Comparison of Spacing Requirements in IEC 60950-1 and IEC 61010-1 Standards

Moe Lamothe, P.Eng, Lamothe Approvals Inc.

Overview

IEC published IEC 60664 entitled "Insulation Coordination for Equipment Within Low-Voltage Systems" which identifies creepage distance and clearance required.  In some cases, these spacing requirements have been interpreted and included in other IEC standards, whereas other standards (such as IEC 60204-1 “Safety of Machinery – Electrical Equipment of Machines”) simply refer the reader to the reference standard IEC 60664.

Unfortunately, when creepage distance and clearance are identified in the standards, differences arise due to different interpretations of IEC 60664.  Not only do differences arise between the individual IEC standard and IEC 60664, but differences arise between the individual standards. 

Two standards that have interpreted and included creepage distance and clearance are IEC 60950-1 First Edition Information Technology Equipment – Safety – Part 1: General Requirements and IEC 61010-1 Second Edition Safety Requirements For Electrical Equipment For Measurement, Control, And Laboratory Use – Part 1: General Requirements.  The differences in creepage distance and clearance between these two standards may pose a problem for equipment designers who design products for which either or both of IEC 60950-1 First Edition and IEC 61010-1 Second Edition apply.  

Typically, a power supply will be certified to IEC 60950-1.  This power supply may be installed in equipment certified to IEC 61010-1.  As you can imagine this may cause problems in the final certification of the product because of the differences in creepage distances and clearances! 

Fortunately, an evaluation of a product to IEC 61010-1 does not require re-evaluation of internal components certified to IEC 60950-1 (such as power supplies).  However for the reverse situation of a product evaluation to IEC 60950-1 containing a component certified to IEC 61010-1, re-evaluation of the IEC 61010-1 component would have to be conducted to ensure that it is suitable.

An examination of the tables at the end of this article shows that the spacings in IEC 61010-1 appear to be slightly lower than those required by IEC 60950-1.  Beware that this is not always the case!  Working voltages may be determined in a different manner for each standard, and in the case of IEC 60950-1, a different working voltage may be used for creepage distance than for clearance.  A careful examination of the working voltage measurements detailed in both standards is essential when comparing spacing requirements.

For reference, the definition for clearance is the shortest distance between two conductive parts, or between a conductive part and the enclosure of the equipment, measured through air. The creepage distance is the shortest path between two conductive parts, or between a conductive part and the enclosure of the equipment, measured along the surface of the insulation.

Impact

There is a perception that as long as the component is certified, it can be used in any product, regardless of the standard the component was certified to. Typically, each standard states that all components must meet the requirements of the standard or be re-evaluated.

For evaluation of a product to an international standard, the general rule of thumb is to re-evaluate any component, which is certified to non-international based standards (i.e. older CSA and UL standards). What is not commonly known (and usually ignored) is that components evaluated to one IEC standard sometimes can’t be used in another IEC based standard without further evaluation.

An analysis is required to determine if re-evaluation of the component is required.  A comparison of the minimum requirements contained in the component standard(s) to those in the end-use product standard is done and if the requirements are at least as great as the requirements of the end-product standard, a re-evaluation will not be required. If not, the component should be re-evaluated to the end-use product standard.

Another mistake commonly made in evaluating a product to an IEC standard is to select the end-use standard and assume that there is no need to further evaluate with any of the referenced standards.  IEC 60204-1 makes extensive reference to the requirements contained in other standards (one of which is creepage distance and clearance requirements).  Without evaluating to the reference standards the product may be designed without creepage distances and clearances in mind!  The requirements in these reference standards must be considered just as if they were included in the end-use product standard.

Comparison of 120 and 230V Spacings

The following is a comparison of standards: creepage distance, clearance and electric strength voltages required between primary and secondary windings of an isolation transformer (where reinforced insulation is required).

The creepage distance, clearance and test voltage in the above example are higher for 60950-1 than 61010-1.  As mentioned above, this is not always the case.

Conclusion

To successfully design and assemble a product that meets the spacings in the end-use standard applicable to your product requires a careful consideration of the components to be specified. There is a further complication – traditionally many components included in reports have indicated ‘Various’ for the manufacturer or even worse, the purchasing department selects what they think is an equivalent component.

Companies would be well advised to consider both their initial component selection criteria and their sourcing control procedures to ensure that they remain onside with the requirements of the safety standards applying to their products.

Moe Lamothe is the president of Lamothe Approvals Inc. (Georgetown, ON, Canada). He can be reached at info@lamotheapprovals.com.

More Articles

COPYRIGHT NOTICE

The copyright for all of the text, tables and illustrations remains with Lamothe Approvals Inc. Permission is granted to print or reproduce this document provided that it properly attributed to Lamothe Approvals Inc.

Prepared May 2003