We have outlined the different testing methods for the Absence of Voltage and go through the pros and cons of each method. The most efficient and safest method is the Absence of Voltage Tester device that does the check automatically that is both accurate and prevent human error.
This article is part of The Guide to Absence of Voltage Testing by Factomart
Numerous studies exist pertaining to injuries resulting from electric shock and arc flash events. These studies recognize that establishing the economic payoffs of prevention is a critical factor in promoting workplace safety. Besides personal injury, the costs of property and equipment damage need to be considered. Although estimates vary, studies have shown that the average direct cost of an electrical injury ranges from about US $50,000 to US $80,0001, while the indirect cost
can exceed the direct cost by a factor of nearly four2. Direct costs include lost wages or workers’ compensation payments, medical expenditures, and legal expenses. Indirect costs include:
- wages paid during work stoppage
- administrative costs related to injury
- property damage and repair
- training and compensation for replacement workers
- lost productivity with less experienced workers
- fines related to workplace safety violations
- potential increase in absenteeism
- decrease in morale
Electrical injuries have one of the highest average workers’ compensation costs, second only to motor vehicle accidents3.
Even though testing for the absence of voltage is a pretty straightforward process, it needs to be conducted with care in order to avoid shock, injury and even death. Follow these recommended steps prior to testing for voltage.
NFPA 70E requires that the “operation of the test instrument be verified on any known voltage source before and after an absence of voltage test is performed.” In other words, connect your meter to an outlet or a proving unit whose voltage you already know and make sure your meter reads the correct voltage. If it doesn’t, then you can’t rely on that meter to tell you whether voltage is present and work must stop until a correctly-operating test instrument is used to verify the absence of voltage.
- Are there any obvious defects in the case or meter element?
- Does the selector switch turn smoothly without binding?
- Do the functions change properly when the selector switch is operated?
- Does the test instrument have the correct CAT rating for the part of the electrical system it is being used on?
- Does the display function properly? Are the digits broken or do they fade in and out?
Lead damage can be hard to detect. Test leads can be easily damaged during use (or improper storage), so best safety practice is to replace them annually. They are expendable and low cost. Here are some questions to ask during the test:
- Are there any signs of damage, such as cuts or breaks in the insulation, melted or discoloration of the insulation, or crushing of the test lead?
- Are the probe ends straight and undamaged?
- Are the probe ends tight?
Caution: Never store the test leads wrapped around the test instrument.
Always wear PPE based on NFPA 70E recommendations, until you have verified the equipment is in an electrically-safe work condition. The greater the electrical hazard, the higher the personal protective equipment arc-rating must be to withstand an arc-flash incident. PPE that might be requiredincludes:
- Safety glasses.
- Insulated tools.
- Insulated gloves and leather protector gloves.
- Ear plugs or other hearing protection that is covered by arc-rated PPE.
- Face shield/hood.
- Arc-resistant clothing.
NFPA 70E requires those working on exposed conductors and circuit components operating at 50 volts or more to use lockout/tagout devices and procedures and be properly trained. The following steps make up part of the logout/tagout process:
- Apply temporary protective grounds when necessary.
- Watch for unguarded conductors that are still energized.
- Be certain of a tight clean connection at the point of grounding.
- Always follow the lockout/tagout procedure for the specific equipment being isolated.
Once you’ve gone through the Lockout/Tagout process, are wearing the proper PPE and you have the appropriate (and inspected) voltage test instruments, you’re ready for the absence of voltage test.
The following procedure is a general outline for no-voltage testing on all types of cable except series street lighting cable. Specific instructions for metallic sheath, nonmetallic sheath and concentric neutral cables should be followed as defined by your company’s procedures and practices, as well as the manufacturer’s instructions for testing equipment being utilized.
1. Prove your meter operates on a known voltage source.
2. Bridge shielding before opening sheath.
3. Remove outer jacket or sheath, removing enough jacket to provide clearance between the testing device and the jacket or sheath.
4. Test for no voltage.
5. Verify no-voltage condition is indicated.
6. Remove all non-insulating materials or shielding layers around the entire circumference of the cable, providing ample clearance between the testing device and the shielding.
7. Test for no voltage after each step of shielding removal until the insulation is reached.
8. Verify no-voltage condition is indicated.
9. Test for no voltage on the insulation.
10. Verify no-voltage condition is indicated.
11. Check for stray voltage by testing from each conductor to ground with an approved low-voltage testing device.
12. Verify no-voltage condition is indicated.
13. Prove your meter operates on a known voltage source.
The following procedure is a general outline for testing conductors and electrical equipment, other than cable, for no voltage.
1. Prove your meter operates on a known voltage source.
2. Check for voltage using a properly proven device approved for the voltage involved.
3. Verify no-voltage condition is indicated.
4. Prove your meter operates on a known voltage source.
5. Proceed with the work or with the installation of grounds as required.
When voltage is indicated and the testing device is proven using a known voltage source, no work must be performed or ground installed until the reason for the voltage indication has been identified and removed, or proven to be due to induction. Check the following as possible sources of voltage.
• Incorrect job location
• Incorrect blocking points that have been established including back-feed sources
• Contact with foreign voltage source
• Induced voltage from high-voltage conductors. When this condition is suspected, a voltmeter-type test device must be used to check phase-to-ground and phase-to-phase voltage.
Detailed instructions to be followed when unusual conditions are encountered should be available from your company.
Though these two examples are generic in nature, the intent is the same. No conductor can be considered de-energized unless it is first isolated from the system, tested for absence of voltage and then grounded. Until all these steps occur, all conductors must be treated as energized. By following these basic principles, you can assure your safety and the safety of your crew.
- Typically handheld
- Detect presence and absence of voltage
- Contact and non-contact versions
Voltage test portals are sometimes installed on equipment so workers can use hand-held voltage testers before opening the enclosure. However, there is no way to confirm that the probes of the hand-held tester are in direct contact with the electrical conductors inside the enclosure. The uses of a hand-held tester requires access to a known voltage source to verify the tester is functioning.
- Portable and can be used with many panels
- Readily available
- Contact and non-contact versions
- The process is complex and time-consuming
- Portable instruments are susceptible to mechanical and electrical failure and misuse by the person using the device.
- The process of using a hand-held tester is dependent on human input, interaction, and interpretation, it is vulnerable to mistakes and errors.
- Typically installed
- Only warn of voltage presence
- Do not guarantee absence of voltage
A voltage indicator is an installed device that illuminates when voltage is present; however, a voltage indicator can be unreliable. When lights
on the indicator are off, there could still be voltage if there is a hardware failure, such as the indicator functioning abnormally or if the LEDs fail. Improper installation of a voltage indicator or loose leads can cause the voltage indicator to become disconnected from its source, resulting in false or unreliable indications. Ultimately, voltage indicators do not meet the requirements for Sections B, C, and D.
- Test without exposure
- Self-contained with known voltage source
- Built-in pre-/post-verification test
- Automated test sequence
- Detects AC and DC without need to adjust settings
- Active indication for absence of voltage
- SIL 3 safety functions
- Supports compliance with NFPA 70E (UL 1436 listing)
- Install in direct contact with circuit (no fusing)
- Fixed to a single panel
- Higher cost
|Exception 1, Subsection:||Voltage Meter||Voltage Indicator||Voltage Test Portals||VeriSafe AVT|
|A||It is permanently mounted and installed in accordance with the manufacturer’s instructions.||Yes||Yes||Yes||Yes|
|It tests the conductors and circuit parts at the point of work.||N/A (no test function)||N/A (no test function)||No (no guarantee hand-held tester is in contact with circuit)||Yes|
|B||It is listed and labeled for verifying the absence of voltage||No||No||No||Yes|
|C||It tests each phase conductor or circuit part both phase-to-phase and phase-to-ground||Only phase- to-ground||Only phase- to-ground||Yes, with hand-held tester||Yes|
|D||The test device is verified as operating satisfactorily on any known voltage source before and after verifying the absence of voltage||No||No||No (hand-held tester requires access to a known voltage source)||Yes|