Unit 7: AC Motor Calculations Flashcards
Analyze motor load equations, apply NEC rules for motors, and evaluate motor circuit configurations.
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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 ________.
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), in compliance with the rules established by the NEC®, what is the MAXIMUM horizontal unsupported length permitted of a trade size 2in. 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.
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
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
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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
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An unbroken length of rigid metal conduit (RMC) or intermediate metal conduit (IMC) is permitted to support a luminaire in a billboard sign in lieu of a box where the luminaire is at least ________ when accessible to unqualified persons.
8 feet above grade or standing area
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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 a feeder system includes a short run of trade size 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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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 conditions or locations 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 per the NEC®, the definition of a motor controller is ________.
a device to stop or start a motor by making or breaking the current
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 circuits
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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 ________.
an exit foyer
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.
