What are the adverse effects of an unearthed electrical system as compared to an earthed system?
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This reduces the risk of electric shock and equipment damage. Show more…
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An electrician was removing a metal fish tape from a hole at the base of a metal light pole. A fish tape is used to pull wire through a conduit run. The fish tape became energized, electrocuting him. To this pretext: a) List three violations of construction standards and suggest two ways of prevention. b) Define energized in the context of exposure and describe the appropriate measure for hazard reduction. c) Compare electrocution and electrical shock in the context of electrical injuries. d) Support the finding that workers face many electrical hazards on the job. e) Formulate approach boundaries in the light of exposed live parts.
Sri K.
In general, voltage levels above what value are considered dangerous?
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There have been many studies of the effects on humans of electromagnetic waves of various frequencies. Using these studies, the International Commission on NonIonizing Radiation Protection (ICNIRP) produced guidelines for limiting exposure to electromagnetic fields, with the goal of protecting people against known adverse health effects. At frequencies of $1 \mathrm{~Hz}$ to $25 \mathrm{~Hz}$, the maximum exposure level of electric-field amplitude, $E_{\max },$ for the general public is $14 \mathrm{kV} / \mathrm{m}$. (Different guidelines were created for people who have occupational exposure to radiation.) At frequencies of $25 \mathrm{~Hz}$ to $3 \mathrm{kHz},$ the corresponding $E_{\max }$ is $\frac{350}{f} \mathrm{kV} / \mathrm{m},$ where $f$ is the frequency in $\mathrm{kHz}$. The ICNIRP also has guidelines for magnetic-field exposure for the general public. In the frequency range of $25 \mathrm{~Hz}$ to $3 \mathrm{kHz},$ this guideline states that the maximum allowed magnetic-field amplitude is $5 / f \mathrm{~T},$ where $f$ is the frequency in $\mathrm{kHz}$. Which is a more stringent limit on allowable electromagnetic-wave intensity in this frequency range: the electric-field guideline or the magnetic-field guideline? A. The magnetic-field guideline, because at a given frequency the allowed magnetic field is smaller than the allowed electric field. B. The electric-field guideline, because at a given frequency the allowed intensity calculated from the electric-field guideline is smaller. C. It depends on the particular frequency chosen (both guidelines are frequency dependent). D. Neither-for any given frequency, the guidelines represent the same electromagnetic-wave intensity.
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