Re: I did something stupid!
|
Hi Mark, ? <<The PP produces Delta 3 Phase, which by definition has one leg at 208v to ground, and two legs at 120v to ground.? The 208v leg is called the "high leg.">> ? You may be in for a surprise as to voltage to ground on PP. PP produces pseudo 3 phase. It is something I have posted here but really no one cares but I think it is important for the user to know of the high voltage danger in PP unit. Mine is an older 10HP model, DPC-A10-N so not sure if this applies to newer and bigger HP models. Although, I will be surprised if they work differently. So what do I call pseudo 3 phase? Well PP sends out L1 & L2 unadulterated from the power co. In the attached (deltas) yellow and Cyan are my L1 & L2 from PP and they are 310 Vpkk (220V RMS). Note that as expected, that they are 180 deg out of phase. As you would know in ture 3 phase no 2 phases are at 0V at the same time due to 120 deg phase shift. Example attached (Phase000) from the RPC I built about 18 yrs ago. But when L1 & L2 are both at 0V the T3 has to be 310 Vpkk away. So PP creates T3, as shown by magenta trace in the attached (pp T3 Vppk), which is nearly 310 Vpkk above or below at each simultaneous zero crossing of L1 & L2. Phase to phase voltages are fine but if you lose L1 or L2 down stream then without these reference voltages being present there is 620 Vpkk (440V RMS) present at where ever T3 is connected downstream. I shared this with PP and they said my unit is working fine. Few yrs back, I lost a 10A fuse to KF700 in my distribution box (can¡¯t remember L1 or L2). I should have checke the fuse first but I have never had one go out until then and there was no high current stall etc to make me think that I lost the fuse. I was measuring voltages and noted high voltage but these scope plots from few yrs back did not click right away. Well the transformer in KF was producing 56V instead of 24V. In the end it all made sense. My question to PP was that do they not need to provide this info to users because I am pretty certain 600V requires different treatment in a machines electrical system (connectors, etc.) ? So take a measurement to ground on T3 on your unit and see what you find. Theoretically, all I see makes sense but maybe I am missing something. ? Imran ? From: [email protected] <[email protected]> On Behalf Of mark thomas Sent: Tuesday, February 18, 2020 11:38 AM To: David Kumm <davekumm@...>; [email protected] Subject: Re: [FOG] I did something stupid! ? I would offer a few points of clarification about all this: ? 1) People often refer to PP "manufactured leg", but being manufactured isn't the important point.? The PP produces Delta 3 Phase, which by definition has one leg at 208v to ground, and two legs at 120v to ground.? The 208v leg is called the "high leg."?? ? 2) The high leg conductor is to be red or orange.? ?In fact, some people call it the "red leg" because of this. ? 3) NEC says the high leg must be the B phase on panels: ? 408.3(E) Phase Arrangement. The phase arrangement on 3-phase buses shall be A, B, C from front to back, top to bottom, or left to right, as viewed from the front of the switchboard or panelboard.?The B phase shall be that phase having the higher voltage to ground on 3-phase, 4-wire, delta-connected systems.?? ? 4) NEMA receptacle lugs are labeled X, Y, Z.? ?There is no code spec for mapping phases A, B and C to NEMA lugs X, Y, and Z.? But common sense is that the "middle" phase be consistent.? ?So the Y lug should be the high leg. ? 5) For motors, it makes absolutely no difference whatsoever which phase is connected to what, because motors do not use the leg-to-ground current and so they never see the 208v. ? 6) If you have an electrical component that requires 120v supply-to-ground and you connect it a 208v source (such as a Delta high leg), it's a problem.? ?This problem is not because the supply is "manufactured" nor because it's not "stable".? The problem is that it's the wrong voltage.? ? |
imran
