Free sample · NICET FA I

Try a full lesson: Finding and fixing faults

This is a complete lesson from the course (module 5 of 6, NICET task 1.2.2), followed by 10 practice questions with full explanations. Nothing to sign up for.

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Why this task matters at Level I

NICET task 1.2.2 is troubleshooting: the panel says something is wrong, and you find it and fix it. Maintenance is close to half of the Level I exam, and troubleshooting is the part of it that most separates a technician who can be left alone on a service call from one who can't. Good troubleshooting is method, not luck. You read what the panel is telling you, you work out what kind of fault it is, and you narrow it down with your meter until you are standing in front of the bad splice.

Opens, shorts and ground faults: how each shows at the panel

There are three basic wiring faults. Each one looks different at the panel, and knowing the difference saves hours.

Open

A conductor is broken or a termination has come loose. Supervision current stops flowing, so the panel reports a trouble on that circuit.

On a Class B circuit, every device past the open stops working.
On a Class A circuit, the panel reaches the devices from the other end, so all of them keep working, but it still reports the trouble.
On an addressable SLC, the panel loses communication with the devices past the open and reports each one as missing, or reports a Class A loop break.

Short

The two conductors touch each other, or a device has failed in a way that connects them.

On a conventional IDC, a detector in alarm puts a low resistance across the circuit. A short looks much the same, so on most conventional panels a short on an IDC shows as an alarm on that zone. Some panels can tell the difference and show a trouble.
On a NAC, the panel watches the circuit in standby with reversed polarity. A short shows as a trouble. In alarm, the panel shuts that circuit down to protect itself.
On an SLC, a short can take down the whole loop. Isolator modules limit the damage to the section between two isolators.

Ground fault

A conductor touches earth ground: a metal box, conduit, building steel or a wet ceiling. Most panels have one ground fault detector for all field wiring, so the trouble often says "ground fault" without naming a circuit. A single ground fault usually does not stop the circuit working. Two of them on different conductors can act like a short or cause signals to appear on the wrong circuit, which is why ground faults have to be found and fixed, not ignored.

| Fault | Typical panel indication | Typical cause | |---|---|---| | Open | Trouble on that circuit | Loose terminal, broken wire, missing EOL | | Short (IDC) | Alarm on that zone (most panels) | Pinched cable, failed device, staple through cable | | Short (NAC) | Trouble in standby | Pinched cable, appliance installed backwards | | Ground fault | Ground fault trouble, often not circuit-specific | Wire nicked against a box, water in a box, damaged insulation |

Meter technique for troubleshooting a circuit

You need a good digital multimeter, and you need to use it in the right order.

Read the panel first. Write down every active trouble and the circuit or address. Check the history log for when it started. A trouble that started the day the ceiling contractor arrived tells you where to look.
Measure voltage with the circuit connected. Is the panel putting out what the manual says on that circuit? This step checks the panel before you blame the field wiring.
Disconnect the circuit at the panel before measuring resistance. Remove the field conductors from the terminals and note which goes where. Resistance readings on a live circuit are meaningless and can damage the meter.
Measure loop resistance across the two conductors.

On a Class B IDC or NAC with an EOL, you should read close to the EOL value plus the wire resistance. On a NAC the appliances are polarized, so swap the meter leads and read both ways; one direction can show the appliances' diodes conducting. To read the wire's own loop resistance, remove the EOL and jumper the far end. A reading near zero means a short. A reading of OL (over limit, meaning beyond the meter's range) means an open.

Measure each conductor to ground. Put one lead on the conductor and the other on a good ground (the panel's earth ground terminal). A healthy conductor reads very high resistance, usually beyond the meter's range. A low reading on one conductor is your ground fault.
Be careful with an insulation tester. A megohmmeter puts out hundreds of volts. Disconnect every electronic device on the circuit first, or you will destroy detectors and modules. Many manufacturers say not to use one on installed device circuits at all.

Write your readings down as you go. They are your evidence, and they make the next step faster.

Worked calculation: isolating a ground fault by halving the circuit

When you know a conductor is grounded but not where, you split the circuit in half and test each half. Each test throws away half the remaining possibilities. The readings below are example values.

The circuit. A Class B IDC with 24 devices, numbered 1 (nearest the panel) to 24 (the EOL).

Step 1: confirm the fault. With the circuit lifted at the panel:

Positive conductor to ground: 1.2 kOhm. This is the fault.
Negative conductor to ground: OL (open, very high resistance). This is healthy.

Step 2: first split, between devices 12 and 13. Open the circuit at device 12 and test each side.

Panel side (devices 1 to 12): positive to ground reads OL. Clean.
Field side (devices 13 to 24): positive to ground reads 1.2 kOhm. The fault is in 13 to 24.

Step 3: second split, between 18 and 19. Reconnect device 12 and open at device 18.

13 to 18: positive to ground reads 1.2 kOhm. The fault is here.
19 to 24: OL. Clean.

Step 4: third split, between 15 and 16.

13 to 15: OL.
16 to 18: 1.2 kOhm. The fault is in 16, 17, 18 or the wire between them.

Step 5: fourth split, at 17. Test 16 to 17 and 17 to 18 separately. You find the fault on the run between 17 and 18. When you open the box at device 18, the conductor insulation has been cut against the edge of the box.

How many splits does it take? Each split halves the number of devices left. After one split you have 12, after two 6, after three 3, after four you are down to one or two. In general, the most splits you need is the smallest whole number n for which 2^n is at least the device count. Since 2^4 = 16 is less than 24 and 2^5 = 32 is more, a 24-device circuit needs at most 5 splits. Checking every device one by one could take 24.

What the exam tests here. The method (halve and test), why you lift the circuit at the panel first, and how many steps a given device count needs.

Replacing a device and returning the system to service

Once you find the faulty device or wire:

Use the right replacement. The same model is safest. Any substitute must be listed for the purpose and, for two-wire smoke detectors, listed as compatible with the panel. The panel manual's compatibility list decides this, not the parts counter.
Match the settings. On an addressable system, set the same address and device type. On a strobe, set the same candela. On a heat detector, use the same temperature rating.
Repair the wiring properly. Use listed connectors in a box. Don't leave a splice buried in a ceiling.
Test what you touched. Test the replaced device and the circuit it is on. NFPA 72 Chapter 14 requires testing after any change, and the test must cover the device and the functions it controls.
Restore everything. Clear the trouble, return any bypassed outputs to normal, confirm the panel is normal, and confirm with the supervising station that they see the system in normal condition.
Document it. Write what you found, what you replaced, the test result and the time the system was returned to service. Tell the owner.

Check yourself

The free practice set below has ten original questions across all three Level I domains, including two on troubleshooting, each with a full explanation of why the right answer is right and why every other option is wrong.

Where to look in your own books

NFPA 72-2022 Chapter 12: pathway classes and how each must behave under an open, short or ground fault
NFPA 72-2022 Chapter 14: testing after repairs and replacements, and records
The panel installation manual: troubleshooting tables, expected circuit voltages and the compatibility list

Practice set

Pick an answer in your head, then open the explanation. Every wrong option is explained too.

1. Installation

A new horn-strobe circuit shows a trouble as soon as it is connected, before any alarm. The wiring is continuous and the end-of-line resistor is the right value. One horn-strobe was replaced that morning. What is the most likely cause?

The replacement appliance is landed with its polarity reversed
The end-of-line resistor is at the last appliance
The circuit is wired Class B
The replacement appliance is set to a higher candela

Hint: where to look

NFPA 72 Chapter 18 and the appliance installation sheet. Ask what changed on the circuit today and how a supervised NAC behaves in standby.

Show answer and explanation

Answer: A. The replacement appliance is landed with its polarity reversed

In standby the panel supervises the circuit with reversed polarity, and a diode in each appliance blocks current in that direction. An appliance landed backwards conducts in standby, so the panel sees the wrong supervisory current and reports a trouble. Having the end-of-line resistor at the last appliance is correct practice. A Class B circuit is normal and is not a fault. A higher candela setting changes the alarm current, which the panel does not draw in standby, so it would not cause a standby trouble.

Reference: NFPA 72-2022 ch.18 - notification appliances; appliance installation sheet

2. Installation

A helper suggests adding two smoke detectors by teeing off the middle of a conventional Class B initiating circuit instead of extending it past the last detector. Why is this not acceptable?

The branch would draw too much standby current
A break on the branch would not be seen by the panel, because the branch has no end-of-line device
Teeing off reverses the circuit polarity
The panel would treat the branch as a separate zone

Hint: where to look

NFPA 72 Chapter 12 and the panel manual. Trace how supervision current flows on a Class B circuit and ask whether every conductor would still be in that path.

Show answer and explanation

Answer: B. A break on the branch would not be seen by the panel, because the branch has no end-of-line device

Supervision works by passing current through the circuit to the end-of-line device. A branch teed off the middle has no end-of-line device of its own, so if a wire on the branch breaks the supervisory current does not change and the panel shows nothing. Two extra detectors add only a tiny standby current. A tee does not reverse polarity. The panel cannot see the branch as a separate zone; it is still part of the same circuit.

Reference: NFPA 72-2022 ch.12 - circuits and pathways; panel installation manual

3. Installation

The drawings call for a 2-hour survivability level on the voice evacuation speaker circuits. Which installation meets that requirement?

Standard FPLP cable in EMT
FPLR cable run in a riser shaft
Any fire alarm cable, as long as the building is sprinklered
Circuit integrity (CI) cable rated for 2 hours, installed as its listing requires

Hint: where to look

NFPA 72 Chapter 12 defines pathway survivability levels and the methods that achieve each. Match the level on the drawings to those methods.

Show answer and explanation

Answer: D. Circuit integrity (CI) cable rated for 2 hours, installed as its listing requires

A 2-hour survivability level calls for a 2-hour rated method, such as listed CI cable, a 2-hour rated cable system or a 2-hour rated enclosure, installed as its listing requires. Plenum cable in EMT gives mechanical protection but no 2-hour fire rating. Riser cable resists fire spreading up a shaft but is not rated to keep working for 2 hours in a fire. Sprinklers alone, with ordinary cable, do not meet a 2-hour level.

Reference: NFPA 72-2022 ch.12 - pathway survivability

4. Installation

On a Class A initiating circuit, why should the outgoing and return conductors not run together in the same cable for the whole route?

It reduces voltage drop on the return path
It lets the panel use a smaller end-of-line resistor
One event that damages both runs would defeat the circuit's redundant path
It keeps the circuit power-limited

Hint: where to look

NFPA 72 Chapter 12 on Class A pathways. Think about why Class A exists at all and what a single physical event along the route could do.

Show answer and explanation

Answer: C. One event that damages both runs would defeat the circuit's redundant path

The point of Class A is that the panel can reach every device from either end. If both the outgoing and return conductors share one cable, a single cut or fire at that spot breaks both paths and the redundancy is lost. Routing has nothing to do with voltage drop on the return. A Class A circuit has no end-of-line resistor in the field. Whether a circuit is power-limited depends on the source, not on how the conductors are routed.

Reference: NFPA 72-2022 ch.12 - Class A pathway routing

5. Installation

A technician falls from a ladder on a job and is admitted to the hospital as an in-patient. Within how long must the employer report this to OSHA?

8 hours
24 hours
7 days
30 days

Hint: where to look

OSHA 29 CFR 1904.39 sets different reporting deadlines by type of injury. Find which category an in-patient admission falls in.

Show answer and explanation

Answer: B. 24 hours

Under 29 CFR 1904.39, a work-related in-patient hospitalization, amputation or loss of an eye is reported to OSHA within 24 hours. 8 hours is the deadline for a work-related fatality. 7 days is the time an employer has to record a case on its injury log, not the deadline for reporting a hospitalization to OSHA. 30 days is not a reporting deadline for this event.

Reference: OSHA 29 CFR 1904.39 - reporting fatalities, hospitalizations, amputations and eye losses

6. Maintenance

During an annual test, a technician measures 27.2 V across a 24 V battery set with the panel on AC power and records the batteries as passing. What is wrong with this test?

With the charger connected, the meter reads the charger's float voltage, so the reading says nothing about the batteries' condition under load
Nothing; 27.2 V is a normal battery voltage
The reading should have been taken across one battery only
The test should have been done with the batteries removed from the panel

Hint: where to look

NFPA 72 Chapter 14 battery test methods and the battery spec. Think about what else is on those terminals while the panel is on AC, and what a load test shows.

Show answer and explanation

Answer: A. With the charger connected, the meter reads the charger's float voltage, so the reading says nothing about the batteries' condition under load

With the charger connected, the meter reads the charger holding the batteries at float voltage. A weak battery can show the same reading. A valid check disconnects AC so the batteries carry the load, then measures the set and each battery against the manufacturer's figure. 27.2 V is a normal float voltage, which is exactly why it proves nothing. Measuring one battery only would miss the other. Removing the batteries means there is no load, so it cannot show how they behave under load.

Reference: NFPA 72-2022 ch.14 - battery test methods; battery manufacturer specification

7. Maintenance

During an alarm test in an open office, the technician can see four strobes from one desk and they are flashing at different moments. What should the technician do?

Nothing; strobes only need to flash
Turn the candela setting down on two of them
Record a deficiency, because more than two strobes in one view should flash in synchronization
Disconnect two strobes so only two are visible

Hint: where to look

NFPA 72 Chapter 18 on visible appliances. Look up the rule for multiple strobes within a single field of view.

Show answer and explanation

Answer: C. Record a deficiency, because more than two strobes in one view should flash in synchronization

When more than two strobes can be seen together from one place, they must flash in synchronization, because out-of-step flashing raises the combined flash rate and can trigger seizures. Four strobes are in view here, so the test has found a deficiency to record and report. Lowering the candela does not fix timing and may break the coverage design. Disconnecting appliances creates a new deficiency. Flashing alone is not enough when several are in view.

Reference: NFPA 72-2022 ch.18 - visible appliance synchronization

8. Maintenance

A contractor drives a screw through a notification appliance circuit cable, shorting the two conductors. The building is not in alarm. What will the panel most likely show?

An alarm on that circuit
A supervisory signal
Nothing until the next alarm
A trouble on that circuit

Hint: where to look

NFPA 72 Chapter 12 and the panel manual. Recall how a NAC is supervised while idle, and what an open does to that supervision.

Show answer and explanation

Answer: D. A trouble on that circuit

In standby the panel supervises the notification circuit through the end-of-line resistor, and a short changes that current, so it reports a trouble. A notification circuit is an output, so a short on it cannot create an alarm; an alarm comes from an initiating device. A supervisory signal reports an off-normal condition such as a closed valve, not a wiring fault. Saying nothing would happen ignores the supervision that exists to catch exactly this.

Reference: NFPA 72-2022 ch.12 - circuit faults; panel installation manual

9. Maintenance

A panel has shown a ground fault trouble for weeks, and the system still operates normally. Why does it still need to be found and fixed?

A second ground fault on another conductor can act like a short or put unwanted signals on a circuit
A ground fault drains the batteries in a few hours
A ground fault stops all notification appliances
The panel will clear the trouble by itself after 30 days

Hint: where to look

NFPA 72 Chapter 12 on ground faults. Think about what a single fault removes from the system's safety margin, not what it does today.

Show answer and explanation

Answer: A. A second ground fault on another conductor can act like a short or put unwanted signals on a circuit

One ground fault usually leaves the circuits working, which is why it is easy to ignore. A second ground fault on a different conductor completes a path through ground, which can act like a short, disable a circuit or create false signals. A ground fault does not drain the batteries quickly. It does not stop all notification appliances on its own. Panels do not clear a real ground fault on a timer.

Reference: NFPA 72-2022 ch.12 - ground fault behaviour of pathways; panel installation manual

10. Submittal Preparation and System Layout

In a submittal's sequence of operations matrix, the row 'Waterflow switch, riser 2' has a mark in the column 'Notify supervising station'. What does that mark mean?

The waterflow switch must be tested by the supervising station
The supervising station can shut off riser 2
Operating that waterflow switch sends a signal to the supervising station
The waterflow switch is monitored only, with no outputs

Hint: where to look

NFPA 72 Chapter 7 documentation. Read a sequence matrix as inputs in rows and outputs in columns, then interpret the intersection.

Show answer and explanation

Answer: C. Operating that waterflow switch sends a signal to the supervising station

In an input and output matrix, each row is an input and each column an output. A mark where they cross means operating that input causes that output, so waterflow on riser 2 sends a signal to the supervising station. The matrix does not assign testing duties. It does not give the supervising station control of a valve. A mark in an output column means there is an output, so the last option contradicts it.

Reference: NFPA 72-2022 ch.7 - documentation (sequence of operations)

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Questions are original and written to NICET's published content outline. Code is cited by section number so you can look it up in your own copy. Think something is wrong? Report it.