Electrical construction, maintenance and repair work all involve a great deal of attention towards safe work practices. Industry electrical publications regularly highlight the various safety issues & their remedies, including the use of tools & equipment for energized & deenergized environments, as well as utilizing the correct personal protective equipment according to the situation.
Electrical Test Instruments are discussed very briefly and often shrugged off in safety articles. The incomplete and/or incorrect knowledge & awareness regarding Electrical Test Instruments can have dramatic results. When electric safety is discussed, the subjects of arc flash, shock and arc blast dominate discussions, but one question often pops up, “how to identify the location of hazards using electrical test instruments?” This question can be answered by reviewing the electrical hazards, chalking up the requirements for assessing the workplace and identifying faults using proper use of electrical test instruments.
Electricity is one of the most serious workplace hazards in the world and can lead to shocks, burns, fires and explosions. Employees can get seriously injured or even lose their lives due to the explosions caused by electricity. In addition to the risk posed to human life, electrical hazards such as arc flash & blast can damage equipment, causing fragmented metals to fly in all directions, disrupting operation of nearby machines. Even low-energy arcs have the tendency to cause violent explosions, and serve as the ignition source of a bigger explosion.
Improper use of electrical test instruments can lead to electrocution; test instruments must be selected & utilized properly to ensure safety and verify the presence of voltage.
Selection of Test Instruments
Irrespective of the type of work you’re performing, whether it involves installation, maintenance, verification of absence of voltage, troubleshooting or similar diagnostic work, collecting accurate & consistent information is extremely vital. In order to comply with the electrical industry standards & regulations, the right test instruments must be selected & used.
Whenever voltage verification for energized & deenergized components is being conducted, the electrician must use the right instruments, applicable to the work to be performed. As a minimum, these should include:
- Voltage indicating instrument
- Correct CAT category
- Continuity test instrument
- Insulation resistance test instrument
All test instruments should have clear instructions and must be certified & labelled by an independent verification lab such as UL, CE, CSA, TUV, etc. Make sure that all meters, leads and probes are of an adequate CAT category as sometimes the only thing standing between you and an electricity spike would be leads! If you are uncertain about the equipment you’re using, not only would you put yourself at risk, but also those in your surroundings.
Everyone working electrical environment must have the required safety equipment such as gloves, eye protection, etc. Having the correct electrical testing & measurement instruments can improve on-job safety for everyone.
Use of Electrical Test Instruments
Only qualified persons are permitted to perform tasks such as testing, voltage measuring, troubleshooting, etc. due to the potential electrical hazard associated with the use of test instruments. Improper use of electrical equipment can lead to shock, electrocution as well as arc flashes.
The following requirements apply to test instruments, equipment and their associated leads, power cords and connectors:
- Rating must be that of the circuit and equipment where they are utilized.
- Must be designed for the environment where they will be exposed.
- Must be visually inspected for defects & damage before use, and in the event the equipment is damaged, it must be removed from service
Whenever test instruments are used for testing the absence of voltage on conductors operating at 50 volts or more, the operation of the instrument must be:
- Verified on a known voltage source.
- Test for absence on a de-energized conductor.
- Verified on a known voltage source after conducting absence of voltage test.
There are a total of four CAT ratings, as described below:
- Category 1 - This covers electronics equipment, signal level for telecommunications and low-energy equipment with transient-limiting protection. The peak impulse transient range lies from 600 – 4000 volts within a 30-ohm source.
- Category II - Appliances, portable tools and other household loads fall within this category. In addition, it includes all outlets at more than 10 meters from Category III sources and 20 meters from Category IV sources.
- Category III - Equipment in fixed installations such as switchgear & polyphase motors form the base for this category. Three-phase distribution including single-phase commercial lighting fall within this category. The line between Category III and Category IV is drawn by a minimum of one level of transformer isolation. The peak impulse transient range is from 600 – 8000 volts with a 2-ohms source.
- Category IV - Electricity meters or three-phase at utility connections, any outdoor conductors or primary supply level, all are included within Category IV. The category covers the highest and most dangerous level of transient overvoltage one is likely to encounter. The peak impulse transient range is from 600 – 12000 volts with a less than 1-ohm source.
The following is a breakdown of the various worldwide labs & test facilities that verify electrical safety equipment:
- UL - Underwriters Laboratory is a US-based test lab that has several widely used standards for electrical safety, e.g. UL50 (covers enclosures for electrical equipment).
- CSA - Canadian Standards Association provides protect testing & certification for electrical, mechanical, plumbing and a variety of products.
- CE - Conformite Europeenne is a French verification agency that tests products for a certain conformity standard for the European Economic Zone.
- TUV - A Germany-based testing lab, TUV tests electrical, electronical and programmable systems.
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