A Guide to the 61010-1, 2nd Ed., for North America and Europe

Cherie Forbes

Manufacturers of electrical measurement and control equipment ought to become familiar with new requirements and prepare for possible retesting of their products.

North American manufacturers of safety test equipment must be ready for the new 61010-1 standard.

In July 2004, Underwriters Laboratories (UL), the Instrumentation, Systems, and Automation Society (ISA), and the Canadian Standards Association (CSA) jointly issued the second edition of the standard for electrical equipment for measurement, control, and laboratory use. These agencies’ versions of the new standard are known formally, and respectively, as UL 61010-1, 2nd Ed., ISA-82.02.01 (IEC 61010-1 Mod), and CAN/CSA C22.2 No. 61010-1-04.^1-3 These standards apply only to Canada and the United States.

Based on the second edition of IEC 61010-1 published three years before, all three North American standards contain identical requirements. They replace the previously published standards UL 61010A-1 (issued in 2002), UL 61010B-1 (2003), UL 61010C-1 (2002), CAN/CSA C22.2 No. 1010-1-92 (1992), and ISA-82.02.01 (1999).

This article discusses timelines for adoption of the standard in Canada and the United States, differences between the first edition and the second, and differences between the European, or IEC, version of the standard and the North American version. An understanding of the relevant changes and variations will equip North American manufacturers to target their products at both the North American and the European market effectively.

Effective Dates

Table I. UL listing and recognition effective dates under the second edition of UL 61010-1.5 (click to enlarge).

IEC/EN 61010-1 second edition was published in 2001, at which point most European countries began to adopt it.⁴ The European regulators set a deadline of January 1, 2004, for full adoption. On that date, the first edition was finally and completely phased out, and adherence to requirements of the second edition became mandatory for CE marking.

Unfortunately, Canada and the United States were tardy in adopting the second edition, clinging to the first edition requirements beyond the 2004 deadline. This delay created some problems for many North American manufacturers that were still designing their products according to the current North American standard (the first edition) yet wished to CE mark their products. To CE mark equipment, they had to comply with the second edition of 61010-1, but North America did not have any equivalent. From January to July of 2004, manufacturers experienced frustration in trying to comply with two standards that were similar but had some significant differences. Many products had to be retested to ensure that they complied with the second edition of the standard.

Table II. CSA certification effective dates under the second edition of CSA C22.2 No. 61010-1-04.6,7 (click to enlarge).

Manufacturers often rely on a safety agency to help them certify their products for worldwide use. Therefore, many North American companies were not even aware that their 61010-1 first edition certifications did not allow them to CE mark their product after January 1, 2004. The 61010-1 standard has been touted as an international standard, after all.
One important thing to remember is that safety standards are constantly being reviewed and revamped. In fact, there
are working groups already attending to the 61010-1 third edition. Manufacturers should keep abreast of relevant regulatory developments. They are responsible for ensuring that every export product complies with the standard adopted for each country to which it is being shipped.

To assist North American manufacturers, UL and CSA have issued a timetable for adopting standards that will affect future U.S. and Canadian certifications (see Tables I and II). This is a good reference for manufacturers having a product certified to one of the older standards. When each legacy standard expires, the manufacturer will be required to resubmit its product for reevaluation according to a current standard.

New Requirements

Table III. Creepage distance, clearance distance, and test voltages required for the power supply in Figure 1, according to tables in the second edition of 61010-1. PWB = printed wiring board; CTI = comparative tracking index (click to enlarge).

When any standard is tweaked for its second edition, there will be many minor changes. It is impossible to discuss in this article all of the small changes from the first edition of 61010-1 to the second. But there are a few major differences between the editions, which are covered here. These involve:

• Accessible-circuit voltage limits.
• The concept of measurement category.
• Marking of measurement circuits.
• Creepage distance and clearances.
• Electric strength tests.
• Testing of homogeneous construction.
• Current-measuring circuits.

Accessible-Circuit Voltage Limits. The limits for normal and fault conditions have been raised slightly from those of the first edition. Also, the second edition introduces accessible-circuit voltage limits for wet locations.

Two sets of voltage-level limits for operation under normal conditions are provided, one for normal dry conditions and another for wet locations. Voltage-level limits for dry conditions are 33 V rms, 46.7 V peak, and 70 V dc. Voltage-level limits for wet conditions are 16 V rms, 22.6 V peak, and 35 V dc. Previously, the limits were 30 V rms, 42.4 V peak, and 60 V dc.

Table IV. The Canadian and U.S. national deviations from the second edition of IEC/EN 61010-1 (click to enlarge).

Two sets of voltage-level limits are provided for single-fault conditions, as well, one for normal dry locations and another for wet locations. In this case, voltage levels for dry conditions are 55 V rms, 78 V peak, and 140 V dc, and for wet conditions are 33 V rms, 46.7 V peak, and 70 V dc. The previous limits were 50 V rms, 70 V peak, and 120 V dc.

This change in limits means that circuits that were previously considered to be unsafe for accessible parts may now be considered to be safe. It could also mean that circuits previously considered to be safe, but that were in a wet location, may not be considered to be safe under the second edition. Reevaluation of circuits is necessary when a product certified under a first-edition standard is being reconsidered for compatibility with second-edition requirements.

However, it should also be noted that North American deviations from IEC/EN 61010-1 for the second edition bring the voltage-level limits down to match those of the first edition. This topic is discussed in the next major section of this article.
Measurement Category. The second edition of 61010-1 introduces the concept of measurement category, which is similar to overvoltage category (also known as installation category) as used in the first edition. Measurement categories, applicable only to measurement circuits, are identified as four numbered classifications based on the transient voltages possible on the circuit to be measured, as follows:

• Measurement category I—For measurements performed on circuits not directly connected to mains, such as circuits not derived from mains or protected mains-derived circuits, including low-voltage circuits from power supplies.
• Measurement category II—For measurements performed on circuits directly connected to the low-voltage installation, such as household appliances. This is typically the 120 or 230 V running through buildings for power and light.
• Measurement category III—For measurements performed in the building installation, such as junction boxes, circuit breakers, distribution boards, and equipment for industrial use, including hard-wired equipment. This is generally on the order of 400–600 V.
• Measurement category IV—For measurements performed at the source of the low-voltage installation, such as electricity meters. This is generally greater than 600 V.

Figure 1. Block diagram of a typical power supply having the creepage distances and clearances indicated in Table III (click to enlarge).

As with the overvoltage category in the first edition, the assignment of measurement category with the second affects the clearances required between measurement circuits and other circuits. It is important to determine correctly the appropriate measurement category of the circuit in order to ensure that the circuit can withstand the transient stresses it may possibly experience. Required clearances for measurement circuits complying with the 61010-1 first edition may be less stringent than required clearances according to the second edition. Reevaluation of these circuits is extremely important.

Marking of Measurement Circuits. With measurement circuits now being divided into different measurement categories, marking of each measurement circuit becomes important. This makes sense in the case of the Multimeter electric meter. A technician using a Multimeter should make sure that the meter is appropriate for the circuit to be measured. A Multimeter that is appropriate for measuring low-voltage circuits may not be suitable for use in a power distribution board.

The second edition of the standard states that measurement circuit terminals rated more than 50 V ac or 120 V dc are required to be marked as follows:

• Terminals of measurement category I must be marked with the rated voltage or current and with symbol 14 () .
• Terminals of measurement category II, III, or IV must be marked with the rated voltage or current and with the appropriate measurement category (that is, they must be marked as measurement category II, measurement category III, or measurement category IV).

Not only are these markings required on the equipment terminals, but the same information is required to appear in the documentation provided with the equipment.

Creepage Distance and Clearance. These circuit characteristics are determined differently than in the 61010-1 first edition. The new standard provides various tables to help determine appropriate clearance and creepage distances, as follows:

• Table 4 is used only for mains circuits and contains both clearance and creepage distances. (A mains circuit is what, in the first edition, was considered to be overvoltage category II.)
• Table 5 is used for circuits derived from mains circuits, and contains clearances only.
• Table 6 is used for all other circuits that require a calculation to determine clearance, the calculation involving the working voltage and transient voltage of the circuit. (Note: This calculation has not changed from the first edition.)
• Table 7 provides creepage distances for all circuits except for the mains circuits covered in Table 4.
• Table 8 is used for measurement circuits of categories II, III, and IV, and contains clearances only.

In general, clearance and creepage distance requirements in the second edition of 61010-1 are similar to those in the first edition, but not identical. When a manufacturer upgrades its product to conform with the new edition, it should be careful to use the correct tables in determining the required clearances and creepage distances.

Figure 1 is a block diagram of a typical power supply. From a power input of 100–240 V, the supply generates a voltage of 20 V dc. Taking it as a reference example, determinations of required creepage distances and clearances based on Table 4 in the 61010-1 second edition and Tables D.4 and D.10 of the first edition are presented in Table III of this article. The comparison shows that the required creepage distance and clearance is always either the same or less than that required for conformity to first-edition requirements. This is not necessarily so for all equipment, but it is the case in this example.

Electric Strength Tests. Electric strength tests are conducted slightly differently with the second edition. Test voltages are held for only 5 seconds. The first edition required that the test voltages be held for 60 seconds. Unfortunately, the test voltages have changed from one edition to the next; consequently, retesting may be necessary for compliance with the second edition. Table 9 in the new version of 61010-1 is used to find the test voltage based on the clearance required with basic insulation.

For the power-supply example depicted in Figure 1, two electric strength tests are to be conducted as shown in Table III. As can be seen from the table, the test voltages for P1 (basic insulation) in the second edition are higher than those required in the first. Retesting with the higher test voltage is not always as easy as simply running the test voltage, however. The test must be conducted after performing humidity conditioning, single-fault tests, and impact tests, just to name a few requirements.

Homogeneous Construction. In some constructions, the clearance requirement may be reduced in a homogeneous field. A homogeneous field occurs where the electric field has a constant voltage gradient between electrodes (i.e., has a uniform field). The conductive parts must be designed such that the field between them is homogeneous, or near homogeneous. This reduction in clearance may be applied to all circuits with the exception of mains circuits. As in the first edition, clearances in homogeneous construction are not measured, but instead verified by conducting electric strength testing with the voltage adjusted according to the test site’s altitude. This means that, for test laboratories located significantly above or below 2000 m above sea level, all electric strength tests conducted at the lab must be corrected to simulate testing at 2000 m.

For example, if a technician is required to conduct an electric strength test of 1000 V rms in order to verify a homogeneous construction, but the test lab is situated at 300 m above sea level, the technician would have to multiply the test voltage by the correction factor of 1.12 provided in Table 10. The test would actually be conducted at 1120 V rms. Similarly, if the test lab were located at 3500 m (higher than 2000 m), the test voltage would be decreased by a correction factor of 0.85 (found in Table 10). The electric strength test would be conducted there at only 850 V rms.

Current-Measuring Circuits. Current-measuring circuits can now be tested at a lower current than was allowed by the first edition. The current test now required is only 10 times the rated current for a period of 1 second. Previously, this requirement was 30 times the rated current for a period of 2 seconds. The overall effect of upgrading equipment with measuring circuits to the second edition is that retesting of those circuits is not required.

National Deviations

CSA, UL, and ISA all deviate identically from the second edition of the IEC/EN 61010-1 standard. The deviations are itemized in Table IV. These deviations are required predominantly to achieve conformity with the National Electrical Code and Canadian Electrical Code and existing North American safety standard requirements. Many of them are similar to the deviations issued in association with the first edition. They mainly involve requirements for cords, connectors, and permanently connected equipment, but a few new ones are worth noting.

The voltage-level limits in both normal and single-fault conditions have reverted to what they were in the first edition, for dry locations only. These limits are slightly below the voltages allowed in the second edition of IEC/EN 61010-1. The bottom line is that the CSA and UL second-edition standards did not ease the voltage-level limits for dry locations.

Ultraviolet (UV) radiation limits have been added to the standard in Annex DVC. The guidelines are taken from the American Conference of Government Industrial Hygienists and provide threshold limit values for skin or eye exposure to UV radiation.

Conclusion

The CSA, UL, and ISA second edition of 61010-1 is not very different from the first edition. Nor does it differ much from the IEC/EN version. However, reevaluation and, sometimes, retesting of equipment are necessary to ensure compliance with requirements of the second edition.

References

1. UL 61010-1, “Electrical Equipment for Measurement, Control and Laboratory Use,” 2nd ed. (Northbrook, IL: Underwriters Laboratories, 2004).
2. ISA-82.02.01 (IEC 61010-1 Mod), “Electrical Equipment for Measurement, Control and Laboratory Use” (Research Triangle Park, NC: Instrumentation, Systems, and Automation Society, 2004).
3. CAN/CSA C22.2 No. 61010-1-04, “Electrical Equipment for Measurement, Control and Laboratory Use” (Mississauga, ON: Canadian Standards Association, 2004).
4. IEC 61010-1:2001, “Safety Requirements for Electrical Equipment for Measurement, Control and Laboratory Use—Part 1: General Requirements” (Brussels: International Electrotechnical Commission, 2001).
5. “Effective Date Schedule for the Second Edition of the Standard for Electrical Equipment for Measurement, Control and Laboratory Use; Part 1: General Requirements, UL 61010-1,” UL Bulletin (Northbrook, IL: Underwriters Laboratories, July 12, 2004).
6. CSA Informs Reference No. 97-018, “Measurement, Control and Laboratory Equipment No. 3,” CSA International, July 4, 1997.
7. CSA Informs Reference No. 104-080, “Measurement, Control and Laboratory Equipment No. 5,” CSA International, August 6, 2004.

Cherie Forbes is lab coordinator at M. A. Lamothe & Associates Inc. (Georgetown, ON, Canada). She can be reached at cherie@lamothe-approvals.com.