Session 9
When calculating the multiplier for transformer available fault current, the transformer impedance (%Z) is multiplied by ? to determine the worst-case condition to achieve the highest available fault current.
0.9
The point-to-point method has equations to calculate the available fault current ? . I. at the end of a run of conductor or busway II. at the secondary of a transformer, assuming infinite primary available fault current (this is a conservative calculation) III. at the secondary of a transformer with primary available fault current known
1,2,3
___ is built or torn down with every personal interaction.
Credibility
? is the undesired coupling of signal energy from a transmitting pair into a receiving pair.
Near-end crosstalk
Various methods have been developed to calculate the available fault current. All are based on ? .
Ohms law
Field leaders who do not respect ___ cannot expect to receive respect in return.
Others
People perceive ___ based on what they have heard, seen, or experienced.
Others
? current is an excessive current relative to normal operating current, and one that is confined to the normal conductive path provided by the conductors, circuit components, and loads of the distribution system.
Overload
? is the undesired coupling of signal energy from a number of simultaneously transmitting pairs into a receiving pair, measured at the opposite end of the cable from where the transmitter is located.
PSACRF
? is the undesired coupling of signal energy from a number of simultaneously-transmitting pairs into a receiving pair.
PSNEXT
? cables have a foil shield for each pair to virtually eliminate internal crosstalk, and usually include an overall foil or screen to provide additional EMI immunity.
Pairs in metal foil (PIMF)
___ requires being courteous, honest, and responsible when dealing with individuals or companies.
Professionalism
Which of the following is not a critical point where short-circuit calculations should be completed in a system?
Push button device on 120V control circuit
? is a measurement of the amount of signal energy that is reflected back to a transmitter as it travels down a twisted pair, encountering impedance discontinuities.
Return loss
? is a cable with one or more pairs of twisted copper conductors covered with an overall metallic screen or braid over the group of four pairs to provide AXT and EMI shielding.
Screened twisted pair (Sc/UTP)
For a low voltage distribution system, the available fault current is typically the highest at the ? .
Service point
The professional attitude of an effective field leader influences the attitude of the crew, which ___.
increases morale and productivity
Field leaders are responsible for making ___ decisions regarding safety, efficiency, and production on the job.
informed
Effective apprentices build professional working relationships based on ___.
mutual respect
Effective field leaders put personal wants and needs aside and build positive working relationships based on ___.
mutual respect
The ? is the approximate speed at which a signal moves through a cable. Calibration of this is crucial to obtaining accurate length measurements.
nominal velocity of propagation
The first step to determine the fault current at any point in the system is to draw a(n) ? showing all the sources of the available fault current.
one-line diagram
An overcurrent is either a(n) ? current or a ? current.
overload / fault
Because each of the pairs in a twisted pair cable has a different twist length, the degree of ? is reduced.
pair-to-pair capacitive coupling
A ? consists of up to 90 meters of horizontal cabling, a connection at each end, up to two meters of test equipment cord from the main unit of the field tester to the local connection, and up to two meters of test equipment cord from the remote connection to the remote unit of the field tester.
permanent link
Apprentices interact with many different people each day and need to maintain a(n) ___ attitude during every interaction.
professional
Contractors count on field leaders to set an example by behaving in a(n) ___ and respectful manner.
professional
Field leaders interact with many different people each day and must maintain a(n) ___ attitude during each personal interaction.
professional
In a competitive marketplace where multiple companies provide the same services for around the same prices, the level of ___ exhibited can tip the scale.
professionalism
Field leaders have an enormous amount of ___.
responsibility
If a field leader skirts the ___ that comes with the position, it speaks to a lack of character that will not be respected on the jobsite.
responsibility
Performing any job-site task, including undesirable tasks, demonstrates ___.
responsibility
Professionalism requires being courteous, honest, and ___.
responsible
Effective apprentices ___, regardless of the task assigned.
take pride in their work
When a pair of wires is twisted, each of the wires will have nearly identical electrical characteristics with respect to ground. This results in almost no difference in the levels of induced noise voltage between the two wires.
true
Effective field leaders do not let obstacles stand in the way of ___.
what is right
The performance requirements for Category 5 cables, connectors, basic links, and channels are specified at frequencies up to ? .
100 MHz
The performance requirements for Category 5e cables, connectors, basic links, and channels are specified at frequencies up to ? .
100 MHz
Per NEC ? , the overcurrent protective devices, the total impedance, the component short-circuit current ratings, and other characteristics of the circuit to be protected shall be selected and coordinated to permit the circuit protective devices to clear a fault without extensive damage to the electrical components of the circuit.
110.10
The performance requirements for Category 3 cables, connectors, basic links, and channels are specified at frequencies up to ? .
16 MHz
The performance requirements for Category 6 cables, connectors, basic links, and channels are specified at frequencies up to ? .
250 MHz
The performance testing requirements for Category 6e cables, connectors, basic links, and channels are specified at frequencies up to ? .
250 MHz
The motor fault current contribution, if significant, may be determined and added to all fault locations throughout the system. A practical estimate of the motor fault current contribution can be made by multiplying the total motor load current by ? . A good general rule is to calculate the total motor load current, multiply by ? , and add the result to available short-circuit current calculated without motor contribution.
4 or 6 / 4
The performance requirements for Category 6A cables, connectors, basic links, and channels are specified at frequencies up to ? .
500 MHz
The performance requirements for Class FA cables, connectors, basic links, and channels are specified at frequencies between ? .
600 and 1,000 MHz
? is the ratio of the power of the signal received over the power of the NEXT from the local transmitter.
ACR
? is the undesired coupling of signal energy from a transmitting pair into a receiving pair, measured at the opposite end of the cable from where the transmitter is located.
ACRF
Which of the following are reasons why short-circuit studies involve calculating a bolted 3-phase fault condition? Three phases bolted together create a near-zero impedance connection. A "worst-case" (highest current) condition that results in maximum 3-phase thermal and mechanical stress in the system is established. A "worst-case" condition is typically what is needed to ensure proper equipment ratings, such as OCPD interrupting rating and equipment short-circuit current ratings (SCCR).
All of the above
Which of the following is/are a major source(s) of fault current contribution? On-site generators Electric heating loads Utility source
Both A and C
A field leader who lacks the ___ to do the right thing for a customer or a crew will struggle to succeed.
Character
The responsibility of keeping the job site clean and safe falls on the shoulders of the ___.
entire crew
The success of an effective field leader is determined by how project setbacks and ___ encounters with people are handled.
Daily
An effective field leader ___ the respect of the crew, other field leaders, and members of the construction management team.
Earns
For a given twisted pair cable, as frequency increases, attenuation decreases.
False
Given the available fault current at the source end of a conductor run, the available fault current at the end of a circuit conductor run is not affected by the conductor's size or length.
False
The available fault current can be determined or estimated just by considering the ampere rating of an electrical panel. For instance, all 800-ampere distribution panelboards in a facility will have the same available fault current of 15,000 amperes at their line terminals.
False
Various methods have been developed to calculate the available fault current, but only the point-to-point method is based on Ohm's Law.
False
? uses a thin metallic foil as opposed to a braid.
Foil twisted pair (F/UTP)
A utility replaces an existing 300-kVA transformer with a transformer having either a higher kVA or lower impedance. The available fault current on the secondary of the new transformer will be ? the available fault current of the transformer being replaced.
Higher than
? is a measure of how much a signal is reduced in amplitude or strength as it is carried over a twisted pair or fiber optic strand.
Insertion loss (attenuation)
Which of the following is not a reason why short-circuit calculations are necessary for electrical systems?
They are needed to determine the standard ampere rating of the OCPD.
An arcing fault condition does not have a solid (bolted) connection between conductors or buses at the point of the fault. Instead, an arcing current path is through the air between conductive parts with an associated arc resistance.
True
Category 8 cabling is defined up to 2,000 megahertz but only up to 30 meters (98 feet).
True
For a given twisted pair cable, as frequency increases, crosstalk problems increase.
True
Short-circuit calculations are performed without overcurrent protective devices in the system. Calculations are done as though these devices are replaced with copper bars to determine the available fault current.
True
The magnitude of fault current available at a specific location depends on two key factors:1. The magnitude of fault current that the electrical energy source(s) can deliver2. The impedance of transformers, conductors, and busways from the source(s) to the point of the fault
True
To comply with 110.9 of the NEC, the overcurrent protective device selected must have an interrupting rating equal to or greater than the available fault current.
True
When a short-circuit condition occurs, running motors may contribute four to six times their normal full load into the fault, adding to the magnitude of the available fault current.
True
When doing an arc-flash incident energy hazard analysis, the available bolted fault current is necessary for determining the hazard. It is recommended that the calculation be as accurate as possible.
True
Arcing faults typically produce predictable, smooth oscillograph current curves; that is, smooth sine waves, some being asymmetrical and some symmetrical. However, bolted faults tend to be dynamic with variability in the flow of current, resulting in erratic, unpredictable current flow.
false
? current is a current that flows outside the normal conducting path.
fault
The total opposition to alternating current flow of a twisted pair is called the ? .
impedance
Apprentices should set the example for ___.
all of the above
A ? consists of up to 90 meters of horizontal cable, a work area equipment cord, a telecommunications outlet, an optional consolidation connection close to the work area, and two cross-connect connections in the telecommunications room.
channel
A person of ___ does the right thing, even when no one is watching.
character
Credibility is a combination of competence and ___.
character
Credible leaders make difficult decisions on a daily basis, even when the options are not always ___.
clear
The success of an apprentice is determined by how ___ is (are) handled.
criticism
Parameters used for defining the performance of cables and components are specified using the ? as a unit of measurement.
decibel
Effective field leaders take the time to reference all pertinent information when making project ___.
decisions
In general, the fault current ? as the distance from an electrical source ? due to the increased impedance added by circuit components, such as conductors.
decreases / increases
