ON Your Mark 4.4.2 Electromagnetic compatibility (EMC) To enhance the immunity of the equip- ment against conducted and radiated RF disturbance, measures include: – connection of sensitive electrical cir- cuits to the chassis. Such terminations should be marked or labeled with the symbol IEC 60417-5020: Figure 2: The incorrect drawing of IEC 5019 as shown in the NFPA 70-2011 National Electrical Code. – connection of sensitive electrical equipment or circuits directly to the PE circuit or to a functional earthing con- ductor (FE) (see Figure 2), to minimize common mode disturbance. This latter terminal should be marked or labeled with the symbol IEC 60417-5018: 8.2.6 Protective conductor connecting points The protective conductor connecting points shall have no other function and are not intended, for example, to attach or connect appliances or parts. Each protective conductor connecting point shall be marked or labeled as such using the symbol IEC 60417-5019 or with the letters PE, the graphical symbol being preferred, or by use of the bicolour com- bination GREEN-AND-YELLOW, or by any combination of these. Table 1 Figure 3: IEC 5019 drawn on the ISO/ IEC function/control symbol drawing template. From a U.S. perspective, you might think to look at the NFPA 70-2011 National Electrical Code for guidance on this subject. Don’t. This code’s advice on using ground symbols is useless because they show an illustration of a symbol drawn incorrectly (see Figure 2 - note how the vertical bar touches the circle). The NFPA 70 code indicates that this is an “informational note figure” and that it is “one example of a symbol used to identify the termination point for an equipment grounding conductor”. These words leave you to wonder about the other symbols that might exist and where and how you might best use them. Clearly, IEC 60204 is more useful on this topic. Next issue’s topic will focus on the use of safety symbols to communicate how users must read and understand your product’s manuals before using or servicing your product. THE SCIENCE BEHIND DESIGN AND LEGIBILITY One last point should be made here. Whether it’s a safety symbol or a function/control symbol, there’s a science to creating icons that communicate. ISO and IEC have developed a carefully defined set of rules for drawing various types of symbols. The ISO and IEC committees in charge of function/control symbols use a carefully constructed template (Figure 3) and line width guidelines to ensure that their standardized symbols are drawn with common design principles and consistent visual weight to ensure legibility and readability. For more information about safety signs and symbols, visit www.clarionsafety.com. NOTE 1. The IEC version of this standard is nearly identical to the European ver- sion, EN 60204. For those engineers that build machinery, note that in No- vember 2011 the European Commis- sion acknowledged that 60204 is “har- monised” with Machinery Directive 2006/42/EC. This means that you can use 60204 to fulfill the requirements for electrical safety to meet the intent of the Machinery Directive, an impor- tant aspect for obtaining the CE mark. (the author) GEOFFREY PECKHAM is president of Clarion Safety Systems and chair of both the ANSI Z535.2 Standard for Environmental and Facility Safety Signs and the U.S. Technical Advisory Group to ISO Technical Committee 145- Graphical Symbols. Over the past two decades he has played a pivotal role in the harmonization of U.S. and international safety standards dealing with safety signs, colors, formats and symbols. www.incompliancemag.com January 2012 IN Compliance 21