Which method, also called the transit method, is most commonly used on transmission lines?

• A. Stop watch
• B. Unisag watch
• C. Dynamometer
• D. Sag scope

Answer: (D)

Sag measurement on transmission lines is typically done with the transit method because it uses precise angular observations to determine how much a conductor sags between supports. In this approach, a transit (a theodolite-like instrument) is set up at a ground location and a sag scope is used to sight the conductor. The optical readings, combined with the known ground distances, let you compute the vertical drop of the line in a span. This method is favored because it can be performed from the ground, is accurate for mid-span sag, and avoids climbing towers or manipulating the line directly.

The other tools in the list serve different purposes: a stop watch measures time, which doesn’t give sag; a dynamometer measures tension rather than vertical displacement; an Unisag watch isn’t a standard instrument for this task. The sag scope, used with the transit, is specifically designed to read the conductor’s sag, making it the practical and common choice.