Definition - What does Hum Detector mean?
A hum detector is a device used to detect electricity cables that radiate a magnetic field due to the current flowing through them. Hum detectors can receive signals from live lines but do not respond to direct current cables, cables where current flow is very low or street light cables that are turned off during the day.
Trenchlesspedia explains Hum Detector
There was a time when hum detectors were the only type of detector used to locate utility lines. Since these detectors could not detect cables that did not carry current, its usefulness was limited. Several fatalities and serious accidents would occur since location of utilities could not be comprehensive. However they are excellent for detecting live power cables and are still used today.
Thanks to other utility locating methods such as ground penetrating radar (GPR) and metal detectors, it is now easy to locate all kinds of utility lines that cross beneath our streets.