Electrical PE Review - Practice Test
questions well answered
The C phase line current is the sum of the C phase __________________: - correct answer ✔✔
positive (1), negative (2), and zero (0) sequence current components
If IGBTS are used instead of the diodes shown in the circuit above, then the full wave rectified
output voltage waveform will only be present when the _________ of each IGBT is signaled
between 0.926 ms to 7.41 ms for every period of the rectified voltage. - correct answer ✔✔
gate
To simplify the coming integral, let's convert the firing angles of each IGBT from the time
domain of seconds to ____________. Watch your units! 1 millisecond (ms) is equal to 0.001
seconds, or 1 ms = 1X10-3 s. - correct answer ✔✔ degrees.
According to temperature limitations NEC® 110.14(C), conductor temperature ratings must be
selected in order to _________________________. - correct answer ✔✔ "not exceed the
lowest temperature rating of any connected termination, conductor, or device."
If a conductor with a greater temperature rating (for example, 90 C) is being used on equipment
with a lower temperature rating (for example, 75 C), then ampacity of the conductor must be
selected based on the conductor ampacity values at the ___________ temperature rating of the
equipment (75 C), instead of the conductor ampaciy values at the actual higher temperature
rating of the conductor (90 C). - correct answer ✔✔ lower
The FLC of a three-phase, 208V, 60 HP motor according to NEC® Table ___________ is 169A. -
correct answer ✔✔ 430.250
,According NEC® 430.22, conductors for a continuous duty motor must have a minimum
ampacity of _______% of the motor FLC. - correct answer ✔✔ 125%
The four possible answer choices are 90 C rated conductors according to the problem. We need
to check the standard temperature rating of the motor according to the equipment provisions in
the NEC®: ________________ circuits rated for greater than 100A will be rated for 75 C (our
circuit is rated for 211.3A). - correct answer ✔✔ NEC® 110.14(C)(1)(b)(1)
Arc fault circuit interrupters (AFCI) are designed to de-energize the branch circuit either by
tripping the upstream branch circuit breaker or by opening the circuit directly at the receptacle
when__________________. - correct answer ✔✔ a dangerous level of arcing is detected
AFCIs are not intended to de-energize the branch circuit when ___________ of arcing occur due
to everyday use such as the spark that can sometimes be observed in receptacles when
plugging or unplugging equipment, or when operating a standard 120 volt lighting switch. -
correct answer ✔✔ normal levels
The main goal of an AFCI is to prevent _______ that occur due to dangerous levels of arcing that
may ignite nearby flammable material and is mostly required in residential bedrooms as
applicable to code. - correct answer ✔✔ fires
Arc fault circuit interrupters protect residential circuits by de-energizing the branch circuit when
the difference between the current on the hot and neutral conductor is greater than
approximately zero amps. T/F - correct answer ✔✔ This answer is describing a ground fault
circuit interrupter (GFCI) and not an arc fault circuit interrupter (AFCI), This is not the correct
answer. Ground fault circuit interrupters measure the current entering the circuit on the hot
conductor, and leaving the circuit on the neutral conductor. During normal conditions, the
current is equal (I = I) and the difference is zero (I - I= o).
While AFCIS are intended to prevent fires, they will de-energize the circuit during dangerous
levels of arcing conditions,___________________. - correct answer ✔✔ not overload
conditions.
, Transformer inrush current is a sinusoidal component typically present only during transformer
startup that is not seen by the differential protection relay due to being 180 degrees out of
phase. T/F - correct answer ✔✔ Although transformer inrush current is typically only present
during transformer startup it is not 180 degrees out of phase and it is seen by the differential
relay. Answer (A) is false.
Transformer inrush current does not contain a DC component and can potentially cause a
differential protection relay to operate due to CT saturation. T/F - correct answer ✔✔
Transformer inrush current does contain a DC component, and although inrush current can in
some cases lead to CT saturation and nuisance tripping of over current protection relays, it is
not responsible for what may lead to nuisance tripping of differential protection relays. Answer
(B) is false.
Transformer inrush current is linear in both the primary and secondary winding and does not
result in mismatch differential current. T/F - correct answer ✔✔ Transformer inrush current is
not linear and it only occurs in the primary winding, because of this, it can lead to differential
mismatch. Answer (C) is false.
Transformer inrush current occurs in the primary winding only and can potentially cause a
differential protection relay to operate due to mismatch. T/F - correct answer ✔✔ Since
transformer inrush current only occurs in the primary winding, differential mismatch current
occurs due to a larger increase in the transformer's primary CT relay current compared to the
transformer's secondary CT relay current. This can cause nuisance differential tripping to Occur.
A common practice is to use a filter that blocks signals with non-fundamental frequencies from
the relay to prevent inrush current and harmonics from causing a differential relay to trip when
there is no internal fault present. Answer (D) is true.
The positive sequence voltage component (V (1) ) is always _______ during a three-phase fault.
- correct answer ✔✔ zero
The voltage across a short circuit with no impedance is _______! - correct answer ✔✔ zero!
questions well answered
The C phase line current is the sum of the C phase __________________: - correct answer ✔✔
positive (1), negative (2), and zero (0) sequence current components
If IGBTS are used instead of the diodes shown in the circuit above, then the full wave rectified
output voltage waveform will only be present when the _________ of each IGBT is signaled
between 0.926 ms to 7.41 ms for every period of the rectified voltage. - correct answer ✔✔
gate
To simplify the coming integral, let's convert the firing angles of each IGBT from the time
domain of seconds to ____________. Watch your units! 1 millisecond (ms) is equal to 0.001
seconds, or 1 ms = 1X10-3 s. - correct answer ✔✔ degrees.
According to temperature limitations NEC® 110.14(C), conductor temperature ratings must be
selected in order to _________________________. - correct answer ✔✔ "not exceed the
lowest temperature rating of any connected termination, conductor, or device."
If a conductor with a greater temperature rating (for example, 90 C) is being used on equipment
with a lower temperature rating (for example, 75 C), then ampacity of the conductor must be
selected based on the conductor ampacity values at the ___________ temperature rating of the
equipment (75 C), instead of the conductor ampaciy values at the actual higher temperature
rating of the conductor (90 C). - correct answer ✔✔ lower
The FLC of a three-phase, 208V, 60 HP motor according to NEC® Table ___________ is 169A. -
correct answer ✔✔ 430.250
,According NEC® 430.22, conductors for a continuous duty motor must have a minimum
ampacity of _______% of the motor FLC. - correct answer ✔✔ 125%
The four possible answer choices are 90 C rated conductors according to the problem. We need
to check the standard temperature rating of the motor according to the equipment provisions in
the NEC®: ________________ circuits rated for greater than 100A will be rated for 75 C (our
circuit is rated for 211.3A). - correct answer ✔✔ NEC® 110.14(C)(1)(b)(1)
Arc fault circuit interrupters (AFCI) are designed to de-energize the branch circuit either by
tripping the upstream branch circuit breaker or by opening the circuit directly at the receptacle
when__________________. - correct answer ✔✔ a dangerous level of arcing is detected
AFCIs are not intended to de-energize the branch circuit when ___________ of arcing occur due
to everyday use such as the spark that can sometimes be observed in receptacles when
plugging or unplugging equipment, or when operating a standard 120 volt lighting switch. -
correct answer ✔✔ normal levels
The main goal of an AFCI is to prevent _______ that occur due to dangerous levels of arcing that
may ignite nearby flammable material and is mostly required in residential bedrooms as
applicable to code. - correct answer ✔✔ fires
Arc fault circuit interrupters protect residential circuits by de-energizing the branch circuit when
the difference between the current on the hot and neutral conductor is greater than
approximately zero amps. T/F - correct answer ✔✔ This answer is describing a ground fault
circuit interrupter (GFCI) and not an arc fault circuit interrupter (AFCI), This is not the correct
answer. Ground fault circuit interrupters measure the current entering the circuit on the hot
conductor, and leaving the circuit on the neutral conductor. During normal conditions, the
current is equal (I = I) and the difference is zero (I - I= o).
While AFCIS are intended to prevent fires, they will de-energize the circuit during dangerous
levels of arcing conditions,___________________. - correct answer ✔✔ not overload
conditions.
, Transformer inrush current is a sinusoidal component typically present only during transformer
startup that is not seen by the differential protection relay due to being 180 degrees out of
phase. T/F - correct answer ✔✔ Although transformer inrush current is typically only present
during transformer startup it is not 180 degrees out of phase and it is seen by the differential
relay. Answer (A) is false.
Transformer inrush current does not contain a DC component and can potentially cause a
differential protection relay to operate due to CT saturation. T/F - correct answer ✔✔
Transformer inrush current does contain a DC component, and although inrush current can in
some cases lead to CT saturation and nuisance tripping of over current protection relays, it is
not responsible for what may lead to nuisance tripping of differential protection relays. Answer
(B) is false.
Transformer inrush current is linear in both the primary and secondary winding and does not
result in mismatch differential current. T/F - correct answer ✔✔ Transformer inrush current is
not linear and it only occurs in the primary winding, because of this, it can lead to differential
mismatch. Answer (C) is false.
Transformer inrush current occurs in the primary winding only and can potentially cause a
differential protection relay to operate due to mismatch. T/F - correct answer ✔✔ Since
transformer inrush current only occurs in the primary winding, differential mismatch current
occurs due to a larger increase in the transformer's primary CT relay current compared to the
transformer's secondary CT relay current. This can cause nuisance differential tripping to Occur.
A common practice is to use a filter that blocks signals with non-fundamental frequencies from
the relay to prevent inrush current and harmonics from causing a differential relay to trip when
there is no internal fault present. Answer (D) is true.
The positive sequence voltage component (V (1) ) is always _______ during a three-phase fault.
- correct answer ✔✔ zero
The voltage across a short circuit with no impedance is _______! - correct answer ✔✔ zero!
