readout in the upper right corner shows the frequency of
the voltage.
Using the Non-contact Voltage Detector
. The DMM550’s
NCV detector provides a safe (non-contact) way to check
whether a line, cable or AC outlet is “hot” (energized). At
the top of the meter (Fig. 1, Callout 6) is an NCV sensor
that can detect from a short distance the electromagnetic
field created by AC voltage. If voltage is detected, the
meter produces audible and visual alarms (a beeping
sound, and a flashing red light from an LED near the top
of the front panel (Fig. 1, Callout 1)).
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 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 cannot detect DC voltages, such as those
present in automotive electrical systems. In addition, the
DMM550 typically cannot detect 120VAC from a distance
of more than 0.25 in. (6.2mm), and never through a wall
or metal conduit.
••
Warning
••
The NCV detector in the DMM550 is designed to indicate
the presence of AC voltage with an amplitude of
110VAC
RMS
or greater. However,
do not
assume that the
absence of a positive indication means that the circuit
under test is de-energized (not “hot”). Do not rely solely
on NCV detection to determine the presence of voltage in
a wire. NCV detection may be affected by the design of
the outlet, the type of wiring insulation and other
external factors. Also be aware that “false positive” NCV
indications may be triggered by connection of the meter’s
test leads to a voltage source or by external interference
from a flashlight, motor or other electrical device.
Whenever you have reason to suspect that a line or outlet
is “hot”, confirm your suspicion by measuring the voltage
of the line or outlet using the test leads with the meter’s
rotary function switch in the
position.
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