INTRODUCTION
Thank you for purchasing General Tools & Instruments’
(General’s) VR40 Non-contact Voltage Detector with
Adjustable Sensitivity and IR Thermometer. Please read
this manual carefully and thoroughly before using the
instrument.
The VR40 offers a safe (non-contact) way to check
whether a line, cable or AC outlet is “hot” (energized).
It does so by using a blade tip to sense from a short
distance the electromagnetic field created by AC
voltage. When voltage is detected, the VR40 produces
audible and visual alarms (a beeping sound, and a
flashing red light adjacent to the tip.
Even unloaded AC circuits generate electromagnetic
fields. Although these fields are extremely weak, their
constantly changing nature means that they generate
some current. A sensitive non-contact voltage (NCV)
detector can sense this current via induction, in much
the same way that a sensitive radio receiver can sense
weak radio waves.
NCV detectors, including the VR40, cannot detect DC
voltages, such as those present in automotive electrical
systems. In addition, the VR40 typically cannot detect
120VAC from a distance of more than 0.25 in. (6.2mm),
and never through a wall or metal conduit.
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