Mini Quick Course
Getting a Signal On
Street lighting teaches you the cheapest first move. This is the rest of it. There are four ways to get a signal onto a line, they are not equal, and the order matters: connect if you can, clamp if you cannot, couple onto it if there is nothing to open, and induce only when everything else is exhausted. Each one has a condition that has to be met before it works at all, and knowing that condition is the difference between tracing a cable and tracing your own optimism.
Why any of this matters
A survey starts with a signal applied. Passive modes only report what happens to be radiating at that moment, so a quiet CAT in power or radio tells you very little about what is actually down there.
Putting a signal on is what turns a sweep into a survey. The Genny goes on first: locate, then avoid.
There are four ways to get that signal onto a line. They are not interchangeable, and three of the four have a condition that must be true before they work at all.