Top 5 NEC Articles Every C-10 Candidate Must Know

The NEC contains hundreds of articles, but on the CSLB C-10 exam, certain articles appear far more frequently than others. Mastering these five articles will give you a significant advantage on exam day.

Article 210 — Branch Circuits

Article 210 governs the installation and sizing of branch circuits. On the C-10 exam, expect questions about:

• Circuit ratings and overcurrent protection: The relationship between conductor size, overcurrent device rating, and connected loads.
• Required outlets and receptacles: Spacing requirements for dwelling unit receptacles (every 12 feet along the wall), GFCI protection locations (bathrooms, kitchens, garages, outdoors), and AFCI protection requirements for bedrooms and living areas.
• Small appliance and laundry circuits: The two required 20A small-appliance branch circuits in kitchens and the dedicated laundry circuit requirement.
• Bathroom circuits: Dedicated 20A circuit requirements and GFCI protection.

Article 220 — Branch-Circuit, Feeder, and Service Load Calculations

This is arguably the most important article for the C-10 exam. Article 220 contains the methods for calculating electrical loads, which form the basis of many exam questions.

• Standard Method (220.40-220.60): General lighting loads, small appliance loads, laundry loads, and the application of demand factors from Table 220.42.
• Optional Method (220.82-220.87): Know when this method can be used (existing dwelling units with 100A or larger service) and how to apply it.
• Demand factors: Memorize the demand factor tables for general lighting (Table 220.42), dryers (Table 220.54), cooking equipment (Table 220.55), and fixed appliances.
• Service and feeder sizing: How to sum individual loads and apply appropriate demand factors to determine minimum service entrance requirements.

Article 250 — Grounding and Bonding

Grounding and bonding is one of the most complex and frequently tested topics on the C-10 exam. Article 250 covers the entire grounding system from the service entrance to the equipment level.

• System grounding vs. equipment grounding: Understanding the difference between grounding (connecting to earth) and bonding (connecting conductive parts together) is fundamental.
• Grounding electrode system (250.50): What constitutes a grounding electrode and how they must be connected.
• Grounding electrode conductor sizing (Table 250.66): How to size the GEC based on the largest service-entrance conductor.
• Equipment grounding conductor sizing (Table 250.122): How to size the EGC based on the overcurrent device rating.
• Main bonding jumper and supply-side bonding jumper requirements.

Article 430 — Motors, Motor Circuits, and Controllers

Motor circuits have unique rules that differ from general branch circuit requirements. The C-10 exam frequently tests your understanding of these special requirements:

• Full Load Current (FLC) vs. nameplate FLA: Always use the NEC table values (Tables 430.247-430.250) for conductor sizing and short-circuit protection — never the nameplate rating.
• Conductor sizing: Motor branch circuit conductors must be rated at 125% of the motor FLC (430.22).
• Overload protection: Sized based on nameplate FLA, typically at 115% for service factor 1.15 or higher, or 125% for all other motors.
• Short-circuit and ground-fault protection: Maximum ratings from Table 430.52, which vary by motor type and protective device type.
• Disconnecting means: Requirements for motor disconnect location and rating.

Article 310 — Conductors for General Wiring

Article 310 governs conductor selection, and Table 310.16 is one of the most referenced tables in the entire NEC. For the C-10 exam:

• Conductor ampacity (Table 310.16): Know the ampacity ratings for common conductor sizes in the 60°C, 75°C, and 90°C columns. Most questions reference copper conductors.
• Temperature correction factors: How to adjust ampacity for ambient temperatures above 30°C using the correction factors at the bottom of Table 310.16.
• Adjustment factors for bundling: When more than 3 current-carrying conductors are in a raceway, you must apply adjustment factors from Table 310.15(C)(1).
• Terminal temperature limitations: Even if a conductor is rated for 90°C, the ampacity may be limited by the terminal rating (usually 60°C or 75°C) of the equipment it connects to.