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Low Earth Orbit
Lighting & Electrical
Why An Open Neutral Kills 120V Devices
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<blockquote data-quote="David Buckley" data-source="post: 63806" data-attributes="member: 2235"><p>Re: Why An Open Neutral Kills 120V Devices</p><p></p><p></p><p></p><p>You bet they do.</p><p></p><p>In large buildings with lots of IT equipment, the neutral current often exceeds the phase currents. It also happens badly in data centres. I wish I could find the picture I have somewhere of a multi hundred amp switch which has a missing neutral link; it melted through overload due to excessive triplen harmonics. That neutral letting go caused nearly two hundred thousand pounds worth of damage to power supplies of equipment. None of the equipment itself was damaged, just power supplies.</p><p></p><p></p><p>On a slightly different tack, to all intents and purposes the USA and UK (and most other countries for that matter) power supply arrangements are the same once you are inside a premise. The power all generally looks (for a single phase supply) like this:</p><p></p><p>[TABLE="class: grid, width: 600"]</p><p>[TR]</p><p>[TD]<strong>World Term</strong>[/TD]</p><p>[TD]<strong>USA Term</strong>[/TD]</p><p>[TD]<strong>UK Wiring Colour</strong>[/TD]</p><p>[TD]<strong>Europe Colour</strong>[/TD]</p><p>[TD]<strong>USA Colour</strong>[/TD]</p><p>[/TR]</p><p>[TR]</p><p>[TD]Phase, or more commonly but incorrectly, Live[/TD]</p><p>[TD]Hot[/TD]</p><p>[TD]Red[/TD]</p><p>[TD]Brown[/TD]</p><p>[TD]Black[/TD]</p><p>[/TR]</p><p>[TR]</p><p>[TD]Neutral[/TD]</p><p>[TD]Neutral (rarely!) or Grounded Conductor[/TD]</p><p>[TD]Black[/TD]</p><p>[TD]Blue[/TD]</p><p>[TD]White[/TD]</p><p>[/TR]</p><p>[TR]</p><p>[TD]Earth[/TD]</p><p>[TD]Ground or Grounding Conductor[/TD]</p><p>[TD]Bare or Green / Yellow[/TD]</p><p>[TD]Green / Yellow[/TD]</p><p>[TD]Bare or Green[/TD]</p><p>[/TR]</p><p>[/TABLE]</p><p></p><p>The arrangement of the power in the building is usually (but not always) T-N-CS (in civilised countries) and it is mandated to be so by the NEC in the USA, only they don't call it that as far as I can recall. Description of the magic letters can be found on WikiPedia in the article entitled <a href="http://en.wikipedia.org/wiki/Earthing_system" target="_blank">Earthing Systems</a></p><p></p><p>The big difference in supply arrangements is that in the UK the neutral/earth bond is provided by the utility company, and the utility thus hands you two separate conductors, a neutral and an earth. In the USA (and New Zealand!) the utility hands you just the neutral conductor, and the contractor is responsible for providing the neutral / earth bond, and the grounding rods(s) as required.</p><p></p><p>European electrical folk will raise their hands in horror at a neutral being described with a word like "grounded", as they will recognize the neutral conductor as to be treated as live, one of the big differnces in attitude between the NEC way and the rest of the world way...</p></blockquote><p></p>
[QUOTE="David Buckley, post: 63806, member: 2235"] Re: Why An Open Neutral Kills 120V Devices You bet they do. In large buildings with lots of IT equipment, the neutral current often exceeds the phase currents. It also happens badly in data centres. I wish I could find the picture I have somewhere of a multi hundred amp switch which has a missing neutral link; it melted through overload due to excessive triplen harmonics. That neutral letting go caused nearly two hundred thousand pounds worth of damage to power supplies of equipment. None of the equipment itself was damaged, just power supplies. On a slightly different tack, to all intents and purposes the USA and UK (and most other countries for that matter) power supply arrangements are the same once you are inside a premise. The power all generally looks (for a single phase supply) like this: [TABLE="class: grid, width: 600"] [TR] [TD][B]World Term[/B][/TD] [TD][B]USA Term[/B][/TD] [TD][B]UK Wiring Colour[/B][/TD] [TD][B]Europe Colour[/B][/TD] [TD][B]USA Colour[/B][/TD] [/TR] [TR] [TD]Phase, or more commonly but incorrectly, Live[/TD] [TD]Hot[/TD] [TD]Red[/TD] [TD]Brown[/TD] [TD]Black[/TD] [/TR] [TR] [TD]Neutral[/TD] [TD]Neutral (rarely!) or Grounded Conductor[/TD] [TD]Black[/TD] [TD]Blue[/TD] [TD]White[/TD] [/TR] [TR] [TD]Earth[/TD] [TD]Ground or Grounding Conductor[/TD] [TD]Bare or Green / Yellow[/TD] [TD]Green / Yellow[/TD] [TD]Bare or Green[/TD] [/TR] [/TABLE] The arrangement of the power in the building is usually (but not always) T-N-CS (in civilised countries) and it is mandated to be so by the NEC in the USA, only they don't call it that as far as I can recall. Description of the magic letters can be found on WikiPedia in the article entitled [URL="http://en.wikipedia.org/wiki/Earthing_system"]Earthing Systems[/URL] The big difference in supply arrangements is that in the UK the neutral/earth bond is provided by the utility company, and the utility thus hands you two separate conductors, a neutral and an earth. In the USA (and New Zealand!) the utility hands you just the neutral conductor, and the contractor is responsible for providing the neutral / earth bond, and the grounding rods(s) as required. European electrical folk will raise their hands in horror at a neutral being described with a word like "grounded", as they will recognize the neutral conductor as to be treated as live, one of the big differnces in attitude between the NEC way and the rest of the world way... [/QUOTE]
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