Automation Canada - Cables & Connectors Issue - 39

ABSENCE OF VOLTAGE TESTERS - VERIFY CIRCUIT IS
DEENERGIZED
Absence of Voltage Testers (AVT) are permanently mounted test
devices designed specifically to prove the absence of voltage exists.
With AVTs, the absence of voltage is verified prior to opening an
electrical enclosure. Requirements for AVTs are described in UL 1436.
To operate an AVT, a user pushes a button to initiate the test
sequence. The test sequence is performed automatically and
includes verifying the tester is functioning with a known voltage
source, ensuring the tester is properly installed and in direct contact
with the circuit at the time of testing, and testing for absence of AC
and DC voltage phase-to-phase and phase-to-ground. If all
requirements in the test sequence are satisfied, a green indicator will
illuminate to visually convey that the absence of voltage has been
confirmed.
Requirements in UL 1436 for AVTs are very extensive and include a
variety of features to ensure the absence of voltage test function is
fail-safe and reliable. Active indicators, built-in overcurrent
protection, and SIL 3 reliability for all safety functions are some of the
important features. Built-in overcurrent protection ensures that the
AVT can be installed directly in contact with the circuit being tested
(without the need for in-line fusing) eliminating the failure modes that
voltage indicators and test portals are subject to. In addition, AVTs are
designed to keep hazardous voltage away from the door and user
interface.
Like voltage indicators and test portals, AVTs will only test the point
in the circuit at which the test leads are installed. If there are multiple
test points or multiple sources of electrical energy (including stored
energy sources) additional testers may be required.
AVT manufacturers often include voltage presence indicators as an
additional feature, but this functionality is separate from the absence
of voltage safety function and is not required by UL 1436.
RELIABLE RESULTS WITH AVTS
C A N A D I A N A U TO M AT I O N

Example of Absence of Voltage Tester (AVT)

Built-in protection eliminates the
need for the leads to be fused

Two leads per phase to
verify installation

Front of
Door

VeriSafe TM Absence
of Voltage Tester

AVT isolation module keeps hazardous
voltage away from the door

VOLUME 3, ISSUE 2

39



Automation Canada - Cables & Connectors Issue

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