codeintro Final study Guide
If a sine wave has a period of 10 ms, what is the frequency?
100kHz (1/.000100)
If the primary has 250 turns and the secondary has 1000, what is the turns ratio?
1:4 (1000/250)
What size conductor is required if an ampacity is 80A?
3AWG (NEC 310.16 pg 187)
Why use parallel circuits?
A Parallel circuit is one with several different paths for the electricity to travel. More paths
Define ground fault.
A ground fault is an inadvertent contact between an energized conductor and ground or a grounded equipment frame or box.
What is the purpose of grounding?
Protects people and equipment from electric shock, lightning strikes and electrical noise. SAFETY!
If three resistors of 1.7 k ohms, 3.3 k ohms, and 14.4 k ohms are connected in series with one another across a 24 V source as shown in figure 7-39, calculate: A: Total resistance (RT) B: Total current (IT) C: Individual voltage drops D: Individual and total power dissipated.
A. RT= 19.4kΩ ( 1.7k + 3.3k + 14.4k) B. IT = 1.24mA or 0.00124 (I=E/R, 24v/19400Ω) C. VR1= 2.11v ( 0.00124 X 1700Ω ) VR2 = 4.1v ( 0.00124 X 3300Ω ) VR3 = 17.9v ( 0.00124 X 14400Ω ) Pr1 = 2.6mW ( IT x VR1 ) Pr2 = 5.1mW ( IT x VR2 ) Pr3 = 17.4mW ( IT x VR3 )
When one resistor in a series string is shorted, explain what would happen to the circuit's: A: Current B: Resistance C: Voltage across the shorted component D: Voltage across the other components
A: Goes up B: Goes down C: Zero (0) D: Goes up
When one resistor in a series string is open, explain what would happen to the circuit's: A: Current B: Resistance C: Voltage across the open component D: Voltage across the other components
A: I=0 B: E/I=E/0=∞ C: Is the sum of the source voltage. No current (I) in an open circuit, Voltage across an open = Vs D: Zero (0)
What is the advantage of AC over DC?
AC is less expensive and easy to generate than DC
Define Multiwire branch circuit.
According to NEC Article 100, a multiwire branch circuit consists of two or more ungrounded conductors that have a voltage between them and share a neutral.
What is the unit for Current?
Amps ( I )
What does AHJ stand for?
Authority Having Jurisdiction
NEC Article 358
Electrical Metallic Tubing: Type EMT
NEC Article 110.14 (c) (1)
Equipment Rated for 100 A or Less and Tempatures
What is the unit for Frequency?
Hertz (Hz)
NEC Article 210.5
Identification for Branch Circuits
NEC Article 210.4
Multiwire Branch Circuits
If three bulbs are connected across a 9 V battery in series, and the filament in one of the bulbs burned out, causing an open in the bulb, would the other lamps be on? Explain why.
No, No current in an open circuit.
NEC Article 334
Nonmetallic-sheathed cable
What is the unit for Resistance?
Ohms (Ω)
What is an overcurrent protection device? Give some examples.
Overcurrent protection devices include circuit breakers and fuses. Overcurrent protection devices are meant to protect against the potentially dangerous effects of overcurrents, such as an overload current or a short-circuit current, which creates a fault current.
NEC Article 240.4
Protection of Conductors
3.9V R1 25Ω, R2 73Ω, R3 33Ω in a parallel circuit. calculate: A: Total resistance B: Voltage drop across R2 C: Voltage drop across R3
R1 1/25 = .04a R2 1/73 = .0136a R3 1/33 = .030a RT = 1/.0836a= 11.96Ω Volt Drop: V=RxI VR2= R2 .0136a x 25Ω= .34v VR3= R3 .030a x 33Ω= .99v
What are the identifications for ungrounded, grounded and grounding conductors?
Section 250.119 describes the ways an equipment grounding conductor must be identified. Equipment grounding conductors can be bare, covered or insulated. Individually covered or insulated equipment grounding conductors must have a continuous outer finish that is either green, or green with one or more yellow stripes except as permitted elsewhere in section 250.119.
Using a voltmeter, how would a short be recognized in a series circuit?
Short circuit cuts out resistance ( 1 or more resisters ) and volts add up across circuit.
What are the rules or requirements for branch circuits?
The general requirements for a multiwire branch circuit provides the permission for a multiwire branch-circuit as well as permission for it to be considered as multiple circuits. This section requires that all conductors of a multiwire branch circuit originate from the equipment containing the branch-circuit overcurrent protective device(s). the only exception to this is for those that are permitted by 300.3(B)(4).
Define equipment rating.
The maximum and minimum voltage, current, frequency, real and reactive power flows on individual equipment under steady state, short-circuit and transient conditions, as permitted or assigned by the equipment owner.
What is the purpose of the circuit breaker?
To protect an electrical circuit from damage caused by overcurrent/overload or short circuit. Protects Conductors.
NEC Article 330
Type MC cable (Metal-Clad Cable)
What is the unit for Voltage?
Volt ( V or E )
Calculate VP of a 50 V rms ac supply.
Vp = 70.72 (50/0.707) Vrms / 0.707 = Vp
Calculate V rms of a 30 V peak sine wave.
Vrms = 21.21 (30x0.707) Vp x 0.707
What is the unit for Power?
Watts (W)
If one of three parallel-connected bulbs is open, will the other two bulbs be on? Explain why.
Yes, the burnout or removal of one bulb does not affect the other bulbs in parallel circuits. Multi branch circuit.
If one of three series-connected bulbs is shorted, will the other two bulbs be on? Explain why.
Yes, the path is still complete.
Describe the difference between a series and a parallel circuit.
he main difference between series and parallel circuits is that in a series circuit, the same current flows in each component of the circuit. In a parallel circuit, the components all have the same voltage drop across them.
NEC Article 90
introduction
What are the OCPD requirements for #14 AWG, #12 AWG, and #10 AWG wire?
the maximum OCPD for 14 AWG copper is 15A, but for 12 AWG copper it's 20A. If that 12 AWG conductor were aluminum or copper clad aluminum, its OCPD would be limited to 15A. But replace that 12 AWG copper conductor with a slightly more expensive 10 AWG conductor and you can run a 30A circuit
