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The information provided on this website, is for education and informational purposes only. By accessing this information, you are acknowledging and agreeing to the following terms:
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Intent
The purpose of this webpage is to provide a comprehensive resource for anyone looking to enter the industrial electrical installation field, with a focus on aerospace and rocket engine test facilities. One of the most challenging aspects of this field is navigating the vast array of electrical standards that ensure the safe operation of equipment. Among these, NFPA 70: The National Electrical Code (NEC) is the most commonly referenced document. The NEC is a comprehensive rulebook for electrical installations designed to prevent injury and damage, but its depth and complexity make it difficult to grasp without proper training. For electricians, mastering the code often requires years of coursework and hands-on experience. Engineers, however, typically lack this foundational training when entering the field. This webpage aims to bridge that gap by breaking down the key sections of the NEC that are most relevant to industrial applications, making it more accessible to those transitioning into this space from other disciplines or industries.
Introduction
ARTICLE 90: INTRODUCTION
Article 90: Introduction
The first part of NFPA70 is Article 90 which serves as an introduction to how the code book is structured:
Use and Application (90.2)
The NEC aims to provide practical safeguards for people and property from hazards associated with electricity.
It is not intended to serve as:
What the Code Covers
What the Code Does Not Cover
It is not intended to serve as:
- A design specification.
- An instruction manual for untrained individuals.
What the Code Covers
- Public and private premises, including buildings, structures, mobile homes, recreational vehicles, and floating buildings.
- Outdoor areas, such as yards, lots, parking lots, carnivals, and industrial substations.
- Electrical supply connections, including installations of conductors and equipment that connect to the supply of electricity.
- Utility-related installations:
- Facilities like office buildings, warehouses, garages, machine shops, and recreational buildings not integral to generating plants, substations, or control centers.
- Shore power installations, supplying power to ships and watercraft in marinas and boatyards, including monitoring for leakage currents.
- Vehicle-to-grid installations, allowing electric power export from vehicles to premises wiring or supporting bi-directional current flow.
What the Code Does Not Cover
- Transportation-specific installations, such as:
- Ships, watercraft (excluding floating buildings), railway rolling stock, aircraft, and automotive vehicles (other than RVs or mobile homes).
- Mining-specific installations, including:
- Underground mining and self-propelled mobile surface mining machinery with its attendant electrical trailing cables.
- Railway-specific installations used exclusively for:
- Generation, transformation, transmission, energy storage, or power distribution for rolling stock operations.
- Signaling and communication systems.
- Electric utility-controlled installations, such as:
- Installations under the exclusive control of an electric utility where these installations
Code Arrangement (90.3)
he NEC is divided into nine chapters, each addressing specific aspects of electrical installations:
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Who Enforces the Code? (90.4)
The enforcement of the NEC is assigned to the Authority Having Jurisdiction (AHJ). Article 90.4 provides the following key points regarding enforcement:
1. Role of the AHJ:
1. Role of the AHJ:
- The AHJ is responsible for enforcing the NEC to ensure installations comply with its requirements.
- They have the authority to interpret the rules within the code and determine how they are applied in specific situations.
- The AHJ decides whether equipment, materials, or installations meet the standards outlined in the NEC.
- This includes approving new or innovative technologies that may not be explicitly addressed in the code.
- The AHJ can grant special permissions to modify or waive specific code requirements when deemed appropriate.
- These permissions are typically granted when alternative methods can achieve equivalent safety levels or compliance with the intent of the NEC.
- The AHJ ensures that installations are inspected and maintained in compliance with the code.
- They also have the authority to shut down unsafe or non-compliant installations to protect people and property.
- While the NEC serves as a national standard, local jurisdictions may adopt amendments or additional rules. The AHJ enforces both the NEC and any applicable local requirements.
How to Interpret the Code (90.5)
1. Mandatory Requirements (90.5(A))
2. Permissive Provisions (90.5(B))
3. Explanatory Material (90.5(C))
4. Other Standards and References
- Definition: Rules that use the terms "shall" or "shall not" are mandatory. These requirements must be followed as written, with no exceptions unless explicitly allowed by the code or the Authority Having Jurisdiction (AHJ).
- Purpose: These provisions are designed to ensure the safety of electrical installations and compliance with the code.
2. Permissive Provisions (90.5(B))
- Definition: Rules that use the terms "shall be permitted" or similar language indicate permissive provisions. These provisions describe actions, designs, or materials that are allowed but not required.
- Purpose: Permissive provisions provide flexibility, offering alternative methods or designs that meet the code's intent while maintaining safety.
3. Explanatory Material (90.5(C))
- Definition: Text in the NEC that is included for explanatory purposes is not enforceable as a requirement. This material is typically found in:
- Fine Print Notes (FPNs), now referred to as Informational Notes.
- Examples, calculations, or references to other codes or standards.
- Purpose: Explanatory material helps clarify the intent of a rule or provides additional context but does not impose any requirements.
4. Other Standards and References
- Article 90.5 notes that the NEC may refer to other codes or standards for additional information or requirements. While these references provide valuable context, they may not always be enforceable under the NEC unless adopted separately by the AHJ.
Formal Interpretations (90.6)
Purpose: Allows for the development of formal interpretations of the NEC by the National Fire Protection Association (NFPA)
1. You can Request an Interpretation:
1. You can Request an Interpretation:
- Formal interpretations can be requested when there is uncertainty or disagreement about the meaning of a specific NEC rule.
- These interpretations are issued by the NFPA and are considered authoritative. However, they do not override the authority of the Authority Having Jurisdiction (AHJ) in the enforcement of the code.
- Formal interpretations are intended to provide clarity and consistency in applying the code but are not a substitute for the judgment of the AHJ or local amendments.
Examination of Equipment (90.7)
Purpose: Explains the NEC’s approach to the approval and examination of equipment for safety compliance. It outlines that the NEC relies on the use of equipment that has been properly tested and listed by qualified organizations.
1. Safety Assumptions:
1. Safety Assumptions:
- The NEC assumes that equipment used in installations will:
- Be properly constructed.
- Meet the appropriate safety standards.
- Be approved for its intended use.
- Equipment should be tested and listed by qualified organizations (e.g., UL, CSA) to ensure compliance with applicable safety standards.
- Testing and listing serve as evidence that the equipment meets minimum safety requirements.
- The AHJ may require additional evidence or evaluation of equipment that is not listed or labeled to determine if it is safe for use.
- Article 90.7 reminds users that the NEC is not an equipment design standard. It assumes the use of tested and approved equipment, leaving detailed design and construction to the manufacturers.
Wire Planning (90.8)
Purpose: Emphasizes the importance of planning electrical installations to ensure not just safety but also long-term functionality, efficiency, and adaptability. While compliance with the NEC is mandatory, 90.8 highlights practical considerations for installations beyond the minimum code requirements.
1. Future Expansion (90.8(A)):
1. Future Expansion (90.8(A)):
- Electrical systems should be planned with consideration for potential future expansion or changes in usage.
- This includes sizing conductors, raceways, and panels to accommodate additional loads without requiring major modifications.
- Factors beyond basic safety should be considered in the design of electrical systems, such as:
- Convenience: Ensuring the system is easy to maintain and operate.
- Efficiency: Minimizing energy losses and ensuring optimal system performance.
- Good Service: Designing systems to meet current and foreseeable needs effectively.
- While these considerations are not enforceable under the NEC, they contribute to the overall quality of an installation.
Units of Measurement (90.9)
Purpose: Establishes that measurements and values specified in the NEC are provided in both metric (SI) and inch-pound (imperial) units. The goal is to ensure clarity and consistency in interpretation across different systems of measurement.
1. Preference (90.9(A))
Soft vs. Hard Conversion
1. Preference (90.9(A))
- International System of Units (SI), are the preferred standard of measurement.
- Values in the NEC are presented in both metric and inch-pound units. SI units first, followed by inch-pound units in parentheses.
- Soft conversions are allowed in specific cases where exact conversions (hard conversions) are not practical or may cause issues. These include:
- Trade Sizes:
- When the nominal size of a product differs from its actual measured size, trade size designations (not exact dimensions) should be used.
- Example: Conduit or pipe sizes follow trade size standards, not precise dimensions.
- Extracted Material:
- When the NEC incorporates material from another standard, the context and meaning of the original material must remain intact. Edits are limited to aligning with NEC style.
- Industry Practice:
- In cases where industry standards express units in inch-pound terms, SI units are not required.
- Safety:
- If using hard conversions would negatively affect safety, soft conversions are permitted.
- Trade Sizes:
- Conversions between inch-pound and SI units may be approximate, provided they ensure safety and usability.
- Compliance with the NEC can be achieved using either the SI or inch-pound system, provided all requirements are met.
Soft vs. Hard Conversion
- Soft Conversion: Maintains compatibility with existing sizes or standards without altering the actual dimensions. Example: ½ inch = 12.7 mm.
- Hard Conversion: Adjusts dimensions or properties to align directly with the converted units, sometimes resulting in slightly altered measurements. Example: ½ inch ≈ 13 mm.
Chapter 1: Definitions
Chapter 2: Wiring and Protection
ARTICLE 200: USE & IDENTIFICATION OF GROUNDED CONDUCTORS
Focuses on the identification, isolation, and proper use of grounded conductors (neutral conductors).
Scope (200.1)
Provides requirements for the identification and use of grounded conductors. Grounded conductors are integral to electrical systems and ensure the safe operation of circuits by providing a return path for current to the source.
Do not confuse the term "Grounded Conductor" with "Equipment Grounding Conductor"
- Grounded Conductor (Sometimes known as Neutral Conductor):
- This creates a reference point for the system voltage and ensures fault currents can return to the source safely.
- Equipment Grounding Conductor (EGC)
- Is designed specifically to connect metallic enclosures, raceways, and equipment to the earth ground.
- It serves as the path for fault currents to flow back to the panel, tripping the breaker in case of a fault.
General (200.2)
Grounded Conductors must be:
- Properly identified (In 200.6 you'll see that they must be either: Solid White / White with a Strip / Solid Grey or use wire markers)
- Isolated from ungrounded conductors (They must not accidentally or deliberately be shorting under normal operating conditions)
- They cannot be used as a grounding means for equipment or enclosures (Use EGC wire instead)
- This ensures that the grounded conductor (commonly the neutral) is reserved solely for its intended role, minimizing safety risks.
Connection to Grounded System (200.3)
Requires the grounded conductor of a premises wiring system to be connected to the grounded conductor of the utility service (ie. tie the utility service drop and the building's grounded conductors together at the main panel)
- This connection ensures a stable reference point (0V potential) for the system, essential for safety and fault detection.
Neutral Conductors (200.4)
200.4 (A) states that explicitly prohibits the sharing of a neutral conductor (grounded conductor) between separate circuits. (even through they may be tied together at the main panel)
- Each circuit must have its own neutral conductor, which ensures that the current return path is properly contained within that circuit.
- Sharing neutrals between circuits can lead to:
- Overloading the neutral: If separate circuits are on the same phase, the neutral could carry the sum of the currents from both circuits, potentially exceeding its rated capacity.
- Exception 1: If the raceway or cable entering the enclosure clearly shows the grouping.
- Exception 2: If the circuit simply enters and passes through the enclosure without being terminated or spliced or a service loop is created (adding excess wiring in the enclosure)
Means of Identification for Grounded Conductors (200.6)
Only pertains to the Grounded Conductors. Only applies to systems operating at 60V or more (See Article 720 or 690 for governance)
200.6 (A) Sizes 6 AWG or Smaller must be identified by one of the following means:
200.6 (A) Sizes 6 AWG or Smaller must be identified by one of the following means:
- Continuous White Outer Finish
- Continuous Gray Outer Finish
- Three Continuous White or Gray Stripes on insulation of any color other than green.
- White or Gray Insulation with Tracer Threads in the braid indicating the source of manufacture.
- Photovoltaic Systems: A single-conductor, outdoor-rated cable can be marked at terminations with white or gray.
- Mineral-Insulated, Metal-Sheathed Cable (Type MI): Identified at terminations with a white or gray marking encircling the insulation.
- Fixture Wire: Complies with grounded conductor identification in Article 402.8.
- Aerial Cable: Identified by means such as ridges on the cable exterior.
- Continuous White Outer Finish
- Continuous Gray Outer Finish
- Three Continuous White or Gray Stripes on insulation of any color other than green.
- Field Marking: Mark the conductor with white or gray at its terminations. This marking must completely encircle the conductor insulation and can be applied using tape, paint, or other permanent means.
200.6 (C) Flexible Cords
When grounded conductors from different nominal voltage systems share a common raceway, enclosure, or box:
- Must follow Article 400.22, which specifies white or grey as the standard outer finish or another permitted marking
When grounded conductors from different nominal voltage systems share a common raceway, enclosure, or box:
- Each nominal voltage system's grounded conductor must be distinctly identified.
- Example: Use white for 120/208V systems and gray for 277/480V systems.
- Identification can include:
- Different colored stripes.
- Other markings consistent with 200.6(A) or (B).
- Documentation of the identification method must be:
- Permanently posted at the location where the conductors originate.
- Readily accessible for reference during maintenance or troubleshooting.
200.6 (E) Grounded Conductors in Multiconductor Cables
- Identification must include one of the following:
- A continuous white or gray outer finish
- Three continuous white or gray stripes along the insulation.
- For flat multiconductor cables (4 AWG or larger), an external ridge is permitted for identification.
- Exceptions:
- Conductors in multiconductor cables may be re-identified at their terminations with white or gray markings.
- Varnished-cloth-insulated cables may also be re-identified with appropriate markings at terminations.
Means of Identifying Grounded Conductors for Other Purposes (200.7)
This article specifies the proper use of white or gray insulation (or three continuous white/gray stripes) in grounded and ungrounded conductors. It ensures clarity and prevents confusion in identifying conductors, especially in switch loops and other unique cases.
200.7 (A) Other than as specified in 200.7(B) and (C), the following should only be used for Grounded Conductors:
200.7 (B) Circuits <50V:
The use of white or gray insulation in circuits operating at 50 volts or more is generally limited to grounded conductors but may be re-identified for specific uses:
200.7 (A) Other than as specified in 200.7(B) and (C), the following should only be used for Grounded Conductors:
- A continuous white outer finish.
- A continuous gray outer finish.
- Three continuous white or gray stripes on insulation of any color other than green.
200.7 (B) Circuits <50V:
- Conductors with white or gray insulation or three white stripes must be grounded for circuits under 50 volts, as per 250.20(A).
- White or gray insulation must not be used for ungrounded conductors in these low-voltage systems.
The use of white or gray insulation in circuits operating at 50 volts or more is generally limited to grounded conductors but may be re-identified for specific uses:
- Re-Identification for Ungrounded Conductors:
- A conductor with white or gray insulation may be re-identified at its terminations and at all accessible points to indicate it is being used as an ungrounded conductor.
- Re-identification must:
- Use marking tape, paint, or another permanent method.
- Encircle the conductor insulation completely.
- Examples: Used in switch loops or when powering devices such as motors or heating equipment.
- In switch loops, re-identified white conductors may only supply the switch but cannot be the switched conductor returning to the outlet.
- Flexible Cords:
- White or gray insulation (or three continuous white/gray stripes) in flexible cords is permitted if the cord is used for appliances or equipment in compliance with 400.22.
Means of Identification of Terminals (200.9)
Terminals for grounded conductors must be clearly identified.
- These terminals are silver or marked to distinguish them from those used for ungrounded (hot) conductors, ensuring correct connections during installation.
Identification of Terminals (200.10)
Provides requirements for identifying terminals used to connect grounded conductors (typically neutral wires) in electrical devices, ensuring proper connections and preventing miswiring.
200.10 (A) Device Terminals
200.10 (A) Device Terminals
- Terminals for grounded conductors must be clearly marked unless the intended connection is obvious from the device's design.
- Exclusion: Devices rated over 30 amperes do not require terminal identification unless they are polarized receptacles or plugs.
- For polarized plugs, receptacles, and connectors, the terminal for the grounded conductor must be identified:
- By a white or silver-colored terminal, or a marking adjacent to the terminal with the word "white" or the letter "W."
- If the terminal is not visible, the conductor entrance hole must be colored white or marked with "white" or "W."
- For devices with screw shells (e.g., light bulb sockets), the terminal for the grounded conductor must connect to the screw shell.
- For screw shell devices with attached leads:
- The conductor attached to the screw shell must have a white or gray finish.
- The other conductor must have a distinct, solid color to avoid confusion with the grounded conductor.
- Appliances with single-pole switches, overcurrent devices, or screw shell lampholders connected to the line must have terminals for grounded conductors clearly identified.
- This applies to:
- Permanently wired appliances.
- Field-installed plugs and cords with three or more wires (including an equipment grounding conductor).
Polarity of Connections (200.11)
- The polarity of grounded conductors must be maintained throughout the entire system.
- Proper polarity ensures that the grounded conductor carries current safely under normal operation and that it functions correctly as a return path in the system.
- Reverse polarity can lead to unsafe operation of devices, increased risk of electrical shock, or damage to equipment.
ARTICLE 210: BRANCH CIRCUITS NOT >1000VAC, >1500VDC
Scope (210.1)
This article provides requirements for "Branch Circuits" <1000 VAC OR <1500 VDC. Branch Circuits are the conductors that are between the final overcurrent device protecting the circuit and the outlet(s). These circuits supply power to two or more receptacles or outlets for utilization equipment.
Reconditioned Equipment (210.2)
This section prohibits the "reconditioning" of specific types of equipment critical for electrical safety. In the context of the NEC, "reconditioning" would mean to repair or restore used equipment to like-new functionality.
The following devices shall not be reconditioned:
1. Ground-Fault Circuit-Interrupter (GFCI) Devices:
The following devices shall not be reconditioned:
1. Ground-Fault Circuit-Interrupter (GFCI) Devices:
- Equipment providing ground-fault circuit-interrupter protection for personnel must not be reconditioned.
- GFCI devices are safety-critical and are designed to protect against electrical shock; their reliability must not be compromised by reconditioning.
- Equipment providing arc-fault circuit-interrupter protection must not be reconditioned.
- AFCI devices protect against electrical fires caused by arcing faults, and reconditioning could impair their functionality.
Other Articles for Specific Purpose Branch Circuits (210.3)
This section simply references specific equipment and applications that are not in Chapters 5-7 that supplement the requirements of this article.
Equipment |
Section |
Air-conditioning and Refrigerated Equip. |
440.6, 440.31, and 440.32 |
Busways |
368.17 |
Central Heating Equip. other than fixed Electric Space-Heating |
422.12 |
Fixed Electric Heating Equip. for Pipelines & Vessels |
427.4 |
Fixed Electric Space-Heating Equip. |
424.4 |
Fixed Outdoor Electrical Deicing and Snow-Melting Equip. |
426.4 |
Infrared Lamp Industrial Heating Equip. |
422.48 and 424.3 |
Motors, motor circuits, and controllers |
430 |
Switchboards and panel boards |
408.52 |
Multiwire Branch Circuits (210.4)
This article defines the requirements and conditions for using multiwire branch circuits, which share a neutral conductor between two or more ungrounded (hot) conductors. These circuits are often used to optimize wiring efficiency, reduce raceway fill, and balance loads across phases in single-phase or three-phase systems.
210.4 (A) General
- Multiwire branch circuits are permitted and are considered multiple circuits.
- All conductors of a multiwire branch circuit (ungrounded, grounded, and equipment grounding conductors) must originate from the same enclosure containing the branch-circuit overcurrent protective device(s).
- For such circuits, the use of non-linear loads (e.g., computers or motor drives) can produce harmonic currents that flow on the neutral, this has the potential to damage other devices on the same circuit, necessitating proper design.
- Refer to 300.13(B) for continuity of grounded conductors in multiwire circuits.
- Multiwire branch circuits must have a means to simultaneously disconnect all ungrounded conductors at the point of origin.
- This can be achieved using:
- A single multi-pole circuit breaker.
- Two or more single-pole breakers with an identified handle tie.
- This can be achieved using:
- Purpose: Ensures the circuit can be safely de-energized for maintenance, preventing electric shock risks during work.
210.4 (C) Line-to-Neutral Loads
- Multiwire branch circuits are generally limited to supplying line-to-neutral loads.
- Exceptions:
- A multiwire branch circuit that supplies a single utilization device (e.g., electric range) may supply line-to-line loads.
- A multiwire branch circuit may supply line-to-line loads if all ungrounded conductors are simultaneously disconnected by the branch-circuit overcurrent protective device.
- Multiwire branch circuits are generally limited to supplying line-to-neutral loads.
210.4 (D) Grouping
- Ungrounded and grounded conductors of each multiwire branch circuit must be grouped within the enclosure, as required by 200.4(B).
- This makes it easier to identify which conductors belong to the same circuit during installation or troubleshooting.
Identification of Branch Circuits (210.5)
This section provides requirements for the identification of conductors in branch circuits, focusing on grounded, equipment grounding, and ungrounded conductors in systems supplied by multiple nominal voltages or direct current (DC) sources.
210.5 (A) Grounded Conductor
210.5 (B) Equipment Grounding Conductor
210.5 (C) Identification of Ungrounded Conductors
Ungrounded (hot) conductors must be identified according to 210.5(C)(1) for AC systems or 210.5(C)(2) for DC systems:
210.5 (A) Grounded Conductor
- The grounded conductor of a branch circuit must be identified according to 200.6.
- Typically identified by white or gray insulation.
210.5 (B) Equipment Grounding Conductor
- The equipment grounding conductor must be identified according to 250.119.
- Typically identified by green insulation or a bare conductor.
210.5 (C) Identification of Ungrounded Conductors
Ungrounded (hot) conductors must be identified according to 210.5(C)(1) for AC systems or 210.5(C)(2) for DC systems:
- (1) Branch Circuits Supplied from More Than One Nominal Voltage System
- When a building has multiple voltage systems (e.g., 208Y/120V and 480Y/277V), ungrounded conductors must be identified by phase and nominal voltage system.
- Identification must be applied at all termination, connection, and splice points.
- (a) Means of Identification
- Can include:
- Color coding (most common).
- Marking tape.
- Tagging.
- Other approved means.
- The chosen method must be consistent throughout the premises.
- Can include:
- (b) Posting of Identification Means
- The method of identification must be documented and either:
- Permanently posted at each panelboard or branch-circuit distribution equipment.
- Readily available for reference.
- Exception:
- In existing buildings, only newly added voltage systems must be marked.
- Existing unmarked systems do not require retroactive identification, but a label must be added to indicate their presence.
- (2) Branch Circuits Supplied from Direct-Current (DC) Systems
- DC systems above 60V require ungrounded conductors to be identified by polarity at all terminations, connections, and splice points.
- Identification must be documented and either:
- Permanently posted at each panelboard or distribution equipment.
- Readily available for reference.
- (a) Positive Polarity (6 AWG or Smaller) Each positive ungrounded conductor must be identified by one of the following:
- A continuous red outer finish.
- A continuous red stripe along insulation of a different color.
- Imprinted "+" symbols or “POS” or “POSITIVE” on insulation (color cannot be green, white, gray, or black).
- Approved permanent marking (e.g., sleeving, shrink tubing) with "+" or "POS".
- (b) Negative Polarity (6 AWG or Smaller) Each negative ungrounded conductor must be identified by one of the following:
- A continuous black outer finish.
- A continuous black stripe along insulation of a different color.
- Imprinted "−" symbols or “NEG” or “NEGATIVE” on insulation (color cannot be green, white, gray, or red).
- Approved permanent marking (e.g., sleeving, shrink tubing) with "− or "NEG".
Branch-Circuit Voltage Limitations (210.6)
This section establishes voltage limitations for branch circuits based on different occupancy types and utilization equipment to ensure safe electrical installations.
210.6 (A) Occupancy Limitation
210.6 (B) 120V Between Conductors
210.6 (A) Occupancy Limitation
- In dwelling units, hotels, motels, dormitories, and similar occupancies, branch circuits cannot exceed 120V nominal between conductors for the following:
- Luminaires (lighting fixtures).
- Cord-and-plug connected loads up to 1440 VA or motors less than ¼ HP.
- Purpose: Prevents electrical shock hazards in residential-type sleeping areas by limiting voltage exposure.
210.6 (B) 120V Between Conductors
- Circuits with 120V nominal between conductors can be used for:
- Lampholders (light bulb sockets) rated for 120V.
- Auxiliary equipment for electric-discharge lamps (e.g., ballasts, starters).
- Cord-and-plug connected or permanently connected utilization equipment (e.g., appliances, power tools).
- Typical Uses: Fluorescent lighting, ballasts, small appliances.
210.6 (B) 277V to Ground
- Circuits exceeding 120V but not exceeding 277V to ground can supply:
- Electric-discharge luminaires with integral ballasts.
- LED luminaires with drivers between the branch circuit and lampholders.
- Incandescent or LED luminaires with medium-base screw shell lampholders, as long as the lampholders operate at 120V or less through an integrated step-down transformer or LED driver.
- Mogul-base screw shell luminaires.
- Luminaires with non-screw shell lampholders (non-medium/mogul).
- Luminaires without lampholders.
- Auxiliary equipment for electric-discharge or LED-type lamps.
- Luminaires with listed LED retrofit kits.
- Typical Uses: Commercial and industrial lighting applications where 277V systems are common.
- Special Consideration: Incandescent luminaires are only permitted on 277V circuits if they include an internal step-down autotransformer that limits the voltage at the lampholder to 120V.
210.6 (B) 1000 Volts AC or 1500 Volts DC Between Conductors
- Circuits above 277V but not exceeding 1000V AC or 1500V DC can supply:
- Auxiliary equipment for electric-discharge lamps in permanently mounted luminaires, installed at:
- ≥ 6.7 meters (22 ft) for outdoor structures (highways, roads, bridges, parking lots).
- ≥ 5.5 meters (18 ft) for other structures (e.g., tunnels).
- Cord-and-plug or permanently connected utilization equipment (excluding luminaires).
- Luminaires powered by direct-current (DC) systems where:
- They have a listed DC-rated ballast with electrical isolation to prevent electric shock.
- They have a listed DC-rated ballast and no replaceable lamps.
- Auxiliary equipment for electric-discharge lamps in permanently mounted luminaires, installed at:
- Typical Uses: High-voltage outdoor lighting, tunnels, highways.
Multiple Branch Circuits (210.7)
- When two or more branch circuits supply devices or equipment that are mounted on the same yoke or mounting strap, a simultaneous disconnecting means must be provided.
- This disconnect must be located at the point where the branch circuits originate (typically at the panelboard or breaker box).
- A duplex receptacle with one outlet on one circuit and another outlet on a different circuit.
- Multi-way switching configurations where separate circuits supply switches mounted on the same yoke.
GFCI Protection for Personnel (210.8)
General Requirements
- A listed Class A GFCI must provide protection in specific locations.
- GFCIs must be installed in a readily accessible location.
- The shortest path of the power supply cord is used to determine distance to receptacles.
- GFCIs detect imbalances in current between the hot and neutral conductors.
- If current leaks to ground (e.g., through a person or object), the GFCI trips the circuit to prevent electrocution.
- GFCIs do not require an equipment grounding conductor to function, making them useful as replacements where grounding is missing.
(A) Dwelling Units GFCI protection is required for 125V–250V receptacles on single-phase branch circuits rated 150V or less to ground in the following locations:
- Bathrooms – Includes all receptacles in the bathroom, whether near sinks or not.
- Garages & Accessory Buildings – Required for all receptacles, including those in sheds and storage areas.
- Outdoors – Applies to all outdoor receptacles, except certain dedicated equipment like snow-melting systems.
- Crawl Spaces – Required in all crawl spaces at or below grade.
- Basements – All receptacles in finished and unfinished basements must be GFCI protected.
- Kitchens – Required for all kitchen receptacles.
- Areas with sinks & permanent food preparation areas – Covers wet bars, beverage prep stations, and similar areas.
- Sinks – Any receptacle within 6 feet of a sink.
- Boathouses – All receptacles must be GFCI protected.
- Bathtubs & Shower Stalls – Receptacles within 6 feet of the bathtub or shower must be GFCI protected.
- Laundry Areas – All receptacles in laundry areas require GFCI protection.
- Indoor Damp & Wet Locations – Includes any location where moisture is a concern.
(B) Non-Dwelling Units (Commercial, Industrial, & Public Spaces) GFCI protection is required for 125V–250V receptacles in the following locations:
- Bathrooms
- Kitchens
- Areas with sinks & permanent food preparation areas
- Buffet serving areas with food or beverage prep
- Rooftops
- Outdoors
- Sinks within 6 feet of receptacles
- Indoor damp or wet locations
- Locker rooms with showers
- Garages, service bays, and showrooms
- Crawl spaces at or below grade
- Unfinished areas of basements
- Aquariums, bait wells, or other aquatic vessels
- Laundry areas
- Bathtubs & shower stalls
Circuits Derived From Autotransformers (210.9)
General Rule:
- Branch circuits cannot be derived from autotransformers unless the supplied circuit has a grounded conductor that is electrically connected to a grounded conductor of the system supplying the autotransformer.
Exceptions:
- Voltage Conversion (208V to 240V or 240V to 208V)
- An autotransformer can be used without a grounded connection when converting from a 208V to 240V system or vice versa.
- Industrial Settings with Qualified Personnel
- In industrial environments where maintenance and supervision ensure that only qualified persons handle the system, autotransformers may be used to:
- Supply 600V loads from 480V systems
- Supply 480V loads from 600V systems
- Without requiring a grounded conductor connection.
- In industrial environments where maintenance and supervision ensure that only qualified persons handle the system, autotransformers may be used to:
Buck-Boost Autotransformer Applications:
- Used for small voltage adjustments (typically within 20%).
- Common applications include:
- Stepping up 208V to 240V for air conditioners, ranges, and motors.
- Stepping down 240V to 208V for 208V-rated appliances.
- Increasing 240V single-phase to 277V single-phase for lighting.
- Used in 3-phase systems to modify voltage levels.
article 215: feeders
article 220: branch circuit, feeder, and service load calculations
article 240: overcurrent protection
article 250: grounding and bonding