Free EVT FA4 practice test: Fire Apparatus Advanced Electrical Systems

Free EVT FA4 practice test: 10 questions

Questions from our FA4 bank, written to EVTCC's learning objectives and the 2024 NFPA 1900 and 1910. Tap an answer to see if you're right and why, or switch to Timed for the real test's pace. Every answer is below each question.

1. With the ignition key off, a technician measures resistance across the J1939 CAN-High and CAN-Low backbone conductors. A properly terminated bus should read approximately:

   A60 ohms B120 ohms C0 ohms DInfinite (open)
   Show answer

   Answer: A. 60 ohms

   A J1939 backbone is terminated by a 120-ohm resistor at each end, and the two in parallel measure about 60 ohms across CAN-H and CAN-L. A reading near 120 ohms suggests one terminator is missing or open.

   • B: 120 ohms indicates only one terminator is present, the other open.
   • C: 0 ohms indicates a short between the two conductors.
   • D: An open reading indicates a broken backbone or both terminators missing.

2. A J1939 bus that normally reads about 60 ohms is measured key-off at roughly 120 ohms. This most directly indicates:

   AOne 120-ohm terminating resistor is open or disconnected BBoth terminating resistors are shorted together CThe bus is terminated normally at both ends DOne module is drawing excessive current on the bus
   Show answer

   Answer: A. One 120-ohm terminating resistor is open or disconnected

   Two parallel 120-ohm terminators give 60 ohms, so losing one leaves a single 120-ohm resistor in the circuit. The remaining reading of about 120 ohms points to one open or missing terminator.

   • B: Shorting the terminators would read far below 60 ohms, not 120.
   • C: Normal termination reads about 60 ohms, not the 120 measured.
   • D: A key-off resistance reading says nothing about current draw.

3. The J1939 data-bus conductors are twisted together as a pair primarily to:

   ACancel electromagnetic interference so the differential signal stays reliable BIncrease the current-carrying capacity of the two conductors CProvide each connected module with its ground path through the pair DSlow the data rate down so that fewer transmission errors occur
   Show answer

   Answer: A. Cancel electromagnetic interference so the differential signal stays reliable

   Twisting the CAN-H and CAN-L wires makes them pick up noise equally so it cancels in the differential receiver. This preserves signal integrity in the electrically noisy apparatus environment.

   • B: Twisting two wires together does not change how much current they carry.
   • C: The pair carries the signal; module grounds are separate conductors.
   • D: The data rate is set by the network, not by how the wires are twisted.

4. An apparatus load manager responds to a falling system voltage during a long incident by:

   AShedding preset low-priority loads first to protect critical systems BRaising engine speed to redline for the rest of the incident CDisconnecting the batteries from the alternator output DEnergizing every electrical load to test system capacity
   Show answer

   Answer: A. Shedding preset low-priority loads first to protect critical systems

   A load manager monitors system voltage and, as it drops, sheds predetermined low-priority loads such as scene or compartment lighting to preserve voltage for critical warning systems. This is a core electrical-management function on modern apparatus.

   • B: A load manager sheds loads; it does not command a redline engine speed.
   • C: It manages loads and never disconnects the charging source.
   • D: Switching on more load would pull the falling voltage down further.

5. A load sequencer is used at engine start-up mainly to:

   AEnergize electrical loads in timed stages to limit inrush and voltage sag BShed all electrical loads permanently once cranking is finished CBoost the alternator's output above its rated capacity at start-up DBypass the ignition switch so the loads can energize without it
   Show answer

   Answer: A. Energize electrical loads in timed stages to limit inrush and voltage sag

   Sequencing turns loads on in steps rather than all at once, reducing the momentary current inrush and voltage dip that would occur if every device energized simultaneously. This eases demand on the charging system right after start.

   • B: A sequencer brings loads on in stages; it does not shed them for good.
   • C: No controller can make an alternator exceed its rated output.
   • D: A sequencer times loads on and has no role in ignition switching.

6. On most apparatus, the high-idle (fast-idle) feature will engage only when:

   AThe parking brake is set and the transmission is in neutral BThe vehicle is moving at a road speed above 20 mph CA compartment door is open with the engine running DThe aerial is raised and fully extended from the bed
   Show answer

   Answer: A. The parking brake is set and the transmission is in neutral

   High idle is interlocked to safe stationary conditions, typically parking brake applied and transmission in neutral, so engine speed cannot be raised while the truck could move. These interlocks prevent unintended movement.

   • B: High idle is blocked while the vehicle can move, not enabled by it.
   • C: An open compartment door is not part of the high-idle interlock.
   • D: Aerial position has no part in enabling high idle.

7. NFPA requires a power-operated light mast to have an automatic means that:

   ARemoves electrical power from the mast and its wiring when stowed BShuts off the cab hazard warning light once the mast is fully raised CTurns the mast lights on whenever the parking brake is released DPrevents the mast from being lowered while its lights are on
   Show answer

   Answer: A. Removes electrical power from the mast and its wiring when stowed

   NFPA 1901 (2016, now NFPA 1900) 22.14.2.8 requires an automatic de-energizing means so no electrical power reaches the mast or its light wiring while the mast is stowed. The same section requires the cab hazard warning light to stay lit whenever the mast is not stowed, and a secondary means of emergency lowering.

   • B: The hazard warning light must stay lit whenever the mast is not stowed.
   • C: NFPA does not tie mast lighting to the parking brake; a released brake with the mast up should light the cab hazard light.
   • D: NFPA requires a way to lower the mast, including a secondary emergency-lowering control.

8. An excessive voltage drop measured across a connector or length of wire while the circuit is energized indicates:

   AUnwanted resistance in that part of the circuit BA short to ground CToo much current-carrying capacity DA properly functioning ground
   Show answer

   Answer: A. Unwanted resistance in that part of the circuit

   Voltage drop is the voltage used up across resistance while current flows, so a high reading across a connection or wire reveals corrosion, a loose terminal, or a damaged conductor. A good connection drops very little voltage.

   • B: A short to ground shows as blown fuses or high current, not a localized drop.
   • C: Excess ampacity would lower resistance, not cause a drop.
   • D: A good ground exhibits minimal voltage drop.

9. Per NFPA requirements, 120 V, 15 or 20 A receptacles within 6 ft of a sink, toilet, shower or tub in a special service vehicle must be protected by:

   AGround-fault circuit interrupter (GFCI) protection BA 12-volt load manager on the branch circuit CA pump-shift interlock on the receptacle circuit DA battery equalizer as the only protection
   Show answer

   Answer: A. Ground-fault circuit interrupter (GFCI) protection

   NFPA 1901 22.3.3.1 (now NFPA 1900) requires GFCI protection on 120 V, 15 or 20 A receptacles within 6 ft of a lavatory, sink, toilet, shower or tub in a special service vehicle. Elsewhere on the apparatus GFCIs are permitted but not required, since water on the fireground causes nuisance trips. A GFCI trips on small ground-fault currents to protect personnel from shock.

   • B: A 12V load manager does nothing for a 120 V AC receptacle.
   • C: A pump-shift interlock has no role in an AC receptacle circuit.
   • D: A battery equalizer is a DC device and trips on no ground fault.

10. While verifying the shed program of an automatic load manager on an apparatus built to NFPA 1901 (now NFPA 1900), a technician finds these loads set to shed. Which one should NOT be on the shed list?

    AA cab air conditioner that is not part of the minimum continuous electrical load BScene floodlights that the purchaser did not define as mission-critical loads CWarning lights in excess of the minimum optical warning system the standard requires DThe minimum optical warning system needed while the apparatus blocks the right-of-way
    Show answer

    Answer: D. The minimum optical warning system needed while the apparatus blocks the right-of-way

    An automatic load manager sheds predetermined loads in a set order as voltage falls, but NFPA 1901 (now NFPA 1900) says the minimum continuous electrical loads may not be load managed. The minimum optical warning system used while blocking the right-of-way is one of those loads, so finding it on the shed list is a programming fault to correct. Warning lights beyond the minimum, and other loads outside the minimum continuous load, may be shed in the order the purchaser specified; NFPA 1911 also has the system's hardware, wiring and controls inspected and its low-voltage warning devices checked for activation.

    • A: A load that is not part of the minimum continuous load may be load managed.
    • B: Loads outside the minimum continuous load, like these floodlights, may be shed in the purchaser's order.
    • C: The annex says optical warning devices in excess of the minimum can and should be load managed.