Authoring environment

Scenario Studio

Field Simulator

Content Library

3 scenarios

House Model

1418 Maple Ridge Dr.
Built
1974
Service
150A
Circuits
4
Devices
12

  • Kitchen Small Appliance A

    20A · gfci · leg A · 4 nodes · shared neutral

  • Kitchen Small Appliance B

    20A · gfci · leg B · 2 nodes · shared neutral

  • Kitchen & Dining Lighting

    15A · afci · leg A · 4 nodes

  • Bathroom Receptacles

    20A · standard · leg B · 2 nodes

Original aluminum branch wiring replaced in the 1990s except for two bedroom circuits. Kitchen remodeled 2016 with an added multiwire branch circuit.

Fault Injection

1 injected

  • open conductor · neutral

    at k_jbox

    The shared neutral of the kitchen multiwire branch circuit is open at the feed junction box. With the neutral open, the two 120V legs are placed in series across 240V. Load on one leg raises voltage on the other, which is why brightness changes when appliances are switched.

    Visual evidence: The white conductor pigtail at the junction box is heat-discoloured and pulls free of the wirenut with light tension.

Lesson Design

Learning objectives

  • Recognise the signature of an open neutral on a multiwire branch circuit
  • Understand why hot-to-ground reads normal while hot-to-neutral does not
  • Use load changes on one leg to confirm a shared-neutral condition

Expected diagnostic path

  1. Interview the homeowner about what changes the symptom
  2. Measure hot-to-neutral and hot-to-ground at an affected receptacle
  3. Compare neutral-to-ground potential against a known-good circuit
  4. Switch a load on the opposite leg and observe the voltage seesaw
  5. Open the panel and identify the multiwire pair, then trace to the first shared box

Instructor notes

Strong scenario for teaching MWBC theory. Ask the student to predict readings before probing.

Review Pipeline

v1.3.0
  1. draft
  2. technical review
  3. educational review
  4. quality assurance
  5. published

Version History

  • v1.3.02026-01-08

    QA passed; released to cohort library

  • v1.2.02025-12-01

    Objectives rewritten to diagnostic outcomes

  • v1.1.02025-11-14

    MWBC pairing verified against panel schedule

  • v1.0.02025-11-02

    Initial authoring

Assessment Model

  • Time to diagnosis
  • Tests performed vs. tests required
  • Incorrect or redundant tests
  • Missed hazards
  • Parts replaced unnecessarily
  • Diagnostic efficiency
  • Safety violations