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Author Topic: 3 phase 220 volt wiring Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 12-15-2009 02:57 PM                     I was at a theater the other day and came across something new to me. While measuring the 3 phases at the panel, two of them measured 120 volts to ground. The third phase measured 220 volts to ground. I didn't know that you could hook this up to a 3 phase rectifier. How doesn't it damage anything?  |  IP: Logged Robert Minichino Master Film Handler Posts: 350 From: Haskell, NJ, USA Registered: Dec 2005 posted 12-15-2009 03:11 PM                        That's a high-leg delta service. The phase-phase voltage for all 3 phases is 240V, but one of the sides of the delta is center-tapped and grounded (that's the neutral). This gives you two phases of 120V for lighting and small loads, and 240V 3 phase for your larger loads. The 3rd leg should be about 208V to ground, and shouldn't be used phase-ground.  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 12-15-2009 03:14 PM                     So then the 3 phase rectifiers should be set to the setting closest to 240volts incoming voltage I assume.  |  IP: Logged Gordon Bachlund Jedi Master Film Handler Posts: 696 From: Monrovia, CA, USA Registered: Aug 1999 posted 12-15-2009 04:18 PM                        Robert is quite correct. This used to be a fairly common service for commercial buildings with single-phase "light" meters and three-phase "power" meters. This was driven by (1) a higher kw-h rate for lighting service than for power service, and (2) the use of a larger tapped transformer connected in delta with two smaller transformers. You would be correct in setting the rectifier transformer taps for 240-volts.  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 12-15-2009 04:22 PM                     Thanks guys.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 12-15-2009 08:52 PM                     Measure between the phases and set the taps accordingly. Don't measure between each phase and neutral to determine this. You'll still get 208...210 or what ever the building is set up for when you measure between any two phases. Mark  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 12-15-2009 09:13 PM                       This would be the famed "wild leg"...  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 12-16-2009 12:48 AM                     (thought it was called, "crazy leg" .. )  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 12-16-2009 12:59 AM                  Hot Legs - Rod Stewart  |  IP: Logged Randy Bowden Expert Film Handler Posts: 146 From: Portland, OR, USA Registered: Aug 2000 posted 12-16-2009 02:03 AM                     We have the same wiring set up at our shop. we call it the "Hot Leg"  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 12-16-2009 08:33 AM                       All of the legs are hot in a 3-phase system. High leg delta (aka, "wild leg")  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 12-16-2009 10:24 AM                     Thanks Tim. That was very helpful.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 12-16-2009 04:10 PM                        Usually you see 2 breakers in the panel, a spacer, then a repeat. Dead givaway that "wild leg" is a possibility. Sometimes you can use the wild leg as one side of a 220/240 single phase load, opening up more 120v breaker positions. Louis  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 12-16-2009 04:28 PM                     Like a single phase 220 Orc power supply?  |  IP: Logged Randy Bowden Expert Film Handler Posts: 146 From: Portland, OR, USA Registered: Aug 2000 posted 12-16-2009 04:34 PM                     All of the legs are hot in a 3-phase system I think that goes without saying.  |  IP: Logged

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