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<blockquote data-quote="Mike Sokol" data-source="post: 59030" data-attributes="member: 1989">Re: Why An Open Neutral Kills 120V DevicesBack OT....Sometimes the neutral can open up as the result of harmonic Triplen currents building up on 3-phase transformers used with Triac dimmers. See the thread at <a href="http://soundforums.net/lighting-electrical/4915-lighting-system-causes-buzz-hum-circuit-breaker-panels.html" target="_blank">http://soundforums.net/lighting-electrical/4915-lighting-system-causes-buzz-hum-circuit-breaker-panels.html</a> Triplen currents are odd order harmonics that add rather than subtract on the neutral bus between the feed transformers themselves. So if the neutral bus wasn&#039;t oversized properly when first installed, it can overheat and open up in the middle of a gig. I&#039;ve not personally seen this at a concert, but did live through it in an industrial plant where it overheated and opened the neutral on the transformers feeding a 3-phase WYE 480/277 volt, 600 amp panel. That did all sorts of electrical damage as well as shutting down most of the plant for a day or two. We ran around with an infrared camera looking for overheated bus connections after that. Unbalanced heater loads and variable speed motors with Triac control (think light dimmers) were most likely the cause. Sometimes you don&#039;t have a choice, but I really dislike tapping power from the lighting panel for just that reason, too many harmonics on the Neutral bus.&nbsp; Neutral is probably the most important bus of all...</blockquote>

[QUOTE="Mike Sokol, post: 59030, member: 1989"] Re: Why An Open Neutral Kills 120V Devices Back OT.... Sometimes the neutral can open up as the result of harmonic Triplen currents building up on 3-phase transformers used with Triac dimmers. See the thread at [URL]http://soundforums.net/lighting-electrical/4915-lighting-system-causes-buzz-hum-circuit-breaker-panels.html[/URL] Triplen currents are odd order harmonics that add rather than subtract on the neutral bus between the feed transformers themselves. So if the neutral bus wasn't oversized properly when first installed, it can overheat and open up in the middle of a gig. I've not personally seen this at a concert, but did live through it in an industrial plant where it overheated and opened the neutral on the transformers feeding a 3-phase WYE 480/277 volt, 600 amp panel. That did all sorts of electrical damage as well as shutting down most of the plant for a day or two. We ran around with an infrared camera looking for overheated bus connections after that. Unbalanced heater loads and variable speed motors with Triac control (think light dimmers) were most likely the cause. Sometimes you don't have a choice, but I really dislike tapping power from the lighting panel for just that reason, too many harmonics on the Neutral bus. Neutral is probably the most important bus of all... [/QUOTE]

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