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1.
A unit of measurement when describing how much (electrical) wire is pulled past the destination it should have ended at.

How to tell when to start measuring is when enough wire is pulled to the given location to be able to comfortably complete a termination and then finding more wire was pulled than needed, most often in excess, and ironically most often its copper wire. Once you've determined theres way more wire than needed, its a dave length.. No actual "measuring" is done with any tool. It will be obvious just from "eyeballing it" when you have a dave length to deal with,

Some dave lengths can be short, usually because its only small guage wire such as #14, however a genuine dave length will be found when #10 and larger are involved because thats where the money is
"Okay boys its time to splice this place up... Oh look someone pulled 10 extra feet of 8/3 past the panel, i wonder who could have done that.. What a dave length!"

"Hey how much wire do we need at location?" - "im not sure, you never know how often things change, better make it a dave length. Should be good"
by Yellow strippers February 16, 2014