Equipment for General Use — NH Master Electrician Exam Study Chapter

Learning Objectives

By the end of this chapter, you will be able to:

4.Identify the scope and application of NEC Article 400 through 490 as they apply to "equipment for general use."

5.Apply correct sizing, overcurrent protection, and installation rules for flexible cords, fixture wires, and receptacles in commercial and industrial settings.

6.Calculate and verify switch ratings, including horsepower and ampere ratings for motor-circuit applications.

7.Distinguish between general-purpose, heavy-duty, and specific-purpose receptacles and their required configurations.

8.Apply the rules for fixed electric space heating equipment, including branch-circuit sizing and clearance requirements.

9.Understand the special requirements for motors, generators, and transformers as they intersect with general-use equipment.

10.Navigate the NEC efficiently during the open-book exam using article and table references.

1.1 Scope and Structure of NEC Chapter 4

Chapter 4 of the 2023 NEC covers "Equipment for General Use." This is a broad category that includes wiring devices, switches, receptacles, lighting fixtures, motors, generators, transformers, and space-heating equipment. For the Master exam, you must not only know the individual requirements but also understand how these equipment rules interact with branch-circuit, feeder, and service calculations from Chapters 2 and 3.

The chapter is organized into articles:

Article 400 – Flexible Cords and Cables

Article 402 – Fixture Wires

Article 404 – Switches

Article 406 – Receptacles, Cord Connectors, and Replacement

Article 408 – Switchboards and Panelboards

Article 410 – Luminaires (Lighting Fixtures)

Article 422 – Appliances

Article 424 – Fixed Electric Space Heating

Article 430 – Motors, Motor Circuits, and Controllers

Article 445 – Generators

Article 450 – Transformers and Transformer Vaults

Article 490 – Equipment Over 1000 Volts (nominal)

For the Master license, the most heavily tested areas are Articles 404, 406, 408, 424, 430, and 450. You will be expected to apply these rules in the context of a complete installation, not just memorize individual code sections.

1.2 Flexible Cords and Cables (Article 400)

Flexible cords are permitted only for specific uses listed in 400.10. These include pendants, wiring of fixtures, connection of portable appliances, and connection of stationary equipment to facilitate interchange. A common master-level trap is the use of flexible cord as a substitute for fixed wiring — this is explicitly prohibited in 400.12.

Key points for the exam:

Ampacity: Use Table 400.5(A)(1) for flexible cords. Note that the ampacity of a cord is based on the number of current-carrying conductors in the cord, not the physical size alone.

Overcurrent protection: Flexible cords must be protected at their ampacity, per 240.5. If the cord feeds a motor, the motor rules of Article 430 may allow a higher rating.

Minimum bend radius and strain relief are field-inspection items. A master must verify that cords are not routed through walls, ceilings, or floors (400.12(1)).

Ampacity adjustment: When more than three current-carrying conductors are in a cord, apply the adjustment factors of Table 400.5(A)(3).

Master-level consideration: When supervising a temporary installation (Article 590), flexible cords are often used more liberally, but the same ampacity and protection rules apply. Temporary wiring must still comply with 590.4 for overcurrent protection.

1.3 Switches (Article 404)

Switches are categorized by their construction and application. For the Master exam, you must know the horsepower rating requirements for switches used in motor circuits.

General-use snap switches (404.14) must be rated for the connected load. If the load is a motor, the switch must have a horsepower rating equal to or greater than the motor's rating.

AC general-use snap switches are rated for inductive loads up to 80% of their ampere rating. This is a common exam trap — a switch rated 20 A can control a motor with a full-load current of up to 16 A, not 20 A.

Switches with pilot lights (404.9) must be wired so the pilot light indicates the "on" position of the switch, not the load. This is a frequent inspection point.

Dimmer switches must be listed for the type of load (incandescent, LED, fluorescent). A master must verify that dimmers are not used on receptacles or on circuits supplying both lighting and motors.

Master-level consideration: When a switch is used to control a motor, the switch must open all ungrounded conductors simultaneously. For a 3-phase motor, this means a 3-pole switch is required. Single-pole switches on 3-phase motor circuits are a code violation.

1.4 Receptacles and Cord Connectors (Article 406)

Receptacle requirements are among the most frequently tested topics. For the Master exam, focus on the commercial and industrial applications, not just residential.

1.4.1 Receptacle Configurations

Receptacles must be of the proper configuration for their voltage and current rating (406.6). The NEMA configuration chart is referenced, but you must know the common ones:

5-15R: 125 V, 15 A (standard residential)

5-20R: 125 V, 20 A (T-slot neutral)

6-15R: 250 V, 15 A

6-20R: 250 V, 20 A

14-50R: 125/250 V, 50 A (range/dryer)

L6-20R: 250 V, 20 A locking (industrial)

Exam trap: A 20 A receptacle is not permitted on a 15 A branch circuit, but a 15 A receptacle is permitted on a 20 A circuit if the circuit supplies two or more receptacles (210.21(B)(3)). A single receptacle on an individual branch circuit must have an ampere rating not less than the branch circuit rating.

1.4.2 Receptacle Ratings for Motor Loads

When a receptacle supplies a motor load, the receptacle must have an ampere rating not less than the motor's full-load current. For a motor with a full-load current of 12 A, a 15 A receptacle is acceptable. For a motor drawing 18 A, a 20 A receptacle is required.

1.4.3 Grounding and Polarization

Receptacles must be grounded and polarized per 406.4. Replacement receptacles must be of the same type and rating as the original. A master must verify that replacement receptacles in older installations are grounded — if no equipment grounding conductor exists, a GFCI-type receptacle may be used and marked "No Equipment Ground" (406.4(D)(2)(b)).

1.4.4 Tamper-Resistant and Weather-Resistant

Tamper-resistant receptacles are required in all 125 V, 15 A and 20 A receptacles in areas accessible to children (406.12). Weather-resistant receptacles are required in wet or damp locations (406.9). For commercial kitchens and outdoor areas, both features are often required.

1.5 Switchboards and Panelboards (Article 408)

Panelboards are a critical area for the Master exam. You must understand the relationship between the panelboard rating, the main overcurrent device, and the number of circuits.

1.5.1 Panelboard Overcurrent Protection

Per 408.36, each panelboard must be protected on the supply side by an overcurrent device with a rating not greater than the panelboard's rating. A 200 A panelboard must be fed from a 200 A or smaller overcurrent device.

Exception: A panelboard may be fed from a larger overcurrent device if the panelboard is rated for the higher fault current and the supply conductors are protected at their ampacity. This is common in "main lug only" panels fed from a service disconnect.

1.5.2 Circuit Identification

Every circuit must be clearly identified at the panelboard (408.4). A master must verify that the directory is legible and accurate. This is a frequent inspection finding.

1.5.3 Phase Arrangement

For 3-phase panelboards, the phase arrangement must be such that the loading is balanced. While the NEC does not mandate a specific phase rotation, the master must ensure that the panelboard is marked with the system voltage and phase (408.3). A 208Y/120 V panelboard must not be used on a 240 V delta system unless it is listed for that purpose.

1.6 Fixed Electric Space Heating (Article 424)

Fixed electric space heating includes baseboard heaters, radiant heating cables, and heat pumps with electric resistance elements. For the Master exam, focus on the branch-circuit sizing.

1.6.1 Branch-Circuit Sizing

Per 424.3, fixed electric space heating equipment is considered a continuous load. Therefore, the branch circuit must be sized at 125% of the total connected load. A 10 kW heater at 240 V draws 41.7 A. The branch circuit must be rated at 52.1 A, which requires a 60 A circuit with conductors rated for at least 52.1 A (use 60°C column for terminations unless otherwise marked).

1.6.2 Multiple Heaters on One Circuit

Multiple heaters may be on one branch circuit, but the total load must not exceed the circuit rating after the 125% continuous load factor. A 20 A circuit can supply heaters totaling 16 A (20 A ÷ 1.25).

1.6.3 Clearances

Heaters must maintain clearance from combustible materials (424.9). The manufacturer's instructions govern, but a general rule is 12 inches from the floor and 6 inches from drapes or furniture. A master must verify that heaters are not installed below receptacles where cords could drape over the heater.

1.7 Motors and Generators (Articles 430 and 445)

Motor applications are the most complex area of Chapter 4. A Master electrician must be able to size conductors, overcurrent protection, and controllers for any motor installation.

1.7.1 Motor Full-Load Currents

Use Tables 430.247 through 430.250 to determine full-load currents. For a 3-phase, 460 V motor of 25 hp, Table 430.250 gives 34 A. Do not use the nameplate current for branch-circuit and feeder sizing — use the table values. The nameplate is used only for overload protection.

1.7.2 Branch-Circuit Conductors

Per 430.22, branch-circuit conductors must have an ampacity of 125% of the motor's full-load current. For the 25 hp motor above (34 A), conductors must be rated at 42.5 A. Using 75°C terminations, this requires 8 AWG copper (50 A at 75°C).

1.7.3 Overload Protection

Overload devices (heaters, electronic relays) are sized from the nameplate full-load current, per 430.32. The overload must be set at no more than 125% of the nameplate for motors with a service factor of 1.15 or greater, or a temperature rise of 40°C or less. For other motors, the maximum is 115%.

1.7.4 Short-Circuit and Ground-Fault Protection

The branch-circuit short-circuit and ground-fault protective device (typically a breaker or fuse) is sized per Table 430.52. For a 3-phase squirrel-cage motor, the maximum rating is 250% of the full-load current for inverse-time breakers, or 175% for non-time-delay fuses. The 25 hp motor at 34 A can have a breaker up to 85 A (34 × 2.5 = 85 A). A standard 90 A breaker would be too large; you would need to use a 80 A breaker or a fuse.

1.7.5 Motor Controllers

The controller must have a horsepower rating not less than the motor's rating (430.83). A 25 hp motor requires a controller rated for at least 25 hp. A controller with a higher horsepower rating is always acceptable.

1.7.6 Disconnecting Means

A motor disconnecting means must be within sight of the motor and controller (430.102). "Within sight" means visible and not more than 50 feet away. The disconnect must open all ungrounded conductors.

1.7.7 Generators (Article 445)

Generators are treated similarly to motors for conductor sizing. The ampacity of the generator output conductors must be at least 115% of the generator's rated output (445.13). Overcurrent protection must be provided per 445.12. A master must verify that a generator used as a separately derived system has the neutral bonded to ground at the generator only if it is the first disconnecting means.

1.8 Transformers (Article 450)

Transformers are a critical component of commercial and industrial installations. The Master exam will test your ability to size transformer overcurrent protection and understand the implications of transformer connections.

1.8.1 Overcurrent Protection

Per 450.3, transformers must be protected against overcurrent on both the primary and secondary sides.

Primary protection only: If the primary overcurrent device is rated at 125% or less of the transformer's primary full-load current, no secondary protection is required.

Primary and secondary protection: If the primary device is rated between 125% and 250% (for transformers over 600 V) or up to 125% (for transformers 600 V or less), the secondary must have protection at 125% of the secondary full-load current.

Example: A 75 kVA transformer, 480 V primary, 208Y/120 V secondary. Primary full-load current = 75,000 ÷ (480 × 1.732) = 90.2 A. Primary protection at 125% = 112.8 A. A 110 A breaker is acceptable. Secondary full-load current = 75,000 ÷ (208 × 1.732) = 208 A. Secondary protection at 125% = 260 A. A 250 A breaker is acceptable.

1.8.2 Transformer Impedance and Fault Current

A master must understand that transformer impedance affects available fault current. A 75 kVA transformer with 5% impedance will have a short-circuit current of approximately 20 times its full-load current. This must be considered when selecting equipment with adequate interrupting ratings.

1.8.3 Separately Derived Systems

A transformer secondary is a separately derived system. The neutral must be bonded to the equipment grounding conductor at the transformer or at the first disconnecting means (250.30). The grounding electrode conductor must be sized from Table 250.66 based on the largest ungrounded conductor.

1.9 Code Navigation — Where to Find It

Topic	NEC Reference
Flexible cord ampacity	Table 400.5(A)(1)
Flexible cord uses	400.10
Switch ratings	404.14
Receptacle configurations	406.6
Receptacle in wet locations	406.9
Tamper-resistant receptacles	406.12
Panelboard protection	408.36
Panelboard circuit identification	408.4
Fixed space heating branch circuits	424.3
Heater clearances	424.9
Motor full-load currents	Tables 430.247–430.250
Motor branch-circuit conductors	430.22
Motor overload protection	430.32
Motor short-circuit protection	Table 430.52
Motor disconnecting means	430.102
Generator conductors	445.13
Transformer protection	450.3
Separately derived systems	250.30

1.10 Inspection and Supervision Points

As a Master electrician, you are responsible for the work of others. On site, verify the following:

120.Flexible cords are not run through walls, under carpets, or through doorways.

121.Receptacles in commercial kitchens and outdoor areas are both GFCI-protected and weather-resistant.

122.Panelboard directories are filled out completely and legibly.

123.Motor disconnects are within sight of the equipment and are capable of being locked in the open position.

124.Transformer secondary neutrals are bonded correctly, and the grounding electrode conductor is properly sized.

125.Space heating circuits are sized at 125% of the connected load.

126.All equipment has the correct interrupting rating for the available fault current.

1.11 Common Exam Traps

129.Using nameplate current instead of table current for motor branch-circuit sizing.

130.Sizing a 20 A circuit for 20 A of continuous load — must use 16 A for continuous loads.

131.Forgetting the 80% rule for inductive loads on switches.

132.Using a single-pole switch on a 3-phase motor circuit.

133.Installing a 15 A receptacle on a 20 A individual branch circuit.

134.Failing to apply the 125% continuous load factor to space heating.

135.Oversizing transformer primary protection without adding secondary protection.

136.Using a 90 A breaker for a motor that calculates to 85 A maximum — must round down.

Summary

This chapter covers the core of NEC Chapter 4. As a Master candidate, you must be able to apply these rules in real-world scenarios — sizing conductors for a 3-phase motor feeder, protecting a transformer, and supervising the installation of receptacles and switches. The NEC is your primary reference during the exam, but you must know where to look and how to apply the tables. Practice navigating the code quickly, and always verify the latest amendments in the New Hampshire Laws and Rules, which may adopt or modify specific NEC sections.

Equipment for General Use