Electrical Safety When Utilizing Test Equipment and Instruments
Dennis. K. Neitzel, CPE, CESCP,
AVO Training Institute
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 deenergized work, as well as utilizing the correct personal protective equipment (PPE) for each workplace situation. However, electrical test instruments are given very little, if any, discussion in safety articles, which would include using the wrong test instrument 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 issues with using a non-contact or proximity device is that the requirement to test a circuit to ensure that it is deenergized 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 are predominate in the discussions. In these discussions the 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? This article discusses the electrical hazards, along with requirements for assessing the workplace to identify the electrical hazards and personal protective equipment (PPE) associated with using test instruments.
Electricity is widely recognized as 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.
Additional considerations in relation to the electrical hazards of arc flash and arc blast, is that extremely high energy arcs can damage equipment, causing 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.
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. This paper addresses these issues, along with the requirements for selecting and utilizing the test instruments to verify the presence of voltage.
Selection of Electrical Test Instruments
Regardless of whether you are performing electrical installation work, equipment maintenance, verifying the absence of voltage for deenergized work, troubleshooting, voltage measurements, or similar diagnostic work, collecting accurate and consistent information from these tests is imperative. In order 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 deenergized 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
- Correct category (I, II, III, or IV)
- Continuity test instrument
- Insulation resistance test instrument
All test instruments include specific manufacturer’s operational instructions. The test instruments must be certified and display a label of an independent verification lab, such as UL, CSA, CE, ETL or TUV. 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.
To do this, a quick review of the four category (CAT) ratings is in order:
Use of Electrical Test Instruments
- Category I — 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.
- Category 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 10m (30 feet) from Category III sources and all outlets at more than 20m (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
As previously stated, 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 deenergized 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
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 deenergized 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.
(o) Testing and test facilities. (1) Application.
Paragraph (o) of this section provides for safe work practices for high-voltage and high-power testing performed in laboratories, shops, and substations, and in the field and on electric transmission and distribution lines and equipment. It applies only to testing involving interim measurements utilizing high voltage, high power, or combinations of both, and not to testing involving continuous measurements as in routine metering, relaying, and normal line work.
Routine inspection and maintenance measurements made by qualified employees are considered to be routine line work and are not included in the scope of paragraph (o) of this section, as long as the hazards related to the use of intrinsic high-voltage or high-power sources require only the normal precautions associated with routine operation and maintenance work required in the other paragraphs of this section. Two typical examples of such excluded test work procedures are "phasing-out" testing and testing for a "no-voltage" condition.
(2) General requirements. (i)
The employer shall establish and enforce work practices for the protection of each worker from the hazards of high-voltage or high-power testing at all test areas, temporary and permanent. Such work practices shall include, as a minimum, test area guarding, grounding, and the safe use of measuring and control circuits. A means providing for periodic safety checks of field test areas shall also be included. (See paragraph (o)(6) of this section.)
Employees shall be trained in safe work practices upon their initial assignment to the test area, with periodic reviews and updates provided as required by paragraph (a)(2) of this section.
Guarding of test areas. (i) Permanent test areas shall be guarded by walls, fences, or barriers designed to keep employees out of the test areas.
In field testing, or at a temporary test site where permanent fences and gates are not provided, one of the following means shall be used to prevent unauthorized employees from entering:
The test area shall be guarded by the use of distinctively colored safety tape that is supported approximately waist high and to which safety signs are attached,
The test area shall be guarded by a barrier or barricade that limits access to the test area to a degree equivalent, physically and visually, to the barricade specified in paragraph (o)(3)(ii)(A) of this section, or
The test area shall be guarded by one or more test observers stationed so that the entire area can be monitored.
The barriers required by paragraph (o)(3)(ii) of this section shall be removed when the protection they provide is no longer needed.
Guarding shall be provided within test areas to control access to test equipment or to apparatus under test that may become energized as part of the testing by either direct or inductive coupling, in order to prevent accidental employee contact with energized parts.
(4) Grounding practices. (i)
The employer shall establish and implement safe grounding practices for the test facility.
All conductive parts accessible to the test operator during the time the equipment is operating at high voltage shall be maintained at ground potential except for portions of the equipment that are isolated from the test operator by guarding.
Wherever ungrounded terminals of test equipment or apparatus under test may be present, they shall be treated as energized until determined by tests to be deenergized.
Visible grounds shall be applied, either automatically or manually with properly insulated tools, to the high-voltage circuits after they are deenergized and before work is performed on the circuit or item or apparatus under test. Common ground connections shall be solidly connected to the test equipment and the apparatus under test.
In high-power testing, an isolated ground-return conductor system shall be provided so that no intentional passage of current, with its attendant voltage rise, can occur in the ground grid or in the earth. However, an isolated ground-return conductor need not be provided if the employer can demonstrate that both the following conditions are met:
An isolated ground-return conductor cannot be provided due to the distance of the test site from the electric energy source, and
Employees are protected from any hazardous step and touch potentials that may develop during the test.
See Appendix C to this section for information on measures that can be taken to protect employees from hazardous step and touch potentials.
In tests in which grounding of test equipment by means of the equipment grounding conductor located in the equipment power cord cannot be used due to increased hazards to test personnel or the prevention of satisfactory measurements, a ground that the employer can demonstrate affords equivalent safety shall be provided, and the safety ground shall be clearly indicated in the test set-up.
When the test area is entered after equipment is deenergized, a ground shall be placed on the high-voltage terminal and any other exposed terminals.
High capacitance equipment or apparatus shall be discharged through a resistor rated for the available energy.
A direct ground shall be applied to the exposed terminals when the stored energy drops to a level at which it is safe to do so.
If a test trailer or test vehicle is used in field testing, its chassis shall be grounded. Protection against hazardous touch potentials with respect to the vehicle, instrument panels, and other conductive parts accessible to employees shall be provided by bonding, insulation, or isolation.
Control and measuring circuits. (i) Control wiring, meter connections, test leads and cables may not be run from a test area unless they are contained in a grounded metallic sheath and terminated in a grounded metallic enclosure or unless other precautions are taken that the employer can demonstrate as ensuring equivalent safety.
Meters and other instruments with accessible terminals or parts shall be isolated from test personnel to protect against hazards arising from such terminals and parts becoming energized during testing. If this isolation is provided by locating test equipment in metal compartments with viewing windows, interlocks shall be provided to interrupt the power supply if the compartment cover is opened.
The routing and connections of temporary wiring shall be made secure against damage, accidental interruptions and other hazards. To the maximum extent possible, signal, control, ground, and power cables shall be kept separate.
If employees will be present in the test area during testing, a test observer shall be present. The test observer shall be capable of implementing the immediate deenergizing of test circuits for safety purposes.
(6) Safety check. (i)
Safety practices governing employee work at temporary or field test areas shall provide for a routine check of such test areas for safety at the beginning of each series of tests.
The test operator in charge shall conduct these routine safety checks before each series of tests and shall verify at least the following conditions:
That barriers and guards are in workable condition and are properly placed to isolate hazardous areas;
That system test status signals, if used, are in operable condition;
That test power disconnects are clearly marked and readily available in an emergency;
That ground connections are clearly identifiable;
That personal protective equipment is provided and used as required by Subpart I of this Part and by this section; and
That signal, ground, and power cables are properly separated.
Insulation testers, multimeters, ground-resistance testers, and noncontact voltage testers are among the most common instruments for making routine electrical tests. One of the most common risks during testing is using an incorrect instrument for the test that is not rated for the voltage at the test point. Minimally, instruments should comply with 300V, CAT III standards and as high as 1,000V, CAT IV.
“The person doing the test must understand and use the proper PPE clothing and procedures required for the work environment and operate testers as instructed in the product manual. They should read the safety instruction section of the product manual.
The single most important aspect of electrical measurement safety is following NFPA 70E. Work de-energized whenever possible. Know the arc flash potential of the cabinet and verify test tools are functional and rated high enough for that electrical environment and for the measurements to be made. Wear the appropriate PPE for the environment until the cabinet is confirmed de-energized.
“Again, the single biggest risk is working live and not wearing proper PPE. Following that is using a test instrument that has not been properly verified as appropriately rated, fused and functional before the live testing. Another common mistake: Test leads plugged into the amp jacks of a meter, then attempting to measure voltage—causes an immediate internal short.
- 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 only test leads that have shrouded connectors and finger guards.
- Use only 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.