- How the 9 NASCLA-EC Domains Are Weighted
- Domain 1: Project Design & Management (8%)
- Domain 2: Safety (9%)
- Domain 3: Electrical Theory & Principles (11%)
- Domain 4: General Code Requirements (17%)
- Domain 5: Wiring & Protection (17%)
- Domain 6: Wiring Methods & Materials (16%)
- Domain 7: Equipment for General Use (13%)
- Domain 8: Special Occupancies, Equipment & Conditions (8%)
- Domain 9: Communication Systems (1%)
- Open-Book References and How They Map to Domains
- Scheduling Your Prep Around the Domain Weights
- FAQ
- General Code Requirements and Wiring & Protection each carry 17% - the two largest domains.
- Domains 4, 5, and 6 combined account for 50% of the 100 scored questions.
- Communication Systems is only 1% of the exam, so treat it as a light review item, not a priority.
- The test is open-book with 270 minutes for 110 questions (100 scored, 10 unscored experimental).
How the 9 NASCLA-EC Domains Are Weighted
The NASCLA Accredited Trade Examination for Electrical Contractors (Master Electricians/Unlimited Electricians) is built from a single content outline administered by PSI on behalf of the National Association of State Contractors Licensing Agencies. That outline is broken into nine content areas, and the percentage assigned to each one comes directly from PSI's official allocation of the 100 scored items on the exam. Ten additional unscored, experimental items are mixed in for a total of 110 questions, but they don't count toward your result.
Unlike some licensing exams where weighting is vague, NASCLA-EC publishes exact percentages: 8, 9, 11, 17, 17, 16, 13, 8, and 1. Two domains - General Code Requirements and Wiring & Protection - are tied at the top with 17% each. Add Wiring Methods & Materials at 16% and those three domains alone represent half of every scored exam form. If you're deciding where to spend your limited study hours, this is the single most useful fact in this guide.
For a broader look at how this weighting affects overall exam difficulty, see How Hard Is the NASCLA-EC Exam? Complete Difficulty Guide 2026. If you want a condensed version of everything below for last-minute review, the NASCLA-EC Cheat Sheet 2026 pulls the highest-yield facts into one page.
Domain 1: Project Design & Management (8%)
Project Design & Management
This domain evaluates whether a candidate can plan and manage an electrical project from a contracting and business perspective, not just a technical one. Expect questions tied to project management fundamentals and business/legal frameworks referenced in the exam's approved literature.
- Project planning, scheduling, and scope concepts drawn from PMBOK-style project management principles
- Business and legal fundamentals covered in the NASCLA Contractors Guide to Business, Law and Project Management, Basic (fourteenth edition)
- Coordinating drawings, specifications, and the Diagram/Blueprint Packet supplied at the test center
Because this domain draws on the NASCLA Contractors Guide and PMBOK-derived concepts rather than the National Electrical Code itself, it rewards familiarity with your approved reference index at least as much as raw electrical knowledge.
Domain 2: Safety (9%)
Safety
Safety questions test your ability to apply OSHA and electrical safety standards on real jobsites, including hazard recognition and safe work practices around energized equipment.
- OSHA 29 CFR 1926 (construction) and 1910 (general industry), 2024 editions
- Electrical safety-related work practices from NFPA 70E (2024)
- Personal protective equipment, lockout/tagout, and arc-flash boundary concepts
Key Takeaway
Tab both your OSHA references and your NFPA 70E copy by topic (PPE, boundaries, lockout/tagout) before test day - Domain 2 questions are scenario-based and reward quick lookups over memorization.
Domain 3: Electrical Theory & Principles (11%)
Electrical Theory & Principles
This domain checks foundational understanding of electrical concepts that underpin everything else on the exam - the kind of material found in Mike Holt's Understanding Electrical Theory for NEC Applications.
- Ohm's Law, power calculations, and series/parallel circuit behavior
- AC vs. DC fundamentals, transformers, and motor theory
- Applying theory to size conductors, overcurrent devices, and equipment correctly
A silent, battery-operated, nonprinting, nonprogrammable calculator without alphabetic capability is permitted for the math-heavy questions in this domain and others like Wiring & Protection.
Domain 4: General Code Requirements (17%)
General Code Requirements
Tied for the highest weight on the exam, this domain covers the structural and definitional backbone of the National Electrical Code (NEC or NEC Handbook, 2020 or 2023 editions) - the articles that govern how the rest of the Code is applied.
- NEC scope, definitions, and general requirements articles
- Branch circuit, feeder, and service load calculations
- Grounding and bonding fundamentals as a prerequisite to Domain 5 topics
Domain 5: Wiring & Protection (17%)
Wiring & Protection
Also weighted at 17%, this domain focuses on protecting circuits, equipment, and people through correct application of overcurrent protection and NEC wiring rules.
- Overcurrent protection device sizing and coordination
- GFCI and AFCI protection requirements by location and occupancy
- Conductor ampacity, derating, and protection against overload
Because General Code Requirements and Wiring & Protection are jointly the largest domains, candidates should plan multiple review passes through the NEC articles covering both before attempting practice questions on the ../ practice test platform.
Domain 6: Wiring Methods & Materials (16%)
Wiring Methods & Materials
This domain rounds out the "big three" weighting group. It tests knowledge of the raceways, cables, boxes, and installation methods that make an installation physically compliant.
- Raceway types, sizing, and fill calculations
- Cable types and permitted installation methods by location
- Boxes, conduit bodies, and fitting selection requirements
Key Takeaway
Domains 4, 5, and 6 together represent 50% of scored questions - treat this trio as the core of your study plan rather than three separate topics.
Domain 7: Equipment for General Use (13%)
Equipment for General Use
This domain covers the equipment installed after the wiring is in place - switches, receptacles, motors, transformers, and related hardware.
- Switch and receptacle requirements, including specific-use outlets
- Motor and transformer installation, overload, and disconnect requirements
- Panelboards, switchboards, and general equipment clearances
At 13%, Equipment for General Use is the fourth-largest domain and deserves a dedicated review pass, especially motor and transformer calculations that connect back to the theory covered in Domain 3.
Domain 8: Special Occupancies, Special Equipment & Special Conditions (8%)
Special Occupancies, Special Equipment & Special Conditions
This domain addresses NEC rules that apply only in specific settings or with specific equipment types rather than universally.
- Hazardous (classified) locations and special occupancy rules
- Special equipment articles such as those governing renewable energy systems or EV charging equipment
- Emergency systems and other special-condition wiring requirements
Because this domain is broad but only 8% of the exam, focus on recognizing which NEC article applies to a given scenario rather than memorizing every subsection.
Domain 9: Communication Systems (1%)
Communication Systems
The smallest domain on the exam, Communication Systems covers low-voltage and communications wiring requirements at a basic, conceptual level.
- Separation requirements between communications wiring and power conductors
- Basic communications circuit protection concepts
Open-Book References and How They Map to Domains
NASCLA-EC is a computer-based, open-book exam, which changes how you should prepare relative to a closed-book test. The PSI bulletin (revised July 7, 2026) lists the approved references: NEC or NEC Handbook (2020 or 2023), OSHA 29 CFR 1926 and 1910 (2024), PMBOK seventh edition (2021), ANSI/ASHRAE/IES 90.1 (2022), the NASCLA Contractors Guide to Business, Law and Project Management, Basic (fourteenth edition, 2024), NFPA 70E (2024), Ugly's Electrical References (2023), and Mike Holt's Understanding Electrical Theory for NEC Applications.
You're allowed to highlight, underline, and index these books before testing, and permanent tabs are permitted - but written notes and any loose or attached papers are prohibited. If you also bring the optional Ferm's Fast Finder or Tom Henry indexes, they must remain unmarked, unhighlighted, and untabbed.
| Domain | Weight | Primary Reference(s) |
|---|---|---|
| Project Design & Management | 8% | NASCLA Contractors Guide, PMBOK |
| Safety | 9% | OSHA 1926/1910, NFPA 70E |
| Electrical Theory & Principles | 11% | Mike Holt's Understanding Electrical Theory |
| General Code Requirements | 17% | NEC / NEC Handbook |
| Wiring & Protection | 17% | NEC / NEC Handbook, Ugly's |
| Wiring Methods & Materials | 16% | NEC / NEC Handbook |
| Equipment for General Use | 13% | NEC / NEC Handbook |
| Special Occupancies/Equipment/Conditions | 8% | NEC / NEC Handbook, ASHRAE 90.1 |
| Communication Systems | 1% | NEC / NEC Handbook |
Notice how heavily the National Electrical Code is used across Domains 4 through 9 - six of nine domains. That's why indexing your NEC by article number, not just by chapter, pays off far more than indexing any other single reference. For a full walkthrough of building an index system and managing your 270 minutes, see the NASCLA-EC Study Guide 2026: How to Pass on Your First Attempt.
Scheduling Your Prep Around the Domain Weights
Since NASCLA-EC approval lasts one year and allows up to three attempts, most candidates have room to plan a structured, multi-week schedule rather than cramming. The sequence below prioritizes domains by weight rather than by their order in the outline.
Foundations
- Review Domain 3 (Electrical Theory & Principles) so later NEC-heavy domains make sense
- Begin indexing your NEC and NFPA 70E references
The 50% Core
- Work through Domain 4 (General Code Requirements) and Domain 5 (Wiring & Protection) in depth
- Follow with Domain 6 (Wiring Methods & Materials)
Equipment and Safety
- Cover Domain 7 (Equipment for General Use) and Domain 2 (Safety)
- Practice timed sets using the diagram/blueprint style questions
Lower-Weight Domains and Simulation
- Review Domain 1, Domain 8, and Domain 9 briefly
- Take full-length timed practice exams on the main practice test platform under open-book conditions
Spaced repetition and timed practice sets are useful tools, but apply them specifically to the 4-5-6 domain cluster first - that's where repetition yields the largest score gains given the weighting.
Frequently Asked Questions
Start with Domain 3 (Electrical Theory & Principles) to build a foundation, then move immediately into Domain 4 (General Code Requirements) and Domain 5 (Wiring & Protection), since those two are tied for the highest weight at 17% each.
General Code Requirements, Wiring & Protection, and Wiring Methods & Materials together make up 50% of the 100 scored questions on the exam.
Yes. The entire computer-based exam is open-book, and the same set of approved references - including the NEC, OSHA standards, and NFPA 70E - applies across all nine domains, though usage varies by topic.
No. NASCLA does not require education or work experience for direct examination applicants, though participating licensing agencies may have their own separate requirements. See NASCLA-EC Requirements 2026: Eligibility, Prerequisites & How to Qualify for details.
Passing is not domain-by-domain; you need 75 correct answers out of 100 scored questions overall, regardless of how those correct answers are distributed across the nine domains. Full scoring mechanics are covered in NASCLA-EC Passing Score 2026: Exactly What You Need to Pass.