Electrical Code Essentials—Last-Minute Review

Accessible: capable of being removed or exposed without damaging the building; not permanently enclosed by finish.
Readily accessible: can be reached quickly without removing obstacles or using ladders.
Drop ceilings and above-ceiling areas are often considered accessible regions for wiring; certain wiring methods (e.g., Romex) are restricted in these spaces.
Clear working space around panels must be free of obstructions; flow around the panel is required for safe access.
Service disconnect on a higher floor can still be considered readily accessible if it can be reached at a reasonable level (e.g., by stairs).

Ampacity: continuous current a conductor can carry without exceeding its temperature rating under operating conditions.
When multiple conductors are in a raceway or a panel, ampacity must be derated due to heating and thermal effects.
Derating factors depend on temperature and number of conductors; example factors mentioned: $f1 = 0.8$ (86°C condition) and $f2 = 0.87$ (temperature derating).
Adjusted ampacity formula (conceptual): $A{ ext{adj}} = A{ ext{base}} imes f1 imes f2.$ If the base ampacity is 100 A, the adjusted value will be reduced accordingly by the factors.

Attachment plug: device that creates a connection between a flexible cord and a receptor.
A listed, properly installed attachment plug is required by NEC; non-listed assemblies (e.g., a quick mount on a cord) may not count as an attachment plug.
Water- and weatherproof attachment plugs exist for outdoor or damp locations.

Bonded: establishes a conductive path between metal parts to ensure electrical continuity.
Grounded (earth): connected to the actual earth or a grounding electrode system.
Bonding and grounding can coincide but are conceptually different; components can be bonded and still be part of a broader grounding system.
Main Bonding Jumper: the primary bonding conductor that connects the service equipment to the grounding electrode system.
Pools and similar environments require bonding grids to manage potential differences and ensure safety.
Concept of potential difference: devices rely on differences in electrical potential to operate (e.g., “water wheel” analogy used in class).

Grounding conductor (Equipment Grounding Conductor, EGC): conductor that carries fault current and connects equipment to the grounding system.
Grounding electrode conductor (GEC): connects the service grounding system to the grounding electrode (e.g., a stake, water pipe, or similar electrode).
Two types of grounds:
- EGC: grounds individual circuits and equipment within a building.
- GEC: connects the building’s grounding system to the external earth grounding electrode system.
Conduits can provide grounding paths; if a conduit becomes separated, the grounding path may be lost, so an explicit EGC is generally preferred.
Concrete and rebar note (context): rebar’s expansion/contraction properties contribute to its effectiveness in concrete; not a formal NEC point, but a useful engineering note observed in the lecture.

GFCIs trip when there is a difference between current in the hot and the neutral of at least $6\ \text{mA}$ (or higher).
Principle: monitor input vs. output; if imbalance occurs, power is interrupted to prevent shock.
In retrofit scenarios, GFCIs may provide protection even if there is no equipment grounding conductor, depending on code allowances and installation specifics.

Equipment grounding conductor (EGC): size is typically based on the overcurrent protection device (breaker) protecting the circuit, per NEC tables.
Grounding electrode conductor (GEC): size is determined by the service size (cross-sectional area of service conductors) and connects the electrical system to the grounding electrode system.
Practical note: running a dedicated grounding conductor with the circuit is common and reduces risk if conduit grounds become separated.

Exposed wiring and surface-mounted raceways are, by definition, exposed and accessible; plan for protection and accessibility accordingly.
The building inspector’s enforcement of some safety codes can be post-incident, so adherence to safety practices is essential even if enforcement is reactive.
When in doubt about terminology (branch circuit vs feeder vs service entrance conductor), remember:
- Branch circuit: a circuit that extends from a distribution point to a load.
- Feeder: a circuit that supplies a panel or large section of a building.
- Service entrance conductor: conductors that connect the utility supply to the service equipment, including the main disconnect.