Application Note

3 Fluke Corporation Understanding capacitive voltage sensors
Fluke Corporation
PO Box 9090, Everett, WA USA 98206
Fluke Europe B.V.
PO Box 1186, 5602 BD
Eindhoven, The N
etherlands
For more information call:
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ax (425) 446-5
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ax (3
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00) 36-
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LU
K
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ax [phone]
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©2005 Fluke Corporation
. All rights reser
ved
.
Printed in U.S.A. 7/2005 2065880 A-EN-N Rev B
Fluke. Keeping your world
up and running.
frame test described earlier. The
reason the sensor indicated live
voltage on the frame was
because the ungrounded metal
frame had stray voltage on it
coupled from the hot conductor.
In the case of the ungrounded
metal enclosure, the voltage
sensor won’t tell you if the
enclosure is just “hot” from
capacitively coupled voltage, or
if it’s really hot from, let’s say,
contact with a live wire (frayed
insulation on a phase conduc-
tor). The difference can be life or
death. It’s worth checking out.
Try this yourself with a pair
of two-prong extension cords.
Plug one cord into a wall outlet
and plug the second cord into
the first but connect only the hot
side leaving the neutral open.
Go to the loose end of the sec-
ond cord and try the voltage
sensor in both sides. They both
should indicate live voltage.
Under certain conditions we
can use the voltage sensor to
detect a bad ground connection
on a metal enclosure or section
of conduit. In fact, this is a good
habit to get into before contact-
ing or working on any electrical
enclosure. Think of the lamp
Matching ac detectors to applications
Not all ac detectors are created equal. Most ac detectors on the mar-
ket today have a specific sensing range and sensitivity levels within
which they are specified to operate properly. Some are designed to
be used on lower voltage control circuit applications such as found
in the HVAC marketplace, others specified for residential use and
still others specified for use in different industrial environments.
Most ac detectors also offer different means of alerting users to
whether voltage is present or not. Some use visual stimulation, such
as the tip lights when voltage is present, some use an audible tone,
some offer both and still others have additional enhancements such
as a built in flashlight. The batteries used to power the ac detectors
also vary by manufacturer. Some use standard easy to obtain batter-
ies like AA or AAA sizes and others use “watch” style batteries
which may be more difficult to find when you need them the most.
So, when selecting your ac detector of choic
e, be sure to carefully
consider what style or type of detector best meets with your job
requirement and your application environment.