NETA Switchgear and Busway Inspection 3 — Questions and Answers
Question 1: In NETA terminology, what does the term 'metal-enclosed switchgear' distinguish from 'metal-clad switchgear'?
- Metal-enclosed uses draw-out breakers while metal-clad uses fixed breakers
- Metal-clad has grounded metal barriers between compartments while metal-enclosed does not (Correct answer)
- Metal-enclosed is rated above 35 kV while metal-clad is rated below
- Metal-clad uses oil insulation while metal-enclosed uses air insulation
Correct answer: Metal-clad has grounded metal barriers between compartments while metal-enclosed does not
Metal-clad switchgear requires grounded metal barriers between all primary circuit compartments; metal-enclosed switchgear does not have this requirement.
Question 2: During busway inspection, which test method is best suited to locate a section with degraded phase-to-ground insulation without de-energizing the entire run?
- Megohmmeter test
- Infrared thermography
- Ultrasonic partial discharge detection (Correct answer)
- Hi-pot dielectric withstand test
Correct answer: Ultrasonic partial discharge detection
Ultrasonic partial discharge detection can locate degraded insulation on energized busway by detecting the acoustic signature of partial discharge activity.
Question 3: What ANSI/IEEE standard governs the testing of metal-clad switchgear and is referenced in NETA acceptance testing specifications?
- ANSI/IEEE C37.20.2 (Correct answer)
- ANSI/IEEE C57.12
- ANSI/IEEE 519
- ANSI/IEEE 1584
Correct answer: ANSI/IEEE C37.20.2
ANSI/IEEE C37.20.2 is the standard for metal-clad switchgear and is the primary reference for acceptance testing requirements cited by NETA.
Question 4: A switchgear cubicle's primary disconnect stabs show pitting and arcing marks. What does this most likely indicate?
- Normal wear from routine racking operations
- The breaker was racked under load (closed position) (Correct answer)
- Inadequate lubrication of the racking mechanism
- Loose grounding of the cubicle frame
Correct answer: The breaker was racked under load (closed position)
Pitting and arcing marks on disconnect stabs indicate the breaker was inserted or withdrawn while closed (energized), which is prohibited.
Question 5: When measuring insulation resistance of switchgear bus with a megohmmeter, what minimum test voltage is typically specified by NETA for equipment rated 1 kV to 5 kV?
- 250 V DC
- 500 V DC
- 1000 V DC
- 2500 V DC (Correct answer)
Correct answer: 2500 V DC
NETA specifies 2500 V DC for megohmmeter testing of insulation on equipment rated 1 kV to 5 kV.
Question 6: What is the primary purpose of the interlocking mechanism on draw-out switchgear?
- To prevent the breaker from being racked to the connected position unless it is in the open (tripped) state (Correct answer)
- To lock the compartment door when the bus is energized
- To prevent two breakers from closing simultaneously on the same bus section
- To ensure the breaker cannot be racked out without releasing the racking handle safety latch
Correct answer: To prevent the breaker from being racked to the connected position unless it is in the open (tripped) state
The primary interlock prevents the circuit breaker from being moved to or from the connected position while it is in the closed (ON) state, preventing arcing on the stabs.
Question 7: During a feeder busway inspection, you discover that a section's housing has a significant dent that partially deforms the enclosure inward. What is the primary concern?
- Increased thermal resistance reducing ampacity
- Reduced clearance between the enclosure and energized conductors creating an arc flash risk (Correct answer)
- Increased audible noise from magnetostriction
- Reduced IP rating of the enclosure
Correct answer: Reduced clearance between the enclosure and energized conductors creating an arc flash risk
A deformed enclosure can reduce the air clearance between the housing and energized bus bars, creating a risk of flashover or arc flash to ground.
NETA Switchgear and Busway Inspection 3
In NETA terminology, what does the term 'metal-enclosed switchgear' distinguish from 'metal-clad switchgear'?