By Bruce Meier, Electrical Standards and Safety Expert for Fluke Corporation.
The increased occurrence and levels of transient overvoltages on today’s power systems have once again called attention to requirements for safety in troubleshooting, maintenance, and repair. Safety concerns have become paramount as occupational-safety risks are recognized and businesses take action to safeguard their employees. The safe use of test instruments is one critical matter. Fortunately, formal definitions exist to guide users on the selection of appropriately rated test instruments for a specific measurement environment.
High-voltage and high-current environments are perhaps the greatest concern for those using test instruments to diagnose power systems. Engineers, technicians, and electricians working on power systems must seriously consider the “measurement environment” in which they are working. Measurement environment refers to an installation environment in which a high transient voltage could occur on a system being maintained. The level of the transient defines the specific measurement category for the environment. Typically, the farther the system is from the main distribution lines coming from the utility, the lower the potential transient level, due to inherent damping in the system.
The transient alone may or may not have sufficient energy to be life-threatening, but the fact that the transient rides on top of a power source, such as 480 volts at 200 amps, could have devastating follow-through effects. Thanks to the efforts of safety agencies in the U.S. and Europe, definitions of installation environments and the risks inherent in each have been formalized in writing.
The International Electrotechnical Commission, or IEC, develops international general standards for safety of electrical equipment for measurement, control and laboratory use. In 1988 IEC voted to replace an older standard, IEC-348, with a more stringent standard, IEC-1010-1, which was later renamed to IEC 61010-1. In 2001, the IEC released IEC 61010-1 2 nd Edition. It carries a new requirement that multifunction meters not pose a hazard as a result of foreseeable misuse. Simply put, that means that if the user makes a mistake, such as applying volts with the knob switched to Ohms, the meter cannot cause fire, shock, arcing or explosion.
IEC 61010 is the basis for the following standards:
- US ISA-82.02.01 (IEC 61010-1 Mod)
- Canadian CAN/CSA C22.2 No. 61010-1-04
- European EN 61010-1:2001
The following are common questions about IEC-61010-1, especially as it applies to electrical and electronic test equipment.
Q. What are the “spacing requirements” referenced in IEC-61010?
A. The IEC standard refers to these spacings as “creepage” distance (along surfaces) and “clearance” distance (shortest distance through the air) for a given maximum input-voltage rating. Larger clearance distances enable the meter to withstand the higher overvoltage transients that may be found on the system being measured. When the standard was updated to 1010-1, the spacing requirements increased.
Q. What is a Measurement Category, and what is the significance of CAT III vs. IV?
A. IEC-61010 specifies measurement category ratings, which relate to the probability of a voltage occurring (at some location) that is significantly higher than the voltage expected. For example, an unexpected voltage transient would be considered an overvoltage. Measurement categories range from I to IV, in increasing order of transient level expected. They are not necessarily related to the nominal voltage level of the system. Measurement Category IV is typically the utility service to an installation. Measurement Category III typically refers to mains voltage feeder or branch circuit lines that are separated from the utility service by at least a single level of transformer isolation. Categories I and II are successively more isolated and distant from the utility service than Categories III and IV. Instruments designed to meet Measurement Category III and IV are able to withstand overvoltage transients better than instruments designed to Measurement Category II.
Anyone working on mains voltage feeder or branch circuit lines up to 600V should use instruments rated for a minimum of Category III.
Q. How does IEC differ from UL and CSA?
A. Underwriters Laboratories (UL), Canadian Standards Association (CSA), and TÜV (a German standards organization) are approval/listing agencies. IEC is an international standards writing organization. Local governments may use the IEC standards to write their own national standards, complete with enhancements influenced by local needs (for example, ANSI/ISA-S82.01-94 based on IEC-1010-1 in the U.S.). The approval/listing agencies are independent testing laboratories that test products against national standards or their own standards, such as UL61010-1, 2 nd Edition based on IEC-1010-1.
Q. What does “UL listed” mean?
A. A manufacturer may state that a product is designed to meet the requirements of IEC-1010-1, UL 3111, or both. However, to be UL-listed, CSA‑certified, or TÜV-certified, the manufacturer must employ the services of the approval/listing agency to test the product’s conformity to the standard. Only upon successful completion of this independent testing, and receipt of authorization from the approval/listing agency, may the manufacturer display the mark of the agency on the product.
A manufacturer may claim that its product is “designed to IEC-61010 standards,” but that does not mean the instrument has successfully passed the independent evaluation and testing of an approval/listing agency such as UL. The corollary is also true: a product with a UL listing may or may not meet the requirements of IEC-61010, depending on what standard the Underwriters Laboratories tested the product to.
