There is more to choosing a meter than finding one with the right functions and features for the job. To protect your investment and—more importantly—yourself, choose a meter that can withstand the electrical hazards present in the environment in which you plan to use the meter.
The International Electrotechnical Commission (IEC) develops international general standards for safety of electrical equipment for measurement, control, and laboratory use. In 1988, IEC replaced an older standard, IEC-348, with a more stringent standard, IEC-1010-1.
The most significant thing to come out of IEC-1010 is the separation of the various electrical environments into installation categories based on the hazards in each category:
Category IV, called the primary supply level, refers to the overhead or underground utility service to an installation.
Category III, called the distribution level, refers to the line voltage feeder or branch circuits. These circuits typically are separated from the utility service by at least a single level of transformer isolation. The equipment consists of fixed installations.
Category II refers to the local level, such as appliances and portable equipment.
Category I refers to the signal level, such as telecommunications and electronic equipment.
Within each installation category, there are voltage classifications. The voltage rating alone does not determine the safety of the meter. It is the combination of the installation category and voltage classification that determines the maximum transient withstand capability of the meter.
First, identify the highest installation category you will be using the meter in and make sure it is clearly marked for use in that category. Not only should the meter show this category rating, but also the meter leads. The measurement system is only as safe as the weakest link. Many times, the meter leads are overlooked, especially when they are damaged and need to be replaced.
To ensure that the manufacturer has not just put the category label on the product and used the words “designed to meet Category ___,” look for some indication of independent testing by a qualified testing laboratory. Underwriters Laboratories (UL), Canadian Standards Associations (CSA), TÜV and VDE (German standards organizations) are approval/listing agencies. They are independent laboratories that test products against national/international standards or their own standards that are based on national/international standards. For example, UL3111, CSA C22.2 No. 1010-1-92, and EN61010 are based on IEC-1010-1.
To be UL-listed or CSA-, TÜV-, or VDE-certified, the manufacturer must use the services of the approval/listing agency to test the product’s conformance to the agency’s standard. Only upon successful completion of this independent testing may the manufacturer display the mark of the agency on the product.
When deciding what you need in a meter, identify all of the attributes of the application, including the electrical environment or category where the meter will be used. Next, look at the meters that have the functions and features you need and see if they are rated for the highest category in which you plan to use the meter. Last, but most importantly, look for the logo of the independent agency that has tested the meter and confirmed it meets the latest standards.
Copyright 1998 Nelson Publishing Inc.
February 1998
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