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Lighting & Electrical
NEC 2013 Draft, OSHA, and Generators - Details and Discussion (long)
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<blockquote data-quote="Phil Graham" data-source="post: 90754" data-attributes="member: 430"><p>Re: NEC 2013 Draft, OSHA, and Generators - Details and Discussion (long)</p><p></p><p></p><p></p><p>TJ,</p><p></p><p>You're welcome! It is a soup, and I needed to make sure I was current before putting something out in the world. Still not sure I've got it all nailed down, but I have thought about it a lot <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /></p><p></p><p>However, in the case of a Honda EU6500, the ground is bonded to the frame, and I'll wager the frame has as much, or more, current sinking ability than the inverter electronics on that particular unit. It is impossible to know without looking at the guts of the inverter. I'll suspect the neutral current carrying capacity comes from the copper in the PWM output filter.</p><p></p><p>---</p><p></p><p>Think about what happens on a conventional bonded generator, or on a home pole transformer. The fault current travels down the ground wire until it reaches the neutral bond point. At the neutral bond point, the current primarily transfers to the neutral circuit, following ohms law. Then the generator (or transformer) windings sink the current from the neutral via ohmic heating. The heat is absorbed by the winding's thermal mass, and the breaker trips.</p><p></p><p>On a Honda EU6500 (assuming some current return path), the same process would happen, but the frame would be the current sink. As long as the impedance to the frame is low, the voltage rise of the frame would also be low(ish). Say you have a fault current of the full 55amps nominal supply, and the frame impedance is 0.5 Ohms. Then by Ohms law V=IR, the voltage rise of the frame would be 27.5 Vrms. Now, is this an ideal to rely on tripping a breaker vs. GFCI? Not in my opinion, but it does meet the breaker's true goal of over current protection.</p><p></p><p>---</p><p></p><p>The Honda EB6500 and EB10,000 are conventionally bonded generators, but they aren't inverter gensets.</p></blockquote><p></p>
[QUOTE="Phil Graham, post: 90754, member: 430"] Re: NEC 2013 Draft, OSHA, and Generators - Details and Discussion (long) TJ, You're welcome! It is a soup, and I needed to make sure I was current before putting something out in the world. Still not sure I've got it all nailed down, but I have thought about it a lot :) However, in the case of a Honda EU6500, the ground is bonded to the frame, and I'll wager the frame has as much, or more, current sinking ability than the inverter electronics on that particular unit. It is impossible to know without looking at the guts of the inverter. I'll suspect the neutral current carrying capacity comes from the copper in the PWM output filter. --- Think about what happens on a conventional bonded generator, or on a home pole transformer. The fault current travels down the ground wire until it reaches the neutral bond point. At the neutral bond point, the current primarily transfers to the neutral circuit, following ohms law. Then the generator (or transformer) windings sink the current from the neutral via ohmic heating. The heat is absorbed by the winding's thermal mass, and the breaker trips. On a Honda EU6500 (assuming some current return path), the same process would happen, but the frame would be the current sink. As long as the impedance to the frame is low, the voltage rise of the frame would also be low(ish). Say you have a fault current of the full 55amps nominal supply, and the frame impedance is 0.5 Ohms. Then by Ohms law V=IR, the voltage rise of the frame would be 27.5 Vrms. Now, is this an ideal to rely on tripping a breaker vs. GFCI? Not in my opinion, but it does meet the breaker's true goal of over current protection. --- The Honda EB6500 and EB10,000 are conventionally bonded generators, but they aren't inverter gensets. [/QUOTE]
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