Electrical & Electronic Systems Flashcards
7 cards from real ITMC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Electrical & Electronic Systems flashcards as text
Which grounding method is required for equipment in a classified (hazardous) location to prevent static discharge ignition?
Answer: Bonding and grounding to a common reference point
Bonding and grounding equalizes potential between conductive parts, eliminating the voltage difference that causes static sparks capable of igniting flammable atmospheres.
A limit switch is wired in series with a motor starter coil as a safety interlock. The motor won't start even though the limit switch is in the correct position. Using a voltmeter, you read 120V across the closed limit switch. This indicates:
Answer: The limit switch contacts are open (faulty)
Voltage measured across a closed switch in a series circuit indicates the switch contacts are actually open; a properly closed switch has near-zero voltage drop across it.
What is the purpose of a neutral grounding resistor (NGR) in an industrial medium-voltage power system?
Answer: Limit ground fault current to protect equipment and personnel
An NGR limits ground fault current to a safe level (typically 1–10A), preventing equipment damage and giving personnel time to identify and clear the fault.
When replacing an encoder on a servo motor, which specification is most critical to match to the original?
Answer: Pulses per revolution (PPR) and output signal type
The servo drive uses encoder PPR for position and velocity feedback; a mismatch in PPR or signal type (HTL vs. TTL vs. SIN/COS) will cause control errors or drive faults.
A technician measures 277V between a phase conductor and ground in a 480/277V wye system. This reading is:
Answer: Normal — it is the phase-to-neutral voltage of the system
In a 480/277V wye system, 480V is line-to-line and 277V is the normal phase-to-neutral (phase-to-ground) voltage.
What does a sustained low DC bus voltage alarm on a VFD most commonly indicate?
Answer: Low incoming AC supply voltage or a blown input fuse
The DC bus is charged by rectifying AC input; low AC voltage or a failed input fuse/diode will cause the DC bus voltage to drop below normal levels.
In a ladder logic diagram, what is the function of a normally closed (NC) contact instruction versus a normally open (NO) contact instruction?
Answer: NO passes power when its referenced bit is 1 (true); NC passes power when its bit is 0 (false)
A NO contact instruction allows power flow when the referenced tag is true (1); an NC contact allows power flow when the tag is false (0), providing inverted logic.