Electrical test instruments: Safety is still the first tool

Safety is paramount with electrical test instruments and great care must be taken when using equipment or understanding the codes involved.


Figure 1: Technician testing breaker box wearing the proper PPE. Courtesy: AVO Training InstituteThere 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.

Electrical hazards

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

Figure 2: Electrical cable testing instrument used to find faults in a cable system. Courtesy: AVO Training InstituteRegardless 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:

  • Voltage indicating instrument suitable for conditions
  • Environment
  • Correct CAT category I, II, III, or IV
  • Continuity test instrument
  • Insulation resistance test instrument.

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: 

  • Must be rated for circuits and equipment where they are utilized.
  • Must be designed for the environment to which they will be exposed and for the manner in which they will be utilized.
  • Must be visually inspected for external defects and damage before each use. If there is a defect or evidence of damage that might expose an employee to injury, the defective or damaged item shall be removed from service.

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:

  • Verified on a known voltage source before an absence of voltage test is performed. 
  • Test for the absence of voltage on the de-energized conductor or circuit part. A zero reading might mean that no voltage is present during the testing, or it could mean that the instrument has failed. 
  • Verified on a known voltage source after an absence of voltage test is performed.

Figure 3: In AVO Training Institute’s lab, a student works with an instructor to practice correct procedures to test electrical apparatus. Courtesy: AVO Training InstituteThis 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:

  • Use a meter that meets accepted safety standards for the environment in which it will be used.
  • Use a meter with fused current inputs and be sure to check the fuses before making current measurements.
  • Inspect test leads for physical damage before making a measurement.
  • Use the meter to check continuity of the test leads.
  • Use test leads that have shrouded connectors and finger guards.
  • Use meters with recessed input jacks.
  • Select the proper function and range for your measurement.
  • Be certain the meter is in good operating condition.
  • Follow all equipment safety procedures.
  • Always disconnect the "hot" (red) test lead first.
  • Don't work alone.
  • Use a meter that has overload protection on the ohms function.
  • When measuring current without a current clamp, turn the power off before connecting into the circuit.
  • Be aware of high-current and high-voltage situations and use the appropriate equipment, such as high-voltage probes and high-current clamps.

CAT ratings and their definitions

Here's a brief review of the four category (CAT) ratings and their basic definitions:

Category I

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.

  • Protected electronic equipment
  • Equipment connected to (source) circuits in which measures are taken to limit transient overvoltages to an appropriately low level
  • Any high-voltage-low-energy source derived from a high-winding resistance transformer, such as the high-voltage section of a copier.

Figure 4: Conducting an electrical risk assessment wearing the proper PPE. Courtesy: AVO Training InstituteCategory II

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.

  • Appliance, portable tools and other household and similar loads
  • Outlet and long branch circuits
  • Outlets at more than 10 meters from CAT III source
  • Outlets at more than 20 meters from CAT IV source.

Category III

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.

  • Equipment in fixed installations, such as switchgear and polyphase motors
  • Bus and feeders in industrial plants
  • Feeders and short branch circuits, distribution panel devices
  • Lighting systems in larger buildings
  • Appliance outlets with short connections to service entrance.

Category IV

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.

  • "Origin of installations," such as where low-voltage connection is made to utility power
  • Electricity meters, primary overcurrent protection equipment
  • Outside and service entrance, service drop from pole to building, run between meter and panel
  • Overhead line to detached building, underground line to well pump.

Global verification

Here's a look at the various worldwide labs and test facilities that evaluate electrical safety:

  • UL: Underwriters Laboratory, the U.S.-based test lab. Among its many standards for electrical safety is UL 50, which covers enclosures for electrical equipment.
  • CSA: Canadian Standards Association, which provides product testing and certification services for electrical, mechanical, plumbing, gas and a variety of other products.
  • CE: An abbreviation of the French phrase Conformité Européenne, CE is the marking on products which meet conformity standards for the European Economic Area.
  • ETL: A North American testing laboratory that tests to UL standards. It is recognized at a Nationally Recognized Testing Laboratory.
  • TÜV: Based in Germany, TÜV Rheinland tests electrical, electronical and programmable electronic components and systems which are applied in safety-related applications.

Dennis K. Neitzel, CPE, CESCP is a trainer with AVO Training Institute.

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