Technically Speaking

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More on the 25-Amp Grounding Impedance Test

For production-line testing, the 25- or 30-amp grounding continuity test is not likely to identify construction anomalies that would not also be identified by a simple low-current test.
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The 25-Amp Grounding Impedance Test

High-current grounding impedance tests have been specified in safety standards for many years. There are two, independent sources for these tests.
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Derivation of Ground Impedance

Did you ever wonder why we use 0.1 ohm (and sometimes 0.5 ohm) for the ground impedance value for plug-and-socket connected equipment?

Power Systems and Polarization

The “power distribution system” is all parts of an electric system between the “bulk power source” and the consumer’s service-entrance equipment.
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Absolute Safety

Recently, a colleague remarked to me, “Philosophically, of course, there is no such thing as absolute safety.” Could this be true? Is there a situation where a man could not possibly injure himself?
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Operational Insulation in IEC 950

This issue’s topic is rather unique because this column addresses safety requirements for a non-safety critical device, “operational” or “functional” insulation.
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Two Measures, Two Levels

What is a “level of protection”? What are “measures of safety”? Why do they apply only to electric shock and not to other injuries?