NEC Part 2.4 In-depth Notes

  • Concealed Wires:

    • Concealed refers to wires that are not visible and are rendered inaccessible by structural elements or finishes of a building.
    • Wires inside of concealed raceways are considered concealed, even if they can be accessed by withdrawing them from junction boxes or similar accessible locations.

  • Conductors:

    • Bare Conductor:
    • No covering or insulation; primarily found as grounding in non-metallic Romex or as grounding electrode conductors.
    • Covered Conductor:
    • Enclosed in a material not recognized as electrical insulation but offers some protection.
    • Insulated Conductor:
    • Enclosed in materials recognized by code as electrical insulation.

  • Conduit Bodies:

    • Portions of conduit systems that provide access to the interior through removable covers at junctions or terminals.
    • Common types include tees and LBs; used in locations where bending might be complicated.
    • Not to be confused with junction boxes (e.g., FS and FD boxes).

  • Connectors:

    • Pressure or Solderless Connectors:
    • Establish a mechanical connection between conductors without solder.
    • Receptacles serve as examples where mechanical pressure connects the plug.

  • Continuous Load:

    • Defined as a load where maximum current is expected to persist for three hours or longer.
    • Important for sizing and understanding circuit demands.

  • Control Circuits:

    • Circuits carrying electric signals that command the performance of controllers without carrying main power.
    • Typically operate at lower voltage levels (e.g., 8 - 24 volts).
    • Examples include relays and contactors.

  • Controller:

    • Device that governs electric power delivery to connected apparatus.
    • May refer to devices like variable frequency drives (VFD) or programmable logic controllers (PLCs).

  • Cooking Units:

    • Appliances designed for counter mounting with multiple heating elements, internal wiring, and controls.

  • Selective Coordination:

    • An overcurrent condition management concept aiming to restrict outages to affected circuits only.
    • Achieved through the careful selection and installation of protective devices based on expected overload and fault currents.

  • Copper Clad Aluminum Conductors:

    • Wires with a metallurgically bonded copper layer over an aluminum core; comprises at least 10% copper by cross-sectional area.
    • Often used in grounding rods for cost-effectiveness.

  • Cutout Box:

    • An enclosure designed for surface mounting, featuring doors that secure within the box walls for easy access.

  • DC to DC Converters:

    • Devices that change input DC voltage and current levels to higher or lower outputs.

  • Dead Front:

    • Equipment design that prevents exposure to live electrical parts for safety.

  • Demand Factor:

    • The ratio of maximum demand to the total connected load in a system; important for sizing electrical systems.

  • Disconnecting Means:

    • Devices allowing disconnection of circuit conductors from their power source (e.g., switches, breaker panels).

  • Dormitory Unit:

    • Accommodations for groups of people (more than 16) without individual cooking facilities.

  • Types of Duty:

    • Continuous Duty: Substantially constant load indefinitely.
    • Intermittent Duty: Operation varies between load and no load.
    • Periodic Duty: Regularly repeated load variations.
    • Short Time Duty: Constant load for a specified short time.
    • Varying Duty: Loads and operation intervals that vary significantly.

  • Dwellings:

    • Single Family Dwelling: One dwelling unit.
    • Two Family Dwelling: Two dwelling units (e.g., duplex).
    • Multifamily Dwelling: Three or more units (e.g., apartments).
    • Dwelling Unit: Identifies a living space with facilities for living, sleeping, cooking, and sanitation.