Jim Katen Posted October 28, 2007 Report Share Posted October 28, 2007 Originally posted by Bob White When you measure across a DELTA 240 leg, you're essentially measuring across two 120V secondarys that are 180 degrees out of phase. 120v plus 120v = 240v Not quite. Any two points on a delta system are 120-degrees apart. A single phase system has two voltages that are 180 degrees apart. Also, you're not measuring across two 120-volt secondarys. It's a 240-volt secondary. The 120-volts appears because we've placed a neutral in the middle of the secondary winding. When you measure across a the phases ofd a WYE secondary, you are measuring across two secondaries that are only 120 (i think)degrees out of phase (vice 180) , hence the nominal 208VAC vice 240. Well, kind of. You get 208 volts because that's the vector sum of the two phases. ....We really don't need to know this, do we..... Well, it's helpful to understand the basics. For instance, in Ken's original post, it's a good idea for an inspector to know why that panel had all those gaps where breakers weren't placed. An inspector who didn't understand the basics of a center-tapped delta system might make a harmful recommendation if he didn't understand the nature of the high leg. "Sure, you can add a circuit for a plasma TV. Just put the breaker in this empty spot . . . " - Jim Katen, Oregon Quote Link to comment Share on other sites More sharing options...
Bob White Posted October 28, 2007 Report Share Posted October 28, 2007 Thank, Jim, for clearing that up for me. My version is a foggy remembrance from basic electricity and elctronics training back in my younger days. My pastor also corrects me in my misstatements and non-systematic thinking. If only I had more mentors (now that I'm old enough to know to listen to them...) Quote Link to comment Share on other sites More sharing options...
Kyle Kubs Posted October 28, 2007 Report Share Posted October 28, 2007 I had a little time on my hands so here is something for those of you who learn visually like me... It helps to have a basic understanding of the physics of a simple transformer. A primary coil that induces a magnetic field (flux) in a iron/steel core, the magnetic flux induces a current in a secondary coil. This is how voltage is stepped down or up. Half the number of windings in a secondary coil will take the half the voltage of the primary coil... With that said, hope this helps. Download Attachment: 1_Phase_Coil.pdf 22.51 KB Download Attachment: 3_Phase_Delta.pdf 40.99 KB Download Attachment: 120v_Single_Phase.pdf 38.8 KB Download Attachment: 240v_Single_Phase.pdf 39.01 KB Download Attachment: 240v_Sinlge_Phase_Alt.pdf 39.96 KB Download Attachment: Hot_Leg.pdf 39.81 KB Jims latest link actually explains the separation of Phases fairly well so I will leave it here. Quote Link to comment Share on other sites More sharing options...
chicago Posted October 28, 2007 Report Share Posted October 28, 2007 Thanks speaking for everyone else and myself for the links and info. As for me I am on a mission to comprehend. Quote Link to comment Share on other sites More sharing options...
Jim Katen Posted October 28, 2007 Report Share Posted October 28, 2007 Originally posted by Kyle Kubs I had a little time on my hands so here is something for those of you who learn visually like me... Kyle, Excellent drawings. They explain the issue perfectly. - Jim Katen, Oregon Quote Link to comment Share on other sites More sharing options...
hausdok Posted October 28, 2007 Report Share Posted October 28, 2007 Ugh, my hair hurts, but I think that I'm starting to get it. [:-headach Thanks, Kyle. Quote Link to comment Share on other sites More sharing options...
Kyle Kubs Posted October 29, 2007 Report Share Posted October 29, 2007 Originally posted by Jim Katen Originally posted by Kyle Kubs I had a little time on my hands so here is something for those of you who learn visually like me... Kyle, Excellent drawings. They explain the issue perfectly. - Jim Katen, Oregon Thank You, Hair hurts... LOL - I've had days like that. Quote Link to comment Share on other sites More sharing options...
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