| Lacquer | A liquid resin or compound applied to textile braid to prevent fraying, moisture absorption, etc. |
| Laminated Tape | A tape consisting of two or more layers of different materials bonded together |
| Lay | The axial distance required for one cabled conductor or conductor strand to complete one revolution about the axis around which it is cabled |
| Lay Direction | The twist in the cable as indicated by the top strands while looking along the axis of the cable away from the observer. Described as "right hand" or "left hand". |
| Leakage Current | The undesirable flow of current through or over the surface of an insulation |
| Life Cycle | A test to determine the length of time before failure in a controlled, usually accelerated, environment |
| Limits of Error | The maximum deviation (in degrees or percent) of a thermocouple or thermocouple extension wire from standard emf-temperature to be measured |
| LOCO | Abbreviation for loss of coolant accident, a system malfunction associated with nuclear generating stations |
| Longitudinal Shield | A tape shield, flat or corrugated, applied longitudinally with the axis of the core being shielded |
| Loop Resistance | The total resistance of two conductors measured round trip from one end |
| Loss Factor | The product of the dissipation and dielectric constant of an insulating material |
| Low Loss Dielectric | An insulation material that has a relatively low dielectric loss, such as polyethylene or Teflon |
