NEC Code Fundamentals

100 flashcards by MentisLibrary

How the National Electrical Code is built and how to use it: chapter structure, definitions, ampacity and termination limits, overcurrent sizing, branch circuit rules, grounding and bonding, wiring methods, box and raceway fill.

What is the NEC, and does it have the force of law on its own?
The National Electrical Code, published by the NFPA as NFPA 70. It is a model code with no legal force until a state, county or city adopts it, and jurisdictions routinely adopt an older edition and amend it.
How often is the NEC revised?
On a three year cycle. Editions are named for the year, and adoption by a jurisdiction always lags publication.
What does the NEC say its purpose is?
The practical safeguarding of persons and property from hazards arising from the use of electricity.
What does the NEC explicitly say it is not?
It is not a design specification, and it is not an instruction manual for untrained persons. Compliance with the code plus proper maintenance results in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for future expansion.
Who is the authority having jurisdiction, and what can they do?
The AHJ is the office or individual responsible for enforcing the code, usually the electrical inspector. The code gives the AHJ authority to interpret its rules, approve equipment and materials, grant special permission, and waive specific requirements where equivalent safety is assured.
How are the NEC's chapters organized?
Chapters 1 through 4 apply generally to all installations. Chapters 5, 6 and 7 cover special occupancies, special equipment and special conditions, and they supplement or modify the earlier chapters. Chapter 8 covers communications systems. Chapter 9 holds tables.
What is special about Chapter 8?
Chapter 8, covering communications systems, is not subject to the requirements of the other chapters except where those chapters are specifically referenced within Chapter 8.
Which parts of the NEC book are enforceable and which are not?
The chapters and the Chapter 9 tables are enforceable. Informational notes are explanatory only. Informative annexes are not part of the requirements unless the adopting jurisdiction specifically adopts them.
How does the NEC use the words shall, shall not, and shall be permitted?
Shall and shall not state mandatory requirements. Shall be permitted and shall not be required state permissive allowances, describing something optional or an alternative method.
How is an NEC citation such as 210.8(A)(1) read?
210 is the article, 8 is the section within it, and the letters and numbers in parentheses are subdivisions. The first digit of the article number tells you the chapter, so 210 sits in Chapter 2.
Where do you look first when a code question involves an unfamiliar term?
Article 100, the definitions. A term defined in Article 100 carries that meaning everywhere in the code, and recent cycles consolidated most article-specific definitions there.
What is a practical search order for looking up a rule you do not know?
Start with the index or the table of contents to find the article, read the article's scope, check Article 100 for any defined term, then read the section and its exceptions. Check any special occupancy chapter that applies.
Define ampacity.
The maximum current, in amperes, a conductor can carry continuously under the conditions of use without exceeding its temperature rating.
What is the difference between a branch circuit, a feeder, and service conductors?
Service conductors run from the utility to the service disconnect. A feeder runs from the service equipment or another power source to a downstream overcurrent device. A branch circuit is the conductors between the final overcurrent device and the outlets it supplies.
Distinguish outlet, receptacle, receptacle outlet, and device.
An outlet is any point where current is taken to supply utilization equipment. A receptacle is the contact device installed for a plug. A receptacle outlet is an outlet where one or more receptacles are installed. A device carries or controls electrical energy but does not consume it.
What is the difference between the grounded conductor and the grounding conductor?
The grounded conductor is the circuit conductor intentionally connected to ground that carries current in normal operation, usually the neutral. The equipment grounding conductor connects non-current-carrying metal parts to the source and carries current only during a fault.
What is the difference between grounding and bonding?
Grounding is connecting to earth or to a conductive body that extends the earth connection. Bonding is connecting metallic parts together so they are electrically continuous and conductive.
What is a continuous load?
A load where the maximum current is expected to continue for three hours or more.
What is the difference between accessible and readily accessible?
Accessible means it can be reached without damaging the building finish, though tools, a ladder or removing a panel may be needed. Readily accessible means it can be reached quickly without climbing over obstacles or using a ladder or tools.
What do listed, labeled, identified and approved mean in the NEC?
Listed means a qualified testing organization has evaluated the product and published it in a list. Labeled means it carries that organization's mark. Identified means suitable for the specific use. Approved means acceptable to the authority having jurisdiction.
What obligation comes with installing listed equipment?
It must be installed and used in accordance with any instructions included in the listing or labeling.
How does the NEC define a dwelling unit?
A single unit providing complete and independent living facilities for one or more persons, including permanent provisions for living, sleeping, cooking and sanitation.
What are the three location classifications for equipment suitability?
Dry, damp and wet. A wet location includes installations underground, in concrete slabs in direct contact with earth, and locations subject to saturation or unprotected weather exposure.
What are the three temperature columns in the conductor ampacity table, and what do they represent?
60, 75 and 90 degrees Celsius, which are insulation temperature ratings. A conductor's ampacity is read from the column matching the conductor's insulation rating and the installation's temperature limits.
What is the termination temperature limitation, and why does it usually cap you at 60 or 75 degrees?
Conductor ampacity may not exceed the rating of the lowest rated termination in the circuit. Equipment rated 100 A or less, or marked for 14 AWG through 1 AWG conductors, is generally limited to the 60 degree column unless it is listed and identified for a higher temperature; most modern equipment is marked for 75 degrees.
If terminations cap you at 75 degrees, what is the 90 degree column good for?
Derating. The 90 degree ampacity may be used as the starting point for ambient temperature correction and conductor bundling adjustment, as long as the final adjusted ampacity does not exceed what the terminations allow.
What are the overcurrent protection limits for 14, 12 and 10 AWG copper?
Under the small conductor rule, 15 A for 14 AWG, 20 A for 12 AWG, and 30 A for 10 AWG copper, regardless of what the ampacity table shows for those sizes.
What are the 75 degree copper ampacities for 8, 6, 4, 3 and 2 AWG?
50 A for 8 AWG, 65 A for 6 AWG, 85 A for 4 AWG, 100 A for 3 AWG and 115 A for 2 AWG.
What are the 75 degree copper ampacities for 1/0 through 4/0?
150 A for 1/0, 175 A for 2/0, 200 A for 3/0 and 230 A for 4/0.
When must you apply ampacity adjustment for the number of conductors?
When more than three current-carrying conductors are bundled together or run in the same raceway or cable. Common factors are 80 percent for 4 through 6 conductors, 70 percent for 7 through 9, and 50 percent for 10 through 20.