Unit 1: Pie Circle Formulas Flashcards
Understanding the relationship between power, voltage, current, and resistance using Ohm’s Law and Watt’s Law, applying circular formulas (P=VI, V=IR, etc.) to electrical calculations for the Master Electrician 2020 exam.
Fill in the blank:
Where multiple driven ground rods are installed at a service, they shall be spaced NOT less than ________ apart.
6 feet
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Where a one-family dwelling has a 200 ampere,120/240-volt, single-phase main service panel and is being supplied with size 2/0 AWG THW copper ungrounded (line) service-entrance conductors in rigid metal conduit (RMC), the MINIMUM required size of the bonding jumper for this service-entrance conduit is ________ copper.
4 AWG
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A disconnect switch enclosure installed in a Class II, Division 2, hazardous location in an industrial establishment shall be ________.
dusttight
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The interior of enclosures or raceways installed underground shall be considered to be a ________ location.
wet
Determine the ampacity of four (4) size 1/0 AWG THW copper current-carrying conductors installed in a common raceway with an ambient temperature of 86 degrees F.
120 amperes
Size 1/0 AWG THW ampacity = 150 amperes before adjusting 150 amperes x 80% (adjustment factor) = 120 amperes
Fill in the blank:
The NEC® defines a continuous load to be a load where the maximum current on the circuit is expected to continue for at LEAST ________ hours or more.
three
Determine the MINIMUM size THW copper branch-circuit conductors the NEC® requires to supply a 3-phase, continuous-duty, ac motor that draws 70 amperes per phase. Consider all terminations are rated for 75 deg. C.
3 AWG
Given: You have determined a conductor has a computed ampacity of 75 amperes. What is the MAXIMUM standard ampere rating of the overcurrent protection device the NEC® permits to protect this circuit here this is not a motor circuit or part of a multioutlet branch circuit supplying more than one receptacle?
80 amperes
FLC of motor = 70 amperes x 125% = 87.5 amperes
Size 3 AWG THW with an ampacity of 100 amperes should be selected.
Fill in the blank:
A 208-volt, 3-phase, 50 hp, squirrel-cage, continuous-duty, ac motor has a full-load running current rating of ________.
143 amperes
What is the MAXIMUM distance that a disconnect switch is permitted to be located from the operator’s station for a portable carnival ride?
6 feet
Determine the MINIMUM trade size electrical metallic tubing (EMT) required to enclose eight (8) size 6 AWG copper conductors with THHW insulation, when installed in a 50-foot conduit run.
1 1⁄4 in.
Fill in the blank:
Where exceptions are not applicable, when a feeder supplies a continuous load of 240 amperes, the overcurrent protection device protecting this feeder circuit shall have a rating of at LEAST ________.
300 amperes
240 amperes x 125% = 300 amperes
Fill in the blank:
Liquidtight flexible metal conduit (LFMC) shall be securely fastened in place WITHIN ________ of each box or other conduit termination.
12 inches
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When a pull box or junction box contains conductors of size 4 AWG and larger and a straight pull of the conductors is to be made, the length of the box shall NOT be less than ________ times the trade diameter of the largest conduit entering the pull box or junction box.
eight
Fill in the blank:
Conduit nipples not over 24 inches long may be filled to a MAXIMUM of ________ of their cross sectional area.
60 percent
Determine the MAXIMUM number of size 14 AWG THHN conductors permitted to be installed in a trade size 3/8 in. flexible metal conduit (FMC) that contains a bare size 14 AWG grounding conductor, when the FMC has external fittings.
four
Fill in the blank:
According to the NEC®, conductors supplying wet-niche underwater pool luminaires must be enclosed in ________.
schedule 40 rigid polyvinyl chloride conduit (PVC)
Fill in the blank:
Underground wiring is not permitted under a permanently installed swimming pool or within ________ of the pool, unless the wiring is supplying the associated pool equipment.
5 feet
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The NEC® does NOT permit ________ batteries as a source of power for emergency systems.
automative
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In new installations, the MINIMUM clear working space the NEC® requires between a 480Y/277- volt, switchboard and a 480-volt motor control center when facing each other is ________.
4 feet
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In the guest rooms of hotels, motels, and sleeping rooms of dormitory units a MINIMUM of ________ 125-volt, 15- or 20-ampere, general purpose receptacles installed in the room is/are required to be readily accessible.
two
Fill in the blank:
When branch circuit conductors are installed inside a ballast enclosure of a luminaire and are within three (3) inches of the ballast, the conductors shall have a temperature rating NOT lower than ________, unless supplying a luminaire marked as suitable for a different insulation temperature.
90 deg C
Fill in the blank:
When size 4 AWG or larger conductors enter a panelboard, ________ must be provided.
an identified bushing or threaded hub
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Class ________ locations are those that are hazardous because of the presence of easily ignitable fibers or where materials producing combustible flyings are handled, but in which such fibers/flyings are not likely to be in suspension in the air in quantities sufficient to produce ignitible mixtures.
III
