This comprehensive guide provides a detailed overview of key electrical engineering terms and definitions, ensuring clarity and accessibility for professionals and enthusiasts alike.
Each term is meticulously explained, with all relevant information preserved, including article numbers, references, and informational notes.
1. Modular Data Center (MDC)
Prefabricated units rated at 1000 volts or less, housing IT equipment (e.g., servers) and support systems like electrical distribution, HVAC, and cooling systems.
Construction: Often uses ISO shipping containers or similar structures.
Installation: Fixed installation indoors or outdoors, depending on environmental resistance.
Configuration: Can be all-in-one or with separate enclosures for support equipment.
Informational Note: A typical construction may use a standard ISO shipping container or other structure as the outer enclosure, racks or cabinets of ITE, service-entrance equipment and power distribution components, power storage such as a UPS, and an air or liquid cooling system. Modular data centers are intended for fixed installation, either indoors or outdoors, based on their construction and resistance to environmental conditions. MDCs can be configured as an all-in-one system housed in a single equipment enclosure or as a system with the support equipment housed in separate equipment enclosures.
Reference: CMP—12
2. DC Plugging Box
A DC device with one or more 2-pole, 2-wire, nonpolarized, non-grounding receptacles for DC circuits only.
Reference: CMP—15
3. Dead-Front
Equipment designed without exposed live parts on the operating side.
Reference: CMP—9
4. Demand Factor
The ratio of the maximum demand of a system (or part) to its total connected load.
Reference: CMP—2
5. Dental Office
A building or part of a building where dental examinations and minor treatments are performed under professional supervision.
Key Features: Limited sedation, no overnight stays, and no 24-hour operations.
Reference: CMP—15
6. Device
A unit in an electrical system (other than a conductor) that carries or controls electric energy.
Reference: CMP—1
7. Dielectric Heating
Heating of insulating materials due to dielectric losses in a varying electric field.
Reference: CMP—12
8. Disconnecting Means
A device or group of devices used to disconnect conductors from their power source.
Reference: CMP—1
9. Distribution Point
An electrical supply point for service drops, feeders, or branch circuits to buildings under single management.
Informational Note: The service point is typically located at the distribution point.
Reference: CMP—7
10. Diversion Controller
Equipment that regulates power output by diverting it to DC/AC loads or utility services.
Reference: CMP—13
11. Diversion Load
A load connected to a diversion charge controller, also known as a dump load.
Reference: CMP—4
12. Docking Facility
A structure (fixed or floating) providing water access for securing boats.
Reference: CMP—7
13. Dormitory Unit
A building or space with group sleeping accommodations for more than 16 unrelated persons, without individual cooking facilities.
Reference: CMP—2
14. Drop Box
A box with pendant- or flush-mounted receptacles attached to a multiconductor cable via strain relief or a multipole connector.
Reference: CMP—15
15. Dust-Ignitionproof
Equipment designed to exclude dust and prevent internal arcs, sparks, or heat from igniting external dust.
Informational Note No. 1: See ANSI/UL 1203, Explosion-Proof and Dust-Ignition-Proof Electrical Equipment for Use in Hazardous (Classified) Locations, for additional information on dust-ignitionproof enclosures.
Informational Note No. 2: See NEMA 250, Enclosures for Electrical Equipment (1000 Volts Maximum), for additional information on dust-ignitionproof enclosures that are sometimes additionally marked Type 9.
Reference: CMP—14
16. Dusttight
Enclosures constructed to prevent dust entry under specified test conditions.
Informational Note No. 1: See ANSI/UL 121201, Nonincendive Electrical Equipment for Use in Class I and II, Division 2 and Class III, Divisions 1 and 2 Hazardous (Classified) Locations, for additional information.
Informational Note No. 2: See NEMA 250, Enclosures for Electrical Equipment (1000 Volts Maximum), and ANSI/UL 50E, Enclosures for Electrical Equipment, Environmental Considerations, for additional information on enclosure Types 3, 3X, 3S, 3SX, 4, 4X, 5, 6, 6P, 12, 12K, and 13 that are considered dusttight.
Reference: CMP—14
17. Duty Types
- Continuous Duty: Operation at a substantially constant load for an indefinitely long time.
- Intermittent Duty: Operation for alternate intervals of (1) load and no load; or (2) load and rest; or (3) load, no load, and rest.
- Periodic Duty: Intermittent operation in which the load conditions are regularly recurrent.
- Short-Time Duty: Operation at a substantially constant load for a short and definite, specified time.
- Varying Duty: Operation at loads, and for intervals of time, both of which may be subject to wide variation.
Reference: CMP—1
18. Dwelling Types
- One-Family Dwelling: A building that consists solely of one dwelling unit.
- Two-Family Dwelling: A building that consists solely of two dwelling units.
- Multifamily Dwelling: A building that contains three or more dwelling units.
Reference: CMP—1
19. 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.
Reference: CMP—2
Summary Table
| Term | Description | Reference |
|---|---|---|
| Modular Data Center (MDC) | Prefabricated units housing IT equipment and support systems. | CMP—12 |
| DC Plugging Box | Device with nonpolarized receptacles for DC circuits. | CMP—15 |
| Dead-Front | Equipment without exposed live parts on the operating side. | CMP—9 |
| Demand Factor | Ratio of maximum demand to total connected load. | CMP—2 |
| Dental Office | Building for dental examinations and minor treatments. | CMP—15 |
| Device | Unit in an electrical system that carries or controls energy. | CMP—1 |
| Dielectric Heating | Heating of insulating materials in a varying electric field. | CMP—12 |
| Disconnecting Means | Device to disconnect conductors from their power source. | CMP—1 |
| Distribution Point | Electrical supply point for service drops or feeders. | CMP—7 |
| Diversion Controller | Regulates power output by diverting it to loads or utilities. | CMP—13 |
| Diversion Load | Load connected to a diversion controller (dump load). | CMP—4 |
| Docking Facility | Structure providing water access for boats. | CMP—7 |
| Dormitory Unit | Building with group sleeping for >16 unrelated persons. | CMP—2 |
| Drop Box | Box with receptacles attached to a multiconductor cable. | CMP—15 |
| Dust-Ignitionproof | Equipment designed to prevent dust ignition. | CMP—14 |
| Dusttight | Enclosures designed to prevent dust entry. | CMP—14 |
| Duty Types | Continuous, Intermittent, Periodic, Short-Time, Varying. | CMP—1 |
| Dwelling Types | One-Family, Two-Family, Multifamily. | CMP—1 |
| Dwelling Unit | Single unit with complete living facilities. | CMP—2 |
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