Unit 7: AC Motor Calculations Flashcards
Learn to solve motor circuit calculations, analyze motor protection requirements, and apply NEC 2023 rules to different motor loads.
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As a general rule, for an ac electrical system operating at less than 1000 volts, a main bonding jumper shall connect the grounded conductor(s) to _________.
each service disconnecting means enclosure
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Every circuit breaker having an interrupting rating other than _________ shall have its interrupting rating shown on the circuit breaker.
5,000 amperes
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Electrically operated residential in-sink kitchen waste disposers shall be permitted to be cord-and-plug connected however, the flexible cord is to be not less than 18 inches in length and not over _________ in length.
36 in.
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Excluding neon signs, branch circuits that supply all other electric signs and outline lighting systems shall be rated not to exceed _________.
20 amperes
When considering the support distance for rigid metal conduit (RMC), incompliance with the rules established by the NEC®, what is the maximum horizontal unsupported length permitted of a trade size 2 in. RMC raceway?
16 feet
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Generally, receptacle outlets provided for the small appliance countertop or work surface circuits in the kitchen of a dwelling shall be located above the countertop or work surface, but not more than _________ above the countertop or work surface.
20 in.
20 ft. x 30 ft. = 600 sq. ft. per office x 1.3 VA = 780 VA
780 VA x 4 offices = 3,120 VA demand load
What is the general lighting demand load, in VA, on the ungrounded(phase) service entrance conductors, of an office building consisting of four(4)offices each having a floor space of 20 feet by 30 feet?
3,120 VA
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For electrical systems of 1,000 volts or less, overhead spans of open individual conductors up to 50 feet in length and not supported by a messenger wire, shall be at least size _________ copper.
10 AWG
Under what condition is an unbroken length of rigid metal conduit (RMC) or intermediate metal conduit (IMC) permitted to support a luminaire in a billboard sign instead of a box?
When the luminaire is at least 8 feet above grade or standing area when accessible to unqualified persons.
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Isolated ground receptacles that incorporate an isolating grounding conductor connection intended for the reduction of electrical noise or electromagnetic interference, shall be clearly identified by a/an _________located on the front or face of the receptacle.
orange triangle
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A mobile home that is factory-equipped with gas or oil-fired central heating equipment and cooking appliances may be provided with a listed mobile home power-supply cord rated not less than _________.
40 amperes
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The sum of the cross-sectional areas of all contained conductors at any cross-section of a non metallic wireway shall not exceed _________ of the interior cross-sectional area of the wireway.
20%
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The disconnecting means for motors and their controllers shall open _________ conductors of the circuit.
simultaneously all ungrounded phase
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Where the wiring method used includes a run of less than 6 ft. of tradesize 1 in. listed liquidtight flexible metal conduit (LFMC), the circuit conductors contained in the LFMC must be protected by overcurrent devices rated not more than _________ in order for the LFMC to be an approved type of equipment grounding conductor.
60 amperes
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According to the NEC®, a general-use, 125-volt, 15-ampere rated receptacle located in a hallway of a dwelling unit is required to be _________.
listed tamper-resistant
Under which condition or location is Type NM cable not permitted for use?
in a wet or damp location
According to the NEC®, which minimum enclosure type letter would be required where the installation is a motor controller located outdoors, in an area that is subject to heavy rain, snow and sleet?
Type 3
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Given: A commercial building provided with a 208Y/120-volt, 3-phase,electrical system has a calculated demand load of 72,200 VA; the ungrounded (phase) service entrance conductors must have an ampacity of at least _________.
200 amperes
I = 7,200 VA/208 x 1.732 = 7,200/360 = 200 amperes
Fill in the blank:
As explained in the NEC®, each motor controller shall be _________.
capable of starting and stopping the motor it controls and be capable of
interrupting the locked-rotor current of the motor
What is the minimum of 20-ampere, 120-volt, general lighting branch circuits required for a dwelling unit having a lighting load of 9,600 VA?
four
120 volts x 20 amperes = 2,400 VA (one circuit)
9,600 VA (load)/2,400 VA (ckt.) = 4 – 20-amp, 120-volt circuits
Fill in the blank:
Where a sub-panel is fed with CU Type NM cable and the circuit is protected by a 60-ampere overcurrent protective device, in compliance with the NEC®, the equipment grounding conductor should be at least size _________.
10 AWG
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A service disconnect may be installed in all of the following locations,except _________.
a bathroom
Where a sign in a public parking lot is fed with 100 ampere, 120/240-volt, single phase conductors installed in a rigid metal conduit (RMC), what is the minimum required burial depth of the conduit?
24 in.
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Where all of the multiconductor cables are smaller than 4/0 AWG, the sum of the cross-sectional areas of all cables shall not exceed _________ when installed in a 9-inch wide ladder-type cable tray.
10.5 sq. in.
