Diagnose an Open, Short, or Broken Branch Circuit

A. Finished-Project Specification

Quantity: one defined affected circuit, isolated and verified de-energized, inspected in source-to-load order, tested by continuity or resistance only at confirmed isolated conductor paths, with the last confirmed good point and first confirmed failed point identified, and documented on one completed Branch-Circuit Diagnostic Worksheet with a repair plan ready for separate authorization.

B. Diagnostic Schedule

Item	Target Condition	Verification Method
Symptom record	Reported condition, affected loads, timing, and recent work documented in writing	Written record on worksheet
Circuit isolation	Affected circuit de-energized and verified dead by the live-dead-live procedure before any box is opened	Direct observation and test record
Fault classification	Symptom classified as likely open, short, ground fault, failed device, loose connection, damaged cable, or unresolved	Written classification with supporting evidence
Source-to-load inspection	Every accessible box inspected in logical order before testing begins	Visual inspection and written findings
Isolated continuity testing	Continuity and resistance tested only on confirmed de-energized, isolated conductor paths, one path at a time	Direct observation and meter readings recorded
Boundary identification	Last confirmed good point and first confirmed failed point identified for the fault	Written record with test sequence
Repair plan	Fault location, evidence, required materials, permit needs, and retest method documented	Written repair plan on worksheet

C. Material Takeoff

• Testing equipment: one adequately rated contact voltage tester, one digital multimeter with continuity/resistance function, and one non-contact voltage detector for preliminary screening only.
• Diagnostic setup materials: jumper leads rated for the de-energized diagnostic setup and labeling supplies for identified conductor ends.
• Lockout materials: a breaker lockout device, hasp, and padlock, plus warning tags identifying the controlled breaker, reason, and responsible person.
• Documentation: one Branch-Circuit Diagnostic Worksheet per project, plus photographs of the symptom condition, inspected boxes, and identified fault evidence.

D. Acceptance Standards

Check	Standard
Isolation and verification	Affected circuit de-energized and verified dead by the live-dead-live procedure before any box, device, or conductor is disturbed
Fault classification	Symptom correctly classified as open, short, ground fault, failed device, loose connection, damaged cable, or unresolved, with supporting evidence recorded
Testing discipline	Every continuity or resistance test performed only on a confirmed de-energized, isolated conductor path with connected equipment disconnected
Fault location	Last confirmed good point and first confirmed failed point identified and consistent with the recorded test sequence
Escalation	Concealed damage, aluminum wiring outside scope, shared-neutral uncertainty, panel defects, or inaccessible junctions identified and escalated rather than worked around
Documentation	Branch-Circuit Diagnostic Worksheet complete with symptom, classification, test record, evidence, and repair plan entries
Procedure	Symptom recording, isolation, classification, inspection, testing, and repair-plan documentation completed independently and in sequence

E. Symptom Recording and Emergency Screening

1. Record the reported symptom, affected loads, timing, recent work, breaker behavior, weather, and intermittent conditions. Write the full symptom report before proceeding to Step 2.
2. Inspect for fire, smoke, heat, water, damaged equipment, or other emergency conditions. Stop and address any emergency condition before continuing the diagnostic sequence.

F. Circuit Isolation and Comparison

1. De-energize and control the circuit before opening boxes or equipment. Apply the identified breaker's lockout and tag using the Chapter 1 procedure.
2. Verify absence of voltage using the approved live-dead-live procedure. Confirm the tester on a known energized source, test the target conductors, and reverify the tester.
3. Compare the circuit map, wiring diagram, and panel directory with actual affected loads. Note any discrepancy between the documented circuit and the observed symptom.
4. Classify the symptom as likely open conductor, short circuit, ground fault, failed device, loose connection, damaged cable, or unresolved. Record the classification and the evidence supporting it.

G. Source-to-Load Box Inspection

1. Inspect accessible device and junction boxes in logical source-to-load order. Begin at the panel end of the circuit and proceed toward the reported load.
2. Look for loose terminals, backstab failures, scorched insulation, broken conductors, incorrect splices, damaged connectors, and moisture. Record every observed condition, even if it is not the confirmed fault.

H. Isolation for Testing

1. Separate loads and branch sections as required for safe isolation. Disconnect splices or terminations needed to isolate the conductor path under test.
2. Confirm that capacitors, electronic devices, surge protectors, lamps, and connected equipment are disconnected before resistance testing. Remove or disconnect every such device from the test path.

I. Continuity and Resistance Testing

1. Use continuity or resistance testing only on confirmed de-energized and isolated conductors. Do not connect the meter until isolation is confirmed.
2. Test one conductor path at a time using identified endpoints. Label each endpoint before testing.
3. Check for unintended continuity between ungrounded, grounded, and equipment-grounding conductors. Record any unintended continuity as a short circuit or ground fault indicator.
4. Use jumper leads only as approved for the de-energized diagnostic setup. Remove jumper leads immediately after the associated test.

J. Fault Location and Framing-Route Inspection

1. Identify the last confirmed good point and first confirmed failed point. Record both locations and the test evidence supporting each.
2. Inspect the framing route for nails, screws, crushing, rodents, heat, water, or renovation damage. Document any physical damage found along the route between the two identified points.
3. Do not energize an isolated damaged conductor to locate a fault. Complete all remaining diagnosis using de-energized testing only.

K. Repair Planning and Escalation

1. Determine whether the repair can be made at an accessible box or requires cable replacement and building access. Record the determination and its basis.
2. Stop work for concealed damage, aluminum wiring outside the approved scope, shared-neutral uncertainty, panel defects, or inaccessible junctions outside the project scope. Escalate per the Failure Points section before continuing.
3. Prepare a repair plan identifying fault location, evidence, circuit isolation, required materials, permit needs, and retest method. Complete every field on the Branch-Circuit Diagnostic Worksheet.
4. Complete the authorized repair only when separately approved. Do not proceed to correction without separate authorization for the repair scope.
5. Inspect, reassemble, and test the circuit according to the controlled restoration procedure. Follow the same isolation and verification discipline used during diagnosis.
6. Document findings, meter settings, isolated conductors, repair, and final results. Complete the worksheet before closing the project.