Short answer: Troubleshoot in the same order every time: get the full symptom, write a safe test plan with a stop condition, check the obvious, measure, split the circuit in half to box in the fault, fix it, prove the fix and record it. Stop and call your supervisor when the next test needs work you are not qualified for.
Troubleshooting is applied theory: Ohm’s law, voltage drop and how circuits are built. The PSI outline puts Electrical Theory in both parts of the Texas Journeyman exam. The Texas Journeyman Practice Pack has step-by-step solutions for 299 calculation questions, so you can practice the electrical theory behind troubleshooting. US$39 once.
Tsai Electro is an independent learning site. Not affiliated with TDLR, PSI or NFPA. This is a learning framework, not a work procedure. Follow your employer’s electrical safety program and NFPA 70E training. Apprentices test energized circuits only when they are trained, qualified for that task and directed by their supervisor.
Why a fixed process matters
The US Bureau of Labor Statistics lists inspecting electrical components such as transformers and circuit breakers among typical electrician duties (BLS Occupational Outlook Handbook). Experienced electricians look fast because they follow the same steps without thinking about them. Apprentices who guess swap parts, waste time and take risks they did not plan. A written process fixes all three.
For a homeowner-level look at one common symptom, see why the same breaker keeps tripping. This page is the method behind it.
The seven steps
| Step | What you do | Output |
|---|---|---|
| 1. Get the symptom | Ask what happened, when, what changed, and whether it is constant or intermittent | One sentence that describes the fault |
| 2. Plan the test safely | Decide which tests are de-energized and which need energized measurements; decide who is qualified for each | A test list with a stop condition |
| 3. Check the obvious | Tripped breaker, GFCI, switch off, blown fuse, loose plug, recent work nearby | Quick wins found, or ruled out |
| 4. Measure | Voltage, current, continuity or resistance at the points in your plan | Readings written down with locations |
| 5. Split in half | Test the middle of the suspect section; keep the half that is bad | The fault boxed into one device or run |
| 6. Fix and verify | Repair, then repeat the test that first showed the fault | Proof the symptom is gone |
| 7. Record | What failed, why, readings before and after | A note the next person can use |
The stop condition is part of the plan. Write it down before you start: for example, “if the next test needs the cover off an energized panel, stop and call the journeyman.” Also stop when readings do not make sense; a reading you cannot explain usually means the circuit is not what you think it is.
Before any de-energized work, follow lockout and verify absence of voltage as trained (see NFPA 70E and lockout). For meter basics, see how to use a multimeter.
Worked example 1: a receptacle that sags under load
Complaint: a space heater on a bedroom receptacle “runs weak.” The circuit is 12 AWG copper NM, about 60 feet from the panel. Your supervisor has the measurements taken by a qualified person with the cover plates and panel cover in place, using the heater as a 12.0 A load.
- With the heater drawing 12.0 A, a qualified electrician records 121.0 V at the circuit’s supply point and 112.6 V at the receptacle, both under the same load. These are illustrative readings, taken under the employer’s electrical safety procedures.
- Measured drop: 121.0 − 112.6 = 8.4 V. As a percent: 8.4 ÷ 121.0 = 6.94%.
- Resistance of the whole loop that would cause that drop: 8.4 ÷ 12.0 = 0.700 ohms.
- What the wire alone should be: 12 AWG solid copper is about 1.93 ohms per 1,000 feet (NEC Chapter 9, Table 8). The loop is 60 feet out and 60 back, 120 feet: 120 × 1.93 ÷ 1,000 = 0.23 ohms (0.2316).
- Expected drop from wire alone: 12.0 × 0.2316 = 2.78 V.
- Extra drop: 8.4 − 2.78 = 5.62 V, which is about 0.47 ohms (5.62 ÷ 12.0) of extra resistance somewhere in the loop.
- Conclusion: the measured drop is higher than the drop the conductor resistance alone would explain. A high-resistance connection is one possibility, but the calculation does not identify the cause or the location. Stop energized testing unless you are authorized and qualified. Have the circuit de-energized, locked out and verified before a qualified person inspects accessible connections under the employer’s safety procedure.
Check: rebuild the loop. 0.2316 + 0.4684 = 0.7000 ohms, and 0.700 × 12.0 = 8.4 V. Same drop. The wire resistance of 1.93 ohms per 1,000 feet is a table value that changes with temperature and conductor type, so treat the extra 0.4684 ohms as a clue, not as proof of one bad connection.
Worked example 2: half-splitting a dead run
Eight receptacles are fed in a chain from one breaker. The first two work; receptacles 3 to 8 are dead. In this simplified example, treat the six successive sections leading to receptacles 3 through 8 as the six possible fault sections. Each section includes its connections and wiring. Assume exactly one open fault along this known, unbranched path.
- Suspect section: 6 receptacles (3 to 8). Test at the middle, receptacle 5.
- In this simplified example, assume a single open-circuit fault in a known daisy-chain path. If a qualified person confirms that receptacle 5 is properly supplied, the fault lies in one of the sections leading to receptacles 6 through 8. If supply is absent at receptacle 5, the fault lies in one of the sections leading to receptacles 3 through 5. This depends on the single-fault, unbranched path and reliable test results. Real circuits can have branches, more than one fault or misleading voltage readings, so confirm the wiring path before you narrow the search.
- Split again until one device or one cable run is left.
- Three ideal yes-or-no tests can separate up to 8 candidates, because 2 × 2 × 2 = 8, so 3 tests are enough for these six. Twelve candidates need up to 4, because 8 is not enough and 16 is. This assumes each test reliably splits the remaining candidates and the circuit path is known.
Check: testing one receptacle at a time from the start could take up to 6 tests for this run. Halving takes at most 3.
What to write down
- Date, location, circuit, and who reported the problem.
- Every reading with its location and the load at the time.
- What you replaced or tightened, and the reading after the fix.
- Anything you saw but did not fix, and who you told.
Check yourself
Our own practice questions. Answers below each.
- Under the same 10.0 A load, the supply-point voltage is 120.0 V and the load-point voltage is 118.0 V. What equivalent loop resistance accounts for the 2.0 V drop? Answer: 2.0 ÷ 10.0 = 0.20 ohms.
- A circuit has 16 possible fault points. Most half-split tests? Answer: 4, because 2 × 2 × 2 × 2 = 16.
- Your next test needs a panel cover off with the bus energized and you are not qualified for it. What do you do? Answer: Stop and call your supervisor. That is the stop condition.
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A meter built for the readings on this page
Fluke 117 digital multimeter. Per the product listing: true RMS, automatic AC/DC voltage selection, a low input impedance mode, non-contact voltage detection and an LED backlight. Non-contact detection does not prove a circuit is de-energized; follow your employer’s approved procedure for testing for absence of voltage. Many employers supply meters; check what your shop requires and what category rating the work needs before you buy.
FAQ
What are the steps of electrical troubleshooting?
Get the symptom, plan safe tests with a stop condition, check the obvious, measure, split the circuit in half to box in the fault, fix and verify with the same test, and record what you found.
What is half-splitting in troubleshooting?
Testing at the middle of the section that could hold the fault, then keeping only the half that tests bad. Each test cuts the search in half, so 8 possible points take at most 3 tests.
How can voltage drop find a bad connection?
Measure voltage at the supply point and at the far point while the circuit carries the same known load. The drop divided by the current gives the loop resistance. If it is much higher than the wire alone should be, there may be extra resistance at a connection, which a qualified person then looks for with the circuit de-energized and verified.
Can an apprentice troubleshoot live circuits?
Only when trained and qualified for that task under the employer’s electrical safety program and directed by a supervisor. Many troubleshooting steps can be done de-energized after lockout and verification.
Sources checked October 2026
- US Bureau of Labor Statistics, Occupational Outlook Handbook, Electricians: https://www.bls.gov/ooh/construction-and-extraction/electricians.htm
- PSI Candidate Information Bulletin for TDLR (updated 9/15/2026): https://test-takers.psiexams.com/api/content/bulletin/1682
- NFPA 70 (NEC), 2026 edition, Chapter 9 conductor properties table, read in your own copy: https://www.nfpa.org/codes-and-standards/nfpa-70-standard-development/70
