| D.C. | Abbreviation for "Direct Current" |
| Decibel (dB) | A unit to express difference of power level. Used to express power gaining amplifiers or power loss in passive circuits of cables. |
| Delay Line | A cable made to provide very low velocity of propagation with long electrical delay for transmitted signals |
| Derating Factor | A factor used to reduce the current carrying capacity of a wire when used in environments other than that for which the value was established |
| Dielectric | Any insulating material between two conductors which permits electrostatic attraction and repulsion to take place across it |
| Dielectric Absorption | That property of an imperfect dielectric whereby there is an accumulation of electric charges within the body of the material when it is placed in an electric field |
| Dielectric Breakdown | The voltage at which a dielectric material is punctured, which is divisible by thickness to give dielectric strength |
| Dielectric Constant (K) | The ratio of the capacitance of a condenser with dielectric between the electrodes to the capacitance when air is between the electrodes. Also called Permittivity and Specific Inductive Capacity. |
| Dielectric Strength | The voltage which an insulation can withstand before breakdown occurs. Usually expressed as a voltage gradient (such as volts per mil). |
| Dielectric Test | A test in which a voltage higher than the rated voltage is applied for a specified time to determine the adequacy of the insulation under normal conditions |
| Direct Burial Cable | A cable installed directly into the earth |
| Direct Capacitance | The capacitance measured directly from conductor to conductor through a single insulating layer |
| Direct Current (DC) | An electric current which flows in only one direction |
| Direct Current Resistance (D.C.R.) | The resistance offered by any circuit to the flow of direct current |
| Dissipation Factor | The tangent of the loss angle of the insulating material. (Also referred to as loss tangent, tan S, and approximate power factor). |
| Double Foot | Combined length of one linear foot of paired material; i.e., one double foot is equal to one foot of positive material plus one foot of negative material. Usually used in determining thermocouple wire loop resistance. |
| Drain Wire | In a cable, the uninsulated wire in intimate contact with a shield to provide for easier termination of such a shield to a ground point |
| Drawing | In wire manufacturing, pulling the metal through a die or series of dies to reduce diameter to a specific size |
| Duct | An underground or overhead tube for carrying electrical conductors |
| Duplex Insulated | In the thermocouple industry, a combination of dissimilar metal conductors of a thermocouple or thermocouple extension wire |
