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Low Earth Orbit
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Why An Open Neutral Kills 120V Devices
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<blockquote data-quote="Mike Sokol" data-source="post: 59106" data-attributes="member: 1989"><p>Re: Why An Open Neutral Kills 120V Devices</p><p></p><p></p><p></p><p>I agree that a single ground rod can have way more than the code required max of 25 ohms, but modern "Fall of Potential" ground resistance testers have come down in price a lot over the last few years. I have a B&K Model 309 which list for $195 and takes about 10 minutes to do an earth resistance test. Plus it uses a 400 Hz test tone and a high-pass filter to ignore any 60 Hz currents flowing in the ground rod already. So you don't have to disconnect the ground rod from the building to do a test like in the old days. </p><p></p><p>See <a href="http://www.bkprecision.com/products/electrical-battery-testers/earth-resistance-meter/309-digital-earth-resistance-meter.html" target="_blank">Model 309, Digital Earth Resistance Meter - B&K Precision</a> </p><p></p><p>Here's a pretty good tutorial from Fluke about the Fall-of-Potential test procedure. <a href="http://www.fluke.com/Fluke/usen/solutions/earthground/Fall-of-Potential.htm" target="_blank">Fall-of-potential test method</a></p><p></p><p>Most electricians will still just drive a second ground rod, but I feel that ground rods should be tested for earth resistance after any lightning strike on the building. I saw one last year that melted the sandy soil around the ground rod into a glassy popsicle with very high resistance. I talked to my local inspector and power company engineer, who both confirmed there was no requirement for testing ground rod resistance after a lightning strike.</p></blockquote><p></p>
[QUOTE="Mike Sokol, post: 59106, member: 1989"] Re: Why An Open Neutral Kills 120V Devices I agree that a single ground rod can have way more than the code required max of 25 ohms, but modern "Fall of Potential" ground resistance testers have come down in price a lot over the last few years. I have a B&K Model 309 which list for $195 and takes about 10 minutes to do an earth resistance test. Plus it uses a 400 Hz test tone and a high-pass filter to ignore any 60 Hz currents flowing in the ground rod already. So you don't have to disconnect the ground rod from the building to do a test like in the old days. See [URL="http://www.bkprecision.com/products/electrical-battery-testers/earth-resistance-meter/309-digital-earth-resistance-meter.html"]Model 309, Digital Earth Resistance Meter - B&K Precision[/URL] Here's a pretty good tutorial from Fluke about the Fall-of-Potential test procedure. [URL="http://www.fluke.com/Fluke/usen/solutions/earthground/Fall-of-Potential.htm"]Fall-of-potential test method[/URL] Most electricians will still just drive a second ground rod, but I feel that ground rods should be tested for earth resistance after any lightning strike on the building. I saw one last year that melted the sandy soil around the ground rod into a glassy popsicle with very high resistance. I talked to my local inspector and power company engineer, who both confirmed there was no requirement for testing ground rod resistance after a lightning strike. [/QUOTE]
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Why An Open Neutral Kills 120V Devices
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