiting transformer, what is the MAXIMUM voltage this coaxial cable may carry?
60 volts
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Where a 15-ampere rated general-use ac snap switch is used as a disconnecting means for an ac motor, the NEC® requires the MAXIMUM full-load current rating of the motor to be NO more than ________.
12 amperes
Determine the MAXIMUM number of 125-volt, 20-ampere general-purpose duplex receptacles the NEC® permits to be protected by a 20-ampere, 120-volt, single-pole inverse time circuit breaker in a commercial occupancy.
13
Which of the following statements, if any, is/are true regarding illumination for service equipment installed in electrical equipment rooms?
I. The illumination shall not be controlled by means of three way switches.
II. The illumination shall not be controlled by automatic means within the working space.
II only
In a retail shopping mall, when is an occupant not required to have access to the main disconnecting means?
When the service and maintenance are provided by the building management.
Determine the conductor ampacity where given the following related conditions:
- ambient temperature of 44 deg. C
- 250 kcmil THWN copper conductors
- four (4) current-carrying conductors are in the raceway
- length of raceway is 25 feet
167 amperes
Determine the MAXIMUM overcurrent protection permitted for size 14 THWN copper motor control circuit conductors tapped from the load side of a motor overcurrent protection device. Given: the conductors require short-circuit protection and do not extend beyond the motor control equipment enclosure.
100 amperes
Fill in the blank:
Circuit breakers rated ________ or less and 1000 volts or less shall have the ampere rating molded, stamped, etched or similarly marked into their handles or escutcheon areas.
100 amperes
Fill in the blank:
In the kitchen of a dwelling unit where a single-phase, 125-volt, 15-or 20-ampere rated receptacle outlet is installed on an island below the work surface, the receptacle outlet shall be located not more than ________ below the island work surface.
12 in.
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In a high school welding shop, a 120/240-volt, single phase feeder is to supply four (4) transformer arc welders each with a 50% duty-cycle. The welders have primary current ratings of 60 amperes, 50 amperes, 40 amperes and 30 amperes. The feeder conductors supplying the welders must have an ampacity of at least ________.
118 amperes
Which conductor insulations is oil resistant?
MTW
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All exposed non-current-carrying metal parts of an information technology system shall ________ or shall be double insulated.
be bonded to the equipment grounding conductor
Determine the MINIMUM number of 15-ampere, 120-volt general lighting branch circuits required for a multifamily condo having a total habitable area of 12,000 square feet where each dwelling unit has cooking facilities provided.
20
Fill in the blank:
Storage batteries used as a source of power for emergency systems shall be of a suitable rating and capacity to supply and maintain the total load for at LEAST________.
1½ hours
When a conduit containing service-entrance conductors runs beneath a building, what is the MINIMUM depth of concrete required to cover the conduit for it to be considered “outside” the building?
2 in.
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The entire area of an aircraft hangar, including any adjacent and communicating areas not suitably cut off from the hangar, shall be classified as a Class I, Division 2 or Zone 2 location up to a level ________ above the floor.
18 in.
Where a 240-volt, single-phase 90 ampere load is located 225 feet from a panelboard and supplied with size 3 THWN copper conductors, what is the approximate voltage drop on this circuit? (K = 12.9)
10 volts
Fill in the blank:
The continuity of the equipment grounding conductor system for portable electrical carnival equipment shall be verified ________.
each time the equipment is connected
Fill in the blank:
Electrical services and feeders for recreational vehicle parks shall be calculated on the basis of not less than ________ per RV site equipped with both 20-ampere and 30-ampere supply facilities.
3600 volt-amperes
In a commercial repair garage service bay, which of the following 125-volt, single-phase receptacles, if any, are required to have GFCI protection?
I. 15-ampere general-purpose receptacles for hand tools and portable lighting equipment.
II. 20-ampere receptacles serving electrical diagnostic equipment only.
both I and II
Fill in the blank:
When sizing time-delay Class CC fuses for motor branch-circuit, short-circuit and ground-fault protection, they are to be sized at the same value as ________.
nontime-delay fuses
Fill in the blank:
The MINIMUM spacing required between the bottom of a 600 volt rated switchboard and the non insulated busbars mounted in the switchboard cabinet is ________.
10 in.
