Exploring Permanently Mounted
Voltage Testing Products
The myths, the differences,and the benefits

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There are a variety of different electrical safety products that are permanently
mounted, each with different functionality and limitations. They all have different
purposes and should not be discussed interchangeably. Three common types ofpermanently mounted products are Voltage Indicators, Test Portals, and Absenceof Voltage Testers.

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Voltage Indicators – Detect Presence of Voltage
Voltage indicators are permanently mounted and use LED-style indicators that
illuminate when presence of voltage is detected. They typically illuminate at
approximately 40V to 1000V, depending on the device and manufacturer.
These devices are an excellent way to provide a visual warning whenvoltage is present.
Voltage indicators should never be used to verify the absence of voltage.
Equipment may be energized, even if the voltage indicator is not illuminated.
Lack of illumination can be caused by a failed LED, a bad installation, or a failed
device. Installation codes often require voltage indicators to be fused. If the fuseis open, the voltage indicator will not illuminate when voltage is present.
Additionally, voltage indicators bring line voltage (for example, 480V) directly tothe door or external surface where the indicator is installed. This could presenta shock hazard, especially when troubleshooting with the door open as door
mounted devices typically operate at control voltages and workers may not be
expecting the wires to the indicator to carry hazardous voltages. Wires that carry
three-phase voltage across a hinge need to be protected to ensure that repeatedopening and closing of doors does not pinch or damage the wire or insulation.
These are some of the reasons why OSHA stated in an Interpretation Letter1
that voltage indicators are not allowed to be used to verify the isolation anddeenergization of a machine or equipment. Regardless of whether electrical ormechanical work will be performed, voltage indicators are not a test instrument
and should not be used when verifying the absence of voltage.

Examples of Voltage Indicators
Galassi, T. (2012, December 12). Whether an LED type device can be used for the isolation and deenergization
verification requirements of 1910.147 and 1910.333. Retrieved from https://www.osha.gov/laws-regs/
standardinterpretations/2012-12-12www.osha.gov/laws-regs/standardinterpretations/2012-12-12.
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Test Portals – Measure the Presence of Voltage
Test portals are permanently mounted devices that can be usedwith 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 berequired. Test portals may have features such as IP20 “finger safe”
ingress protection as well as a high impedance circuit located at thedoor 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.

Examples of Test Portals

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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
NPFA 70E Article 120.5 and OSHA 1910.333 (b)(2)(iv)(B). Using test portals with a portable test instrument canlead to unreliable results when testing for absence of voltage and is not recommended. Here are some of thereasons 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 apermanently 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 thetime 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
		 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 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 theactual 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.

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Limitations of Voltage Indicators and Test Portals
ImpedanceLine voltage,
unprotected leads

Test
PortalBoth Test Portal and Voltage Indicator
leads bring hazardous voltage tothe door.

Front of
Door

Voltage
Indicator

Sensor leads
not connected
Test
PortalPoor workmanship or installation
failures can lead to a zero voltage
indication when the conductor
is energized.

Front of
Door

Voltage
Indicator

No voltage at test
point when fuse is open
Test
PortalFUSE
FUSE

Front ofDoor

If the fuse is open, zero voltage will
be indicated when the conductor
is energized.

Voltage
Indicator

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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, auser pushes a button to initiate the test sequence. The test sequence isperformed 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 avariety 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 directlyin 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 awayfrom the door and user interface.
Like voltage indicators and test portals, AVTs will only test the point in thecircuit 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 anadditional feature, but this functionality is separate from the absenceof voltage safety function and is not required by UL 1436.

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Example ofAbsence of Voltage Tester(AVT)More Meaningful Connections

Reliable Results with AVTs
Built-in protection eliminates theneed for the leads to be fused

Two leads per phase toverify installation

Front of
Door

VeriSafeTM Absenceof Voltage Tester

AVT isolation module keeps hazardous
voltage away from the door

Case Study: Ground Lead Failure

Ground leads are
not connected

Situation
Worker approaches the enclosure and thedisconnect switch for the 480V power source isin the OFF position. The disconnect switch has
failed with one phase (L1) in the closed position(L2, L3 are open). The ground leads of thedevices are NOT connected to ground becauseof an improper installation or termination failure.
The worker applies a lock. Following safety
procedures, the worker performs an absence ofvoltage test with the electrical enclosure closed
using a permanently mounted device.
Permanently
Mounted Device

Failure Mode

Potential Cause

L1 L2 L3

Test
PortalFront of
Door

VeriSafeTM Absenceof Voltage Tester

System State

Absence ofVoltage
Tester (AVT)
Test
PortalVoltage Test
Station (VTS)8Ground lead(s)are NOT
connected to
groundImproperinstallation or
termination failure

Red wired areenergized at 480V

Disconnect is in
the OPEN/OFF
position with L1energized

Detection

Failure EffectIncident Consequence

YES – the AVT will detect open
ground (or phase) lead(s) andcommunicate the installationof sensor leads is not verified

AVT will detect
open ground lead(s)and communicate
installation is thereason the absence ofvoltage test cannot be
confirmed

None - Incident
AvoidedNO – voltage measurement
results in zero voltage whenvoltage is present

NO – the L1 LED for thevoltage indicator will not be
illuminated and measurement
results in zero voltage whenvoltage is present

Worker erroneously
considers electricalenclosure as
deenergized

WHITE PAPER – Exploring Permanently Mounted Voltage Testing Products – The myths, the differences, and the benefits

Worker opens
equipment whileenergized• Probable shock or
arc flash event• Equipment
damage is likely

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Permanently Mounted Test Devices in Standards & Regulations
Best practice for verifying the absence of voltage is described in NFPA 70E. NFPA 70E has requirementsfor verifying the absence of voltage with portable test instruments (120.5(7)) and permanently mounted test
instruments (120.5(7) Exception 1).

NFPA 70E
120.5 Process for Establishing and Verifying an Electrically Safe Work Condition

NFPA 70E states:“(7) Use an adequately rated portable test instrument to test each phase 		conductor or circuit part to verify it is de-energized. Test each phase conductor
or circuit part both phase-to-phase and phase-to-ground. Before and after eachtest, determine that the test instrument is operating satisfactorily through 		verification on any known voltage source.
Exception No.1: An adequately rated permanently mounted test device shallbe permitted to be used to verify the absence of voltage of the conductors or
circuit parts at the work location, provided it meets the all following requirements:			a. It is permanently mounted and installed in accordance with the 							 manufacturer’s instructions and tests the conductors and circuit				 parts at the point of work			b. It is listed and labeled for the purpose of verifying the				 absence of voltage
			c. It tests each phase conductor or circuit part both				 phase-to-phase and phase-to-ground			d. The test device is verified as operating satisfactorily on any				 known voltage source before and after verifying the				 absence of voltage”

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NFPA 70E Handbook, 2018 Edition
In NFPA documents, an exception is defined as an “approved alternative.” This means that there is an option
to use the primary process or follow the requirements of the exception. In the case of 120.5 step (7) and
Exception No. 1, this means that a portable test instrument or permanently mounted test device can beused to verify the absence of voltage, but both are not necessary.
Exception No. 1 was new to NFPA 70E in the 2018 edition and refers to AVTs. Because the language in NFPA
70E was voted on before the 6th Edition of UL 1436 was published with AVT requirements and absenceof voltage testers were defined, the initial language is vague and can be confusing to interpret. However,additional commentary is provided in the NFPA 70E Handbook. Neither voltage indicators nor test portals
meet UL 1436. Voltage indicators and test portals are often have a UL listing, typically to UL 508 or UL
61010-1 as an “auxiliary device” suitable for use in an industrial control panels. However, this listing has no
performance or safety requirements for proving absence of voltage. Test portals are permanently mounted
but rely on a portable tester. As a hybrid, test portals would have to meet the requirements of both Step 7
and Exception No. 1 to ensure a reliable result. This involves having an installation test for the permanently
mounted leads or ensuring the portable tester is in contact with the actual circuit part.
Test portals were proposed as additions into the standard for absence of voltage verification in the 2021
edition, but were rejected by the NFPA 70E Technical Committee. Use of test portals or voltage indicators f
or absence of voltage testing are not addressed in any edition NFPA 70E.

NFPA 70E
Handbook states:“Typically measurement devices indicate when voltage is present, but lack of
indicating a voltage does not guarantee the equipment has ben de-energized.
For this reason, these mounted devices are designed to run internal 		diagnostics, verify operation on a known voltage source, confirm contact withthe circuit, and verify the lack of voltage. These measurement devices do notuse equipment voltage to verify the operation of the device. A secondary test
source is available to perform this function. See Exhibit 120.14 for an installed
absence of voltage tester indicating that equipment is de-energized. Absenceof voltage testing equipment for fixed installations is listed to UL 1436, 		
Standard for Outlet Testers and Similar Indicating Devices.”

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OSHA
Within OSHA 29 CRF 1910, test equipment used for the purpose ofverifying the absence of voltage in either -.147 (control of hazardous
energy) or Subpart S (electrical work) is not well-defined and has very
few performance requirements. No distinction is made between portableor permanently-mounted voltage test instruments. OSHA regulations are
rarely updated, so the latest in best practices and technology are often not
specifically mentioned. However, OSHA has a history of relying on industry
consensus standards, like NFPA 70E (updated every three years), to provide
prescriptive requirements and enforce best practices.
NFPA describes the relationship between OSHA and NFPA 70E
requirements in their Fact Sheet on NFPA 70E.1
NFPA. (2017, November). Fact Sheet – NFPA 70E®, 2018 Edition.
Retrieved from https://www.nfpa.org/~/media/3B937D481EAE4B8DA74C0C1CE5BFBE9E.pdf
1

FAQs
What is the relationship between
OSHA’s standards and the NFPA 70E?
OSHA looks to the perspective-based
requirements of NFPA 70E to fulfill
the performance-based requirements
included in it’s standards. NFPA 70E
fleshes out how the performance-based
requirements in the OSHA standards
should be met by providing the defining
the minimum standard industry practicenecessary for electrical safety. OSHA
is the law, but NFPA 70E outlines how
to comply with OSHA’s electrical safety
requirements.1

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Comparison of Devices and Capabilities
The VeriSafe™ AVT is Unique
It combines voltage presence indicators with
absence of voltage testing technoloogy.

Red indicatesvoltage presence

Green indicatesabsence of voltage

VeriSafe™ AVT

Voltage Indicator

Indicates presence of voltage

Test Portal*requires a portable
test instrument andconversion

Built-in known voltage source
Tests for absence of voltage
Verification tester is in contact
with the test point
Keeps hazardous voltage off thedoor
Diagnostic codes provide
intelligence
Built-in overcurrent protection
Automatically self-calibrates
UL listed and labeled for verifying
the absence of voltage (UL 1436)
Meets the requirements to verify
the absence of voltage describedin NFPA 70E 120.5(7) Exception 1

12 WHITE PAPER – Exploring Permanently Mounted Voltage Testing Products – The myths, the differences, and the benefits*requires a portable
test instrument &known voltage
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