Automation Canada - Cables & Connectors Issue - 37

TEST PORTALS - MEASURE THE PRESENCE OF VOLTAGE
Test portals are permanently mounted devices that can be used with a
portable tester, such as a digital multimeter, to measure voltage. These
devices are an excellent tool for troubleshooting and determining the
magnitude or value of any voltage that is present. Test portals will test at
the point in the circuit at which the test leads are installed.
If there are multiple test points, more than one test portal may be
required. Test portals may have features such as IP20 " finger safe "
ingress protection as well as a high impedance circuit located at the
door to limit current at the test points to less than 5mA. The impedance
reduces the likelihood of shock or arc flash when measuring voltage
presence via the portals, but the added impedance requires a
conversion to determine the actual voltage value.
SHOULD TEST PORTALS BE USED TO VERIFY ABSENCE OF
VOLTAGE?
The process for verifying the absence of voltage, often referred to as
the " live-dead-live test, " is described in CSA Z462 4.2.5. Using test
portals with a portable test instrument can lead to unreliable results
when testing for absence of voltage and is not recommended. Here are
some of the reasons why voltage test portals are not adequate for
absence of voltage testing:
a) Installation test - verifying absence of voltage through a
permanently mounted device requires assurance that you are in contact
with the test point when the measurement is taken. If the leads from a
permanently mounted device are not properly terminated or
disconnected, voltage will not be detected, regardless of whether or
not the conductor is energized. This is why permanently mounted
voltage testers are required to have an installation test to confirm that
the device is in contact with the conductor at the time the voltage
measurement is taken.
Test portals do not have a feature to verify leads are connected to
the source conductor when a measurement with a portable test
instrument is taken. This condition could result in reading zero voltage
C A N A D I A N A U TO M AT I O N

when voltage is present. Even if it is possible to use a portable tester to
measure voltage presence through test portals before opening the
disconnect, it does not guarantee that the test portal installation is valid
after the disconnect is opened. A known voltage source is also required
to verify the portable tester is functional after measuring through the
portals, which may require PPE.
b) Installation code requirements - the local authority having
jurisdiction (AHJ) will often require overcurrent protection for test
portals with leads longer than 12 inches in order to meet NEC, CEC, or
UL 508A requirements. If fusing is required, testing through the portals
will only test the load side of the fuse, not the actual circuit part. The
circuit part could be energized if the fuse is open and a portable tester
would not detect voltage through the test portal. Use of fuses or
terminal blocks to extend test portal leads to comply with installation
codes introduces additional installation failure points.
c) Bringing hazardous voltage to the door - installing test portals
requires routing wires that carry hazardous line voltage across the hinge
and/or to the external enclosure. Bringing source voltage (ex. 480V)
directly to an accessible surface is not a best practice, particularly when
that surface moves, like a door. The wire will be subject to wear and tear
and could eventually present shock hazards if not properly installed and
maintained (another reason why the installation test described earlier is
so critical). Test portals are designed with the impedance at the portal;
therefore, the wire is not protected.
Test portals are a great tool to reduce risk when troubleshooting and
measuring voltage presence. However, proving absence of voltage
through a permanently mounted device has additional requirements.
The test portal can be thought of as an extension of the circuit part
or source conductor - not the actual circuit part. Portals are okay to
do a preliminary verification check at the portal. However, before
removing PPE or performing any work, best practice is to perform an
additional test with the portable test instrument directly at the
source conductor or actual circuit part to conclusively prove a
de-energized condition exists.
VOLUME 3, ISSUE 2

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Automation Canada - Cables & Connectors Issue

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