Neutral conductor sizing questions show up on Journeyman licensing exams because they test whether you can identify unbalanced load, apply NEC demand rules, and treat nonlinear loads correctly. The most common code reference used in these questions is NEC 220.61 (Neutral Load).
This guide is written to be exam-fast (no extra fluff) and helps you solve these problems in a repeatable way.
What these questions are really asking
Most exam neutral-sizing questions boil down to:
- What is the minimum neutral ampacity needed to carry the calculated neutral load?
- Which parts of the load are allowed to be reduced?
- Which loads must be counted at 100% (especially nonlinear loads)?
How to identify a Neutral Conductor Sizing question (exam keywords)
If you see any of these, it’s almost always a 220.61 neutral load problem:
- “neutral conductor ampacity”
- “unbalanced load” / “peak unbalanced current”
- “nonlinear loads” (computers, LED drivers, electronic ballasts, UPS, VFD controls)
- “fluorescent lighting” / “harmonics”
- “minimum allowable neutral” / “service neutral”
The exam workflow (4 steps)
Step 1 — List what contributes to neutral
Neutral carries unbalanced current on 120/240 systems and line-to-neutral loads.
Examples:
- 120V lighting/receptacles
- kitchen small appliance circuits
- laundry circuit load
- certain ranges/dryers (neutral portion)
- nonlinear loads (often called out directly)
Step 2 — Separate nonlinear loads (always treat carefully)
If the problem mentions nonlinear loads, treat that portion as 100% neutral load (don’t reduce it).
Step 3 — Apply the common exam demand method for neutral (220.61 style)
Many licensing-prep problems use this pattern:
- First 200A of neutral load @ 100%
- Remaining neutral load over 200A @ 70%
- Add nonlinear neutral load @ 100% (separately)
Step 4 — Final answer = minimum neutral ampacity
Once you compute required neutral amps, choose a neutral conductor with ampacity ≥ calculated.
Exam tip: They’re testing your process, not real-world perfect system design.
“Formula” version (common exam pattern)
If NO nonlinear loads are included:
Minimum Neutral Ampacity = 200A + [(Neutral Load − 200A) × 0.70]
If nonlinear loads ARE included:
- Subtract the nonlinear portion from the total (so you don’t reduce it).
- Apply the 200A/70% method to the remaining neutral load.
- Add nonlinear back at 100%.
Minimum Neutral Ampacity = 200A + Nonlinear + [(Remaining Neutral Load − 200A) × 0.70]
Example 1: Peak unbalanced current question (fast solve)
Question: What is the minimum allowable ampacity for the neutral conductor of a service with a peak unbalanced current of 890A, assuming no fluorescent lighting is present?
Given: Neutral load = 890A, no nonlinear load mentioned.
- First 200A @ 100% → 200A
- Remaining = 890 − 200 = 690A
- Apply 70% → 690 × 0.70 = 483A
- Total neutral = 200 + 483 = 683A
✅ Answer: 683A minimum neutral ampacity
Example 2: Nonlinear load included (must stay at 100%)
Question: The minimum ampacity is ______ for a neutral conductor feeding a 600A load with 100A of nonlinear loads.
- Nonlinear = 100A (count at 100%)
- Remaining neutral-load portion = 600 − 100 = 500A
- First 200A @ 100% → 200A
- Remaining = 500 − 200 = 300A
- Apply 70% → 300 × 0.70 = 210A
- Add nonlinear at 100% → 200 + 210 + 100 = 510A
✅ Answer: 510A minimum neutral ampacity
Example 3: Dwelling neutral load style question (what the exam wants)
These questions usually test:
- general lighting load (VA)
- small appliance + laundry circuits
- demand factors (where applicable)
- ranges/dryers treatment in neutral calculation
- final conversion from VA → Amps
How to approach it quickly:
- Convert loads into VA
- Apply permitted demand factors per the problem’s method
- Apply the neutral treatment rule set (what gets reduced vs what stays 100%)
- Convert neutral VA to amps: A = VA / V
If the exam provides simplified assumptions (“assume X”), follow them exactly.
Common mistakes that fail these questions
1) Reducing nonlinear loads
Nonlinear loads are typically counted at 100% toward neutral in exam problems. Don’t apply the 70% reduction to them.
2) Applying 70% to the first 200A
The first 200A stays at 100%.
3) Mixing up “total load” vs “neutral load”
The neutral is not always the same as service load—these questions are specifically about neutral current / unbalanced current.
4) Forgetting units (VA vs A)
Dwelling calculations often start in VA, but your neutral answer might be required in amps.
Quick “Exam Checklist”
Before you calculate:
- ✅ Is it single-phase dwelling/service neutral sizing?
- ✅ Did they mention nonlinear loads?
- ✅ Did you keep nonlinear at 100%?
- ✅ Did you apply 200A @ 100% + remainder @ 70% (if that’s the method used)?
- ✅ Did you convert VA → amps correctly (if required)?
FAQs
What NEC article covers neutral load calculations?
Most exam neutral sizing questions reference NEC 220.61 (Neutral Load).
Do nonlinear loads increase neutral size?
Yes—nonlinear loads can increase neutral current, and many exam problems require them to be counted at 100%.
What’s the most common exam rule for neutral sizing?
A very common exam method is: first 200A at 100%, remainder at 70%, nonlinear at 100%.
