Overview of Chapter 4
Chapter 4 covers the installation requirements for the most commonly encountered electrical equipment. From the switches and receptacles in every room to the motors that power industrial processes, this chapter provides the rules for connecting and protecting general-use equipment. Motor circuit calculations and luminaire installation rules are particularly prominent on the NEC exam.
Exam Tip: Motor circuit questions are among the most calculation-intensive on the exam. Focus on understanding the difference between motor overload protection and branch-circuit short-circuit protection, and know how to use Tables 430.248 and 430.250.
Flexible Cords and Cables (Article 400)
Flexible cords and cables connect portable equipment, pendant luminaires, and appliances to permanently installed receptacles. They are not intended as a substitute for fixed wiring.
- Flexible cords must not be run through holes in walls, ceilings, or floors.
- They must not be concealed behind building structures.
- Each cord must be connected to a plug or be directly wired to the equipment.
- Common types include SJ, SJO, SO, and SJOOW cords, each rated for specific conditions and uses.
Switches (Article 404)
Article 404 governs the installation of switches that control lighting, receptacles, and other equipment.
- Switches must be rated for the voltage and current they control.
- Three-way and four-way switches must be wired so that the switching occurs only in the ungrounded (hot) conductor. The grounded (neutral) conductor must not be switched.
- A grounded conductor (neutral) must be provided at switch locations where switches control lighting loads, unless certain exceptions apply. This requirement ensures compatibility with electronic switches and dimmers.
- Snap switches must be installed in boxes or enclosures, and the box must be accessible.
Receptacles (Article 406)
Receptacle outlets are the most numerous devices in most electrical installations.
- Receptacles installed on 15A and 20A, 125V branch circuits must be listed tamper-resistant (TR) in dwelling units, guest rooms, and child care facilities.
- Weather-resistant receptacles are required for outdoor, wet, and damp locations.
- Receptacles must be installed with the grounding slot properly oriented and the grounding terminal connected to the equipment grounding conductor.
- Replacement receptacles at locations that require GFCI protection must be GFCI-protected, even if the original receptacle was not.
Luminaires (Article 410)
Article 410 covers the installation of lighting fixtures (luminaires), lampholders, and lamps.
General Requirements
- Luminaires must be listed and installed according to the listing instructions.
- In clothes closets, specific clearance requirements prevent fire hazards. Surface-mounted incandescent or LED luminaires must maintain at least 12 inches of clearance from the nearest point of a storage space.
- Recessed luminaires must be installed so that adjacent combustible material is not subjected to temperatures in excess of 90 degrees C.
Support and Connection
- Luminaires weighing more than 6 pounds or exceeding 16 inches in any dimension must not be supported by the screw shell of a lampholder.
- Outlet boxes used as the sole support for luminaires must be listed and identified for that purpose and must support the weight of the fixture.
Appliances (Article 422)
Article 422 covers permanently connected and cord-and-plug-connected appliances such as water heaters, dishwashers, and garbage disposals.
- A disconnecting means must be provided for each appliance, located within sight of the appliance or capable of being locked in the open position.
- Branch-circuit conductors supplying a single continuous-load appliance must be rated at not less than 125% of the appliance marked rating.
- Storage-type water heaters must have a branch circuit rated at not less than 125% of the nameplate rating.
Motors and Motor Controllers (Article 430)
Article 430 is one of the most extensive articles in the NEC. It establishes a layered system of protection for motor circuits.
Motor Circuit Protection Layers
- Branch-circuit short-circuit and ground-fault protection (430.52): Protects the circuit conductors and motor from short circuits. Sized as a percentage of the full-load current from Table 430.248 (single-phase) or 430.250 (three-phase), not the nameplate current.
- Motor overload protection (430.32): Protects the motor from sustained overcurrent that could cause overheating. Typically set at 115% to 125% of the motor nameplate full-load current rating.
- Branch-circuit conductor sizing (430.22): Conductors must be sized at 125% of the motor full-load current from the applicable table.
Critical Rule: Always use the full-load current values from NEC Tables 430.248 or 430.250 for conductor sizing and overcurrent protection calculations, not the motor nameplate current.
Disconnecting Means
Every motor must have a disconnecting means within sight of the motor and the controller. The disconnect must be rated at least 115% of the motor full-load current.
Transformers (Article 450)
Article 450 covers the installation of transformers rated up to 1000 volts, including overcurrent protection, ventilation, and accessibility.
- Transformer overcurrent protection is determined by Table 450.3(B) for transformers rated 1000 volts or less. Primary-only protection is set at a maximum of 125% of the rated primary current.
- Dry-type transformers installed indoors must be readily accessible unless they meet specific exceptions for mounting above suspended ceilings or in certain rated enclosures.
- Adequate ventilation must be provided to prevent transformer temperatures from exceeding their rated limits.
