Code Calculations Part 1
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An individual branch circuit to one load can be what size? PP 5
Branch circuits to more than one load are rated at what amperage?
15, 20, 30, 40, and 50 only.
Lampholders using branch circuits in excess of 20 amp shall be not less than how many watts and of what type? PP 5
660 W heavy-duty type. 210.21a
A 20 amp rated duplex receptacle is to be loaded to 20 amps. And a single 20 amp receptacle is to be loaded to what? PP 6 Tom Henry’s 2011
- A single 20 amp receptacle can only be loaded to 16 A. According to the table to 210.21 B2, which is titles "Receptacle" indicating one and not multiple.
According to section 210.23(A1) the rating of any one cord-and plug-connected utilization equipment, not fastened in place, shall not exceed ______% of the branch circuit rating. Whereas, utilization equipment fastened in place, other than luminares, shall not exceed _______% of the branch circuit rating.
- A. 80/125
According to section 210.23(A2) the total rating of utilization equipment fastened in place shall not exceed _____ % of the branch circuit rating.
What can be used where the ampacity of the conductor does not meet the standard size of the ocpd? PP 10
The next higher size OCPD. 240.4B2
What is the reason for limiting a load to 80%? PP 11
The reason for limiting the load to 80% is not that the conductors can't carry the continous load. The 80% is a current limitation on the over current device to limit the heat that may affect the breaker in the panel.
Are nuetral conductor load calculated at continous?
NO. PP 11 Since the Nuetral conductor has no heating effect on the OCPD
Are line side service conductors calculated as continuos? Why? PP 11
No. Because they are not connected to an OCPD and therefore have no heating effect to the OCPD and do not need to be rated at 80%
Branch circuits for electric heat and 120 gallon or less water heaters are calculated at what?
as continous per 424.3B and 422.13
Table 220.44 is for branch circuits? yes or no? Why?
No. It is for feeders because it is in Article 220: branch circuit, FEEDER, and service calculations and the table gives values at 10kva and over, which would exceed a branch circuit value.
Receptacle are considered a continuos load? T or F?
No. Receptacles are generally not considered a continous load. PP 14 Tom Henry’s 2011
The term Equipment: is a general term including fittings, and devices? used in connection with an electrical installation?
Yes. PP 18
according to section 210.23A1 the rating of any one cord and plug connected utilization equipment shall not exceed what % of the branch circuit rating? consider this as a continuos or non-continuous load to answer the question.
80% for any one cord and plug connnected equipment. This would be the same as continuous rating even though a receptacle is not a continous load.
What loads add heat to the neutral? Please give some examples.
- Non-linear loads. pp 22
- Some examples of nonlinear loads that can generate harmonic currents are computers, fax machines, printers, PLCs, refrigerators, TVs and electronic lighting ballasts. Personal computers constitute nonlinear loads since they incorporate switched-mode power supplies. The PC current is mainly dominated by the third and fifth harmonic components.
- A nonlinear load in a power system is characterized by the introduction of a switching action and consequently current interruptions. This behavior provides current with different components that are multiples of the fundamental frequency of the system. These components are called harmonics. The amplitude and phase angle of a harmonic is dependent on the circuit and on the load it drives. For a fundamental power frequency of 60 Hz, the 2nd harmonic is 120 Hz, the 3rdharmonic is 180 Hz, and so on. The harmonic currents flow toward the power source through the path of least impedance.
Does an optional method exist for calculating feeder loads for a commercial building?
No. PP 270 Code calculations 2008
Are the feeder demand for receptacle loads in a commercial building calculated with the lighting load as they are for a residence?
No, they are not. PP 271 Code Calculations 2008
The code recognizes two methods of calculation. One is the standard method, usually called the _______method, and the other is the optional method, usually referred to as the _________ method.
long, and short. PP 246 Code Calculations 2008
general purpose receptacles in a dwelling unit are included, or not, in the volt a meres per square foot (VA per sq ft) calculation?
They are. PP 247 Code Calculations 2008 and Table 220.12 note
Which is greater, the BCSC (branch circuit selection current) or the RLC (Rated load current)? What type of motor is BCSC usually found on?
The branch circuit selection current is always equal to or greater than the rated load current. This applies to Hermetic refrigerant motor compressors generally. The nameplate usually gives circuit breaker rating. PP 187 Code Calculations 2008
Pertaining to motors, the horsepower rating of the disconnect switch can be the same as the horsepower rating of the motor as long as?
As long as there is no code letter, or the code letter is between A and F, the horsepower rating of the disconnect switch can be the same as the horsepower rating of the motor.
the formula for applying correction factor regarding ambient temperature to Table 310.15B16 to achieve the required minimum ampacity is what?
- Or 20 amps = 16 amps
Tom Henry’s Calculations PP 39, 2011
The ** in table 310.15B16 apply to motor circuits? True or False?
The ** rules for over current protection do not apply to motor circuits per 240.4G, 2011 NEC & Tom Henry’s Code Calculations PP 41, 2011
Motors have overload or thermal protection versus lighting circuits, etc.
required working clearance is 30 inches for 600 volts and less, or the ___________ whichever is greater. NEC 110.26A2 2011
Width of the gear
If the equipment is not marked, what must be remembered regarding derating for temperature and ampacity?
If the equipment is not marked, it is 60 Celsius rated for 100 amps and less. Note: Over 100 amps is 75 Celsius rated
The general rule is 100 amps or less is wire sizes ____________ with ______C ampacity and for over 100 amps the wire size is _________ and larger with _____C.
- 14-1 is 60C
- 1/0 and larger is 75C
A neutral conductor which carries only the unbalanced current from the other conductors, of the same circuit (shall) shall not, be required to be derated per 310.15B3a?
A 3 wire (2 hots and a neutral) in a Wye connected system (shall) shall not be derated?
A neutral conductor which carries only the unbalanced current from the other conductors shall not be derated per 310.15b3a. NEC 310.15b5a, 2011 and Tom Henry’s code calcs PP 55, 2011.
A 3 wire system such as a wye system with 2 hots and a neutral shall be derated
Identified as used in the code in reference to a conductor or it’s terminals means that such a conductor or terminal is to be recognized as?
A grounded conductor 200.1
When soldering conductors flux is used to? Tom Henry’s JW Book PP 5
To keep the surface clean
A motor with a wide speed range is a? AC, synchronous, induction, or DC? Tom Henry’s PP 4
To lubricate a motor sleeve bearing you would use what? Tom Henry’s PP 5
An instrument used to measure electrical energy is called the wattmeter or watt-hour meter? Tom Henry’s PP 5
What is the difference between resistance and reluctance?
Resistance is the Property of a circuit to tend to prevent the flow of current and at the same time causing energy to be converted into heat. Whereas In a DC field, the reluctance is the ratio of the "magnetomotive force” (MMF) in a magnetic circuit to the magnetic flux in this circuit. In a pulsating DC or AC field, the reluctance is the ratio of the amplitude of the "magnetomotive force” (MMF) in a magnetic circuit to the amplitude of the magnetic flux in the circuit.
In a residence the wall switch controlling the ceiling light is usually? Tom Henry’s PP 7
a.Connected across both lines
b.The double pole switch
c.Connected in one line only
d.A four way switch
- a.Connected across both lines
- b.The double pole switch
- c.Connected in one line only
- d.A four way switch
The branch circuit loads specified by the code for lighting and receptacles are considered? 220.14 Tom Henry’s PP 7
A. Minimum loads
B. maximum loads
C. Loads to be served
D. Peak loads
What is the use for a wound rotor? Tom Henry’s Code Calcs, PP 70
- wound rotors are AC motors with slip rings used in speed control applications.
The non-time delay fuse will hold ________ times its rated current for about _______, Dual element (time delay fuses) will hold ______their rating for _______. Tom Henry’s Code Calcs, PP 70
- 5 times for 1/4th of a second
- 5 times for 10 seconds
Will fuses open all ungrounded conductors at the same time? Tom Henry’s Code Calcs, PP 70
no. An example would be a transformer for temp power fed from a 60 amp disconnect opening one leg because the xfmr never derived a neutral. IE; not connected. Causing 240 with the load plugged in, but otherwise appearing normal with a voltage tester.
The commutator of the generator should be cleaned with which of the following?
A. Emery cloth
C. smooth file
D. fine sandpaper
s JW exam book PP 8
- A. Emery cloth
- B. graphite
- C. smooth file
- D. fine sandpaper
Electron is a Greek word for? Tom Henrys JW exam book PP 10
True or false? A large series motor should not be started without some load on it because it will Develop excessive speed and damage itself. Tom Henrys JW exam book PP 11
A wattmeter mesures?
A. AC power only
B. DC reactive power only
C. AC and DC
D. none of these
- A. AC power only
- B. DC reactive power only
- C. AC and DC
- D. none of these
If the needle of the VOM (voltmeter) will no longer align with the zero mark at the lowest range of resistance but will align on the other resistance ranges the probable cause is the? Tom Henrys JW exam book PP 11
supply battery is weak.
A battery that cannot be recharged is a? Tom Henrys JW exam book PP 11
Define inter tier connector: where is this found in the NEC?
- an electrical conductor used to connect two cells on different tiers or shelves of the same rack.
- article 480 storage batteries.
The most common nominal battery cell voltage are what for what type of battery?
- 2 volts per cell for the lead acid systems.
- article 480 nec.
On a drawing: a circle with the B stands for? Tom Henrys JW exam book PP 12
- outlet with blank cover
The meter used to test the armatures and stators of electric motors generators and other equipment for a short circuit is called a? PP 13
- Note: A short in the coil creates a closed circuit that will act like the secondary coil of a transformer, with the growler acting like the primary coil. This will induce an alternating current in the shorted armature that will in turn cause an alternating magnetic field to encircle the shorted armature coil. A flat, broad, flexible piece of metal containing iron is used to detect the magnetic field generated by a shorted armature. A hacksaw blade is commonly used as a feeler. The alternating magnetic field induced by a shorted armature is strong at the surface of the armature, and when the feeler is lightly touched to the iron core of an armature winding, small currents are induced in the feeler that generate a third alternating magnetic field surrounding the feeler.
What type of motor has no commutator? Tom Henrys JW exam book PP 13
- A. Shunt
- B. induction
- C. universal
- D. repulsion
- AC Motor is an adequate answer.
Which of the following has the least number of valence electrons? Tom Henrys JW exam book PP 14
B. semi insulator
D. semi conductor
- A. Insulator
- B. semi insulator
- C. conductor
- D. semi conductor
- Four covalent bonds. Carbon has four valence electrons and here a valence of four. Each hydrogen atom has one valence electron and is univalent.
Feeder conductor size section 430.24; conductors supplying two or more motors shall have an ampacity equal to what? Tom Henry Calculations 2011
Equal to the sum of the full current rating of all of the motors, plus 125% of the highest rated motor in the group.
Article 517 is what?
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