There is a great deal of attention devoted to safe work practices during electrical construction, maintenance and repair work. Industry electrical publications regularly report on safety issues, including the use of the proper tools and equipment used for energized and de-energized work, as well as utilizing the correct personal protective equipment (PPE) for each workplace situation.
Electrical test instruments are given very little discussion, if any, in safety articles. Examples include using the wrong test instruments or improperly using them, which can have catastrophic results. Some of the most frequently used test instruments include noncontact voltage testers, multimeters, insulation testers and ground-resistance testers. The issue with using a non-contact or proximity device is that the requirement to test a circuit to ensure that it is de-energized requires the circuit to be tested phase-to-phase and phase-to-ground, which cannot be done using this type of tester.
When electrical safety is discussed, the subjects of shock, arc flash, and arc blast dominate the discussions. One question is often asked: "How do I identify when these hazards are present, or likely to be present, when I am using electrical test instruments on electrical circuits and equipment?" A review of these electrical hazards, along with requirements for assessing the workplace to identify the electrical hazards and PPE associated with using test instruments, is one way to get to the answer.
Electricity is a serious workplace hazard, exposing employees to electrical shock, electrocution, burns, fires and explosions. Employees have been killed or injured in fires and explosions caused by electricity.
Besides the electrical hazards of arc flash and arc blast, extremely high energy arcs can damage equipment and cause fragmented metal to fly in all directions. In atmospheres that contain explosive gases or vapors, or combustible dusts, even low-energy arcs can cause violent explosions. In these cases, the electric arc may be the ignition source for a much bigger explosion and fire.
Improper use of electrical test instruments can result in shock or electrocution, as well as an arc flash incident. This article addresses these issues, along with the requirements for selecting and utilizing the test instruments to verify the presence of voltage.
Selection of test instruments
Regardless of whether you are performing electrical installation work, equipment maintenance, verifying the absence of voltage for de-energized work, troubleshooting, voltage measurements or similar diagnostic work, collecting accurate and consistent information from these tests is imperative. To comply with electrical industry standards and regulations, there is a need to select and use the right test instruments according to the application.
When conducting voltage verification, for energized and de-energized work, the electrical worker must select the right test instruments and equipment applicable to the work to be performed. As a minimum, these should include the following:
All test instruments include specific manufacturer's operational instructions. Test instruments must be certified and display a label of an independent verification lab, such as UL, CSA, CE, ETL or TÜV. Make sure all meters, test leads and probes have an adequate category (CAT) safety rating. Sometimes, the only thing standing between an electrical worker and an unexpected spike is their meter and test leads. If you use the wrong equipment with the wrong voltage, you could be putting yourself and others at risk. So, before conducting any test, make sure your choice of instrument is correct.
Electrical standards, such as UL, ANSI, IEC, and CAN, specify protection from currents at levels well above a system's rated capacity. Without this additional protection, transient overvoltages, which are becoming increasingly common, can lead to equipment failure and serious injury or death.
Minimizing such risks requires that everyone working in electrical environments has safety equipment as required. They need properly rated gloves, eye protection and electrical measurement test instruments that provide appropriate protection. Having the correct electrical testing and measurement instruments and using the correct procedures can improve job safety.
Use of electrical test instruments
Due to the potential electrical hazards associated with the use of electrical test instruments, only qualified persons are permitted to perform tasks such as testing, troubleshooting and voltage measuring when working within the Limited Approach Boundary of exposed energized electrical conductors or circuit parts operating at 50 volts or more, or where any other electrical hazard may exist. Improper use of electrical test instruments can result in shock or electrocution, as well as creating an arc flash incident.
The following additional requirements apply to test instruments, equipment, and all associated test leads, cables, power cords, probes, and connectors:
When test instruments are used for testing the absence of voltage on conductors or circuit parts operating at 50 volts or more, the operation of the test instrument must be:
This verification primarily applies to conductors or circuit parts operating at 50 volts or more. However, under certain conditions (such as wet contact or immersion) even circuits operating under 50 volts can pose a shock hazard.
Only qualified persons are permitted to perform tasks such as testing, troubleshooting, and voltage measuring, due to the electrical hazards associated with energized work. All required PPE, for the associated hazards, must be utilized when performing these tasks. Test instruments must be rated for the conditions under which testing is to be performed. When selecting voltage testing instruments, an assessment must be performed to determine the proper category (CAT) rating required, based on the highest hazard exposure.
When test instruments are used for testing the absence of voltage, for de-energized work, on conductors or circuit parts operating at 50 volts or more, the operation of the test instrument must be verified on a known voltage source before and after an absence of voltage test is performed.
Electrical safety checklist
The fundamentals of electrical safety can be overlooked, especially by seasoned electricians. It's worth reviewing a few safety tips, both for the novice electrician and the veteran:
CAT ratings and their definitions
Here's a brief review of the four category (CAT) ratings and their basic definitions:
This typically covers electronic equipment. Signal level for telecommunications, electronic equipment and low-energy equipment with transient-limiting protection. The peak impulse transient range is from 600 to 4,000 volts with a 30-ohm source.
Single-phase receptacle connected loads. Local level for fixed or non-fixed powered devices-everything from lighting to appliances to office equipment. Also, all outlets at more than 10 meters (30 feet) from Category III sources and all outlets at more than 20 meters (60 feet) from Category IV sources. The peak impulse transient range is from 600 to 6,000 volts with a 12-ohm source.
Three-phase distribution, including single-phase commercial lighting. Distribution level-fixed primary feeders or branch circuits. These circuits are usually separated from Category IV (whether utility service or other high-voltage source) by a minimum of one level of transformer isolation; for example, feeders and short branch circuits, distribution branch panels and heavy appliance outlets with "short" connections to service entrance. The peak impulse transient range is from 600 to 8,000 volts with a 2-ohm source.
Three-phase at utility connection, any outdoor conductors or primary supply level. It will cover the highest and most dangerous level of transient overvoltage you are likely to encounter-in utility service to a facility both outside and at the service entrance, as well as the service drop from the pole to the building, the overhead line to a detached building, and the underground line to a well pump. The peak impulse transient range is from 600 to 12,000 volts with a less than 1-ohm source.
Here's a look at the various worldwide labs and test facilities that evaluate electrical safety:
Dennis K. Neitzel, CPE, CESCP is a trainer with AVO Training Institute.